Sleep-disordered breathing and hypertension: past lessons, future directions

Cognitive impairment in obstructive sleep apnea syndrome: a descriptive review

PURPOSE

Obstructive sleep apnea syndrome is a clinical sleep disorder defined by total or partial airflow restraint during sleep that results in fragmented sleep and hypoxemia, impacting negatively with cognitive functioning. This review was conducted on studies investigating structural brain alteration and cognitive impairment in obstructive sleep apnea syndrome.

METHOD

We searched on PubMed databases and screening references of included studies and review articles for additional citations. From initial 190 publications, only 17 met search criteria and described the cognitive impairment in obstructive sleep apnea syndrome.

RESULTS

Findings showed that patients with this syndrome had worse performance than healthy controls in attention, memory, and executive functions, showing specific neuroanathomical features. Cognitive impairment is also related to the severity of pathology. Treatment could improve certain cognitive aspects.

CONCLUSIONS

Cognitive deficits seem to be mainly attributable to decreased daytime vigilance and nocturnal hypoxemia.

Brain activation changes before and after PAP treatment in obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea syndrome (OSAS) is associated with cognitive and functional deficits, most of which are corrected after positive airway pressure (PAP) treatment. Previous studies investigating the neural underpinnings of OSAS failed to provide consistent results both on the cerebral substrates underlying cognitive deficits and on the effect of treatment on these anomalies. The aims of the study were a) to investigate whether never-treated OSA patients demonstrated differences in brain activation compared to healthy controls during a cognitive task; and b) to investigate whether any improvements in cognitive functioning found in OSA patients after treatment reflected a change in the underlying cerebral activity.

DESIGN

OSA patients and healthy controls underwent functional magnetic resonance imaging (fMRI) scanning. They were compared on performance and brain activation during a 2-back working-memory task. Patients were also re-evaluated after 3 months treatment with PAP. Cognitive functions were evaluated using neurocognitive tests. Sleepiness (ESS), mood (Beck Depression Inventory) and, quality-of-life (SF-36) were also assessed.

SETTING

The Sleep Disorders Center and CERMAC at the Vita-Salute San Raffaele University.

PATIENTS OR PARTICIPANTS

17 OSA patients and 15 age- and education-matched healthy controls.

INTERVENTIONS

PAP treatment for 3 months.

MEASUREMENTS AND RESULTS

Compared to controls, never-treated OSA patients showed increased activations in the left frontal cortex, medial precuneus, and hippocampus, and decreased activations in the caudal pons. OSA patients showed decreases in activation with treatment in the left inferior frontal gyrus and anterior cingulate cortex, and bilaterally in the hippocampus. Most neurocognitive domains, impaired at baseline, showed significant improvement after treatment.

CONCLUSIONS

OSA patients showed an overrecruitment of brain regions compared to controls, in the presence of the same level of performance on a working-memory task. Decreases of activation in prefrontal and hippocampal structures were observed after treatment in comparison to baseline. These findings may reflect a neural compensation mechanism in never-treated patients, which is reduced by effective treatment.

The relationship between aortic stiffness and cardiac function in patients with obstructive sleep apnea, independently from systemic hypertension

OBJECTIVE

We sought to evaluate aortic function and its relationship with left ventricular (LV) function in patients with obstructive sleep apnea syndrome (OSAS), with or without systemic hypertension.

METHODS

A total of 29 patients with OSAS, 28 patients with systemic hypertension without OSAS, and 19 patients having both disorders were chosen as a study group, and 29 participants without these two disorders were taken as the control group; none of the patients had a history of cardiac disease. All of them underwent echocardiography and polysomnography. Aortic strain and distensibility were calculated from the aortic diameters measured by echocardiography and blood pressure obtained by cuff-sphygmomanometer. Cardiac functions were determined using echocardiography comprising standard 2-dimensional and conventional Doppler and Doppler tissue imaging.

