Sleep related breathing disorders in older men: a search for underlying mechanisms

Sleep apnoea in the elderly: a great challenge for the future

Due in part to overall improvements in health, the population of elderly individuals is increasing rapidly. Similarly, obstructive sleep apnoea (OSA) is both gaining increased recognition and also increasing due to the worldwide obesity epidemic. The overlap of OSA and aging is large, but there is strong plausibility for causation in both directions: OSA is associated with pathological processes that may accelerate aging and aging related processes; aging may cause physical and neurological changes that predispose to obstructive (and central) apnoea. In addition, the common symptoms (e.g. excessive daytime somnolence, defects in memory and cognition), possible physiological consequences of OSA (e.g. accelerated cardiovascular and cerebrovascular atherosclerosis), and changes in metabolic and inflammatory markers overlap with the symptoms and associated conditions seen in aging. There is also the possibility of synergy in the effects of these symptoms and conditions on quality of life, as well as a need to separate treatable consequences of OSA from age-related complaints. Taken together, the above make it essential to review the interaction of OSA and aging, both proven and suspected. The present review examines some aspects of what is known and points to the need for further investigation of the relationships, given the large number of potentially affected subjects.

A multicentre randomised controlled trial and economic evaluation of continuous positive airway pressure for the treatment of obstructive sleep apnoea syndrome in older people: PREDICT

BACKGROUND

The therapeutic and economic benefits of continuous positive airway pressure (CPAP) for the treatment of obstructive sleep apnoea syndrome (OSAS) have been established in middle-aged people. In older people there is a lack of evidence.

OBJECTIVE

To determine the clinical efficacy of CPAP in older people with OSAS and to establish its cost-effectiveness.

DESIGN

A randomised, parallel, investigator-blinded multicentre trial with within-trial and model-based cost-effectiveness analysis.

METHODS

Two hundred and seventy-eight patients, aged ≥ 65 years with newly diagnosed OSAS [defined as oxygen desaturation index at ≥ 4% desaturation threshold level for > 7.5 events/hour and Epworth Sleepiness Scale (ESS) score of ≥ 9] recruited from 14 hospital-based sleep services across the UK.

INTERVENTIONS

CPAP with best supportive care (BSC) or BSC alone. Autotitrating CPAP was initiated using standard clinical practice. BSC was structured advice on minimising sleepiness.

COPRIMARY OUTCOMES

Subjective sleepiness at 3 months, as measured by the ESS (ESS mean score: months 3 and 4) and cost-effectiveness over 12 months, as measured in quality-adjusted life-years (QALYs) calculated using the European Quality of Life-5 Dimensions (EQ-5D) and health-care resource use, information on which was collected monthly from patient diaries.

SECONDARY OUTCOMES

Subjective sleepiness at 12 months (ESS mean score: months 10, 11 and 12) and objective sleepiness, disease-specific and generic quality of life, mood, functionality, nocturia, mobility, accidents, cognitive function, cardiovascular risk factors and events at 3 and 12 months.

