Obstructive sleep apnea (OSA) is one of the most common causes of hypertension (HTN) and cardiovascular disease (CVD). It is also a quite common underlying factor in resistant HTN (RHTN). The main etiological factor of OSA is obesity, which is a rapidly growing global epidemic. To control obesity, patients should be encouraged by health care professionals to lose weight and be educated about weight loss strategies such as lifestyle modifications, which include regular exercise, low-calorie diet, low sodium intake, smoking cessation, and decreased alcohol consumption. This review also emphasizes the importance of screening for OSA as the major underlying cause of essential, and RHTN, which can lead to CVD and can cause end-organ damage. It also stresses the importance of using continuous positive airway pressure (CPAP) and its beneficial effects, along with other antihypertensive regimens, in treating HTN, and RHTN. Treatment with CPAP therapy decreases sympathetic activity, high blood pressure (BP), heart rate, and CVD as well as its associated mortality.

Keywords: cardiovascular disease, continuous positive airway pressure, hypertension, obstructive sleep apnea, resistant hypertension

OSA, obstructive sleep apnea; HTN, hypertension; CVD, cardiovascular disease; RHTN, resistant hypertension; CPAP, continuous positive airway pressure; BP, blood pressure; EDS, excessive daytime sleepiness; T2DM, type-2 diabetes mellitus; ABPM, ambulatory blood pressure monitoring; MetS, metabolic syndrome; SBP, systolic blood pressure; AA, African Americans; CHF, congestive heart failure; ILs, interleukins; TNFα, tumor necrosis factor alpha; IFNγ, interferon gamma; CRP, C-reactive protein; ED, endothelial dysfunction; FMD, flow-mediated dilatation; ODI, oxygen desaturation index; AHI, apnea-hypopnea index; ADMA, asymmetric dimethylarginine; JNC, joint national committee; CDK, chronic kidney disease; uNMT, urinary normetanephrine

The prevalence of HTN is 1.13 billion people worldwide, measured during healthcare office visits in 2015 Oscullo et al.¹ OSA is a major risk factor of HTN, CVD, type-2 diabetes mellitus (T2DM), stroke, and an underlying cause of a RHTN Ohayon et al.²; Punjabi et al.³; Floras et al.⁴; Gonzaga et al.⁵ There is a bidirectional relationship between OSA and HTN Torres et al.⁶ In one study, participants with HTN showed a greater risk of OSA as compared to those in the control group Njamnshi et al.⁷ The study by Correa et al.,⁸ shows that higher systolic and diastolic blood pressure (BP) readings noted during 24-h ambulatory blood pressure monitoring (ABPM) in patients with mild and severe OSA as compared to obese control patients without OSA. In cases of severe OSA, excessive daytime sleepiness (EDS) is a greater risk factor for HTN, RHTN, and CVD Feng et al.⁹ For OSA patients, hypoxic/apneic episodes due to upper respiratory tract obstruction can cause sleep disturbance, where the person gasps for air and arises from sleep. Hypoxemia stimulates the sympathetic system; there is a release of inflammatory markers which cause oxidative stress resulting in endothelial damage. Further, activation of the renin-angiotensin system releases angiotensin 1, which is converted into angiotensin 2 by the action of angiotensin-converting enzyme and fluid retention occur, which also contributes in pharyngeal edema and high BP Marcus et al.¹⁰ & Feldstein et al.¹¹ Diagnosing HTN in patients with OSA is difficult during routine office visits as 24-hBP monitoring is required Baguet et al.¹² Studies show that, in OSA patients, ambulatory diastolic BP increases throughout both the day and night while systolic BP increases only during night in hypertensive patients Davies et al.¹³; Planes et al.¹⁴; Shi et al.¹⁵

However, treatment and adherence with CPAP therapy can greatly improve HTN and RHTN which are the leading risk factor of CVD in OSA patients Faccenda et al.¹⁶; Norman et al.¹⁷; Feng et al.⁹; Pengo et al.¹⁸ A retrospective cohort study included 205 750 patients diagnosed with incidental HTN were followed up for four years, (2002-2006) and put on antihypertensive medications, RHTN was diagnosed in 1.9% patients within a median of one year and a half from starting of their treatment (0.7 cases/100 person). The CVD incidence became higher with a median of over 3.8 years of follow up in RHTN patients (unadjusted 18.0% versus 13.5%, P<0.001); additionally, RHTN patients showed more risk of CVD compared to non-RHTN patients (hazard ratio, 1.47; 95% confidence interval, 1.33-1.62) Daugherty et al.¹⁹ CPAP decreases both the sympathetic activity and the level of aldosterone concentration in hypertensive patients Furlan et al.²⁰ While managing OSA patients with HTN pharmacologically, diuretics should be the first-line treatment among antihypertensive medications, especially antialdosteronic diuretic medications. These drugs decrease OSA severity and reduce BP by decreasing upper respiratory tract obstruction and parapharyngeal edema Torres et al.⁶

OSA and hypertension prevalence

OSA is prevalent in the general population, but even greater severity and higher prevalence is noted specifically in males and patients with HTN, RHTN, CVD, and metabolic syndrome (MetS) Logan et al. ²¹; Hedner et al.²²; Baguet et al.²³ Studies show 24-h systolic blood pressure (SBP) was greatly higher (P<0.05) in severe OSA patients as compared to control groups Noda et al.²⁴ In a study of 99 hypertensive patients, 56% of patients had OSA Drager et al.²⁵ OSA prevalence is markedly increased in patients with RHTN; increased levels of aldosterone are found in patients with RHTN along with OSA, and increased levels of aldosterone also contribute to the severity of OSA Gonzaga et al.²⁶ The study also shows the severity of OSA depends on the severity of high BP; among African Americans (AA), patients with a family history of HTN complained more of OSA and its severity as compared to a current diagnosis of HTN in an individual without a family history of HTN Jean-Louis et al.²⁷ Table 1.

Figure 1 In Japan, a population-based cross-sectional study was conducted among 1,424 men aged 40-69, HTN was noticed in these patients during nocturnal oxygen desaturation periods Tanigawa et al.³¹ In a study of 301 Canadian patients with congestive heart failure (CHF), those with comorbid OSA had 2.89 times (1.25-6.73, 95% CI) greater systolic BP (BP≥140 mmHg) than the controlled group without OSA, after controlling risk factors. This is problematic as an increase in systolic BP has been directly associated with the severity of OSA, even in medically treated patients with CHF Sin et al.³²

Figure 1 OSA etiology and its related comorbidities.

