Hypersomnolent and nonhypersomnolent patients with upper airway obstruction during sleep

Treatment of Hypoxemia in Obstructive Sleep Apnea

Many patients suffering from obstructive sleep apnea (OSA) have intermittent oxygen desaturation associated with periods of apnea or hypopnea. Oxygen saturation levels below 90% are considered harmful.1 Usually, treatment is directed at correcting the apnea, which will in turn prevent hypoxemia. Unfortunately, many patients fail or are not candidates for nasal continuous positive airway pressure (CPAP) or surgical correction of their OSA. Forty-three patients with persistent OSA and nocturnal hypoxemia below 90% who were not candidates for additional surgical or CPAP therapy were treated with nocturnal oxygen supplementation. Standard symptoms associated with OSA and the Epworth Sleepiness Scale (ESS) were recorded before treatment and 30 days after the start of the treatment. In 21 patients, polysomnography studies were performed to compare the Respiratory Disturbance Index (RDI) score and minimum oxygen saturation levels when the patients were breathing room air or breathing 4 L/minute of oxygen by nasal cannula. Subjective symptoms of obstructive sleep apnea improved, and the ESS score significantly decreased after a 30-night treatment with oxygen. Split-night polysomnography showed a significant increase in minimum oxygen saturation during oxygen administration. The RDI did not significantly change with treatment. Oxygen administration for the correction of OSA-related nocturnal hypoxemia was both safe and effective in alleviation of OSA-related symptoms. It also appeared to have a beneficial effect on minimum oxygen saturation levels. Thus, oxygen therapy may be considered a treatment option in patients who fail to comply with CPAP and are not candidates for a surgical procedure.

Sleep Apnoea in Diabetic Patients with Autonomic Neuropathy

Breathing during sleep was monitored in 8 diabetic patients with objective evidence of autonomic neuropathy and in 8 diabetic patients without neuropathy. Thirty or more periods of apnoea lasting 10 seconds or longer during one night's sleep were demonstrated in 3 of the diabetic patients with autonomic neuropathy. Such apnoeic periods may be related to the high incidence of cardiorespiratory arrests reported in such patients, particularly in association with anaesthesia or pneumonia.

Extrapulmonary Causes of Respiratory Failure

The causes of respiratory failure can be divided into two main groups: extrapulmonary and pulmonary. Extrapulmonary causes of respiratory failure include conditions that exclusively or primarily cause respiratory failure by their effect on structures other than the lungs (i.e., the extrapulmonary compartment). To place the topic of extrapulmonary respiratory failure into perspective, we briefly review normal and abnormal gas exchange and then examine how one can use this information to suspect or confirm the diagnosis of an extrapulmonary cause of respiratory failure. We then review the individual causes of extrapulmonary respiratory failure. These have been divided into two main functional categories: (1) those that involve a decrease in normal force generation, and (2) those that involve an increase in resistance to (bulk flow) ventilation. We then briefly consider the treatment of these disorders from a respiratory point of view.

Individual differences in vulnerability to sleep loss in the work environment

There are considerable individual differences in cognitive performance deficits resulting from extended work hours and shift work schedules. Recent progress in sleep and performance research has yielded new insights into the causes and consequences of these individual differences. Neurobiological processes of sleep/wake regulation underlie trait individual variability in vulnerability to performance impairment due to sleep loss. Trait vulnerability to sleep loss is observed in the laboratory and in the work environment, even in occupational settings where (self-)selection pressures are high. In general, individuals do not seem to accurately assess the magnitude of their own vulnerability. Methods for identifying workers who are most at risk of sleep loss-related errors and accidents would therefore be helpful to target fatigue countermeasure interventions at those needing them most. As yet, no reliable predictors of vulnerability to sleep loss have been identified, although candidate genetic predictors have been proposed. However, a Bayesian forecasting technique based on closed-loop feedback of measured performance has been developed for individualized prediction of future performance impairment during ongoing operations. Judiciously selecting or monitoring individuals in specific tasks or occupations, within legally and ethically acceptable boundaries, has the potential to improve operational performance and productivity, reduce errors and accidents, and save lives. Trait individual variability in responses to sleep loss represents a major complication in the application of one-size-fits-all hours of service regulations--favoring instead modern fatigue risk management strategies, because these allow flexibility to account for individual vulnerability or resilience to the performance consequences of extended work hours and shift work schedules.