RESULTS

Two hundred and seventy-eight patients were randomised to CPAP (n = 140) or BSC (n = 138) over 27 months and 231 (83%) patients completed the trial. Baseline ESS score was similar in both groups [mean (standard deviation; SD) CPAP 11.5 (3.3), BSC 11.4 (4.2)]; groups were well balanced for other characteristics. The mean (SD) in ESS score at 3 months was -3.8 (0.4) in the CPAP group and -1.6 (0.3) in the BSC group. The adjusted treatment effect of CPAP compared with BSC was -2.1 points [95% confidence interval (CI) -3.0 to -1.3 points; p < 0.001]. At 12 months the effect was -2.0 points (95% CI -2.8 to -1.2 points; p < 0.001). The effect was greater in patients with increased CPAP use or higher baseline ESS score. The number of QALYs calculated using the EQ-5D was marginally (0.005) higher with CPAP than with BSC (95% CI -0.034 to 0.044). The average cost per patient was £1363 (95% CI £1121 to £1606) for those allocated to CPAP and £1389 (95% CI £1116 to £1662) for those allocated to BSC. On average, costs were lower in the CPAP group (mean -£35; 95% CI -£390 to £321). The probability that CPAP was cost-effective at thresholds conventionally used by the NHS (£20,000 per QALY gained) was 0.61. QALYs calculated using the Short Form questionnaire-6 Dimensions were 0.018 higher in the CPAP group (95% CI 0.003 to 0.034 QALYs) and the probability that CPAP was cost-effective was 0.96. CPAP decreased objective sleepiness (p = 0.02), increased mobility (p = 0.03) and reduced total and low-density lipoprotein cholesterol (p = 0.05, p = 0.04, respectively) at 3 months but not at 12 months. In the BSC group, there was a fall in systolic blood pressure of 3.7 mmHg at 12 months, which was not seen in the CPAP group (p = 0.04). Mood, functionality, nocturia, accidents, cognitive function and cardiovascular events were unchanged. There were no medically significant harms attributable to CPAP.

CONCLUSION

In older people with OSAS, CPAP reduces sleepiness and is marginally more cost-effective than BSC over 12 months. Further work is required in the identification of potential biomarkers of sleepiness and those patients at increased risk of cognitive impairment. Early detection of which could be used to inform the clinician when in the disease cycle treatment is needed to avert central nervous system sequelae and to assist patients decision-making regarding treatment and compliance. Treatment adherence is also a challenge in clinical trials generally, and adherence to CPAP therapy in particular is a recognised concern in both research studies and clinical practice. Suggested research priorities would include a focus on optimisation of CPAP delivery or support and embracing the technological advances currently available. Finally, the improvements in quality of life in trials do not appear to reflect the dramatic changes noted in clinical practice. There should be a greater focus on patient centred outcomes which would better capture the symptomatic improvement with CPAP treatment and translate these improvements into outcomes which could be used in health economic analysis.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN90464927.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 40. See the NIHR Journals Library website for further project information.

Sleep disordered breathing at the extremes of age: the elderly

KEY POINTS

Sleep disordered breathing (SDB) is common and its prevalence increases with age. Despite this high prevalence, SDB is frequently unrecognised and undiagnosed in older people.There is accumulating evidence that SDB in older people is associated with worsening cardio- cerebrovascular, cognitive and functional outcomes.There is now good evidence to support the use of continuous positive airway pressure therapy in older patients with symptomatic SDB.

EDUCATIONAL AIMS

To highlight the prevalence and presentation of sleep disordered breathing (SDB) in older people.To inform readers about the risk factors for SDB in older people.To explore the impact of SDB in older people.To introduce current evidence based treatment options for SDB in older people. Sleep disordered breathing (SBD) increases in prevalence as we age, most likely due to physiological and physical changes that occur with ageing. Additionally, SDB is associated with comorbidity and its subsequent polypharmacy, which may increase with increasing age. Finally, the increased prevalence of SDB is intrinsically linked to the obesity epidemic. SDB is associated with serious outcomes in younger people and, likewise, older people. Thus, identification, diagnosis and treatment of SDB is important irrelevant of age. This article reviews the age-related changes contributing to SDB, the epidemiology and the risk factors for SDB in older people, the association of SDB with adverse outcomes, and diagnostic and treatment options for this population.

Increased sympathetic and decreased parasympathetic cardiac tone in patients with sleep related alveolar hypoventilation

OBJECTIVE

To assess autonomic function by heart rate variability (HRV) during sleep in patients with sleep related alveolar hypoventilation (SRAH) and to compare it with that of patients with obstructive sleep apnea (OSA) and control patients.

DESIGN

Cross-sectional study.

SETTING

Sleep Unit, University Hospital of University of Navarra.

