Pressure-heart rate responses to alpha-adrenergic stimulation and hormonal regulation in normotensive patients with obstructive sleep apnea

Sympathetic overactivity and nocturnal diuresis in obstructive sleep apnea alter the response to hypertension therapy

BACKGROUND

Obstructive sleep apnea (OSA) is associated with high blood pressure that responds poorly to usual antihypertensive therapy.

METHODS AND RESULTS

Forty-one subjects with OSA had 25% higher plasma norepinephrine and 42% higher epinephrine measured every 2 h over 24 h than 20 control subjects. They also excreted more sodium during sleep. This suggested that that a sympatholytic would be a more successful antihypertensive than a diuretic. To test this hypothesis we treated a second group of 23 hypertensive apneics with placebo, 6 weeks of the sympatholytic guanfacine and 6 weeks of hydrochlorothiazide in a crossover study. Guanfacine lowered 24-hour blood pressure by 9.6/6.7 mmHg, more than the 5.4/2.9 mmHg effect of hydrochlorothiazide (P < 0.05). Nighttime systolic blood pressure dipping was poor at 6.6 ± 1.8%. Hydrochlorothiazide did not alter blood pressure dipping but guanfacine improved dipping to 9.1 ± 1.2%, a better result (P = 0.03) than from the diuretic. Central aortic pressure by pulse wave analysis was 120/84 mmHg on hydrochlorothiazide and 109/72 on guanfacine, (P < 0.05). Guanfacine, but not hydrochlorothiazide, improved baroreflex sensitivity, heart rate variability and flow mediated vascular dilation, suggesting that decreasing the elevated sympathetic nerve activity of obstructive sleep apnea returned vascular function toward normal.

CONCLUSIONS

OSA is the most common condition associated with antihypertensive treatment failure. It increased sympathetic nerve activity day and night. Drugs that block sympathetic nerve function are not among the 4 most commonly recommended classes of antihypertensives but diuretics are. Sympatholytic therapy was superior to diuretic treatment for hypertension associated with sleep apnea.

TRIAL REGISTRATION

NCT, NCT02699125, Registered 26 February 2016 - Retrospectively registered, https://clinicaltrials.gov/study/NCT02699125 .

Influence and implications of the renin-angiotensin-aldosterone system in obstructive sleep apnea: An updated systematic review and meta-analysis

Obstructive sleep apnea is a chronic, sleep-related breathing disorder, which is an independent risk factor for cardiovascular disease. The renin-angiotensin-aldosterone system regulates salt and water homeostasis, blood pressure, and cardiovascular remodelling. Elevated aldosterone levels are associated with excess morbidity and mortality. We aimed to analyse the influence and implications of renin-angiotensin-aldosterone system derangement in individuals with and without obstructive sleep apnea. We pooled data from 20 relevant studies involving 2828 participants (1554 with obstructive sleep apnea, 1274 without obstructive sleep apnea). The study outcomes were the levels of renin-angiotensin-aldosterone system hormones, blood pressure and heart rate. Patients with obstructive sleep apnea had higher levels of plasma renin activity (pooled wmd+ 0.25 [95% confidence interval 0.04-0.46], p = 0.0219), plasma aldosterone (pooled wmd+ 30.79 [95% confidence interval 1.05-60.53], p = 0.0424), angiotensin II (pooled wmd+ 5.19 [95% confidence interval 3.11-7.27], p < 0.001), systolic (pooled wmd+ 5.87 [95% confidence interval 1.42-10.32], p = 0.0098) and diastolic (pooled wmd+ 3.40 [95% confidence interval 0.86-5.94], p = 0.0086) blood pressure, and heart rate (pooled wmd+ 3.83 [95% confidence interval 1.57-6.01], p = 0.0009) compared with those without obstructive sleep apnea. The elevation remained significant (except for renin levels) when studies involving patients with resistant hypertension were removed. Sub-group analysis demonstrated that levels of angiotensin II were significantly higher only among the Asian population with obstructive sleep apnea compared with those without obstructive sleep apnea. Body mass index accounted for less than 10% of the between-study variance in elevation of the renin-angiotensin-aldosterone system parameters. Patients with obstructive sleep apnea have higher levels of renin-angiotensin-aldosterone system hormones, blood pressure and heart rate compared with those without obstructive sleep apnea, which remains significant even among patients without resistant hypertension.

