Idiopathische und kongenitale schlafbezogene Hypoventilation

Congenital central hypoventilation syndrome (CCHS) is a disorder of the central chemical respiratory drive, whereby the peripheral chemoreceptors are intact. The prevalence is estimated at 1:200,000 live births. The disease is often associated with disturbances of the autonomic nervous system as well as with Hirschsprung??s disease. To confirm the diagnosis, detection of a mutation of the PHOX2 gene is useful. The mutated gene encodes a protein for the development of reflex pathways in the autonomic nervous system control. The disease is characterized by superficial breathing with hypoventilation, hypopnea, and in particular cyanosis during sleep during the first days of life, with p_aCO₂ values well above 60?mmHg being observed. Diagnosis using polysomnography with analysis of sleep structure, oxygen saturation, and end-tidal pCO₂ during spontaneous or mechanical ventilation in the various sleep stages is, therefore, essential. Using invasive and later noninvasive ventilation (NIV), normal alveolar ventilation and a good quality of life can be achieved. Even mild cases with later onset in adulthood (late onset CCHS), which required no mechanical ventilation during the neonatal period have been identified. Relatively rare to find are acquired hypoventilation syndromes. Central hypoventilation episodes are often caused by lesions in the brain stem area.     

Effect of continuous positive airway pressure versus supplemental oxygen on sleep quality in obstructive sleep apnea: a placebo-CPAP-controlled study

STUDY OBJECTIVE: We investigated the short-term effectiveness of continuous positive airway pressure (CPAP) and oxygen in improving sleep quality in patients with obstructive sleep apnea (OSA). DESIGN: Randomized, double-blind, placebo-controlled, parallel study. SETTING: General Clinical Research Center at a university hospital. PATIENTS: Seventy-six patients with untreated OSA. INTERVENTIONS: Patients were randomly assigned to 1 of 3 treatments (CPAP, placebo-CPAP, or nocturnal oxygen at 3 L per minute) for 2 weeks. Sleep quality was assessed at baseline and after 1 and 14 days of therapy. Repeated-measures analysis of variance was used to evaluate treatment and time effects, and their interaction. MEASUREMENTS AND RESULTS: Sixty-three patients completed the protocol. When compared with placebo-CPAP and nocturnal oxygen, CPAP increased rapid eye movement (REM) sleep and significantly reduced stage 1 sleep and the number of stage shifts (p < or = .003). CPAP improved, to within normal limits, the apnea-hypopnea index, total arousal index, and mean oxyhemoglobin saturation (p < or = .001). The effects of CPAP were apparent during the first night of therapy. Oxygen improved only mean nocturnal saturation (p = .009). CPAP had no significant effect on stage 2 sleep or slow-wave sleep. CONCLUSIONS: CPAP was associated with an improvement in sleep quality in patients with OSA by consolidating sleep, reducing stage 1 sleep, and improving REM sleep. CPAP was effective in correcting the respiratory and arousal abnormalities of OSA. The effectiveness of supplemental oxygen was limited to oxyhemoglobin desaturation.     

Nocturnal hypoventilation in chronic respiratory failure (CRF) due to neuromuscular disease

Decrease of respiratory muscle capacities in neuromuscular disease can lead to chronic respiratory failure with permanent alveolar hypoventilation. Respiratory centers elaborate a strategy of breathing dedicated to prevent overt respiratory muscles fatigue. This strategy may worsen chronic hypercapnia. During sleep, ventilation decreases because a lessening in respiratory centers function. During NREM sleep hypoventilation is only an exacerbation of what is seen during wakefulness. During REM sleep, atonia worsens much more hypoventilation particularly when diaphragmatic function is impaired. The effects of atonia are amplified by a very low reactivity of respiratory centers. Nocturnal mechanical ventilation improves nocturnal hypoventilation and daytime arterial blood gases (ABG). Mechanism of improvement in ABG and how nocturnal hypoventilation and diurnal hypoventilation interact, are still a matter of debate.     