PATIENTS

Fifteen idiopathic and obesity related-SRAH patients were studied. For each patient with SRAH, a patient with OSA, matched in age, sex, body mass index (BMI), minimal oxygen saturation (SatO2), and mean SatO2 was selected. Control patients were also matched in age, sex, and BMI with patients with OSA and those with SRAH, and in apnea/hypopnea index (AHI) with patients with SRAH.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Time- and frequency-domain HRV measures (R-R, standard deviation of normal-to-normal RR interval [SDNN], very low frequency [VLF], low frequency [LF], high frequency [HF], LF/HF ratio) were calculated across all sleep stages as well as during wakefulness just before and after sleep during a 1-night polysomnography. In patients with SRAH and OSA, LF was increased during rapid eye movement (REM) when compared with control patients, whereas HF was decreased during REM and N1-N2 sleep stages. The LF/HF ratio was equally increased in patients with SRAH and OSA during REM and N1-N2. Correlation analysis showed that LF and HF values during REM sleep were correlated with minimal SatO2 and mean SatO2.

CONCLUSIONS

Patients with SRAH exhibited an abnormal cardiac tone during sleep. This fact appears to be related to the severity of nocturnal oxygen desaturation. Moreover, there were no differences between OSA and SRAH, supporting the hypothesis that autonomic changes in OSA are primarily related to a reduced nocturnal oxygen saturation, rather than a consequence of other factors such as nocturnal respiratory events.

EPIDEMIOLOGY OF AGE-DEPENDENCE IN SLEEP DISORDERED BREATHING (SDB) IN OLD AGE: THE BAY AREA SLEEP COHORT (BASC)

Sleep Disordered Breathing (SDB) is highly prevalent in elderly populations and is thought to reflect, at least in part, age-dependence. Several studies suggest that SDB in elderly populations may hold different functional outcomes relative to SDB in middle-aged populations. Risk factors for SDB specific for the elderly remain uncertain. In this report, we examined changes in SDB, body weight and pulmonary function in 103 individuals over an average interval of 7 years to determine whether changes in these measures covaried. In-lab polysomnography was performed on members of an elderly cohort (Bay Area Sleep Cohort) on two separate occasions (Time 1, Time 2) with multiple nights of measurement typically made on each occasion. Results indicated that: a) SDB progressed over time in both men and women; b) changes in body weight were unrelated to the progression in SDB; c) relative declines in lung volumes (Forced Vital Capacity, Forced Expiratory Volume in 1.0 second) were associated with relative increases in SDB, with the effects slightly stronger in men. These data suggest that age-dependence in one commonly ascribed aging biomarker (lung function) were coupled to increments in SDB. Maintenance of healthy lung function into old age may confer some protective benefits in the development of age-dependent SDB.

Sleep apnea in the elderly

Obstructive sleep apnea (OSA) is a common clinical condition associated with obesity. A high prevalence of sleep apnea exists in the elderly, presumably because of changes in oropharyngeal collapsibility. Elderly patients may be less likely to seek medical attention for this condition, because they are less likely to be symptomatic. Excessive daytime somnolence is a known consequence of untreated OSA, but adverse cardiovascular consequences, such as hypertension, arrhythmias, and congestive heart failure, are more serious in older patients. Continuous positive airway pressure therapy is the most effective treatment of OSA, although compliance remains an issue.

Progressive aging does not alter the interaction between autonomic cardiac activity and delta EEG power

OBJECTIVE

We tested the hypothesis that the reductions of the changes in the respective influence of the cardiac sympathetic and vagal activity control and delta EEG activity with aging alter the interactions between the heart rate variability (HRV) and the delta sleep EEG power band.

METHODS

A polysomnography was performed on 16 healthy young men and 19 healthy middle-aged men across the first 3 NREM-REM cycles. Spectral analysis was applied to electrocardiogram and electroencephalogram recordings. High Frequency (HF(nu)) of HRV as well as the maximum of cross-spectrum, coherency, gain and phase shifts between HF(nu) and delta sleep EEG power band were compared between both groups.