Poincaré analysis of an overnight arterial oxygen saturation signal applied to the diagnosis of sleep apnea hypopnea syndrome

The analysis of oxygen desaturations is a basic variable in polysomnographic studies for the diagnosis of sleep apnea. Several algorithms operating in the time domain already exist for sleep apnea detection via pulse oximetry, but in a disadvantageous way--they achieve either a high sensitivity or a high specificity. The aim of this study was to assess whether an alternative analysis of arterial oxygen saturation (SaO2) signals from overnight pulse oximetry could yield essential information on the diagnosis of sleep apnea hypopnea syndrome (SAHS). SaO2 signals from 117 subjects were analyzed. The population was divided into a learning dataset (70 patients) and a test set (47 patients). The learning set was used for tuning thresholds among the applied Poincaré quantitative descriptors. Results showed that the presence of apnea events in SAHS patients caused an increase in the SD1 Poincaré parameter. This conclusion was assessed prospectively using the test dataset. 90.9% sensitivity and 84.0% specificity were obtained in the test group. We conclude that Poincaré analysis could be useful in the study of SAHS, contributing to reduce the demand for polysomnographic studies in SAHS screening.

Outcome measurement in sleep medicine practice and research. Part 1: assessment of symptoms, subjective and objective daytime sleepiness, health-related quality of life and functional status

The documentation of treatment outcomes has gained increased importance as those responsible for paying for healthcare focus on the delivery of cost-effective care. The practitioner and researcher, challenged with documenting the clinical significance of their endeavors, must depend on conceptually appropriate, valid and reliable instruments. Outcomes of particular relevance for sleep disorders include self-reported general symptoms, subjective and objective daytime sleepiness, neurobehavior, health-related quality of life (HRQL) or functional status, incidence of accidents and cardiovascular morbidity, and health care utilization and cost. This paper will limit its focus to the outcomes of self-reported general symptoms, subjective and objective daytime sleepiness, and HRQL or functional status. In addition to describing measures that could be applied to evaluate these outcomes, this paper will also discuss factors affecting the selection of outcome measures for use in research and practice, and consider evidence generated with the application of these instruments in research. Reductions in self-reported symptoms, such as snoring and daytime hypersomnolence following treatment, have been documented with the application of measures with strong psychometric properties such as the Survey Screen for Sleep Apnea and Epworth Sleepiness Scale. In addition to statistical reliability, calculation of the effect size and standardized response mean indicate that these changes are also clinically meaningful. Similar improvements have also been demonstrated using the Multiple Sleep Latency Test (MSLT), although the resulting increased latency has not typically been within normal values. Important improvements following treatment have been documented with the Maintenance of Wakefulness Test (MWT). Evidence suggests that the MWT may be more sensitive in situations, such as narcolepsy, where there are high levels of physiologic sleepiness, reserving the MSLT where the physiologic sleep tendency is more restricted, such as in obstructive sleep apnea (OSA). Patients>> perceptions of the benefit of treatment to their daily lives have been documented by such generic measures of HRQL, such as the SF-36 and Nottingham Health Profile. However, the impact of sleep disorders and the benefit of treatment on those aspects of daily behavior likely to be most affected have more clearly been demonstrated with the utilization of disease-specific HRQL measures such as the Functional Outcomes of Sleep Questionnaire and the Calgary Sleep Apnea Quality of Life Index. 2001 Harcourt Publishers Ltd

Obstructive sleep apnea and hypertension: are peripheral chemoreceptors involved?

The mechanism of pathogenesis of hypertension in patients with obstructive sleep apnea (OSA) is unknown. Many investigators point to the high sympathetic nervous system activity (SNS) observed in OSA patients. However, there is no clear explanation as to the mechanism for the development of SNS hyperactivity in these patients. A common feature of patients with OSA is repetitive bouts of transient hypoxemia during sleep. Repetitive transient hypoxemia in rats has resulted in hypertension. In OSA patients, resolution of nocturnal hypoxemia with CPAP has corrected nocturnal and diurnal hypertension. Also, exposure to hyperoxia reduces blood pressure and sympathetic activity in OSA patients, but not in normals. These data suggest a significant role of peripheral chemoreceptors in the regulation of vascular tone. We hypothesize that peripheral chemoreceptors significantly contribute to the pathogenesis of hypertension in patients with OSA and that this is associated with chemoreceptor hyperactivity. This implies that correcting the intermittent nocturnal hypoxemia alone may prevent the cardiovascular morbidity associated with obstructive sleep apnea.

The behavioral morbidity of obstructive sleep apnea

The behavioral morbidity associated with obstructive sleep apnea (OSA) includes symptoms of excessive daytime sleepiness (EDS), neurocognitive deficits, psychological problems, and possibly an increased chance of accidents. EDS is among the most frequently reported symptoms in patients diagnosed with OSA. The available data suggest that the primary cause of EDS is sleep fragmentation. The subjective measures of sleepiness include the sleep wake activity inventory and the epworth sleepiness scale. Sleepiness can also be evaluated objectively in the sleep laboratory using the multiple sleep latency test or the maintenance of wakefulness test. The neurocognitive manifestations of OSA include impairments in vigilance, concentration, memory, and executive function. There is no agreed on consensus as to how to best quantify neurocognitive deficits in this population. Symptoms consistent with depression or personality changes have also been described, but are likely to be correlates of EDS and/or the chronicity of the disorder. Manifestations of the behavioral morbidity of OSA are reversible, but dependent on the degree of normalization in sleep-disordered breathing and the individual's sleep habits.