RESULTS

Aortic strain (mean +/- SD; 6.1 +/- 2.7% vs 6.4 +/- 2.4%, 4.7 +/- 1.8%, and 13.7 +/- 4.5%, P < .001, respectively) and distensibility (mean +/- SD 2.8 +/- 1.6 vs 2.5 +/- 0.9, 1.7 +/- 0.7, and 6.2 +/- 3.2 10(-6) cm(2) dyn(-1)P < .001, respectively) were significantly decreased in the patient groups (OSAS, hypertensive, and OSAS and hypertensive) compared with the control group. LV long-axis and diastolic functions were also impaired in the study group. There were good correlations between the aortic stiffness and LV function parameters. In a multivariate analysis, aortic strain was the parameter found to be most strongly associated both with the Doppler tissue imaging mean peak early/late diastolic velocity ratio and the LV mitral lateral annular plane systolic excursion.

CONCLUSION

Aortic stiffness parameters (aortic strain and distensibility), LV systolic long-axis function indicators (mitral lateral annular plane systolic excursion, peak systolic myocardial velocity at lateral annulus, peak systolic myocardial velocity at septal annulus), and Doppler tissue imaging-derived LV diastolic indices were found abnormal in patients with OSAS, hypertension, or both. Thus, subclinical cardiac dysfunction has been found in patients with OSAS independent from the systemic hypertension.

Effect of repetitive hypoxic apnoeas on baroreflex function in humans

Baroreflex function is impaired in patients with obstructive sleep apnoea. We tested the hypothesis that short-term exposure to repetitive hypoxic apnoeas (RHA) produces prolonged impairment in baroreflex function. Baroreflex function was determined using the modified Oxford technique in 14 subjects (26 +/- 1 years). Baroreflex sensitivity (BRS) was quantified from the R-R interval-systolic blood pressure (BP; cardiovagal BRS), heart rate-systolic BP (HR BRS) and muscle sympathetic nerve activity (MSNA)-diastolic BP (sympathetic BRS) relations. RHA involved subjects performing repetitive end-expiratory apnoeas (20 s) every minute for 30 min during intermittent hypoxia to accentuate oxygen desaturation. After RHA, BP and MSNA at rest were elevated. BRS was measured approximately 7 (Post 1), approximately 30 (Post 2) and approximately 50 min (Post 3) after RHA to provide insight into the temporal pattern of responses. Cardiovagal BRS (16.8 +/- 1.3, 16.5 +/- 1.6, 17.6 +/- 2.0 and 17.4 +/- 1.5 ms mmHg(-1) for Pre, Post 1, Post 2 and Post 3, respectively), HR BRS (-1.1 +/- 0.1, -1.1 +/- 0.1, -1.3 +/- 0.1 and -1.4 +/- 0.1 beats min(-1) mmHg(-1)) and sympathetic BRS (-4.5 +/- 0.6, -4.4 +/- 0.7, -3.7 +/- 0.5 and -4.7 +/- 1.0 arbitrary units (au) beat(-1) mmHg(-1)) were unchanged by RHA. In contrast, the operating points of the baroreflexes were shifted rightward (to higher levels of BP) and upward (to higher levels of heart rate and MSNA) after RHA (P < 0.05). Time control studies performed in five additional subjects showed no change in any of the measured variables over time. Collectively, these data indicate that short-term exposure to RHA shifts ('resets') the baroreflex stimulus-response curve to higher levels of BP without influencing BRS for extended periods of time.