Leptin receptor expression in the dorsomedial hypothalamus stimulates breathing during NREM sleep in db/db mice

Study ObjectivesObesity leads to obstructive sleep apnea (OSA), which is recurrent upper airway obstruction during sleep, and obesity hypoventilation syndrome (OHS), hypoventilation during sleep resulting in daytime hypercapnia. Impaired leptin signaling in the brain was implicated in both conditions, but mechanisms are unknown. We have previously shown that leptin stimulates breathing and treats OSA and OHS in leptin-deficient ob/ob mice and leptin-resistant diet-induced obese mice and that leptin’s respiratory effects may occur in the dorsomedial hypothalamus (DMH). We hypothesized that leptin receptor LepR^b-deficient db/db mice have obesity hypoventilation and that restoration of leptin signaling in the DMH will increase ventilation during sleep in these animals.MethodsWe measured arterial blood gas in unanesthetized awake db/db mice. We subsequently infected these animals with Ad-LepR^b or control Ad-mCherry virus into the DMH and measured ventilation during sleep as well as CO₂ production after intracerebroventricular (ICV) infusions of phosphate-buffered saline or leptin.ResultsAwake db/db mice had elevated CO₂ levels in the arterial blood. Ad-LepR^b infection resulted in LepR^b expression in the DMH neurons in a similar fashion to wildtype mice. In LepR^b-DMH db/db mice, ICV leptin shortened REM sleep and increased inspiratory flow, tidal volume, and minute ventilation during NREM sleep without any effect on the quality of NREM sleep or CO₂ production. Leptin had no effect on upper airway obstruction in these animals.ConclusionLeptin stimulates breathing and treats obesity hypoventilation acting on LepR^b-positive neurons in the DMH.     

Nocturnal low back pain in pregnancy: polysomnographic correlates.

Thirteen women in late stages of pregnancy underwent a polysomnographic study. Eight women (61%) complained of mild nocturnal back pain or back discomfort. Five women (39%) did not complain of nocturnal back pain. The two groups did not differ in total bed time, total sleep time, sleep latency, and wake after sleep onset (WASO). A significant decrease in rapid eye movement (REM) sleep and an increase in stage 2 were observed in the pain group. The same group had a statistically significant decrease in the basal O2 saturation level. The pain group also spent a longer time sleeping in the supine position. We hypothesize that a prolonged stay in the supine position leads to obstruction of the vena cava. In the presence of inadequate collateral circulation, increased pressure and venostasis in combination with a decrease in basal oxygen saturation may lead to hypoxemia, compromise the metabolic supply of the neural structures, and result in pain. It appears, therefore, that the vascular system plays an important role in the pathogenesis of pain. The role played by the disturbed sleep architecture in the production of pain remains to be established. It is possible that the changes observed in sleep architecture result from pain rather than contribute to pain production.     

Sleep disturbance at simulated altitude indicated by stratified respiratory disturbance index but not hypoxic ventilatory response

At high altitudes, the clinically defined respiratory disturbance index (RDI) and high hypoxic ventilatory response (HVR) have been associated with diminished sleep quality. Increased RDI has also been observed in some athletes sleeping at simulated moderate altitude. In this study, we investigated relationships between the HVR of 14 trained male endurance cyclists with variable RDI and sleep quality responses to simulated moderate altitude. Blood oxygen saturation (SpO₂%), heart rate, RDI, arousal rate, awakenings, sleep efficiency, rapid eye movement (REM) sleep, non-REM sleep stages 1, 2 and slow wave sleep as percentages of total sleep time (%TST) were measured for two nights at normoxia of 600 m and one night at a simulated altitude of 2,650 m. HVR and RDI were not significantly correlated with sleep stage, arousal rate or awakening response to nocturnal simulated altitude. SpO₂ was inversely correlated with total RDI (r=–0.69, P=0.004) at simulated altitude and with the change in arousal rate from normoxia (r=–0.65, P=0.02). REM sleep response to simulated altitude correlated with the change, relative to normoxia, in arousal (r=–0.63, P=0.04) and heart rate (r=–0.61, P=0.04). When stratified, those athletes at altitude with RDI >20 h^–1 (n=4) and those with <10 h^–1 (n=10) exhibited no difference in HVR but the former had larger falls in SpO₂ (P=0.05) and more arousals (P=0.03). Neither RDI (without stratification) nor HVR were sufficiently sensitive to explain any deterioration in REM sleep or arousal increase. However, the stratified RDI provides a basis for determining potential sleep disturbance in athletes at simulated moderate altitude.     