Diagnostic and treatment implications of nasal obstruction in snoring and obstructive sleep apnea

LEARNING OBJECTIVES

The purpose of this review is to highlight fundamental aspects of obstructive sleep apnea (OSA), and to present an overview of the medical literature that pertains to the clinical interplay between various allergy-related disorders, nasal patency, and OSA. This should enable the reader to play a more proactive role in the diagnosis, management, and prevention of OSA.

DATA SOURCES

Relevant reviews, texts, and articles. The MEDLINE database was used to find related literature.

CONCLUSIONS

In predisposed individuals, OSA, sleep fragmentation, and the sequelae of disturbed sleep often result from nasal obstruction. Since breathing through the nose appears to be the preferred route during sleep, nasal obstruction frequently leads to nocturnal mouth breathing, snoring, and ultimately to OSA. Allergists can thus play a vital role in assessing sleep problems in their patients with allergic rhinitis and other upper respiratory disorders, in treating these problems more aggressively, and in some instances, in preventing them.

Neuropsychological investigations and event-related potentials in obstructive sleep apnea syndrome before and during CPAP-therapy

Patients with obstructive sleep apnea syndrome (OSAS) suffer from daytime sleepiness and a decline of cognitive functions. The study evaluated whether special cognitive disabilities predominate in OSAS. Besides the number connection test (ZVT), judging information processing and working velocity, computer-assisted (Wiener Testsystem and Zimmermann Testbatterie) neuropsychological testing was performed in 31 OSAS patients (50.1 +/- 9.4 years) before starting nasal continuous positive airway pressure (nCPAP) therapy. Identical test battery was performed in 10 male healthy volunteers (48 +/- 9.9 years). In addition visual evoked event-related potentials (ERPs) were recorded, the P3-component was evaluated. Impairment of alertness (P < 0.001), selective attention (P < 0.001) and continuous attention (P < 0.001) could be revealed, vigilance was not altered. Cognitive deficits were correlated with the degree of nocturnal hypoxemia. They were not linked to the apnea/hypopnea-index (AHI), arousal index or vigilance parameters. During 6 months of nCPAP-therapy (15 patients) alertness and continuous attention improved significantly (P < 0.01), intra-individual different pathological results persisted however. P3 latencies also remained prolonged. Chronic intermittent nocturnal hypoxemia in OSAS-patients obviously leads to cognitive deficits. ERP partially generated in subcortical cerebral structures represent a neurophysiological tool indicating brain dysfunction which cannot be evaluated by neuropsychological tests. Objective neuropsychological testing is needed in revealing therapeutic effects in OSAS-patients. Remaining deficits during sufficient nCPAP-therapy may reflect irreversible hypoxic cerebral damage.

Hour-to-hour variability of oxygen saturation in sleep apnea

STUDY OBJECTIVES

Methods used to express the severity of oxygen desaturation during polysomnography include the average oxygen saturation (AO2), lowest oxygen saturation (LO2), and the percent of the total time with oxygen saturation level lower than 90% (T<90%). We wanted to determine which one of these methods is least variable during different hours of monitoring.

DESIGN

Prospective, observational study.

SETTING

Sleep center at a medical university.

PATIENTS

One hundred fifty patients with apnea-hypopnea index from 5 to 130.

MEASUREMENTS

AO2, LO2, and T<90% were calculated during each of the 8 h of polysomnography. Data for each hour were compared and the Cronbach alpha coefficients were calculated.

RESULTS

There was a high degree of correlation among the three methods as well as between each method and the severity of sleep apnea. The mean+/-SD values for each method were as follows: AO2, 92.7+/-5.6; LO2, 68.5+/-19.3; and T<90%, 15.7+/-24.2. The alpha coefficients for these methods were AO2, 0.98; LO2, 0.88; and T<90%, 0.98. In all methods, the data of the first hour were significantly different from the data of the subsequent hours.

CONCLUSION

Both AO2 and T<90% methods show less hour to hour variability compared with LO2, and there is more variability in the first hour. Since the AO2 values >90% may not convey the severity of O2 desaturation, T<90% may be the best method of expressing oxygen saturation changes during polysomnography.