Changes of aldosterone levels in patients with type 2 diabetes complicated by moderate to severe obstructive sleep apnea-hypopnea syndrome before and after treatment with continuous positive airway pressure

Objective

Both obstructive sleep apnea–hypopnea syndrome (OSAHS) and type 2 diabetes mellitus (T2DM) are closely related to the renin-angiotensin-aldosterone system. We investigated whether hyperaldosteronemia is found in patients with OSAHS complicated by T2DM and whether continuous positive airway pressure (CPAP) treatment can significantly reduce the aldosterone level.

Methods

Patients with T2DM were classified into an OSAHS group [apnea–hypopnea index (AHI) of ≥15] and a control group (without OSAHS; AHI of <5). The OSAHS group was exposed to CPAP for 7 days (7 h/day).

Results

The plasma aldosterone, plasma renin, and urinary aldosterone levels were higher in the OSAHS than control group. The plasma aldosterone and renin levels were significantly lower after than before treatment in the OSAHS group, but they were still higher than the baseline levels in the control group. The post-treatment urinary aldosterone level was significantly higher in the OSAHS than control group. No correlation was found between the AHI and plasma renin, plasma aldosterone, and 24-hour urinary aldosterone levels. The blood glucose level in the OSAHS group did not significantly change after treatment.

Conclusions

The plasma and urine aldosterone levels are increased in patients with concurrent T2DM and OSAHS and are significantly reduced by CPAP.

Trial registration: ChiCTR-ION-16009837

Soluble (Pro)renin Receptor and Obstructive Sleep Apnea Syndrome: Oxidative Stress in Brain?

(Pro)renin receptor ((P)RR) is a multi-functional molecule that is related to both the renin-angiotensin system (RAS) and vacuolar H⁺-ATPase (v-ATPase), an ATP-dependent multi-subunit proton pump. Soluble (P)RR (s(P)RR), which consists of the extracellular domain of (P)RR, is present in blood and urine. Elevated plasma s(P)RR concentrations are reported in patients with chronic kidney disease and pregnant women with hypertension or diabetes mellitus. In addition, we have shown that plasma s(P)RR concentrations are elevated in patients with obstructive sleep apnea syndrome (OSAS). Interestingly, the levels are elevated in parallel with the severity of OSAS, but are not related to the presence of hypertension or the status of the circulating RAS in OSAS. It is known that v-ATPase activity protects cells from endogenous oxidative stress, and loss of v-ATPase activity results in chronic oxidative stress. We hypothesize that hypoxia and subsequent oxidative stress, perhaps in the brain, may be one of the factors that elevate plasma s(P)RR levels in OSAS.

Meta-analysis of effects of obstructive sleep apnea on the renin-angiotensin-aldosterone system

Background

Obstructive sleep apnea (OSA) is the most common cause of resistant hypertension, which has been proposed to result from activation of the renin–angiotensin–aldosterone system (RAAS). We meta-analyzed the effects of OSA on plasma levels of RAAS components.

Methods

Full-text studies published on MEDLINE and EMBASE analyzing fasting plasma levels of at least one RAAS component in adults with OSA with or without hypertension. OSA was diagnosed as an apnea-hypopnea index or respiratory disturbance index ≥ 5. Study quality was evaluated using the Newcastle-Ottawa Scale, and heterogeneity was assessed using the I² statistic. Results from individual studies were synthesized using inverse variance and pooled using a random-effects model. Subgroup analysis, sensitivity analysis, and meta-regression were performed, and risk of publication bias was assessed.

Results

The meta-analysis included 13 studies, of which 10 reported results on renin (n = 470 cases and controls), 7 on angiotensin II (AngII, n = 384), and 9 on aldosterone (n = 439). AngII levels were significantly higher in OSA than in controls [mean differences = 3.39 ng/L, 95% CI: 2.00–4.79, P < 0.00001], while aldosterone levels were significantly higher in OSA with hypertension than OSA but not with hypertension (mean differences = 1.32 ng/dL, 95% CI: 0.58–2.07, P = 0.0005). Meta-analysis of all studies suggested no significant differences in aldosterone between OSA and controls, but a significant pooled mean difference of 1.35 ng/mL (95% CI: 0.88–1.82, P < 0.00001) emerged after excluding one small-sample study. No significant risk of publication bias was detected among all included studies.