Schlafbezogene Hypoventilationen bei neuromuskul?ren Erkrankungen

Sleep-related breathing disorder is a common diagnosis in neuromuscular diseases. Many patients with neuromuscular disorders are affected by hypoventilation syndrome while sleeping. The main activator of hypoventilation is a malfunction of the diaphragm. Because of physiological muscle atony during rapid eye movement (REM) sleep breathing disorders initially occur during this sleeping state. Nocturnal hypoventilation is often only diagnosed when constrictive ventilation failure also occurs during the daytime. Hence, it is necessary to test patients with neuromuscular diseases for sleep-related breathing disorders even in the early stages of the disease. For patients with verified amyotrophic lateral sclerosis and Duchenne??s muscular dystrophy a life-prolonging effect of adequate artificial ventilation has been shown in randomized studies with a small number of cases. A subject for further research is to investigate whether in addition to life-prolonging effects a precocious adequate non-invasive breathing therapy can also influence the progression of various even non-fatal neuromuscular diseases.     

Sleep in restrictive lung disease

Restrictive lung disease patients exhibit a wide range of breathing and oxygenation abnormalities during sleep. The combination of degree of restriction, whether it is intrapulmonary or extrapulmonary, and confounding factors, such as obesity, age, and sex, will ultimately determine the degree of disturbed nocturnal physiology. The sleep literature is still sparse in most restrictive diseases. For patients with interstitial lung disease, the role of nocturnal oxygen in chronic established fibrosis, and also in acute alveolitis (e.g., farmer's lung, bird fancier's lung, etc.), has not been addressed. As fibrotic lung disease progresses, the degree of nocturnal desaturation and breathing dysrhythmias will progress. Changes in sleep architecture are likely related to the progression of the disease, but this is not known with certainty. Long-term evaluation of sleep and breathing in interstitial lung disease will give further insight into whether or not sleep changes are primary or secondary events. For kyphoscoliosis patients, again, we need more information on sleep as the thoracic deformity changes. In addition, the use of drugs (acetazolomide, medroxyprogesterone, and almitrine) and/or nasal CPAP to treat nocturnal desaturation needs to be assessed in a controlled fashion. In neuromuscular disease, the dynamics of gas exchange and sleep structure need to be defined in a larger group of patients. Factors such as degree of muscle weakness, degree of underlying lung diseases, and medications must be taken into consideration. Nocturnal hypoxemia may cause muscle weakness and fatigue, which in time, could cause more nocturnal hypoventilation and further hypoxemia. Supplemental nocturnal oxygen should be evaluated in this population.     

Nocturnal myocardial ischemia and cardiac arrhythmia in patients with sleep apnea with and without coronary heart disease

Summary To study the effect of apnea and hypoventilation-induced hypoxemia on the heart, we carried out polysomnographic recordings over; 4 nights with electrocardiographic tracings in 30 patients with and without coronary heart disease. Evaluations of the data were based on the 2nd and 4th nights. In six subjects, five with coronary heart disease, we found 85 episodes of nocturnal ischemia, mainly during REM sleep (83.5%), high apnea activity, and sustained and progressive hypoxemia. Complex ventricular ectopy was observed in 14/13 patients (nights 2/4) and repetitive ventricular ectopy in 5/3. There was no significant difference in the quality and quantity of ventricular ectopy during wake and sleep states between the CHD group and the control group. In one patient ventricular bigeminy was observed only at a threshold of SaO₂ below 60%. Bradyarrhythmia was made evident in four subjects from the CHD group and correlated mainly with apnea activity. We suppose that patients with sleep apnea and CHD are at cardiac risk because coronary heart disease can be aggravated by insufficient arterial oxygen supply due to cumulative phases of apnea and hypoventilation. The reduced hypoxic tolerance of the heart may lead to myocardial ischemia: and increased electrical instability.Abbreviations AI apnea index (apnea episodes per hour) - bpm beats per minute (heart rate) - CHD coronary heart disease - NREM non-rapid eye movement - PVC premature ventricular contraction - REM rapid eye movement - SRBD sleep-related breathing disorders     

Renin as a biological marker of the NREM-REM sleep cycle: effect of REM sleep suppression