Pathophysiology of OSA and hypertension

Hypoxemic/apneic episodes and release of inflammatory markers

In OSA patients, hypoxia and oxygen desaturation cause increased intrathoracic pressure, effectively awakening the patient to obtain oxygen at night. This sequence of hypoxemic and apneic episodes or cyclic intermittent hypoxia leads to endothelial dysfunction, as well as activates the renin-angiotensin and sympathetic system. The episodes of hypoxia stimulates peripheral chemoreceptors and, as a result, there is a release of inflammatory markers: hypoxia-inducible factor 1, nuclear factor kappa, vasoconstrictive endothelin-1, interleukins (ILs) 1, 2, and 6, tumor necrosis factor alpha (TNFα), and interferon gamma (IFNγ) Punjabi et al.³; Steiropoulos et al.³³; Zhang et al.^34; Wolf et al.³⁵ These markers both directly and indirectly damage the endothelial lining of the blood vessels, as well as cause an increased aggregation of platelets release leading to further oxidative stress and vascular endothelial damage. Increased arterial stiffness and tone are consequences of these inflammatory markers. The C-reactive protein (CRP), IL-6 and IL-8 released during hypoxemic/apneic episodes have been associated with increasing carotid intima medial thickness which is a precursor for HTN Jelic et al.³⁶ & Minoguchi et al.³⁷ Studies have also shown the plasma level of CRP was higher in OSA patients when compared to controlled groups without OSA, and an increased level of CRP is also directly correlated with the severity of OSA Shamsuzzaman et al.³⁸ Figure 2.

Figure 2 OSA, HTN and other correlated comorbidity pathogenesis.

Oxidative stress and endothelial dysfunction

The release of inflammatory markers and their adherence to endothelium also cause hypercoagulability, which contributes to a dysfunctional endothelium and leads to HTN and CVD Budhiraja et al.³⁹ OSA causes decreased flow-mediated dilatation related to the brachial artery, which shows endothelial dysfunction (ED) Nieto et al.⁴⁰ In OSA patients, flow-mediated dilatation (FMD) is associated with oxygen desaturation index due to hypoxemic/apneic episodes and depends on the severity of OSA. CRP was also found to be elevated in OSA patients, but it did not interfere with flow mediated dilatation Chung et al.⁴¹ In another study of 64 patients with mild OSA symptoms oxygen desaturation index (ODI)=23.1, when compared to 15 controlled subjects without OSA, those even with mild OSA showed endothelial dysfunction, increased arterial stiffness, atherosclerosis, HTN, also showed an increased risk of CVD Kohler et al.⁴² Yet another study was conducted among 32 OSA patients and a 19-patient control group, which showed that OSA patients had an increased level of ENDO, which was strongly associated with the severity of apnea-hypopnea index (AHI) compared to the healthy control group, higher BP was also noted among patients with OSA and was also directly correlated with the severity of AHI Gjorup et al.⁴³

Role of endothelial nitric oxide

In patients with OSA, there is a decreased production of nitric oxide because of hypoxia. However, continuous treatment with oxygen (1-2 L/min) at night stimulates the production of nitric oxide metabolites (nitrates/nitrites) which causes endothelial vasodilation Teramoto et al.⁴⁴ & Wolk et al.⁴⁵ Another cause of decreased nitric oxide in persons with OSA patients is increased levels of Asymmetric dimethylarginine (ADMA), as it inhibits endothelial nitric oxide synthase, which results in a decreased production of endothelial nitric oxide and leads to decreased endothelial vasodilation in response to hypoxemic/apneic episodes in OSA patients. This impaired endothelial dysfunction in OSA patients because of hypoxia can lead to HTN and CVD Kato et al.⁴⁶ However, CPAP treatment greatly improves FMD of the brachial artery as well as ADMA concentration in plasma. These findings were noted both after 1 and 4 weeks of CPAP treatment, respectively. The FMD significantly improved (from 3.3+/-0.3% to 5.8+/-0.4% (p<0.01) and 6.6+/-0.3% (p<0.01) with CPAP therapy in 1 week and 4 weeks respectively; thus CPAP treatment greatly improves endothelial dysfunction Ohike et al.⁴⁷

OSA and incidental hypertension

Incidental HTN or newly diagnosed HTN is defined as a systolic BP≥140mmHg and a diastolic BP≥90 mmHg on a mean 24-h ABPM; (BP≥140/90) Giles et al.⁴⁸ & Oshea et al.⁴⁹ In OSA patients, masked HTN is usually present when 24-h ABPM is monitored and the office measurement of BP shows≥125/83 mmHg Baguet et al.⁵⁰ & Drager et al.⁵¹ OSA and related chronic sleep disturbances are some of the potential causative factors of the development of incidental HTN, and treatment with CPAP therapy can prevent incidental HTN and can also improve existing HTN Guralnick et al.⁵² A cohort study showed an increase in incidental HTN among obese and OSA patients and is more likely in patients when the AHI>30, especially in older and middle-aged people (age≥40) Connor et al.⁵³ Another multiple logistic regression analysis conducted among an elderly population (mean age 68.2 years) with severe OSA; AHI≥30/h is strongly associated with incidental arterial hypertension (P=0.02) Guillot et al.⁵⁴ New HTN can be diagnosed in OSA patients who are not taking treatment for OSA or in undiagnosed OSA patients. The presence of new HTN and RHTN in obese patients with clinical symptoms of OSA, including EDS, snoring, poor sleep, and witnessed apnea, should be considered for the diagnosis of OSA. However, treatment with and adherence to CPAP therapy greatly improve OSA as well as HTN and RHTN Wolk et al.⁴⁵; Roca et al.⁵⁵; Kolanis et al.⁵⁶

Treatment of hypertension in OSA

Lifestyle modifications

Patients diagnosed with obesity, OSA, HTN, RHTN, excessive aldosterone should be treated with lifestyle modifications, low salt diet, CPAP and antihypertensive medications and if there is aldosterone-producing tumors, adenomas, surgical treatment is also necessary Pimenta et al.⁵⁷; Persell et al.⁵⁸; Wolf et al.⁴⁵ Since OSA and associated HTN are major findings in obese patients, it is recommended patients reduce weight by using lifestyle modifications such as using a low carbohydrate diet and physical exercise. DASH (dietary approaches to stop HTN) including diet features such as fruits, vegetables, low sodium intake, low-fat dairy products, and whole grains can help in reducing weight, and HTN prevention and management Graudal et al.⁵⁹; Juraschek et al.⁶⁰; Ozemek et al.⁶¹ Such modifications have beneficial effects to reduce LDL and HDL levels, as well as reducing inflammation by reducing certain inflammatory markers CRP, IL-6, and TNF-α. Using CPAP, antihypertensive, and weight loss measures help to greatly reduce OSA and associated HTN Nicklas et al.⁶²; Seshadri et al.⁶³; Chirinos et al.⁶⁴; Ahmad et al.⁶⁵