Comparison of conventional nighttime with automatic or manual daytime CPAP titration in unselected sleep apnea patients: study of the usefulness of daytime titration studies

Daytime CPAP titration studies with full polysomnography have been successfully performed in patients with severe sleep apnea-hypopnea syndrome (SAHS). The implementation of daytime studies in unselected SAHS patients could help to reduce the waiting lists for CPAP titrations. The main purpose of this study was to compare the effectiveness of conventional versus manual or automatic daytime CPAP titration in unselected patients with SAHS. Ninety-three consecutive patients with SAHS in whom CPAP was indicated were assigned to conventional titration or to manual or automatic (AutoSet) daytime CPAP titration, after sleep deprivation. The number of valid studies, sleep architecture, final pressure selected and mean pressure in the different sleep stages were compared. Changes in sleepiness (Epworth sleepiness score) and hours of CPAP use were assessed after 3 months of treatment. Four patients did not sleep (3 AutoSet, 1 conventional daytime groups). Sleep latency was shorter during automatic daytime titration whereas REM latency was shorter in daytime studies; the percentage of sleep stages was similar during all types of titration. CPAP requirements were significantly higher during REM sleep in conventional and manual daytime titrations while mean pressure was unchanged throughout sleep stages during AutoSet titration. CPAP pressure selected with conventional or daytime manual titration (7.5(2.2) cm H2O and 7.4(1.5) cm H2O, ns) were significantly lower (P< 0.001) than with AutoSet (9.4(1.6) cm H20. All groups showed similar decrease of sleepiness and hours of use of CPAP at 3 months of follow-up. Automatic and manual daytime PSG studies after sleep deprivation are useful for CPAP titration in unselected patients with SAHS. Pressure selected with AutoSet is significantly higher than with conventional daytime or nighttime titration, although not significant in terms of treatment compliance and symptom improvement.

Neuropsychological sequelae of obstructive sleep apnea-hypopnea syndrome: a critical review

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a well-recognized clinical sleep disorder that results in chronically fragmented sleep and recurrent hypoxemia. The primary daytime sequelae of the disorder include patient reports of excessive daytime sleepiness, depression, and attention and concentration problems. It has been well established that OSAHS negatively impacts certain aspects of cognitive functioning. The primary goals of this article are to (1) clarify the pattern of cognitive deficits that are specific to OSAHS; (2) identify the specific cognitive domains that improve with treatment; and (3) elucidate the possible mechanisms of cognitive dysfunction in OSAHS. At the conclusion of the paper, we propose a potential neurofunctional theory to account for the etiology of cognitive deficits in OSAHS. Thirty-seven peer-reviewed articles were selected for this review. In general, findings were equivocal for most cognitive domains. Treatment, however, was noted to improve attention/vigilance in most studies and consistently did not improve constructional abilities or psychomotor functioning. The results are discussed in the context of a neurofunctional theory for the effects of OSAHS on the brain.

Left ventricular hypertrophy and nocturnal hypoxemia in hemodialysis patients

OBJECTIVE

Nocturnal hypoxemia has recently been proposed as a cardiovascular risk factor in patients with chronic renal failure. In this study we have tested the hypothesis that this disturbance is associated with left ventricular hypertrophy (LVH) in dialysis patients.

METHODS

During a mid-week non-dialysis day, 38 hemodialysis patients underwent continuous monitoring of arterial O2 saturation (SaO2) during night-time as well as 24 h ambulatory blood pressure monitoring and echocardiography.

RESULTS

Eighteen patients had one or more episodes of O2 desaturation during night-time (average: 21 episodes; range 1 to 120) while the other 20 had no episode. Neither day-time arterial pressure nor heart rate were significantly associated with nocturnal hypoxemia. However there was a significant correlation between the night/day systolic ratio and the severity of hypoxemia during night-time (r = 0.36, P = 0.03). On multivariate analysis, nocturnal hypoxemia proved to be the stronger independent predictor of relative wall thickness, mean wall thickness and left ventricular mass index, suggesting that nocturnal O2 desaturation is linked to concentric hypertrophy and to concentric geometry of the left ventricle. Accordingly, the proportion of patients with such geometric alteration was higher (chi2 = 4.1, P = 0.04) in patients with a pulse oximetry severity score > 50th percentile [15 of 19 (79%)] than in those below this threshold [nine of 19 (47%)].