SUMMARY  We have previously described that, in normal man, the nocturnal oscillations of plasma renin activity (PRA) exactly reflect the rapid eye movement (REM)–non(N)REM sleep cycles, with increasing PRA levels during NREM sleep and decreasing levels during REM sleep. This study was carried out to determine whether REM sleep suppression affects nocturnal renin profiles and to define which sleep stage is essential for renin release.
In a first experimental series, REM sleep was suppressed by using clomipramine, a tricyclic antidepressant. Seven healthy young men were studied once during a night when a placebo was given and once during a night following a single dose of 50 mg clomipramine. Blood was collected every 10 min from 23.00 hours to 07.00 hours. PRA was measured by radio-immunoassay and the nocturnal profiles were analysed using the pulse detection program ULTRA. Clomipramine suppressed REM sleep in all subjects but one, but did not affect the number of SWS episodes nor their duration. Similar PRA profiles were observed in both experimental conditions. Neither the mean levels, nor the number and the amplitude of the oscillations were modified and the normal relationship between slow wave sleep and increasing PRA levels was preserved.
In a second experimental series, REM sleep was prevented by rapidly awakening the subjects as soon as they fell into REM sleep. The four subjects studied attempted several times to go into REM sleep, but only when PRA levels were decreasing. The interruption of REM sleep by short waking periods did not disturb PRA for which the oscillations remained unaffected. Again, the relationship between SWS and increasing PRA levels was preserved.
These results provide evidence that mechanisms increasing slow-wave activity are principally involved in increasing PRA levels and that replacing REM sleep by waking periods and light sleep does not modify nocturnal PRA oscillations.     

Symposium: Normal and abnormal REM sleep regulation: REM sleep in successful, usual, and pathological aging: the Pittsburgh experience 1980-1993

Successful psychological and physical adaptation in late life correlates with preservation of sleep quality and physiological integrity of nocturnal EEG sleep measures. Failure to adapt is associated with loss of sleep continuity, alterations in the temporal distribution of delta wave activity, and by either a relative increase in REM sleep (e.g. in mood disorders) or a decrease in REM sleep (e.g. neurodegenerative disorders). Maintenance of sleep (particularly REM sleep) into late life may not be just a correlate, but also possibly a mechanism, of successful aging and thus necessary to the long-term maintenance of vitality and engagement in life.     

Changes in emotional responses to aversive pictures across periods rich in slow-wave sleep versus rapid eye movement sleep

OBJECTIVE: Since Freud's "Interpretation of Dreams," sleep has been related to emotional functions, where dreams were assumed to play a cathartic role. In psychophysiological research, this role was attributed mainly to rapid eye movement (REM) sleep. The present study compared processing pictures with negative emotional impact over intervals covering either early sleep dominated by slow-wave sleep (SWS) or late REM sleep-dominated sleep. METHOD: Emotional reactions were assessed by a nonverbal rating procedure along the two emotional dimensions valence (positive vs. negative) and arousal (low vs. high). Two groups of healthy men were tested across 3-hour periods of early and late nocturnal sleep (sleep group) or corresponding intervals filled with wakefulness (wake group). After the intervals, subjects rated new pictures together with old pictures already presented before the interval. Sleep was recorded polysomnographically. RESULTS: As expected, the amount of REM sleep was about three times greater during late than early nocturnal sleep, whereas a reversed distribution was observed for SWS (p<.001). Valence ratings indicated a shift toward enhanced negative ratings after late sleep (p<.05), contrasting with a trend toward more positive ratings after early sleep (p<.10). Arousal habituated slightly to repeated presentation of the same stimuli, but sleep generally enhanced subsequent arousal ratings (p<.05). Effects of sleep did not depend on whether pictures had low or high emotional impact. CONCLUSIONS: Indicating a priming-like enhancement of emotional reactivity after periods rich in REM sleep, results do not confirm a cathartic function of REM sleep or sleep in general.     

Gender differences in patients with obesity hypoventilation syndrome

The role of gender and menopause in obstructive sleep apnoea is well known; however, no study has reported the impact of gender on the clinical presentation and the nocturnal respiratory events in patients with obesity hypoventilation syndrome. Therefore, this study prospectively evaluated differences in the clinical characteristics of women and men with obesity hypoventilation syndrome in a large cohort of patients with obstructive sleep apnoea. During the study period, a total of 1973 patients were referred to the sleep clinic with clinical suspicion of obstructive sleep apnoea. All patients underwent overnight polysomnography, during which time spirometry, arterial blood samples and thyroid tests were routinely obtained. Among 1973 consecutive patients, 1693 (617 women) were diagnosed with obstructive sleep apnoea, among whom 144 suffered from obesity hypoventilation syndrome (96 women). The prevalence of obesity hypoventilation syndrome among women and men was 15.6% and 4.5%, respectively (P < 0.001). Women with obesity hypoventilation syndrome were significantly older than men with obesity hypoventilation syndrome (61.5 ± 11.9 years versus 49.1 ± 12.5 years, P < 0.001). Although there were no significant differences between genders regarding symptoms, body mass index, spirometric data or daytime PaCO₂, women with obesity hypoventilation syndrome suffered significantly more from hypertension, diabetes and hypothyroidism. The prevalence of obesity hypoventilation syndrome was higher in post‐menopausal (21%) compared with pre‐menopausal (5.3%) women (P < 0001). HCO₃ and duration of SpO₂ <90% were the only independent predictors of obesity hypoventilation syndrome. In conclusion, this study reported that among subjects referred to the sleep disorders clinic for evaluation of obstructive sleep apnoea, obesity hypoventilation syndrome is more prevalent in women than men, and that women with obesity hypoventilation syndrome suffer from significantly more co‐morbidities. Post‐menopausal women with obstructive sleep apnoea have the highest prevalence of obesity hypoventilation syndrome.     