RESULTS

Young men experienced more deep sleep than middle-aged men (P<0.001). In middle-aged subjects, HF(nu) was lower than the HF(nu) of their younger counterparts (P<0.001), but they showed similar increases during NREM sleep and similar decreases during REM sleep as the young subjects. Cross-spectrum values, coherency, gain and phase shifts between HF(nu) and delta were identical between the two groups. Modifications in HF(nu) show parallel changes and precede changes in delta EEG band by a similar leads of 11+/-6min in young men and 9+/-7 min in middle-aged men (P=0.23).

CONCLUSIONS

Reduced changes in the respective influence of the cardiac sympathetic and vagal activity and delta EEG activity with progressive aging do not alter the relationship and phase difference between changes in the relative predominant cardiac vagal activity and delta power in middle-aged men.

SIGNIFICANCE

Interaction between the cardiac sympathetic and vagal activity with delta EEG activity is maintained in middle-aged men.

Changes in monoamine release in the ventral horn and hypoglossal nucleus linked to pontine inhibition of muscle tone: an in vivo microdialysis study

A complete suppression of muscle tone in the postural muscles and a reduction of muscle tone in the respiratory related musculature occur in rapid eye movement (REM) sleep. Previous studies have emphasized the role of glycine in generating these changes. Because the activity of norepinephrine- and serotonin-containing neurons is known to decrease in REM sleep, we hypothesized that a decrease in release in one or both of these transmitters might be detected at the motoneuronal level during muscle tone suppression elicited by brainstem stimulation in the decerebrate animal. We compared release in the ventral horn with that in the hypoglossal nucleus to determine whether the mechanism of muscle tone suppression differs in these nuclei as has been hypothesized. Electrical stimulation and cholinergic agonist injection into the mesopontine reticular formation produced a suppression of tone in the postural and respiratory muscles and simultaneously caused a significant reduction of norepinephrine and serotonin release of similar magnitude in both hypoglossal nucleus and spinal cord. Norepinephrine and serotonin release in the motoneuron pools was unchanged when the stimulation was applied to brainstem areas that did not generate bilateral suppression. No change in dopamine release in the motoneuron pools was seen during mesopontine stimulation-induced atonia. We hypothesize that the reduction of monoamine release that we observe exerts a disfacilitatory effect on both ventral horn and hypoglossal motoneurons and that this disfacilitatory mechanism contributes to the muscle atonia elicited in the decerebrate animal and in the intact animal during REM sleep.

Mechanism of sleep-induced periodic breathing in convalescing stroke patients and healthy elderly subjects

Cerebral vascular ischemic strokes are known to precipitate Cheyne-Stokes periodic breathing. Interestingly, Cheyne-Stokes-like breathing during sleep may be associated with obstructive sleep apnea (OSA) in some individuals. Therefore, it was reasoned that stroke patients with periodic breathing in sleep would be susceptible to OSA. Because oscillations in upper airway resistance can occur as a component of sleep-induced periodic breathing, we hypothesized that stroke patients with sleep-induced periodic breathing would have oscillations in upper airway resistance. These oscillations in resistance would be expected to contribute to OSA. We studied stroke patients with sleep-induced periodic breathing and control subjects to evaluate the relationship between upper airway resistance and ventilation in periodic breathing in sleep. Ventilation and upper airway resistance were measured in presleep wakefulness and in stage 2 NREM sleep. Mean tidal volume, minute ventilation, respiratory cycle timing variables, and upper airway resistance were not different between stroke and control subjects, either awake or asleep. Upper airway resistance increased and ventilation volume decreased from wakefulness to sleep in both groups. In an equivalent number of subjects from each group, reciprocal patterned oscillations in tidal volume and upper airway resistance were present at a 5 to 12.5 breath frequency during sleep. As upper airway resistance increased, tidal volume decreased. Stroke patients had wider fluctuations in upper airway resistance than control subjects, likely contributing to the higher number of sleep-disordered breathing events observed in the stroke patients.