Continuous positive airway pressure

The CPAP treatment greatly reduces HTN in severely OSA patients Duran-Cantolla et al.⁶⁶ OSA and HTN are correlated with each other; there is a linear relationship between HTN and the severity of OSA Lavie et al.,⁶⁷ as a result, the treatment of OSA can mitigate elevations in BP. CPAP therapy improves HTN in OSA patients, also OSA, and improves the quality of sleep Silverberg et al.⁶⁸; Alajmi et al.⁶⁹ Continuous use of CPAP therapy reduces systolic as well as diastolic BP during sleep at night and as well as during periods of wakefulness. The effectiveness of such therapy depends upon adherence to the therapy and is more effective in patients with severe OSA. BP improvement requires adherence to both antihypertensive agents as well as CPAP therapy Hui et al.⁷⁰ A long-term study showed that OSA patients were at a higher risk of systemic HTN when compared to those without OSA and treatment with CPAP therapy showed improvements both in BP and in the decrease of incidental HTN Marin et al.⁷¹ In OSA patients, ambulatory BP monitoring improves for 24 hours after CPAP treatment. BP improvements in turn reduce CVD Haentjens et al.⁷² Similarly, the CRP level, which is an important inflammatory marker in OSA and CVD, greatly decreases after treatment with CPAP therapy Ishida et al.⁷³ One study showed that one-week removal of CPAP therapy from patients worsened their OSA and caused increased sympathetic activity Phillips et al.⁷⁴ Thus, treatment efficacy depends on adherence with CPAP and its nocturnal use in HTN, RHTN, and severe OSA—as evidenced by AHI≥30/h Martínez-García et al.⁷⁵

CPAP therapy also improves endothelial damage by increasing NO production and reducing the stress on the endothelium by decreasing oxidative and inflammatory processes Jelic et al.⁷⁶ As a result, continuous CPAP can also reduce BP in persons with OSA during the night with continued effects during the day Dimsdale et al.⁷⁷ & Haentjens et al.⁷² A randomized parallel trial, 118 men were studied to see the therapeutic effects of CPAP on BP for one month; results showed that therapeutic CPAP decreased 24-h AMBP by 2.5 mmHg, and this beneficiary effect was seen in both diastolic and systolic BP during both wake and sleep states in persons with severe OSA. The reduction of BP was noted to be more in those patients who were already taking antihypertensive medications Pepperell et al.⁷⁸ Another study demonstrated showed that there was a decrease in diastolic BP noted in 24-h (P=0.04) by continuous use of CPAP≥3.5 h/night for 4 weeks Faccenda et al.¹⁶ Adherence with CPAP therapy for more than 5.6 hours each night for a year decreases systolic BP by 1.89 mm Hg (p=0.0654) and diastolic BP 2.19 mm Hg (p=0.0008) Barbe et al.⁷⁹ BP during sleep is more strongly associated with CVD, so nighttime BP medications are better suited in controlling HTN and CVD. Hence, ABPM is a better measurement and good prognostic predictor in controlling HTN and preventing CVD risk Hermida et al.⁸⁰ So, CPAP treatment in OSA patients is greatly beneficial and its continuous use significantly reduces high BP Becker et al.⁸¹; Bazzano et al.⁸²; Montesi et al.⁸³

Antihypertensives

According to the eight reports of the Joint National Committee (JNC 8) on Prevention, Detection, Evaluation, and Treatment of High Blood pressure, age is the main risk factor of high blood pressure. People over age 60 have a greater risk of developing high BP. In this age group, the systolic rise in BP is riskier than a rise in diastolic BP as it increases the risk of CVD. The report also emphasized the necessity of careful selection of antihypertensive medications, such as thiazide diuretics, angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, calcium channels blockers, and beta-blockers. The combination of 2 or more medications is often required to achieve the optimum BP control of <140/90 mmHg or <130/80 mmHg in patients with diabetes or chronic kidney disease (CKD). Patients with a systolic rise of 20 mm Hg or a diastolic rise of 10 mm Hg above the desired and optimum BP goal should be treated by the initiation of therapy with one thiazide diuretic and one other antihypertensive medication regimen. The second agent should be determined by assessing co-morbid conditions Shrout et al.⁸⁴

Resistant hypertension and OSA

The definition of RHTN

 RHTN is defined as BP that is ≥130/80 despite using at least three different classes of antihypertensive medications (including a diuretic) at their maximum dosages, or a BP controlled with four or more classes of antihypertensive medications Logan et al.²¹ Calhoun et al.⁸⁵; Demede et al.⁸⁶; Khan et al.⁸⁷; Shrout et al.⁸⁴; Carey et al.⁸⁸; Oscullo et al.⁸⁹ Most patients with RHTN are non-Hispanic Black, older, and have a higher BMI (all P<0.001). RHTN can be found in 19.7% of adults in the US population and 10.3% worldwide Persell et al.⁵⁸; Carey et al.⁹⁰; Noubiap et al.⁹¹ Many patients exhibit a BP≥140/90 despite treatment with three or more antihypertensive medications, including diuretics Doroszko et al.⁹² & Hans et al.⁹³ When BP is not controlled even after using five or more antihypertensive medications, including diuretics (spironolactone, chlorthalidone), it is called “refractory HTN” Czarina et al.⁹⁴ & Oscullo et al.⁸⁹ The prevalence of RHTN and refractory HTN is 27.3% in non-Hispanic Blacks compared to non-Hispanic Whites (18.9%) and 17.7% in Mexican Americans Carey et al.⁸⁸ OSA should be considered as a major underlying risk factor in RHTN and refractory HTN but treatment with CPAP lowers BP Grote et al.⁹⁵; Baguet et al.¹²; Gonçalves et al.⁹⁶ A cross-sectional study was conducted in 599 patients with a history of HTN or who were already on antihypertensive medications to examine the effects of OSA in hypertensive patients; results showed that in uncontrolled HTN, the severity of OSA was significantly higher compared to controlled HTN (34.0 +/- 26.8 versus 27.0 +/- 23.5, P<0.01) Grote et al.⁹⁵ RHTN is thus shown to be correlated with the severity of OSA and was noted with severe AHI (P<0.005) Lavie et al.⁹⁷ The severity of AHI leads to deoxygenation, which causes activation of the sympathetic nervous system and release of natriuretic peptide. Treatment with a beta-blocker with β1 selectivity in these individuals improves BP, heart rate, and brachial artery stiffness Ziegler et al.⁹⁸

The role of aldosterone in resistant hypertension

There is an increased level of aldosterone found in RHTN. An increased aldosterone level worsens the severity of underlying OSA in RHTN Pratt-Ubunama et al.⁹⁹ Excess of aldosterone increases fluid accumulation in the upper respiratory tract, which subsequently increases the severity of OSA by increasing pharyngeal edema. This increased level of aldosterone is mainly related to pulmonary artery stenosis. In patients with RHTN, there should be screening for OSA and the associated pulmonary artery stenosis Gaddam et al.¹⁰⁰; Dudenbostel et al.¹⁰¹; Prejbisz et al.¹⁰²