Conclusions

OSA is associated with higher AngII and aldosterone levels, especially in hypertensive patients. OSA may cause hypertension, at least in part, by stimulating RAAS activity.

Effect of intensified diuretic therapy on overnight rostral fluid shift and obstructive sleep apnoea in patients with uncontrolled hypertension

OBJECTIVES

Fluid displacement from the lower extremities to the upper body during sleep is strongly associated with obstructive sleep apnoea in hypertensive patients. The present pathophysiological study tests the hypothesis that intensified diuretic therapy will reduce the apnoea-hypopnoea index and blood pressure of uncontrolled hypertensive patients with obstructive sleep apnoea in proportion to the reduction in overnight change in leg fluid volume.

METHODS

Uncontrolled treated hypertensive patients underwent overnight polysomnography and measurement of overnight changes in leg fluid volume and neck circumference. Those with an apnoea-hypopnoea index at least 20 events per hour (n=16) received metolazone 2.5 mg and spironolactone 25 mg daily for 7 days after which the daily dose was doubled for 7 additional days. Baseline testing was again repeated.

RESULTS

Intensified diuretic therapy reduced the apnoea-hypopnoea index from 57.7 ± 33.0 to 48.5 ± 28.2 events per hour (P=0.005), overnight change in leg fluid volume from -418.1 ± 177.5 to -307.5 ± 161.9 ml (P<0.001) and overnight change in neck circumference from 1.2 ± 0.6 to 0.7 ± 0.4 cm (P<0.001). There was an inverse correlation between the reduction in overnight change in leg fluid volume and decrease in apnoea-hypopnoea index (r=-0.734, P=0.001). The reduction in overnight change in leg fluid volume was also significantly correlated with the change in morning blood pressure (r=0.708, P=0.002 for SBP; r=0.512, P=0.043 for DBP).

CONCLUSION

The findings provide further evidence that fluid redistribution from the legs to the neck during sleep contributes to the severity of obstructive sleep apnoea in hypertension and may be an important link between these two conditions.

Relationship of circadian pattern of urine sodium excretion to hypertension and obstructive sleep apnoea

OBJECTIVES

Obstructive sleep apnoea (OSA) and hypertension frequently coexist, and both are associated with higher night-time than daytime urine sodium excretion rate (UNaV). However, the relative contribution of each condition is unknown. We compared the circadian pattern of UNaV in hypertensive and normotensive patients with and without OSA.

METHODS

Hypertensive [blood pressure (BP) >140/90 or on antihypertensive medications, excluding diuretics] and normotensive (BP <135/85) patients underwent overnight polysomnography to determine the presence or absence of OSA (apnoea-hypopnoea index ≥10 or <10, respectively), same-day 24-h urine collection divided into day and night-time samples and automated evening BP measurement.

RESULTS

Twenty-six hypertensive (9 without and 17 with OSA) and 26 normotensive (15 without and 11 with OSA) patients were studied. Night-time UNaV was higher in the hypertensive than the normotensive patients. Whereas in the normotensive patients night-time UNaV was unaffected by OSA, in the hypertensive patients, it was higher in those with than without OSA (P = 0.009 for OSA × hypertension interaction). Night : day UNaV ratio was higher in hypertensive than normotensive patients, but was not significantly affected by OSA in either group. On multivariate analysis, SBP and apnoea-hypopnoea index were independent predictors of night-time UNaV (model r = 0.574, P < 0.001) and night : day UNaV ratio (model r = 0.397, P < 0.001). However, SBP was the strongest independent predictor.

CONCLUSIONS

In hypertensive patients, OSA exacerbates the reversal of the normal circadian sodium excretion pattern by elevating nocturnal UNaV, possibly via its BP-elevating effects. However, OSA does not affect nocturnal UNaV in normotensive patients.