Effect of aging on metabolic respiratory control in sleeping dogs

We examined the effects of aging on the metabolic respiratory control system by measuring changes with time in steady-state minute volume of ventilation (VI), alveolar carbon dioxide pressure (PACO2), and ventilatory and arousal responses to hypercapnia and hypoxia during slow-wave sleep (SWS). Studies were performed longitudinally in six healthy dogs over a span of 3 to 7 yr, corresponding biologically to 12 to 24 human yr. In each of the dogs aging was associated with a decrease in steady state VI during SWS, from 6.53 +/- 1.08 (mean +/- SEM) to 5.56 +/- 0.90 L/min (p < 0.01), and with an increase in PACO2 from 36.2 +/- 1.0 to 38.5 +/- 1.1 mm Hg (p < 0.01). However, ventilatory and arousal responses to hyperoxic hypercapnia (four dogs) remained unchanged. In contrast there was a decrement in the response of VI to isocapnic hypoxia during SWS (five dogs), from 1.22 +/- 0.12 to 0.70 +/- 0.07 L/min/% fall in arterial O2 saturation (SaO2) (p < 0.02), and a decrease in arousal SaO2, from 83.3 +/- 3.2 to 73.5 +/- 2.3 percent (p < 0.001). The findings indicate that aging is accompanied by impairment of ventilatory and arousal responses to hypoxia during SWS, and point to a specific effect of aging on the carotid-body chemoreceptors, as opposed to the brainstem respiratory controller or the ventilatory pump.

Sleep-disordered breathing in community-dwelling elderly

These are the final results of a survey of sleep-disordered breathing, which examined objective and subjective information from a large randomly selected elderly sample. We randomly selected 427 elderly people aged 65 yr and over in the city of San Diego, California. Twenty-four percent had an apnea index, AI, greater than or equal to 5 and 62% had a respiratory disturbance index, RDI, greater than or equal to 10. Correlates of sleep-disordered breathing included high relative weight and reports of snoring, breathing cessation at night, nocturnal wandering or confusion, daytime sleepiness and depression. Body mass index, falling asleep at inappropriate times, male gender, no alcohol within 2 hr of bedtime and napping were the best predictors of sleep-disordered breathing. Despite statistical significance, all of the associations between interview variables and apnea indices were small. No combination of demographic variables and symptoms allowed highly reliable prediction of AI or RDI.

Consistency of respiratory measurements from night to night during the sleep of elderly men

Fourteen healthy elderly men had polysomnography performed on two consecutive nights to assess the consistency of sleep and breathing from night to night. The reported first-night effect was seen on electroencephalographic sleep, leading to lighter or fitful sleep on the first night. Mean values for apneas, hypopneas, and oxygen desaturations did not change from night 1 to night 2. Five of 14 subjects would have changed classification from night to night if a cutoff of five apneas and hypopneas per hour were used to define normality. Because this numerical cutoff may not be valid in the elderly, the clinical significance of such a changing classification is not clear.

Arterial oxygen desaturation during sleep in interstitial pulmonary disease. Correlation with chemical control of breathing during wakefulness

Patients with IPD often develop oxygen desaturation during sleep. We investigated whether or not the degree of falls in SaO2 during sleep were correlated with the daytime data of pulmonary function tests, arterial blood gas tensions, or ventilatory responses to chemical stimuli. Fourteen patients with IPD who had restrictive ventilatory impairment were studied to evaluate these relationships. The magnitude of SaO2 depression from awake to REM sleep was inversely correlated with the level of baseline SaO2. Hypercapnic ventilatory response was inversely related to the amount of maximal desaturation in both REM and NREM sleep. These results indicate that patients with IPD who have insufficient ventilatory response to hypercapnia reveal larger falls in SaO2 during sleep, particularly if they have lower baseline SaO2.