Respiratory effort. A factor contributing to sleep propensity in patients with obstructive sleep apnea

To test the hypothesis that respiratory effort during obstructive apneas contributes, together with hypoxemia and sleep fragmentation, to excessive daytime sleepiness, we investigated the relationship between daytime sleepiness and polysomnographic variables in 44 patients with obstructive sleep apnea (OSA). In all patients, daytime sleep propensity was assessed by an 11-item standardized self-questionnaire yielding a sleepiness score and by a modified sleep latency test yielding a mean sleep latency. Respiratory effort during apneas was evaluated by measuring esophageal pressure swings using an esophageal balloon. Within each apneic cycle, we measured the esophageal pressure swings during the first three and the last three occluded efforts during the apnea to define the overall increase, its ratio to apnea duration, and the maximal effort developed during obstruction. In the group of patients as a whole, the sleepiness score was negatively correlated with the mean sleep latency (r=-0.38, p=0.01). The sleepiness score was correlated with the indexes of respiratory effort during apneas (ie, the overall increase, its ratio to apnea duration, and the maximal end-apneic swing in esophageal pressure) and with the apnea+hypopnea index. The mean sleep latency was correlated with all indexes of nocturnal hypoxemia (ie, the mean lowest oxyhemoglobin saturation [SaO2] and the index of apnea associated with a fall in SaO2 below 90% and 80%). We conclude that the degree of respiratory effort during obstructive apneas contributes to self-rated sleep propensity in patients with OSA.

[Propensity for sleep and diurnal somnolence in the course of sleep apnea syndrome]

Daytime sleepiness is one of the major symptoms of obstructive sleep apnea. However, its definition raises problems, since it may be based on either subjective feeling (evaluated by means of questionnaires or analog visual scales), physiological drive or need (inferred by a sleep latency) or on the concept of sleep propensity defined as the probability of falling asleep (measured by the occurrence of sleep in various circumstances of daily life). Data from the literature suggest that sleep fragmentation and hypoxemia, both related to sleep apneas, cause daytime sleepiness. Our own data show that sleep propensity in a group of 44 patients with obstructive sleep apnea was correlated with the increase in esophageal pressure swings during obstructive apneas. This result suggests that the increased respiratory effort against occluded upper airways also contributes to daytime sleepiness in patients with obstructive sleep apnea.

Effect of venous oxygenation on arterial desaturation rate during repetitive apneas in lambs

While arterial oxygen desaturation during apnea is a common occurrence in adults and infants, the factors determining the rate of desaturation are poorly understood. We describe a theoretical model which suggests that arterial desaturation during an apneic episode occurs in two stages. In the initial stage (stage 1) the oxygen store in the lung is depleted, while in the second phase of the desaturation process (stage 2) tissue oxygen needs are met predominantly by depletion of the blood store. Our model predicts that preapneic venous oxygenation (SvO2) will strongly influence the rate of the desaturation in stage 1 but not in stage 2. We therefore examined the effect of changing preapneic SvO2 on the rate of arterial oxygen desaturation (SaO2) during stage 1 and stage 2 apnea in anaesthetised 10-20 day-old lambs. Preapneic arterial oxygen saturation was maintained constant. In agreement with the model's prediction there were two stages to the desaturation process and during stage 1 a significant increase in SaO2 was observed when preapneic SvO2 was lowered; SaO2 was -3.1 +/- 0.4%.sec-1 when SvO2 = 47.4 +/- 2.1% increasing to -5.8 +/- 0.7%.sec-1 when SvO2 = 28.3 +/- 1.2%. During stage 2, SaO2 was -1.62 +/- 0.07%.sec-1 and was independent of preapneic SvO2, also in accord with the model's prediction. In order to assess whether the accelerated desaturation rate we observed in stage 1 could have resulted from a decline in lung volume during apnea rather than lower levels of SvO2, we repeated the experiment with CPAP applied. Under these conditions SaO2 continued to be greater at lower preapneic SvO2 levels. In summary, lowered preapneic SvO2 has a potent influence on SaO2 during stage 1 of the desaturation process but not during stage 2.

Self-reported vs measured compliance with nasal CPAP for obstructive sleep apnea

To estimate reliability of self-reported compliance with nasal continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea (OSA), we studied 63 OSA patients aged 53.7 +/- 1.2 years (mean +/- SEM) with an apnea hypopnea index (AHI) of 50.8 +/- 2.9 and lowest sleep SaO2 of 65.6 +/- 2.3 percent receiving nasal CPAP for 539 +/- 44 days. During a follow-up polysomnography (PSG) on the pressure prescribed for home therapy (10.3 +/- 0.3 cm H2O), the hours of operation shown on the built-in time counter of the patients' devices were read to determine objective compliance by dividing the run time by the days since initiation of therapy. This parameter was compared with subjective compliance reported in a self-administered questionnaire. Mean measured use time was 4.9 +/- 0.3 h per night, whereas reported daily use time calculated from reported nights a week and hours a night was 6.1 +/- 0.3 h per night. As predominantly patients with poor compliance misestimated daily use time, we conclude that self-reports are unable to distinguish between compliant and noncompliant patients.