Phasic activities of rapid eye movement sleep in vegetative state patients

STUDY OBJECTIVES: To assess the phasic components of rapid eye movement (REM) sleep in patients in vegetative state and to evaluate the possible relationship of these activities to patient outcome. SETTING: Sleep disorders unit at a major rehabilitation hospital. DESIGN: Comparative control study. PATIENTS: Eleven patients in vegetative state (10 males and 1 female) aged 17-53 years. INTERVENTIONS: Continuous 24-hour polysomnographic recording. MEASUREMENTS AND RESULTS: All the patients had REM sleep periods during the 24-hr recording session. Mean total REM sleep time for the whole session was 66.5 +/- 34.9 min, and for the nocturnal hours only, 37.3 +/- 19.7 min. Comparison with the control group (79.2 +/- 11.5 min) yielded a significant difference only for nocturnal REM sleep time (p<0.0003). The duration of the REM sleep periods was significantly shorter in the patients than the controls for the whole 24-hr session (10.9 +/- 6.0 vs.19.6 +/- 4.9 min, p<0.008), but not for the nocturnal period alone. Compared to controls, the density of rapid eye movements (REMs) (p=0.001), chin twitches (p=0.002), and leg muscle twitches (p=0.023) was significantly lower in the patient group. The density of the sawtooth waves was also lower in the patients, but the difference did not reach significance (p=0.069). Similar results were obtained when the comparison was done only for the nocturnal period. There was no significant difference for any of the REM sleep characteristics or REM sleep phasic activities (24-hr, nocturnal and diurnal periods) between the patients who recovered consciousness and those who did not. CONCLUSIONS: The present study shows that patients in vegetative state have a significant reduction in the phasic activities of REM sleep. However, the amount of these activities is unrelated to recovery from the clinical condition. These findings may reflect possible damage to the pedunculopontine tegmentum cholinergic mechanisms in vegetative state.     

Respiratory changes and structure of sleep in young high-altitude dwellers in the Andes of Peru

Summary Sleep organisation in eight young [mean (SD); 20·9 (2·6) years] Peruvian high-altitude residents was studied in a laboratory in Cerro de Pasco at 4300 m. Electroencephalograms, electromyograms, electro-oculograms, electrocardiograms, respiratory movements and arterial oxyen saturation were recorded on an 8-channel Medilog recorder and analysed later in England. Haematocrits ranged from 48% to 64% [57.9 (5.6)%]. The amount of slow wave rapid eye movement (REM) sleep was similar to that reported in young lowlanders sleeping at sea level but very different to the disturbed sleep in visitors sleeping at high altitude. All the Peruvians showed episodes of periodic breathing and respiratory apnoeas [29 (15) night^–1] resulting in marked arterial oxygen desaturation [81 (4.5)%; changes of 6 (2.5)%]. These events occurred either during stage 2 or REM sleep and were more frequent in those with lower haematocrits. The amount of wakefulness during the night was 2–3 times greater than would be expected in an age-matched lowland population at sea level. The awakenings were strongly associated with apnoeas (P<0.02) but were negatively correlated with the haematocrit, although this was only significant for seven of the subjects (P<0.05).     

Obstructive sleep-disordered breathing with a dominant cyclic alternating pattern--a recognizable polysomnographic variant with practical clinical implications