Treatment of resistant hypertension in OSA

In general, RHTN is more prevalent in the elderly population and obese people, and the risk of RHTN increases as the person ages and gains weight. As RHTN is strongly associated with OSA, T2DM, CKD, CVD, certain genetic causes, sedentary lifestyle, and noncompliance with medication. Better control of RHTN can be achieved by improving lifestyle modifications, losing weight, and careful selection of antihypertensive medications which includes a diuretic. The main aim of treating RHTN is in diagnosing and treating its underlying cause Calhoun et al.⁸⁵

Continuous positive airway pressure and resistant hypertension

CPAP therapy is a key in the treatment of RHTN with underlying OSA. A study conducted in 24-patients with severe OSA and RHTN to see the effects of CPAP treatment; after 6 months with CPAP therapy a greater reduction in 24-h diastolic (p=0.009), and systolic (p=0.003) BP were noted. Also, an improvement was noticed in AHI (P<0.001) Lai et al.¹⁰³ Diuretics should be included as a first-line treatment of RHTN in OSA patients, as they can play an important role in reducing edema in the upper respiratory tract and can improve OSA as well as high BP Torres et al.⁶

Management of hyper aldosteronism in those with RHTN and OSA

In OSA patients, sympathetic stimulation causes the release of catecholamines, as well as an activation of the renin-angiotensin system, which causes high BP resulting in RHTN. CPAP treatment decreases plasma aldosterone level as well as RHTN Lloberes et al.¹⁰⁴ Although these patients usually do not respond to diuretic therapy, a better response could be obtained with drugs which block sympathetic and renin activity Ziegler et al.⁹⁸ Treatment with the potassium-sparing diuretic spironolactone showed improvements in both RHTN and OSA, high levels of plasma aldosterone concentration, and urinary aldosterone levels Gaddam et al.¹⁰⁰; Dudenbostel et al.¹⁰¹; Prejbisz et al.¹⁰²; Ke al.¹⁰⁵ Spironolactone decreases BP significantly regardless of aldosterone level when included with diuretics, ACE inhibitors, and ARBs Nishizaka et al.¹⁰⁶; Chapman et al.¹⁰⁷; Ziegler et al.¹⁰⁸ Figure 3.

Figure 3 CPAP therapy and its beneficial effects.

When elevated aldosterone levels are caused by the adrenal gland, patients can be managed either medically with spironolactone or in the case of Conn’s Syndrome with surgery Pimenta et al.⁵⁷ The adrenal glands are also implicated in the activation of the sympathetic activation as it leads to the increased production of catecholamines. A 2018 study by Gilardini et al.¹⁰⁹ shows that two-thirds of hypertensive OSA patients have elevated urinary normetanephrine (uNMT) levels. A population-based study was conducted among 116 hypertensive males (40-79y) with AHI≥10/h, and their urine analysis was also obtained during an overnight sleep study. Results showed ↑urinary normetanephrine (182+/-57 versus 141+/-45 micromol x mol(-1) creatinine, p<0.001) and ↑metanephrine (70+/-28 versus 61+/-28 micromol mol(-1) creatinine, p<0.05), as compared to controlled group without OSA Elmasry et al.¹¹⁰ However, when patients were given continuous CPAP therapy, a decrease in levels was noticed. Continuous ventilation therapy has a significant effect in reducing sympathetic nervous system activation, thus a decrease in catecholamine release improves BP Pinto et al.¹¹¹; Casitas et al.¹¹²; Gilardini et al.¹⁰⁹

Use of oral appliances

Treating OSA patients with an oral appliance is also helpful in reducing symptoms of both OSA and BP Otsuka et al.¹¹³ Oral appliances such as mandibular advancement splints improved symptoms and severity of OSA as compared to the inactive oral appliance (control device) Gotsopoulos et al.¹¹⁴ The continuous use of mandibular advancement splints for at least four weeks not only improved OSA symptoms and severity but also improved RHTN Gotsopoulos et al.¹¹⁵

OSA is highly prevalent in both HTN and RHTN Parati et al.,¹¹⁶ and is considered a major risk factor for HTN, RHTN, and CVD Peker et al.¹¹⁷; Durgan et al.¹¹⁸; Hou et al.¹¹⁹ However, treatment with CPAP therapy greatly reduces high BP Alajmi et al.⁶⁹; Bazzano et al.⁸²; Dernaika et al.¹²⁰; Duran-Cantolla et al.⁶⁶ As well as being a major risk factor for HTN, OSA is strongly associated with CVD morbidity and mortality Peppard et al.¹²¹ There is a strong correlation of OSA with vascular abnormalities that leads to atherosclerosis, HTN, and CVD Lanfranchi et al.¹²² Oxygen desaturation in OSA patients can lead to HTN, myocardial infarction, CHF, and an increased risk of stroke Mohsenin.¹²³ CRP is an important inflammatory marker in OSA patients and is strongly associated with CVD, a study conducted in 173 males (AHI>5) showed CRP levels were strongly associated with the severity of AHI Kokturk et al.¹²⁴ Treatment and compliance with CPAP therapy greatly improve BP in OSA patients Kolanis et al.⁵⁶ CPAP use ≥3.5h/night > 24% desaturation/h for 4 weeks showed decreased BP in OSA patients Faccenda et al.¹⁶ A study shows CPAP treatment efficacy for RHTN and OSA is beneficial when used 3 months for >5.8 hours Lozano et al.¹²⁵ Another study shows treatment with CPAP therapy greatly reduces systolic BP (p=0.001) and diastolic BP (p=0.006) and leads to a decreased risk of CVD Dorkova et al.¹²⁶ An additional study shows CPAP adherence reduces 24-h AMBP and risk of CVD in OSA patients with HTN Haentjens et al.⁷² CPAP therapy thus not only reduces BP in OSA patients but can also prevent HTN in OSA patients Bazzano et al.⁸²

In OSA patients, adherence to CPAP therapy greatly reduces associated systolic and diastolic BP Coughlin et al.¹²⁷ There was a significant drop in BP at nighttime after continuous treatment with CPAP, (P=0.032) Dimsdale et al.⁷⁷ OSA is one of the major risk factors of essential HTN and one of the major underlying causes of RHTN, in RHTN OSA usually stimulates aldosterone excretion, which is one of the causes of RHTN Calhoun et al.¹²⁸ CPAP treatment decreases diastolic as well as systolic BP in RHTN Logan et al.¹²⁹ CPAP treatment is highly effective in RHTN associated with OSA, longer use, and its compliance has more beneficial effects in controlling RHTN Lozano et al.¹²⁵ & Kolanis et al.⁵⁶ The treatment of RHTN must include an appropriate anti-hypertensive regimen, modifications of lifestyle changes, and the use of continuous CPAP therapy Furlan et al.²⁰; Chahal et al.¹³⁰; Ip et al.¹³¹; Weiss et al.¹³²

Due to rising obesity worldwide, OSA has become a rising global issue and is highly prevalent in patients with HTN and RHTN. It is highly recommended that patients with HTN and RHTN who do not respond to the usual antihypertensive medication regimen undergo screening for OSA. OSA is the major predisposing factor of HTN, CVD, and stroke. In OSA patients, hypoxemic/apneic episodes initiate the inflammatory process and the release of inflammatory markers that cause ED, resulting in HTN, CVD, and stroke. However, treatment and adherence to CPAP therapy along with other antihypertensive medications greatly reduce and prevent high BP, CVD, and stroke.