CONCLUSIONS

Nocturnal hypoxemia is an important correlate of LVH in hemodialysis patients. Such an association is largely independent of arterial pressure. These data further underscore the importance of disturbed respiratory control as a cardiovascular risk factor in dialysis patients.

Compliance with CPAP in elderly patients with OSA

Background: Obstructive sleep apnea (OSA) is common in the general population and especially in the geriatric age group. Nasal continuous positive airway pressure (CPAP) is a highly effective treatment but can be difficult for some patients to use.Objective: We investigated the question if older patients were less compliant with CPAP therapy than younger patients and may not realize its benefits.Methods: We conducted a prospective, non-randomized study comparing use of CPAP in patients over age 65 with patients under age 65. One hundred and seven consecutive patients with a new diagnosis of obstructive sleep apnea were started on therapy with nasal CPAP. We obtained follow-up data on all 107 patients. Compliance with CPAP was assessed by patients subjective report of use and, in a subset of 21 patients, by objective measurement using a microchip installed in the CPAP unit that measures actual hours of use at therapeutic pressure.Results: The percentage of patients using CPAP regularly was not different in the two groups: 70% of patients in the over age 65 group used CPAP regularly vs. 72% of patients under age 65. The over 65 group used CPAP 6.5 nights per week, an average of 6.5 h of use per night. The under 65 group was not significantly different, using CPAP 6.8 nights per week, a mean of 6.7 h of use per night.Conclusion: Patients over age 65 are able to tolerate CPAP as well as patients under age 65.

Is sleep-disordered breathing an independent risk factor for hypertension in the general population (13,057 subjects)?

OBJECTIVES Sleep-disordered breathing has been hypothesized to have a close relationship with hypertension but previous studies have reported mixed results. This is an important health issue that requires further clarification because of the potential impact on the prevention and control of hypertension.

METHODS

The relationship between hypertension and three forms of sleep-disordered breathing (chronic snoring, breathing pauses and obstructive sleep apnea syndrome (OSAS)) was assessed using representative samples of the non-institutionalized population of the UK, Germany and Italy (159 million inhabitants). The samples were comprised of 13,057 individuals aged 15-100 years who were interviewed about their sleeping habits and their sleep symptoms over the telephone using the Sleep-EVAL system.

RESULTS

OSAS was found in 1.9% (95% CI: 1.2% to 2.3%) of the UK sample, 1.8% (95% CI: 1.4% to 2.2%) of the German sample and 1.1% (95% CI: 0.8% to 1.4%) of the Italian sample. OSAS was an independent risk factor (odds ratio (OR): 9.7) for hypertension after controlling for possible confounding effects of age, gender, obesity, smoking, alcohol consumption, life stress, and, heart and renal disease.

CONCLUSIONS

Results from three of the most populated countries in Western Europe indicate that OSAS is an independent risk factor for hypertension. Snoring and breathing pauses during sleep appeared to be non-significant predictive factors.

Effect of continuous positive airway pressure on blood pressure : a placebo trial

This study examined the effect of continuous positive airway pressure (CPAP) treatment on blood pressure in patients with obstructive sleep apnea. Thirty-nine patients with sleep apnea were studied. Ambulatory blood pressure monitoring was obtained before and after patients were randomized to receive either 1 week of CPAP or placebo CPAP (CPAP administered at ineffective pressure). Blood pressure was examined over daytime hours (6 AM to 10 PM) and during nighttime hours (10 PM to 6 AM). Daytime mean arterial blood pressure decreased significantly but equally in both the active treatment group and the placebo treatment group (P=0.001). Nighttime mean arterial pressure levels decreased to a much greater extent over time in the patients who received active CPAP treatment (P=0. 032). CPAP does appear to decrease nighttime blood pressure. However, the decrease in daytime blood pressure may reflect a nonspecific response (ie, placebo), since both the active treatment group and the placebo treatment group developed comparable decreases in blood pressure.