Sleep disordered breathing in ESRD: acute beneficial effects of treatment with nasal continuous positive airway pressure

Complaints about sleep and daytime alertness are common in ESRD patients. Eight consecutive ESRD patients with a sleep complaint were studied with all-night polysomnography. All were found to have significant sleep apnea with a mean apnea/hypopnea index (AHI) of 64 +/- 41.6 episodes per hour of sleep (range 7.5 to 140/hr of sleep). The majority of apneas were of the central or mixed variety causing severe fragmentation of sleep and frequent awakenings. Treatment was attempted with nasal continuous positive airway pressure (NCPAP). NCPAP was highly successful in six of the eight patients, reducing the mean AHI to normal or near normal levels (6.0 +/- 3.8/hr of sleep, P < 0.02 vs. baseline). The quality of sleep was significantly improved with statistically significant decreases in light stage 1 sleep, and nocturnal oxygenation improved with statistically significant increases in low SaO2 values. Five of six responders reported that they awoke feeling more alert and fewer times from sleep. The etiology of sleep apnea in ESRD is unknown although the frequent central apneas suggest a dysfunction of central respiratory control resulting from the effects of renal failure. Sleep-related complaints in patients with ESRD are likely to result from sleep apnea, a sleep disorder that can be diagnosed with polysomnography and treated with NCPAP.

[Sleepiness and sleep apnea syndrome. Analysis of 188 questionnaires (102 patients and 86 controls)]

A questionnaire was given to 102 obstructive sleep apnea patients and 86 controls. A somnolence index was defined by averaging the scores of the answers to eleven questions concerning sleepiness. This index separated patients and controls (P < 0.0001). It was correlated with the apnea + hypopnea index (r = 0.32, P < 0.001), the body mass index (r = 0.45, P < 0.001) and with an objective measurement of sleepiness obtained from a modified multiple sleep latency test (r = -0.54, P < 0.001). Depending upon the current occupation, the tendency to fall asleep decreased in the following order: watching TV, passenger in a means of transport, reading, attending a show, attending a meeting, driving a car, and eating. This order is the same in patients and controls, irrespective of their "overall sleepiness". Thus, the circumstances of falling asleep are indicative of the severity of sleepiness.

Daytime sleepiness after long-term continuous positive airway pressure (CPAP) treatment in obstructive sleep apnea syndrome

A modified maintenance of wakefulness test was performed in 58 patients with obstructive sleep apnea (OSA) syndrome before treatment and after long-term (554 +/- 28 days) home therapy with nasal continuous positive airway pressure (CPAP). Before treatment the patients had a shorter mean sleep latency than controls (16 +/- 1 vs. 27 +/- 1 min, mean +/- SEM, P less than 0.001). After treatment, the mean sleep latency increased to 20 +/- 1 min (P less than 0.002 as compared to baseline), but was still shorter than in controls (P less than 0.001). The incomplete normalization of the mean latency contrasted with the patients' claim that they no longer felt sleepy. The improvement in daytime alertness was significantly correlated with the reduction in sleep fragmentation after CPAP treatment and with the baseline mean sleep latency. These results support the hypothesis that sleep disruption related to respiratory events plays a role in the pathogenesis of daytime sleepiness.

Sleepiness and hypertension in obstructive sleep apnea

In order to assess the complications of sleep apnea, we have reviewed a data base of 619 consecutive admissions to a university sleep disorders center. Although patients with obstructive sleep apnea (OSA) described more subjective sleepiness than patients with central sleep apnea (CSA) or primary snoring (PS), the multiple sleep latency test (MSLT) indicated similar levels of physiologic sleepiness in the two apneic groups, which was greater than among those with PS. There was no significant relationship between individual subjective estimates of habitual sleepiness and the MSLT values. Among the OSA patients the mean minimum arterial oxygen desaturation during REM sleep accounted for 65 percent of the variance of the mean sleep latency on the MSLT, with an additional, smaller, contribution of the disordered breathing rate per hour. Subjective reports of sleepiness were associated with sleep efficiency and the number of disordered breathing events in NREM sleep. Patients with OSA or CSA had similar diastolic blood pressures and frequencies of history of treatment for hypertension, which were significantly higher in OSA than in the PS group. In the OSA group the absolute minimum arterial oxygen desaturation during NREM sleep was the most significant contributor to waking diastolic blood pressure, with an additional small contribution by weight. A history of treatment for hypertension was most strongly associated with weight, without significant additional contributions by measures of disordered breathing events or oxygen desaturation; however, weight was highly intercorrelated with measures of the apnea/hypopnea index and minimum arterial oxygen desaturation. In summary, these data support recent findings which show a close relation of obesity to a history of hypertension in OSA, and extend to this group a previous observation that in regular heavy snorers, there may be a disparity between levels of physiologic and subjective sleepiness.