This work is supported by the following funding agencies: R25-HL105444 and R25-HL 116378 (NHLBI); R01-MD007716 (NIMHD) to GJL. However, the funders had no role in study design, data collection, analysis, and decision to publish.

The author declares that there are no conflicts of interest.

None.

1. Grace Oscullo, E Sapina-Beltran, Gerard Torres, et al. The potential role of obstructive sleep apnoea in refractory hypertension. Curr Hypertens Rep. 2019;21(8):57.
2. Ohayon MM, Guilleminault C, Priest RG, et al. Is sleep-disordered breathing an independent risk factor for hypertension in the general population (13,057 subjects)? J Psychosom Res. 2000;48(6):593–601.
3. Punjabi NM, Caffo BS, Goodwin JL, et al. Sleep disordered breathing and mortality: a prospective cohort study. PLoS Med. 2009;6(8):e1000132.
4. Floras JS. Hypertension and sleep apnea. Can J Cardiol. 2015;31(7):889–897.
5. Gonzaga C, Bertolami A, Bertolami M, et al. Obstructive sleep apnea, hypertension and cardiovascular diseases. J Hum Hypertens. 2015;29(12):705–712.
6. Gerard Torres, Manuel Sánchez-de-la-Torre, Ferran Barbé. Relationship between OSA and hypertension. Chest. 2015;148(3):824–832.
7. Njamnshi AK, Mengnjo MK, Mbong EN, et al. Hypertension in Cameroon associated with high likelihood of obstructive sleep apnea: a pilot study. BMC Cardiovasc Disord. 2017;17(1):112.
8. Correa CM, Gismondi RA, Cunha AR, et al. Twenty-four-hour blood pressure in obese patients with moderate-to-severe obstructive sleep apnea. Arq Bras Cardiol. 2017;109(4):313–320.
9. Feng J, He QY, Zhang XL, et al. Epworth sleepiness scale may be an indicator for blood pressure profile and prevalence of coronary artery disease and cerebrovascular disease in patients with obstructive sleep apnea. Sleep Breath. 2012;16(1):31–40.
10. Jonathan A Marcus, Aravind Pothineni, Carolina Z Marcus, et al. The role of obesity and obstructive sleep apnea in the pathogenesis and treatment of resistant hypertension. Curr Hypertens Rep. 2014;16(1):411.
11. Carlos A Feldstein. Blood pressure effects of CPAP in nonresistant and resistant hypertension associated with OSA: a systematic review of randomized clinical trials. Clin Exp Hypertens. 2016;38(4):337–346.
12. Baguet JP, Hammer L, Lévy P, JM, et al. Night-time and diastolic hypertension are common and underestimated conditions in newly diagnosed apnoeic patients. J Hypertens. 2005;23(3):521–527.
13. Davies CW, Crosby JH, Mullins RL, et al. Case-control study of 24-hour ambulatory blood pressure in patients with obstructive sleep apnoea and normal matched control subjects. Thorax. 2000;55(9):7          36–740.
14. Planes C, Leroy M, Fayet G, et al. Exacerbation of sleep-apnoea related nocturnal blood-pressure fluctuations in hypertensive subjects. Eur Respir J. 2002;20(1):151–157.
15. Shi J, Piao J, Liu B, et al. Obstructive sleep apnea increases systolic and diastolic blood pressure variability in hypertensive patients. Blood Press Monit. 2017;22(4):208–212.
16. Faccenda JF, Mackay TW, Boon NA, et al. Randomized placebo-controlled trial of continuous positive airway pressure on blood pressure in the sleep apnea-hypopnea syndrome. Am J Respir Crit Care Med. 2001;163(2):344–348.
17. Norman D, Loredo JS, Nelesen RA, et al. Effects of continuous positive airway pressure versus supplemental oxygen on 24-hour ambulatory blood pressure. Hypertension. 2006;47(5):840–845.
18. Pengo MF, Bonafini S, Fava C, et al. Cardiorespiratory interaction with continuous positive airway pressure. J Thorac Dis. 2018;10(Suppl 1):S57–S70.
19. Stacie L Daugherty, J David Powers, David J Magid, et al. Incidence and prognosis of resistant hypertension in hypertensive patients. Circulation. 2012;125(13):1635–1642.
20. Furlan SF, Braz CV, Lorenzi-Filho G, et al. Management of hypertension in obstructive sleep apnea. Curr Cardiol Rep. 2015;17(12):108.
21. Logan AG, Perlikowski SM, Mente A, et al. High prevalence of unrecognized sleep apnoea in drug-resistant hypertension. J Hypertens. 2001;19(12):2271–2277.
22. Hedner J, Bengtsson-Bostrom K, Peker Y, et al. Hypertension prevalence in obstructive sleep apnoea and sex: a population-based case-control study. Eur Respir J. 2006;27(3):564–570.
23. Baguet JP, Barone-Rochette G, Pépin JL. Hypertension and obstructive sleep apnoea syndrome: current perspectives. J Hum Hypertens. 2009;23(7):431–443.
24. Noda A, Yasuma F, Okada T, et al. Influence of movement arousal on circadian rhythm of blood pressure in obstructive sleep apnea syndrome. J Hypertens. 2000;18(5):539–544.
25. Drager LF, Genta PR, Pedrosa RP, CC, et al. Characteristics and predictors of obstructive sleep apnea in patients with systemic hypertension. Am J Cardiol. 2010;105(8):1135–1139.
26. Gonzaga CC, Gaddam KK, Ahmed MI, et al. Severity of obstructive sleep apnea is related to aldosterone status in subjects with resistant hypertension. J Clin Sleep Med. 2010;6(4):363–368.
27. Jean-Louis G, Zizi F, Casimir G, et al. Sleep-disordered breathing and hypertension among African Americans. J Hum Hypertens. 2005;19(6):485–490.
28. Wang L, Li N, Yao X, et al. Detection of secondary causes and coexisting diseases in hypertensive patients: OSA and PA are the common causes associated with hypertension. Biomed Res Int. 2017;2017:8295010.
29. Florczak E, Prejbisz A, Szwench-Pietrasz E, et al. Clinical characteristics of patients with resistant hypertension: the RESIST-POL study. J Hum Hypertens. 2013;27(11):678–685. 
30. Pedrosa RP, Drager LF, Gonzaga CC, et al. Obstructive sleep apnea: the most common secondary cause of hypertension associated with resistant hypertension. Hypertension. 2011;58(5):811–817.
31. Tanigawa T, Tachibana N, Yamagishi K, et al. Relationship between sleep-disordered breathing and blood pressure levels in community-based samples of Japanese men. Hypertens Res. 2004;27(7):479–484.