Nocturnal hypotension in older men with sleep-related breathing disorders

Sleeping and awake blood pressures were related to sleep oxygenation and awake control of breathing in hypertensive and normotensive older men. During sleep, episodes of both hypertension and hypotension were observed, but hypotension was prominent. Five of 26 subjects exhibited episodes with a minimum mean arterial pressure of 60 mm Hg or less. These hypotensive episodes were associated with hemoglobin desaturation below 80 percent, secondary to sleep-related breathing disorders, and elevated supine nasopharyngeal airway resistance. Hypotensive subjects were habitual snorers. Waking hypertension was not associated with sleep-related breathing disorders in this older sample. In some older persons with sleep-related breathing disorders, sympathetic reflexes may be impaired, permitting hypotension and risk of circulatory failure. Epidemiologic evidence supports the hypothesis that this mechanism can explain the elevated incidence of cerebral infarction during sleep.

Sleep apnea and mortality in an aged cohort

In the aged, sleep may be a vulnerable period for death from cardiovascular causes. Because of its high prevalence in the elderly, sleep apnea has been suggested to be one mechanism contributing to such sleep-related mortality. In this study, a cohort of 198 non-institutionalized elderly individuals (mean age at entry = 66) were followed for periods up to 12 years after initial polysomnography. The mortality ratio for sleep apnea (defined as a Respiratory Disturbance Index of over 10 events per sleep hour) was estimated to be 2.7 (95% CI = .95, 7.47). Multiple regression with the Cox proportional hazards model suggested that cardiovascular death was most clearly associated with age in this cohort. These results raise the possibility that "natural" death during sleep in the elderly may be associated with specific pathophysiological events during sleep.

Increased daytime sleepiness and snoring--obstructive sleep apnea syndrome caused by webbing of the soft palate

A case report is presented of a man with increased daytime sleepiness and snoring due to an obstructive sleep apnea syndrome caused by webbing of the soft palate narrowing the velopharyngeal aperture. The diagnosis obstructive sleep apnea syndrome was confirmed by polysomnography. After uvulopalatopharyngoplasty there was a marked objective and subjective improvement of patient's complaints. The authors stress the importance of sleep monitoring in patients with excessive daytime sleepiness and snoring. Otorhinolaryngologic examination is necessary in patients with obstructive sleep apnea syndrome to search for anatomic abnormalities of the oropharynx.

Risk factors for sleep disordered breathing in heterogeneous geriatric populations

This cross-sectional, multivariate study investigated associations between sleep disordered breathing (SDB) and putative risk factors in a heterogeneous group of 720 individuals over the age of 50 years studied during all-night in-lab polysomnography. Results indicated that: aged men were more likely to show impaired respiration during sleep than aged women; excessive daytime somnolence and parasomniac symptoms (snoring, gasping during sleep) were associated with SDB but insomnia was not; obesity accounted for more variance in SDB than age per se, implying that the prevalence of SDB in some elderly persons could be related to the deposition of body fat seen as individuals grow older. All four risk factors (age, sex, obesity, and symptomatic status) were statistically significant and independent predictors of impaired respiration in sleep in the elderly.

Self-reported excessive daytime somnolence and impaired respiration in sleep

The purpose of this study was to determine which measures of impaired respiration in sleep relate to self-reported excessive daytime somnolence (EDS). Previous studies conflict regarding the relative importance of arterial hypoxemia and brief awakenings in relating to EDS. A group of 37 elderly clinic patients with complaints of snoring, a clinical diagnosis of sleep apnea, and varying degrees of self-reported somnolence were evaluated polysomnographically and psychometrically. Results showed that a subgroup of somnolent patients were characterized by more severe oxygen desaturations relative to nonsomnolent patients. These differences were obtained even when obesity was controlled. Psychologic symptoms related to the symptom of EDS but not to the sleep measures. This suggested that patients were clearly distressed by their hypersomnolence, but that individual differences played a major role in how the distress was manifested.