Elevated plasma levels of soluble (pro)renin receptor in patients with obstructive sleep apnea syndrome: association with polysomnographic parameters

(Pro)renin receptor ((P)RR) is a specific receptor for both renin and its precursor prorenin. (P)RR was shown to be involved in pathophysiology of cardiovascular and renal diseases. Soluble (pro)renin receptor (s(P)RR), which is generated by furin from full length (P)RR, is present in blood. The aim of the present study is to clarify the association of plasma s(P)RR levels and the severity of OSAS. Plasma levels of s(P)RR were measured by ELISA in 58 male patients diagnosed as OSAS based on polysomnography, and 14 age-matched male control subjects. Blood samples were obtained at 6:00 a.m. just after overnight polysomnography. Plasma s(P)RR levels were significantly higher in patients with OSAS (9.0±2.0 ng/mL, mean ± SD) than in control subjects (7.4±1.5 ng/mL) (P=0.0026). Plasma s(P)RR levels showed a significant negative correlation with % stage rapid eye movement (REM) sleep (r=-0.377, p<0.005), and significant positive correlations with % stage 1 (r=0.374, p<0.005), arousal index (r=0.341, p<0.01), apnea hypopnea index (AHI) (r=0.352, p<0.01) and desaturation index (r=0.302, p<0. 05). In 12 OSAS patients with AHI ≥20, plasma levels of s(P)RR were studied after 3-month treatment with nasal continuous positive airway pressure (nCPAP). Plasma s(P)RR levels were significantly decreased after the nCPAP treatment (p=0.0016). The present study has shown for the first time elevated plasma s(P)RR levels in patients with OSAS. Plasma s(P)RR levels were associated with the severity of OSAS. Soluble (P)RR may serve as a plasma marker reflecting the severity of OSAS.

Plasma natriuretic peptides in children and adolescents with obstructive sleep apnea and their changes following intervention

OBJECTIVE

This study aimed to evaluate circulating natriuretic peptides (NP) concentration in obese and non-obese children and adolescents with and without obstructive sleep apnea (OSA), and their levels following OSA treatment.

METHODS

Subjects with habitual snoring and symptoms suggestive of OSA were recruited. They underwent physical examination and overnight polysomnography (PSG). OSA was diagnosed if obstructive apnea-hypopnea index (OAHI) was ≥1/h. Fasting serum atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were taken after overnight PSG. The subjects were divided into obese, non-obese, with and without OSA groups for comparisons.

RESULTS

One hundred fourteen children (77 were boys) with a median [interquartile range (IQR)] age of 10.8 (8.3-12.7) years (range: 2.4-11.8 years) were recruited. Sixty-eight subjects were found to have OSA. NP levels did not differ between subjects with and without OSA in both obese and non-obese groups. Stepwise multiple linear regressions revealed that body mass index (BMI) z-score was the only independent factor associated with NP concentrations. Fifteen children with moderate-to-severe OSA (OAHI >5/h) underwent treatment and there were no significant changes in both ANP and BNP levels after intervention.

CONCLUSION

Body mass index rather than OSA was the main determinant of NP levels in school-aged children and adolescents.

Role of nocturnal rostral fluid shift in the pathogenesis of obstructive and central sleep apnoea

Obstructive sleep apnoea (OSA) is common in the general population and increases the risk of motor vehicle accidents due to hypersomnolence from sleep disruption, and risk of cardiovascular diseases owing to repetitive hypoxia, sympathetic nervous system activation, and systemic inflammation. In contrast, central sleep apnoea (CSA) is rare in the general population. Although their pathogenesis is multifactorial, the prevalence of both OSA and CSA is increased in patients with fluid retaining states, especially heart failure, where they are associated with increased mortality risk. This observation suggests that fluid retention may contribute to the pathogenesis of both OSA and CSA. According to this hypothesis, during the day fluid accumulates in the intravascular and interstitial spaces of the legs due to gravity, and upon lying down at night redistributes rostrally, again owing to gravity. Some of this fluid may accumulate in the neck, increasing tissue pressure and causing the upper airway to narrow, thereby increasing its collapsibility and predisposing to OSA. In heart failure patients, with increased rostral fluid shift, fluid may additionally accumulate in the lungs, provoking hyperventilation and hypocapnia, driving below the apnoea threshold, leading to CSA. This review article will explore mechanisms by which overnight rostral fluid shift, and its prevention, can contribute to the pathogenesis and therapy of sleep apnoea.