32. Sin DD, Fitzgerald F, Parker JD, et al. Relationship of systolic BP to obstructive sleep apnea in patients with heart failure. Chest. 2003;123(5):1536–1543.
33. Steiropoulos P, Papanas N, Nena E, et al. Inflammatory markers in middle-aged obese subjects: does obstructive sleep apnea syndrome play a role? Mediators Inflamm. 2010;2010:675320.
34. Zhang W, Si LY. Obstructive sleep apnea syndrome (OSAS) and hypertension: pathogenic mechanisms and possible therapeutic approaches. Ups J Med Sci. 2012;117(4):370–382.
35. Wolf J, Narkiewicz K. Optimizing the management of uncontrolled/resistant hypertension. the importance of sleep apnoea syndrome. Curr Vasc Pharmacol. 2017;16(1):44–53.
36. Jelic S, Bartels MN, Mateika JH, et al. Arterial stiffness increases during obstructive sleep apneas. Sleep. 2002;25(8):850–855.
37. Minoguchi K, Yokoe T, Tazaki T, et al. Increased carotid intima-media thickness and serum inflammatory markers in obstructive sleep apnea. Am J Respir Crit Care Med. 2005;172(5):625–630.
38. Shamsuzzaman AS, Winnicki M, Lanfranchi P, et al. Elevated c-reactive protein in patients with obstructive sleep apnea. Circulation. 2002;105(21):2462–2464.
39. Budhiraja R, Parthasarathy S, Quan SF. Endothelial dysfunction in obstructive sleep apnea. J Clin Sleep Med. 2007;15;3(4):409–415.
40. Nieto FJ, Herrington DM, Redline S, et al. Sleep apnea and markers of vascular endothelial function in a large community sample of older adults. Am J Respir Crit Care Med. 2004;169(3):354–360.
41. Chung S, Yoon IY, Shin YK, et al. Endothelial dysfunction and c-reactive protein in relation with the severity of obstructive sleep apnea syndrome. Sleep. 2007;30(8):997–1001.
42. Kohler M, Craig S, Nicoll D, et al. Endothelial function and arterial stiffness in minimally symptomatic obstructive sleep apnea. Am J Respir Crit Care Med. 2008;178(9):984–988.
43. Gjorup PH, Sadauskiene L, Wessels J, et al. Abnormally increased endothelin-1 in plasma during the night in obstructive sleep apnea: relation to blood pressure and severity of disease. Am J Hypertens. 2007;20(1):44–52.
44. Teramoto S, Kume H, Matsuse T, et al. Oxygen administration improves the serum level of nitric oxide metabolites in patients with obstructive sleep apnea syndrome. Sleep Med. 2003;4(5):403–407.
45. Wolk R, Shamsuzzaman AS, Somers VK. Obesity, sleep apnea, and hypertension. Hypertension. 2003;42(6):1067–1074.
46. Kato M, Roberts-Thomson P, Phillips BG, et al. Impairment of endothelium-dependent vasodilation of resistance vessels in patients with obstructive sleep apnea. Circulation. 2000;102(21):2607–2610.
47. Ohike Y, Kozaki K, Iijima K, et al. Amelioration of vascular endothelial dysfunction in obstructive sleep apnea syndrome by nasal continuous positive airway pressure--possible involvement of nitric oxide and asymmetric NG, NG-dimethylarginine. Circ J. 2005;69(2):221–226.
48. Giles TD, Materson BJ, Cohn JN, et al. Definition and classification of hypertension: an update. J Clin Hypertens (Greenwich). 2009;11(11):611–614.
49. Oshea PM, Griffin TP, Fitzgibbon M. Hypertension: the role of biochemistry in the diagnosis and management. Clin Chim Acta. 2017;465:131–143.
50. Baguet JP, Lévy P, Barone-Rochette G, et al. Masked hypertension in obstructive sleep apnea syndrome. J Hypertens. 2008;26(5):885–892.
51. Drager LF, Diegues-Silva L, Diniz PM, et al. Obstructive sleep apnea, masked hypertension, and arterial stiffness in men. Am J Hypertens. 2010;23(3):249–254.
52. Guralnick AS. Obstructive sleep apnea: incidence and impact on hypertension? Curr Cardiol Rep. 2013;15(11):415.
53. Connor GT, Caffo B, Newman AB, et al. Prospective study of sleep-disordered breathing and hypertension: the sleep heart health study. Am J Respir Crit Care Med. 2009;179(12):1159–1164.
54. Guillot M, Sforza E, Achour-Crawford E, et al. Association between severe obstructive sleep apnea and incident arterial hypertension in the older people population. Sleep Med. 2013;14(9):838–842.
55. Querejeta Roca G, Shah AM. Sleep disordered breathing: hypertension and cardiac structure and function. Curr Hypertens Rep. 2015;17(12):91.
56. Kolanis S, Pilavakis M, Sofogianni A, et al. Is there a role for continuous positive airway pressure treatment in the management of obstructive sleep apnea-related hypertension? Curr Hypertens Rev. 2017;13(2):89–92.
57. Pimenta E, Calhoun DA, Oparil S. Sleep apnea, aldosterone, and resistant hypertension. Prog Cardiovasc Dis. 2009;51(5):371–380.
58. Persell SD. Prevalence of resistant hypertension in the United States, 2003-2008. Hypertension. 2011;57(6):1076–1080.
59. Niels Albert Graudal, Thorbjorn Hubeck-Graudal, Gesche Jurgens. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride. Cochrane Database Syst Rev. 2017;9(11):CD004022.
60. Stephen P Juraschek, Edgar R Miller 3rd, Connie M Weaver, et al. Effects of sodium reduction and the DASH diet in relation to baseline blood pressure. J Am Coll Cardiol. 2017;70(23):2841–2848.
61. Cemal Ozemek, Deepika R Laddu, Ross Arena, et al. The role of diet for prevention and management of hypertension. Curr Opin Cardiol. 2018;33(4):388–393.
62. Nicklas BJ, Ambrosius W, Messier SP, et al. Diet-induced weight loss, exercise, and chronic inflammation in older, obese adults: a randomized controlled clinical trial. Am J Clin Nutr. 2004;79(4):544–551.
63. Seshadri P, Iqbal N, Stern L, et al. A randomized study comparing the effects of a low-carbohydrate diet and a conventional diet on lipoprotein subfractions and C-reactive protein levels in patients with severe obesity. Nutr Clin Pract. 2004;21(2):187–188.
64. Chirinos JA, Gurubhagavatula I, Teff K, et al. CPAP, weight loss, or both for obstructive sleep apnea. N Engl J Med. 2014;370(24):2265–2275.
65. Masood Ahmad, Devan Makati, Sana Akbar. Review of and updates on hypertension in obstructive sleep apnea. Int J Hypertens. 2017;2017:1848375.
66. Duran-Cantolla J, Aizpuru F, Martinez-Null C, et al. Obstructive sleep apnea/hypopnea and systemic hypertension. Sleep Med Rev. 2009;13(5):323–331.