Hypoxemia vs sleep fragmentation as cause of excessive daytime sleepiness in obstructive sleep apnea

To determine the effects of intermittent hypoxemia on daytime sleepiness in the clinical setting of obstructive sleep apnea syndrome, we enrolled seven patients in a prospective, randomized, crossover study. We had two experimental conditions with NCPAP treatment as follow: (1) to correct apneas, sleep fragmentation, and hypoxemia; and (2) to correct apneas and sleep fragmentation and at the same time, induce intermittent hypoxemia. The outcome variable, daytime sleepiness, was measured objectively with the multiple sleep latency test following completion of baseline and each treatment condition. Compared with sleep latencies in the untreated condition, both experimental treatment arms prolonged sleep latencies (p less than 0.05). We found no statistically significant differences between mean MSLT scores obtained after NCPAP treatment under hypoxemic and nonhypoxemic conditions. In summary, two nights of intermittent nocturnal hypoxemia during NCPAP treatment for OSAS did not diminish the objective improvement in daytime somnolence seen with NCPAP treatment in the absence of nocturnal hypoxemia. Results lend further support to the hypothesis relating excessive daytime sleepiness to sleep fragmentation.

Prevalent sleep problems in the aged

Quality of sleep influences the level of daytime functioning, including stress levels, psychosomatic complaints, general health, and overall well-being. As people age, they complain more about disturbed sleep, insomnia, increased time in bed, and sleep fragmentation. These complaints can be related to circadian rhythm desynchronization, hypnotic or other medication use, chronic bedrest, napping, dementia, or to sleep apnea, a disorder of respiratory cessation which is quite prevalent in the elderly. We review here the results of 12 years of research on sleep in the elderly. In studies of three populations of elderly, it was found that between 24% and 42% had five or more apneas per hour of sleep and 4%-14% had 20 or more apneas per hour of sleep. Since apnea is related to dementia and even to mortality, this high prevalence of apnea is of extreme importance.

Nocturnal hypoxemia as a determinant of vigilance impairment in sleep apnea syndrome

In sleep apnea syndrome (SAS), vigilance impairment is typically associated with highly disrupted sleep, but recently, nocturnal hypoxemia has also been identified as a second pathogenetic factor in patients with a high degree of desaturation. However, although sleep disruption has been demonstrated to play a role in both the propensity to fall asleep and the capacity to stay awake, the role of nocturnal hypoxemia has been implicated only in the latter. In the present study, both sleep disruption and nocturnal hypoxemia were assessed in 20 moderately to severely apneic patients. During the day, vigilance was assessed both by the multiple sleep latency test (MSLT), as a measure of the propensity to fall asleep, and by the four-choice reaction time test (FCRTT), as a measure of the capacity to stay awake in a performance task. Severity of nocturnal hypoxemia was found to predict performance on the MSLT, as well as on the FCRTT, but sleep disruption was found to predict performance only on the FCRTT. These results suggest that in moderately to severely affected SAS patients, nocturnal hypoxemia may play a primary role in the pathogenesis of vigilance impairment.

Effects of alterations in pulmonary function and sleep variables on survival in patients with amyotrophic lateral sclerosis

Breathing abnormalities and nocturnal hypoventilation occur in patients with amyotrophic lateral sclerosis (ALS). A prospective study was undertaken to determine the relationship of pulmonary function test abnormalities with quality of sleep and survival in 21 patients with ALS. Results of spirometry including determination of maximal respiratory pressures and arterial blood gases were compared with several formal polysomnographic variables and then also with 18-month survival. The patients had mild to moderate pulmonary function deficits, but the quality of sleep was best related to age (mean age, 58.5 years). The results of pulmonary function tests and arterial blood gas measurements did not correlate well with the presence of nocturnal breathing events or survival time, but the maximal inspiratory pressure was 86% sensitive for predicting the presence of a nocturnal oxygen saturation nadir of 80% or less and 100% sensitive for predicting 18-month survival. Although obstructive breathing events occurred, the primary explanation for the decline in nocturnal oxygen saturation was hypoventilation. We conclude that routine pulmonary function tests may be useful for screening for reductions in nocturnal oxygen saturation and also may have prognostic value. Further studies may determine whether treatment of nocturnal hypoventilation will have an effect on survival in patients with ALS who have breathing impairment.

Symptoms in heavy snorers with and without obstructive sleep apnea

Five hundred and eighty persons who were heavy snorers filled in a questionnaire regarding symptoms on a 5-grade scale. Of these, 178 had a complete polysomnography investigation while 402 patients underwent oxymetric screening during the night only. On the basis of these investigations. 217 were classified as suffering from the obstructive sleep apnea syndrome (OSAS) and 363 as snorers without OSAS. The symptom scores differed between the two groups, but the range was wide and some persons with OSAS claimed only minor daytime sleepiness, somnolence, etc., while a high proportion of persons without OSAS frequently suffered from such symptoms. Thus, it was not possible to discriminate between patients with and without OSAS on the basis of their symptoms only. Furthermore, there are many persons who are "only" heavy snorers but who have symptoms that affect their career and social life and who so far have only received scant interest from the medical profession. Excessive daytime sleepiness and somnolence thus do not seem to be secondary to hypoxemia at night but rather to poor quality of sleep, which may be the case in association with heavy snoring even without appreciable deterioration of oxygen saturation.