Pharmacologic approaches for the management of symptoms and cardiovascular consequences of obstructive sleep apnea in adults

INTRODUCTION

Obstructive sleep apnea (OSA) is characterized by intermittent hypoxemia, arousals from sleep, and daytime sleepiness. Accumulating evidence indicates that hypoxemia and sleep disruption contribute to the development of cardiovascular abnormalities in OSA. OSA is effectively treated with continuous positive airway pressure (CPAP) therapy that splints open the airway during sleep. Studies have shown that CPAP therapy improves daytime sleepiness and attenuates cardiovascular abnormalities in patients with OSA. However, not all patients with OSA tolerate or adhere to CPAP therapy. Even patients who regularly use CPAP therapy may have a few hours each night exposed to the negative effects of untreated OSA. As a result, complementary pharmacologic therapies that can be used with CPAP therapy have the potential to reduce symptoms and consequences of OSA.

DISCUSSION

The wake-promoting medications modafinil and armodafinil effectively improve residual sleepiness in patients treated with CPAP therapy. Although results are equivocal so far, modafinil and armodafinil may also improve quality of life and global clinical condition in patients with OSA and residual sleepiness treated with CPAP therapy. Pharmacologic therapies also have the potential to be used with CPAP therapy to minimize cardiovascular perturbations and risk of cardiovascular disease. Preliminary studies suggest that inhibition of the enzyme xanthine oxidase and inhibition of sympathetic nervous system overactivity may have therapeutic potential to reduce cardiovascular harm in patients with OSA.

CONCLUSION

Future studies of pharmacologic therapies to reduce symptoms and cardiovascular consequences of OSA should be increasingly performed as our understanding of the mechanisms mediating the adverse effects of OSA continues to evolve.

Renin-angiotensin-aldosterone system in patients with sleep apnoea: prevalence of primary aldosteronism

Obstructive sleep apnoea (OSA) is a sleep disorder characterized by recurrent episodes of oxygen desaturation during sleep, representing an independent risk factor for cardiovascular disease, such as myocardial infarction, stroke, congestive heart failure and resistant hypertension. Several neurohormonal mechanisms have been suggested to account for blood pressure increases, such as sympathetic nervous system hyperactivity, oxidative stress, renin—angiotensin—aldosterone system (RAAS) activation, endothelin system activation, and endothelial dysfunction. The aim of this study was to evaluate the behaviour of RAAS and the presence of primary aldosteronism (PA) in these patients and possible correlations between RAAS and the severity of OSA. From October 2007 to November 2008 we studied 325 consecutive newly diagnosed hypertensive patients; 71 patients (21.8%) presented with clinical signs of sleep disorders, evaluated also through a specific questionnaire (Epworth Sleepiness Scale). In hypertensive patients with sleep disorders, 53 patients were affected by OSA; in this group 18 patients were affected by PA (five with aldosterone-producing adenoma (APA) and 13 with bilateral hyperplasia (IHA)); obesity was also demonstrated (BMI >" xbd="961" xhg="938" ybd="2430" yhg="2403"/> 30 kg/m2). Overall, in patients with OSA PRA levels correlated positively with apnoea/hypopnoea index (AHI; r = 0.35; p<0.01), and in all groups the waist circumference and the neck circumference were correlated positively with AHI ( r = 0.3 p<0.02 and r = 0.3 p<0.03, respectively). We revealed a high prevalence of PA in patients with OSA, and we can conclude that patients with hypertension and OSA, especially those who are newly diagnosed, must be evaluated for PA.

Obstructive sleep apnea and aldosterone

BACKGROUND

Obstructive sleep apnea (OSA) is a major risk factor for hypertension and has been associated with increased risk for cardiovascular morbidity. A dysregulated renin-angiotensin-aldosterone system may contribute to excess sodium retention and hypertension and may be activated in OSA. We tested the hypothesis that serum levels of aldosterone and plasma renin activity (PRA) are increased by apneic sleep in subjects without cardiovascular disease, compared to healthy control subjects.

METHODS AND RESULTS

Plasma aldosterone level was measured in 21 subjects with moderate to severe OSA and was compared to 19 closely matched healthy subjects. Plasma renin activity (PRA) was measured in 19 OSA patients and in 20 healthy controls. Aldosterone and PRA were measured before sleep (9 pm), after 5 hrs of untreated OSA ( 2am) and in the morning after awakening (6 am). There were no baseline (9pm) differences in serum aldosterone levels and PRA between the healthy controls and OSA patients (aldosterone: 55.2 +/- 9 vs 56.0 +/- 9 pg/mL; PRA: 0.99 +/- 0.15 vs. 1.15 +/- 0.15 ng/mL/hr). Neither several hours of untreated severe OSA nor CPAP treatment affected aldosterone levels and PRA in OSA patients. Diurnal variation of both aldosterone and PRA was observed in both groups, in that morning renin and aldosterone levels were higher than those measured at night before sleep.