67. Lavie P, Herer P, Hoffstein V. Obstructive sleep apnoea syndrome as a risk factor for hypertension: population study. BMJ. 2000;320(7233):479–482.
68. Silverberg DS, Oksenberg A. Are sleep-related breathing disorders important contributing factors to the production of essential hypertension? Curr Hypertens Rep. 2001;3(3):209–215.
69. Alajmi M, Mulgrew AT, Fox J, et al. Impact of continuous positive airway pressure therapy on blood pressure in patients with obstructive sleep apnea hypopnea: a meta-analysis of randomized controlled trials. Lung. 2007;185(2):67–72.
70. Hui DS, To KW, Ko FW, et al. Nasal CPAP reduces systemic blood pressure in patients with obstructive sleep apnoea and mild sleepiness. Thorax. 2006;61(12):1083–1090.
71. Marin JM, Agusti A, Villar I, et al. Association between treated and untreated obstructive sleep apnea and risk of hypertension. JAMA. 2012;307(20):2169–2176.
72. Haentjens P, Van Meerhaeghe A, Moscariello A, et al. The impact of continuous positive airway pressure on blood pressure in patients with obstructive sleep apnea syndrome: evidence from a meta-analysis of placebo-controlled randomized trials. Arch Intern Med. 2007;167(8):757–764.
73. Ishida K, Kato M, Kato Y, et al. Appropriate use of nasal continuous positive airway pressure decreases elevated c-reactive protein in patients with obstructive sleep apnea. Chest. 2009;136(1):125–129.
74. Phillips CL, Yang Q, Williams A, et al. The effect of short-term withdrawal from continuous positive airway pressure therapy on sympathetic activity and markers of vascular inflammation in subjects with obstructive sleep apnoea. J Sleep Res. 2007;16(2):217–225.
75. MA Martínez-García, R Gómez-Aldaraví, JJ Soler-Cataluña, et al. Positive effect of CPAP treatment on the control of difficult-to-treat hypertension. Eur Respir J. 2007;29(5):951–957.
76. Jelic S, Padeletti M, Kawut SM, et al. Inflammation, oxidative stress, and repair capacity of the vascular endothelium in obstructive sleep apnea. Circulation. 2008;117(17):2270–2278.
77. Dimsdale JE, Loredo JS, Profant J. Effect of continuous positive airway pressure on blood pressure: a placebo trial. Hypertension. 2000;35(1):144–147.
78. Pepperell JC, Ramdassingh-Dow S, Crosthwaite N, et al. Ambulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial. Lancet. 2002;359(9302):204–210.
79. Barbé F, Durán-Cantolla J, Capote F, et al. Long-term effect of continuous positive airway pressure in hypertensive patients with sleep apnea. Am J Respir Crit Care Med. 2010;181(7):718–726.
80. Hermida RC, Ayala DE, Smolensky MH, et al. Sleep-time blood pressure: Unique sensitive prognostic marker of vascular risk and therapeutic target for prevention. Sleep Med Rev. 2017;33:17–27.
81. Becker HF, Jerrentrup A, Ploch T, et al. Effect of nasal continuous positive airway pressure treatment on blood pressure in patients with obstructive sleep apnea. Circulation. 2003;107(1):68–73.
82. Bazzano LA, Khan Z, Reynolds K, et al. Effect of nocturnal nasal continuous positive airway pressure on blood pressure in obstructive sleep apnea. Hypertension. 2007;50(2):417–423.
83. Montesi SB, Edwards BA, Malhotra A, et al. The effect of continuous positive airway pressure treatment on blood pressure: a systematic review and meta-analysis of randomized controlled trials. J Clin Sleep Med. 2012;8(5):587–596.
84. Tara Shrout, David W Rudy, Michael T Piascik. Hypertension update, JNC8 and beyond. Curr Opin Pharmacol. 2017;33:41–46.
85. Calhoun DA, Jones D, Textor S, et al. Resistant hypertension: diagnosis, evaluation, and treatment. a scientific statement from the American heart association professional education committee of the council for high blood pressure research. Circulation. 2008;24;117(25):e510–e526.
86. M Demede, A Pandey, F Zizi, et al. Resistant hypertension and obstructive sleep apnea in the primary-care setting. Int J Hypertens. 2011;2011:340929.
87. Akram Khan, Nimesh K Patel, Daniel JO Hearn, et al. Resistant hypertension and obstructive sleep apnea. Int J Hypertens. 2013:193010.
88. Robert M Carey, Swati Sakhuja , David A Calhoun, et al. Prevalence of apparent treatment-resistant hypertension in the United States. Hypertension. 2019;73(2):424–431.
89. Grace Oscullo, Gerard Torres, Francisco Campos-Rodriguez, et al. Resistant/refractory hypertension and sleep apnoea: current knowledge and future challenges. J Clin Med. 2019;8(11):1872.
90. Robert M Carey, David A Calhoun, George L Bakris, et al. Resistant hypertension: detection, evaluation, and management: a scientific statement from the American heart association. Hypertension. 2018;72(5):e53–e90.
91. Jean Jacques Noubiap, Jobert Richie Nansseu , Ulrich Flore Nyaga , et al. Global prevalence of resistant hypertension: a meta-analysis of data from 3.2 million patients. Heart. 2018;105(2):98–105.
92. Doroszko A, Janus A, Szahidewicz-Krupska E, et al. Resistant hypertension. Adv Clin Exp Med. 2016;25(1):173–183.
93. Hans S, Reilly JP. Resistant hypertension in 2017. Curr Opin Cardiol. 2017;32(4):389–396.
94. Maria Czarina Acelajado, Roberto Pisoni, Tanja Dudenbostel, et al. Refractory hypertension: definition, prevalence, and patient characteristics. J Clin Hypertens (Greenwich). 2012;14(1):7–12
95. Grote L, Hedner J, Peter JH. Sleep-related breathing disorder is an independent risk factor for uncontrolled hypertension. J Hypertens. 2000;18(6):679–685.
96. Gonçalves SC, Martinez D, Gus M, et al. Obstructive sleep apnea and resistant hypertension: a case-control study. Chest. 2007;132(6):1858–1862.
97. Lavie P, Hoffstein V. Sleep apnea syndrome: a possible contributing factor to resistant. Sleep. 2001;24(6):721–725.
98. Ziegler MG, Milic M. Sympathetic nerves and hypertension in stress, sleep apnea, and caregiving. Curr Opin Nephrol Hypertens. 2017;26(1):26–30.