OBJECTIVES: To define the clinical and polysomnographic features of a distinct variant of obstructive sleep-disordered breathing that is remarkably mild during rapid eye movement (REM) sleep. DESIGN: Observational study and evaluation of polysomnographic and clinical records. SETTING: American Academy of Sleep Medicine-accredited multidisciplinary sleep disorders center and laboratory. PATIENTS: 35 medication-free subjects with clinical and polysomnographic severe obstructive sleep-disordered breathing selected for dominance of 1 of 2 disordered breathing patterns. INTERVENTIONS: Positive airway pressure titration. MEASUREMENTS AND RESULTS: Nasal pressure was used to score respiratory events. Sleep was scored by both the standard criteria and cyclic alternating pattern (CAP), and the distribution of respiratory events was tabulated and analyzed. A distinct clinical and polysomnographic syndrome emerged, CAP-dominant sleep-disordered breathing, characterized by severe relatively short cycle obstructive events during non-REM sleep that were mild in REM sleep. Characteristics include lower body mass index, fewer apneas, and a lower hypoxic burden as reflected by frequency and severity of nocturnal oxygen saturation. During positive pressure titration, a remarkable respiratory instability emerged selectively during CAP, in contrast to stability during REM sleep. This partial treatment failure was associated with persistent clinical symptoms. CONCLUSIONS: This variant of sleep apnea may reflect a dominant component of respiratory instability and periodic breathing coupled with upper-airway obstruction. Its existence questions the conventional practice of calculating global respiratory indexes. Besides positive airway pressure, measures to treat periodic breathing may be required.     

Automated mechanical ventilation: adapting decision making to different disease states

The purpose of the present study is to introduce a novel methodology for adapting and upgrading decision-making strategies concerning mechanical ventilation with respect to different disease states into our fuzzy-based expert system, AUTOPILOT-BT. The special features are: (1) Extraction of clinical knowledge in analogy to the daily routine. (2) An automated process to obtain the required information and to create fuzzy sets. (3) The controller employs the derived fuzzy rules to achieve the desired ventilation status. For demonstration this study focuses exclusively on the control of arterial CO₂ partial pressure (p_aCO₂). Clinical knowledge from 61 anesthesiologists was acquired using a questionnaire from which different disease-specific fuzzy sets were generated to control p_aCO₂. For both, patients with healthy lung and with acute respiratory distress syndrome (ARDS) the fuzzy sets show different shapes. The fuzzy set “normal”, i.e., “target p_aCO₂ area”, ranges from 35 to 39 mmHg for healthy lungs and from 39 to 43 mmHg for ARDS lungs. With the new fuzzy sets our AUTOPILOT-BT reaches the target p_aCO₂ within maximal three consecutive changes of ventilator settings. Thus, clinical knowledge can be extended, updated, and the resulting mechanical ventilation therapies can be individually adapted, analyzed, and evaluated.     

Temporal analysis of REM sleep after nest-building behavior in nulliparous albino rat

EEG recording was performed, during nest-building behavior (NBB), from the hippocampus and sensorimotor cortex of nulliparous albino rats with simultaneous recordings of EMGs of neck-muscle and eye movements. The duration of NBB varied with a period of 4–5 days. However, the relative durations of behavioral transitions in NBB, i.e., nest-building, grooming, and sleeping, were regular in both long lasting and early terminated NBB. REM sleep was identified, in every instance, immediately after NBB. The latency of REM sleep was significantly tied to the termination of NBB without regard to the druation of NBB. Differences in the duration of NBB, however, affected REM-propensity: the longer the NBB was, the shorter the latency of REM sleep tended to be. NBB might accelerate the induction of the physiological condition responsible for REM sleep generation.     

Effects of a moderate nocturnal cold stress on daytime sleep in humans

The effects of a nocturnal exposure to a cool environment on daytime recovery sleep was studied in eight young (20–25 years old) healthy volunteers. A set of standardized clothing (KSU ensemble type) was provided to each individual (estimated total thermal resistance: 0.6 clo). The subject kept awake was passively exposed from 22.30 to 07.30 hours to environments perceived as neutral (N) and comfortable or slightly cold (C) and uncomfortable. They were then allowed to sleep ad libitum (light out at 08.00 hours) under thermoneutral conditions (air temperature: 21°C to 22°C; clothing: cotton tee-shirt and pajama-pants; covering: one cotton sheet and one wool blanket). Sleep was recorded and scored according to the Rechtchaffen and Kales standard procedures. Esophageal temperature (T _es) was recorded from 21.30 hours until the end of sleep. The nocturnal drops in T _es were significantly different between N and C (p<0.01), this difference disappearing during sleep. No statistical difference was found between conditions for most of the sleep variables. Compared to N however, C resulted in a significant increase in rapid eye movement (REM) sleep duration (+35%, p<0.01) during the subsequent daytime sleep. It is hypothesized that the REM-sleep increase induced by the exposure to moderate cold is due to the thermal discomfort stress consciously perceived by the subject. Electronic Publication