CONCLUSIONS

Our study shows that patients with moderate to severe OSA without co-existing cardiovascular disease have plasma aldosterone and renin levels similar to healthy subjects. Neither untreated OSA nor CPAP treatment acutely affect plasma aldosterone or renin levels.

Plasma aldosterone is related to severity of obstructive sleep apnea in subjects with resistant hypertension

OBJECTIVE

Obstructive sleep apnea (OSA) and primary aldosteronism are common in subjects with resistant hypertension; it is unknown, however, if the two disorders are causally related. This study relates plasma aldosterone and renin levels to OSA severity in subjects with resistant hypertension, and in those with equally severe OSA but without resistant hypertension serving as control subjects.

METHODS

Seventy-one consecutive subjects referred to the University of Alabama at Birmingham (UAB) for resistant hypertension (BP uncontrolled on three medications) and 29 control subjects referred to UAB Sleep Disorders Center for suspected OSA were prospectively evaluated by an early morning plasma aldosterone concentration (PAC) and renin level, and by overnight, attended polysomnography.

RESULTS

OSA (apnea-hypopnea index [AHI] > or = 5/h) was present in 85% of subjects with resistant hypertension. In these subjects, PAC correlated with AHI (rho = 0.44, p = 0.0002) but not renin concentration. Median PAC was significantly lower in control subjects compared to subjects with resistant hypertension (5.5 ng/dL vs 11.0 ng/dL, p < 0.05) and not related to AHI. In male subjects compared to female subjects with resistant hypertension, OSA was more common (90% vs 77%) and more severe (median AHI, 20.8/h vs 10.8/h; p = 0.01), and median PAC was significantly higher (12.0 ng/dL vs 8.8 ng/dL, p = 0.006).

CONCLUSION

OSA is extremely common in subjects with resistant hypertension. A significant correlation between PAC and OSA severity is observed in subjects with resistant hypertension but not in control subjects. While cause and effect cannot be inferred, the data suggest that aldosterone excess may contribute to OSA severity.

Heart failure and sleep apnoea: to sleep perchance to dream

Heart failure and sleep apnoea are major health problems with an increasingly recognized association; evidence suggests that sleep apnoea may play a role in the progression of heart failure. However, confounding factors such as obesity, hypertension and coronary heart disease make this relationship uncertain and an independent correlation remains unproven. Diagnosis of sleep apnoea is suboptimal, as it is often asymptomatic and polysomnography is expensive and time-consuming. A simple and reliable screening protocol is required. All heart failure patients should be considered to be at high risk of sleep apnoea, as this association might be linked to adverse outcome. Continuous positive airway pressure has shown some beneficial effects, but long-term outcome and improvement in survival remains to be demonstrated. Despite recent advances in the understanding of the complex relationship between heart failure and sleep apnoea, there are a number of areas requiring further investigation, which may have important implications for the management and prognosis of a significant number of patients.

Increased Atrial and Brain Natriuretic Peptides in Adults With Cyanotic Congenital Heart Disease

Background— Brain natriuretic peptide (BNP) levels are used in the evaluation of patients with heart disease, yet there is little understanding of the effect of hypoxia on natriuretic peptide secretion. Furthermore, recent data suggest that oxytocin may mediate stretch-induced atrial natriuretic peptide (ANP) secretion.

Methods and Results— Ten patients with cyanotic congenital heart defects and 10 control subjects were studied. N-terminal proatrial natriuretic peptide and N-terminal probrain natriuretic peptide levels were 4-fold ( P =0.02) and 12-fold ( P =0.03) greater in cyanotic patients than in control subjects. Cyanotic patients had reduced body water compared with control subjects, although the difference did not reach statistical significance ( P =0.22). In a separate group of patients, cardiac myocytes were isolated from the right atrial appendage during CABG. The amount of oxygen in the buffered saline was varied to simulate hypoxia. Isolated hypoxic atrial myocytes had 43% fewer dense surface secretory granules compared with normoxic myocytes ( P <0.0001). Immunohistochemical staining demonstrated decreased ANP and BNP in hypoxic compared with normoxic right atrial tissue. Isolated myocytes also degranulated when incubated with oxytocin ( P <0.0001), but there was no difference in oxytocin levels in cyanotic patients compared with control subjects ( P =0.49).