Severity of obstructive sleep apnea

A four-level severity scale for obstructive sleep apnea is offered using four criteria: maximum oxygen desaturation, apnea/hyponea index, symptoms of excessive day-time sleepiness, and symptoms of related cardiac disease. Oxygen desaturation and the apnea/hyponea index for 175 patients, all having had uvulopalatopharyngoplasty surgery, showed 19% mild, 33% moderate, 17% moderately severe, and 31% severe obstructive sleep apnea. There was a very poor correlation between oxygen desaturations and number of obstructive events, which demands that both be used in any estimation of disease severity.

Persistent hypoxemia and excessive daytime sleepiness in chronic obstructive pulmonary disease (COPD)

Fourteen patients with chronic obstructive pulmonary disease (COPD) and chronic hypoxemia were studied to evaluate the relationship between hypoxemia and objective and subjective daytime sleepiness. Patients were selected with a waking PaO2 of less than 70 mm Hg and less than 50 percent predicted FEV1. Clinically, none of these patients had complaints of significant daytime sleepiness. Each patient underwent standard all-night polysomnographic evaluation followed by a multiple sleep latency test (MSLT). There was no significant correlation between the mean sleep onset latency for the MSLT and the waking PaO2, PCO2, FEV1, or spontaneous desaturations during sleep. Patients with COPD exhibited a mean MSLT that was within normal limits, despite a short total sleep time and numerous arousals from sleep. We conclude that there appears to be no relationship between chronic daytime hypoxemia and subjective reports and objective measures of daytime sleepiness.

Auditory event-related potentials and brain dysfunction in sleep apnea

Auditory event-related potentials (ERPs) were recorded from 14 subjects with obstructive sleep apnea (OSA) before and after treatment with nasal continuous positive airway pressure (nCPAP). After 2 nights of treatment, there was dramatic improvement in the sleep patterns of the OSA patients, improvements in measures of apnea severity and oxygenation, and decrease in daytime sleepiness. The results of neuropsychological tests of a broad range of cognitive functions failed to confirm the patients' subjective reports of improvement in psychological functioning after treatment. The latencies of the N2 and P3 components were significantly prolonged prior to treatment, and there was a trend towards smaller N2 and P3 amplitude in the apneic subjects. The latency of P3 (but not N2) changed with treatment, decreasing almost to normative values. The results suggest that ERPs may be useful in documenting neural dysfunction in patients with OSA, in evaluating treatment efficacy, and possibly in determining the causes of the daytime symptoms of OSA.

Predictors of objective level of daytime sleepiness in patients with sleep-related breathing disorders

Excessive daytime sleepiness, the most prevalent symptom associated with the OSAS, is hypothesized to result from either fragmentation of sleep or hypoxemia during sleep. Measures of nocturnal sleep, respiration during sleep, and daytime sleepiness in 466 patients with apnea were collected to evaluate these two hypotheses. The various parameters were submitted to correlation and multiple regression analyses to predict daytime sleepiness as measured by the MSLT. The RAI, which measures the number of arousals from sleep associated with respiratory disturbances (best fragmentation correlation), produced a higher correlation with MSLT scores than did TMES (best hypoxemia correlation); however, the measures were highly intercorrelated, and multiple regression analyses to determine which parameters independently predicted MSLT showed the single best predictor to be the RAI. Additional independent variance in MSLT score was explained by TST and PSG1. Measures of hypoxemia provided little or no independent predictive information. These data support the hypothesis that sleep fragmentation is an important determinant of daytime sleepiness in patients with apnea.

Obstructive sleep apnoea

A patient with obstructive sleep apnoea is described, who required admission to an intensive care unit on two separate occasions within 2 months. The first admission was after anaesthesia for operation on the upper airway. The second occurred after a relative overdose of an opioid analgesic was administered. The diagnosis, treatment and anaesthetic management of patients with this syndrome are discussed.

Fatigue and fatigability

“One spring, towards the end of March, I happened to be in Rome, and, hearing that the migration of the quails had begun, I went down to Palo on the sea coast in order to ascertain whether these birds, after their journey from Africa, showed any of the phenomena of fatigue.”

Determinants of daytime sleepiness in obstructive sleep apnea

To investigate determinants of daytime sleepiness in obstructive sleep apnea syndrome (OSAS), we studied 100 unselected OSAS patients by nocturnal polygraphic recording and the Multiple Sleep Latency Test (MSLT). Data obtained were submitted to three types of analysis. Respiratory disturbance index, oxygen saturation indices, body mass index, and total nocturnal sleep time did not significantly correlate with daytime sleepiness, as measured by the MSLT. Analysis of subgroups based on weight and degree of alertness also showed a nonsignificant correlation with daytime sleepiness. The best predictor of the excessive daytime sleepiness (EDS) frequently found in OSAS patients was the nocturnal polygraphic recording of the sleep disturbances and sleep structure anomalies that reflect the brain's overall dysfunction in OSAS. Understanding why an electroencephalogram arousal response occurs during sleep in association with abnormal breathing and how this response can become blunted may help us to better predict the development of EDS.