Measurement error in visually scored electrophysiological data: respiration during sleep

Electrophysiological sleep studies employ the simultaneous recording of multiple physiological parameters. These data are often scored and analyzed visually, i.e. by trained human scorers. In this study, we investigated the measurement error inherent in visual evaluation of respiratory disturbances during human sleep. Three trained scorers independently evaluated twenty-eight all-night sleep recordings. Results indicated that the scorers achieved high agreement on only selected variables. Scorers' experience did not affect the reliability and independent judgements of recording quality did not account for the discrepancies. These findings, although most relevant for the specific parameters studied here, as well as for these scoring criteria, subjects, and techniques, document the unreliability of certain visually scored sleep data. The present paradigm may be useful in evaluating other types of measurement error.

Awake abnormalities of control of breathing and of the upper airway. Occurrence in healthy older men with nocturnal disordered breathing

We hypothesized that preexisting diminished chemical control of breathing and narrowing of the upper airway are associated with sleep-related disordered breathing (SRDB) in healthy older men. Twenty-six subjects, aged 55 to 70, were studied. An SRDB episode was a decrease in arterial oxygen saturation (SaO2) of at least 4 percent. Some of these episodes occurred while airflow continued (ie, nonapneic episodes), and the rest occurred with apnea. Sixteen subjects had greater than 12 SRDB episodes per hour of sleep (SRDB subjects) and ten subjects had less than 8 episodes per hour (controls). During waking, the mean hypercapnic ventilatory response was lower, and the mean supine nasal airway resistance (SNAR) was higher in SRDB subjects than in control subjects. During waking, 12 of 16 SRDB subjects had one or more respiratory abnormalities: four had an elevated SNAR; four had a reduced hypercapnic response; three had a reduced hypoxic ventilatory response, and two had an abnormal flow-volume curve. Only one of ten control subjects had a respiratory abnormality (an elevated SNAR). Also, the number of SRDB episodes per hour correlated with the SNAR, and the minimum SaO2 during sleep correlated with the magnitude of the hypercapnic response. We conclude that SRDB occurs commonly in otherwise healthy older men with preexisting abnormalities of control of breathing or of the upper airway.

Sleep apnea syndrome. A critical review of the apnea index as a diagnostic criterion

The utility of the apnea index (number of apneic events per hour of sleep) in diagnosing sleep apnea syndrome is reviewed. Data from currently extant reports indicate that many otherwise normal, aging subjects may be classified as having sleep apnea syndrome based on the current diagnostic threshold of five apneic episodes per hour: A chi 2 analysis suggests a relationship between age and level of sleep apnea. Several other reports indicate that use of a threshold of five apneic episodes per hour does not reliably predict increased health risk or somnolence in aging subjects. Adjustment of the apnea index, based on studies of aging normal subjects and of aging patients with sleep apnea syndrome is necessary to ensure reliable results in clinical and research applications.

Sleep apnea in cluster headache

The impetus to study sleep changes in a cluster population arose from a recent hypothesis that predicted the finding of sleep apnea in this disorder. It holds that cluster attacks may occur in response to oxygen desaturation. Proposed mechanisms involve impairment of carotid body activity secondary to hypothalamic-vasomotor regulatory dysfunction. Five chronic and five episodic cluster patients underwent nocturnal polysomnography, utilizing standard equipment for monitoring sleep status, cardiac activity, nasal and buccal air flow change, chest and abdominal breathing, muscle activity and oxygen saturation. All episodic patients and one of five chronic patients were found to have sleep apnea (60%). Mean apneas per hour during NREM sleep were similar to that of REM sleep; 26.7 and 28.2, respectively. Six patients with sleep apnea experienced 14 cluster headache attacks during the study period. Eight attacks (57%) followed episodes of oxygen desaturation ranging from 65% to 85%. In the sleep apnea group, 8 out of 14 attacks (57%) were associated with REM; three without, and five following oxygen desaturation. Of the non-apnea group, all of whom had chronic cluster headache, none of 5 attacks were associated with oxygen desaturation, and only 2/5 attacks occurred in relation to REM. Thus, our study showed that sleep apnea was a common finding in a randomly selected group of episodic cluster patients; and most nocturnal attacks were preceded by oxyhemoglobin desaturation and REM-related. These findings were uncommon in the chronic cluster group.