Conclusions— ANP and BNP are markedly elevated in adults with cyanotic congenital heart disease despite reduced body water. Our results show that hypoxia is a direct stimulus for ANP and BNP secretion in human cardiac myocytes. These findings may have implications for the interpretation of BNP levels in the assessment of patients with heart and lung disease.

Aldosterone Excretion Among Subjects With Resistant Hypertension and Symptoms of Sleep Apnea

OBJECTIVE

The severity of obstructive sleep apnea (OSA) correlates with the difficulty of controlling BP. The mechanism, however, by which sleep apnea contributes to the development of resistant hypertension remains obscure. Having observed a high prevalence of OSA among hypertensive subjects with primary hyperaldosteronism, we hypothesized a possible association between sleep apnea and aldosterone excretion.

DESIGN

In consecutive subjects referred to a university clinic for resistant hypertension, we prospectively determined plasma renin activity (PRA), plasma aldosterone concentration (PAC), and 24-h urinary aldosterone excretion during high dietary salt ingestion. In addition, all subjects completed the Berlin Questionnaire, a survey designed to identify subjects at risk of having sleep apnea. Primary hyperaldosteronism (PA) was defined as a PRA < 1.0 ng/mL/h and 24-h urinary aldosterone excretion > 12 micro g during high urinary sodium excretion (> 200 mEq/24 h).

RESULTS

Of the 114 subjects evaluated, 72 subjects had a high probability and 42 subjects had a low probability of having sleep apnea based on their responses to the Berlin Questionnaire. Subjects at high risk for sleep apnea were almost two times more likely to have PA diagnosed (36 vs 19%, p < 0.05), tended to have lower PRA (1.2 +/- 1.8 ng/mL/h vs 1.9 +/- 4.1 ng/mL/h), and had significantly greater 24-h urinary aldosterone excretion (13.6 +/- 9.6 micro g vs 9.8 +/- 7.6 micro g, p < 0.05) compared to subjects at low risk of sleep apnea.

CONCLUSION

These data provide evidence of increased aldosterone excretion in subjects with resistant hypertension and symptoms of sleep apnea. While the causality of this association is unknown, it is hypothesized that sleep apnea contributes to the development of resistant hypertension by stimulating aldosterone excretion.

Sleep-disordered breathing and hypotension

We investigated the presence of low blood pressure (BP) in 4,409 subjects referred for overnight polysomnography. A low resting arterial BP (systolic BP < 105 mm Hg, diastolic BP < 65 mm Hg) was present in 101 subjects (2.3%). Low BP was more prevalent in subjects with upper airway resistance syndrome (UARS) (23%) than in subjects with obstructive sleep apnea syndrome (OSAS) (0.06%), parasomnia (0.7%), restless leg syndrome (0.9%), or psychological insomnia (0.9%). In order to investigate BP homeostasis, we conducted polysomnography followed by tilt-table testing on 15 subjects with orthostatic intolerance (OI) and UARS, five normotensive subjects with UARS, five subjects with insomnia and low BP, 15 subjects with OSAS, and 15 healthy control subjects. Fifteen subjects with UARS and OI and 15 healthy controls also underwent 24-h ambulatory BP monitoring. Subjects with OI and UARS had lower mean daytime systolic (119 +/- 28 mm Hg) and diastolic (75 +/- 18 mm Hg) BP than did control subjects (131 +/- 35 mm Hg and 86 +/- 19 mm Hg, respectively) (p < 0.05). During tilt-table testing, subjects with UARS and a history of OI had a greater decrease in systolic BP (27 +/- 3 mm Hg) than did control subjects (7.5 +/- 1.6 mm Hg), subjects with OSAS (6.8 +/- 1.2 mm Hg), normotensive subjects with UARS (7.2 +/- 0.84 mm Hg), or hypotensive insomniacs (7.4 +/- 1.1 mm Hg) (p < 0.01). We conclude that approximately one fifth of subjects with UARS have low BP and complain of OI. Tilt-table testing may be indicated to confirm orthostatic intolerance in subjects with UARS.