Clinical significance of sleep apnea in the elderly

The generally accepted polysomnographic criteria for diagnosis of sleep apnea is exceeded by elderly subjects with such frequency that the validity of its application to this age group has been questioned. We studied a group of elderly volunteers with nocturnal polysomnography and partitioned them into 2 groups based upon an apnea index of greater than or less than 5 per hour. The results of a protocol evaluating the presence of potential complications of sleep apnea including cardiac arrhythmias, systemic hypertension, cor pulmonale, daytime sleepiness, and cognitive impairment were compared for the 2 groups. No excess incidence of cardiovascular complications was found. Although an increase in daytime sleep tendency was shown for the group with more frequent apneas, no appreciable deficits in cognitive performance were demonstrated. Although apnea during sleep in the elderly may be associated with an increase in daytime sleepiness, it may not necessarily result in other physiologic or neuropsychologic consequences. Therapeutic intervention for these abnormalities should be carefully considered prior to the institution of treatment in light of these observations.

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.

Cognitive impairment in patients with obstructive sleep apnea and associated hypoxemia

Twenty-six patients with sleep apnea had neuropsychologic testing prior to nocturnal sleep study in a sleep disorders clinic. The cognitive functioning of patients who had sleep apnea with associated hypoxemia was compared to nonhypoxemic patients with sleep apnea. The patients who had sleep apnea with hypoxemia had more severe cognitive impairment than those with sleep apnea without hypoxemia. The hypoxemic patients with sleep apnea had significantly poorer cognitive functioning on four of eight tests (p less than 0.05). In addition, the patients who had sleep apnea with hypoxemia had mean performance scores in the impaired range on measures of attention, concentration, complex problem-solving, and short-term recall of verbal and spatial information. In contrast, the patients who had sleep apnea without hypoxemia had no mean performance score in the impaired range. The degree of hypoxemia during sleep and wakefulness significantly correlated with the degree of overall cognitive impairment as rated by a neuropsychologist; however, measures of sleep fragmentation did not significantly correlate with overall cognitive impairment in patients with sleep apnea. We conclude that patients who have sleep apnea with associated hypoxemia have cognitive impairment which is more severe than those with sleep apnea without hypoxemia.

Overnight nasal CPAP improves hypersomnolence in sleep apnea

Eleven adult men with sleep apnea underwent nocturnal polysomnography on two successive nights. The first study, done without NCPAP, served as the control. The second (treatment) was done with the application of 7.5 to 15 cm H2O nasal continuous positive airway pressure (NCPAP). A subjective sleepiness index (SSI) was noted upon awakening from each night of polygraphic recording. During the control night, the mean frequency of apnea episodes/sleep hr was 35.95 +/- 4.5 SE, and the mean duration was 28.68 +/- 2.7 sec. Mean frequency of disorder of breathing (DOB) episodes/sleep hr was 19.25 +/- 6.2 and mean duration of DOB episodes was 23.1 +/- 2.8 sec. During the treatment night, all obstructive apnea episodes were abolished. During the control night, the mean decrease in arterial oxygen saturation during obstructive apnea episodes was 11.2 +/- 1.9 percent and the mean lowest saturation was 67.6 +/- 4.0 percent. NCPAP eliminated arterial oxygen desaturation. While 44.5 +/- 5.7 percent of total sleep time was spent in either apnea or disordered breathing during the control night, NCPAP decreased this to 0.73 +/- 0.3 percent. In addition to the improvement in respiration during sleep, SSI decreased from a mean of 3.73 +/- 0.49 after the control night to 1.64 +/- 0.24 after treatment, reflecting an improvement in daytime hypersomnolence. We conclude that nasal CPAP is effective in eliminating obstructive apnea episodes, and results in a marked decrease in daytime hypersomnolence after one treatment night.

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.

Nocturnal hypoxia and neuropsychological variables

Hypoxia is a well known cause of brain dysfunction. Neuropsychological impairments have been observed in normal subjects experiencing hypoxia iatrogenically as well as in patients with chronic lung disease. Recent investigations have demonstrated significant nocturnal hypoxia in subjects with sleep-disordered breathing. In the present study, heavy-snoring males, a group known to experience frequent episodes of sleep-disordered breathing received neuropsychological testing and a night of continuous monitoring of respiratory parameters. Partial correlations, controlling for age, weight, and education, indicated reliable relationships between nocturnal hypoxia and measures of general intelligence, verbal and nonverbal memory, and expressive verbal fluency. It is proposed that heavy-snoring males may potentially serve as a population in which to model the neurobehavioral effects of hypoxia. Further research in subjects with sleep-disordered breathing may help clarify the extent of the possible cognitive deficits as well as point out possible ameliorative treatments.