Hypoglossal motoneurons are postsynaptically inhibited during carbachol-induced rapid eye movement sleep

The obstructive sleep apnea syndrome is characterized by the occurrence of cyclic snoring and frequent apneic episodes during sleep, with consequent hypoxia and hypercapnia. Obstructive sleep apnea syndrome is associated with excess daytime sleepiness, depression, and an increased incidence of ischemic cardiopathy, cardiac arrhythmias, systemic hypertension and brain infarction. Hypoglossal motoneurons, which innervate extrinsic and intrinsic muscles of the tongue, play a key role in maintaining the patency of the upper airway and in the pathophysiology of obstructive sleep apnea syndrome. Based on data obtained by using extracellular recording techniques, there is a consensus that hypoglossal motoneurons cease to discharge during rapid eye movement sleep, because they are disfacilitated. Since other somatic motoneurons are known to be postsynaptically inhibited during rapid eye movement sleep, we sought to determine, by the use of intracellular recording techniques during cholinergically induced rapid eye movement sleep, whether postsynaptic inhibitory mechanisms act on hypoglossal motoneurons. We found that, during this state, a powerful glycinergic premotor inhibitory system acts to suppress hypoglossal motoneurons. This finding opens new avenues for the treatment of obstructive sleep apnea syndrome, and provides a foundation to explore the neural and pharmacological control of respiration-related motoneurons during rapid eye movement sleep.

Sleep apnoea in ischaemic heart disease: differences between acute and chronic coronary syndromes

OBJECTIVE

To evaluate the incidence of sleep apnoea in acute and chronic coronary syndromes.

DESIGN

Analysis of sleep and breathing characteristics in a polysomnographic study.

SETTING

Cardiology department in tertiary referral centre.

PATIENTS

23 patients were studied soon after acute myocardial infarction (group 1), 22 after clinical stabilisation of unstable angina (group 2), and 22 who had stable angina (group 3). Conditions liable to cause sleep apnoea, such as obesity, chronic obstructive pulmonary disease, neurological disorders, or the use of benzodiazepines, were exclusion criteria.

MAIN OUTCOME MEASURES

Sleep apnoea and hypopnoea, oxygen saturation, and sleep indices evaluated soon after clinical stabilisation in groups 1 and 2 and also in group 3.

RESULTS

Sleep apnoea, mainly of the central type, was equally present in groups 1 and 2 (mean (SD) apnoea-hypopnoea index: 11.10 (19.42) and 14.79 (20.52), respectively) and more severe than in group 3 (2.82 (6.43), p < 0. 01). Total time spent at SaO(2) < 90%, although significantly greater in group 1 and 2 (0.89 (2.4), 1.42 (3.23) min) than in group 3 (0.01 (0.05) min, p < 0.05), was clinically irrelevant. More arousals per hour of sleep (p < 0.05) were detected in group 1 (5.15 (3.71)) and group 2 (5.31 (2.14)) than in group 3 (2.83 (1.51)).

CONCLUSIONS

Sleep apnoea, chiefly of the central type, not only characterises acute myocardial infarction, as found by others, but also unstable angina studied after recent stabilisation. Patient selection by exclusion of other causes of breathing disorders shows that coronary disease related apnoea is absent in the chronic coronary syndrome. In acute syndromes the lack of clinically significant apnoea related oxygen desaturation, together with the low associated incidence of major ischaemic and arrhythmic events, suggests that sleep apnoea is benign in these circumstances, despite a worsening of sleep quality.

Positive pressure therapy

Positive airway pressure in the treatment of obstructive sleep-disordered breathing (OSDB) is reviewed. Continuous positive airway pressure (CPAP), bilevel positive airway pressure, and variable (auto-CPAP) pressure, their mechanisms of action, benefits, and complications are examined. A perspective on the future of positive airway pressure therapy for OSDB is provided.