99. Pratt-Ubunama MN, Nishizaka MK, Boedefeld RL, et al. Plasma aldosterone is related to severity of obstructive sleep apnea in subjects with resistant hypertension. Chest. 2007;131(2):453–459.
100. Gaddam K, Pimenta E, Thomas SJ, et al. Spironolactone reduces severity of obstructive sleep apnoea in patients with resistant hypertension: a preliminary report. J Hum Hypertens. 2010;24(8):532–537.
101. Dudenbostel T, Calhoun DA. Resistant hypertension, obstructive sleep apnoea and aldosterone. J Hum Hypertens. 2012;26(5):281–287.
102. Prejbisz A, Kołodziejczyk-Kruk S, Lenders JWM, et al. Primary aldosteronism and obstructive sleep apnea: is this a bidirectional relationship? Horm Metab Res. 2017;49(12):969–976.
103. Lai S, Mordenti M, Mangiulli M, et al. Resistant hypertension and obstructive sleep apnea syndrome in therapy with continuous positive airway pressure: evaluation of blood pressure, cardiovascular risk markers and exercise tolerance. Eur Rev Med Pharmacol Sci. 2019;23(21):9612–9624.
104. Lloberes P, Sampol G, Espinel E, et al. A randomized controlled study of CPAP effect on plasma aldosterone concentration in patients with resistant hypertension and obstructive sleep apnea. J Hypertens. 2014;32(8):1650–1657.
105. Ke X, Guo W, Peng H, et al. Association of aldosterone excess and apnea-hypopnea index in patients with resistant hypertension. Sci Rep. 2017;7:45241.
106. Nishizaka MK, Zaman MA, Calhoun DA. Efficacy of low-dose spironolactone in subjects with resistant hypertension. Am J Hypertens. 2003;16(11 Pt 1):925–930.
107. Chapman N, Dobson J, Wilson S, et al. Effect of spironolactone on blood pressure in subjects with resistant hypertension. Hypertension. 2007;49(4):839–845.
108. Ziegler MG, Milic M, Lu X, et al. Effect of obstructive sleep apnea on the response to hypertension therapy. Clin Exp Hypertens. 2017;39(5):409–415.
109. Gilardini L, Lombardi C, Redaelli G, et al. Effect of continuous positive airway pressure in hypertensive patients with obstructive sleep apnea and high urinary metanephrines. J Hypertens. 2018;36(1):199–204.
110. Elmasry A, Lindberg E, Hedner J, et al. Obstructive sleep apnoea and urine catecholamines in hypertensive males: a population-based study. Eur Respir J. 2002;19(3):511–517.
111. Pinto P, Barbara C, Montserrat JM, et al. Effects of CPAP on nitrate and norepinephrine levels in severe and mild-moderate sleep apnea. BMC Pulm Med. 2013;13:13.
112. Casitas R, Martínez-Cerón E, Galera R, et al. The effect of treatment for sleep apnoea on determinants of blood pressure control. Eur Respir J. 2017;50(5):1701261.
113. Otsuka R, Ribeiro de Almeida F, Lowe AA, et al. The effect of oral appliance therapy on blood pressure in patients with obstructive sleep apnea. Sleep Breath. 2006;10(1):29–36.
114. Gotsopoulos H, Chen C, Qian J, et al. Oral appliance therapy improves symptoms in obstructive sleep apnea: a randomized, controlled trial. Am J Respir Crit Care Med. 2002;166(5):743–748.
115. Gotsopoulos H, Kelly JJ, Cistulli PA. Oral appliance therapy reduces blood pressure in obstructive sleep apnea: a randomized, controlled trial. Sleep. 2004;27(5):934–941.
116. Parati G, Ochoa JE, Bilo G, et al. Obstructive sleep apnea syndrome as a cause of resistant hypertension. Hypertens Res. 2014;37(7):601–613.
117. Peker Y, Hedner J, Norum J, et al. Increased incidence of cardiovascular disease in middle-aged men with obstructive sleep apnea: a 7-year follow-up. Am J Respir Crit Care Med. 2002;166(2):159–165.
118. Durgan DJ. Obstructive sleep apnea-induced hypertension: role of the gut microbiota. Curr Hypertens Rep. 2017;19(4):35.
119. Hou H, Zhao Y, Yu W, et al. Association of obstructive sleep apnea with hypertension: a systematic review and meta-analysis. J Glob Health. 2018;8(1):010405.
120. Dernaika TA, Kinasewitz GT, Tawk MM. Effects of nocturnal continuous positive airway pressure therapy in patients with resistant hypertension and obstructive sleep apnea. J Clin Sleep Med. 2009;5(2):103–107.
121. Peppard PE, Young T, Palta M, et al. Prospective study of the association between sleep-disordered breathing and hypertension. N Engl J Med. 2000;342(19):1378–1384.
122. Lanfranchi P, Somers VK. Obstructive sleep apnea and vascular disease. Respir Res. 2001;2(6):315–319.
123. Mohsenin V. Obstructive sleep apnea and hypertension: a critical review. Curr Hypertens Rep. 2014;16(10):482.
124. Oguz Kokturk , Tansu Ulukavak Ciftci, Elif Mollarecep, et al. Elevated c-reactive protein levels and increased cardiovascular risk in patients with obstructive sleep apnea syndrome. Int Heart J. 2005;46(5):801–809.
125. Lourdes Lozano, José Luis Tovar, Gabriel Sampol, et al. Continuous positive airway pressure treatment in sleep apnea patients with resistant hypertension: a randomized, controlled trial. J Hypertens. 2010;28(10):2161–2168.
126. Dorkova Z, Petrasova D, Molcanyiova A, et al. Effects of continuous positive airway pressure on cardiovascular risk profile in patients with severe obstructive sleep apnea and metabolic syndrome. Chest. 2008;134(4):686–692.
127. Coughlin SR, Mawdsley L, Mugarza JA, et al. Cardiovascular and metabolic effects of CPAP in obese males with OSA. Eur Respir J. 2007;29(4):720–727.
128. Calhoun DA, Nishizaka MK, Zaman MA, et al. Aldosterone excretion among subjects with resistant hypertension and symptoms of sleep apnea. Chest. 2004;125(1):112–117.
129. Logan AG, Tkacova R, Perlikowski SM, et al. Refractory hypertension and sleep apnoea: effect of CPAP on blood pressure and baroreflex. Eur Respir J. 2003;21(2):241–247.
130. Chahal CA, Somers VK. Secondary hypertension: obstructive sleep apnea. J Am Soc Hypertens. 2015;9(3):244–247.
131. Ip MS, Tse HF, Lam B, et al. Endothelial function in obstructive sleep apnea and response to treatment. Am J Respir Crit Care Med. 2004;169(3):348–353.
132. Weiss JW, Liu Y, Huang J. Physiological basis for a causal relationship of obstructive sleep apnoea to hypertension. Exp Physiol. 2007;92(1):21–26.