We determined the effects of changing ventilatory stimuli on the hypocapnia-induced apneic and hypopneic thresholds in sleeping dogs. End-tidal carbon dioxide pressure (PET(CO2)) was gradually reduced during non-rapid eye movement sleep by increasing tidal volume with pressure support mechanical ventilation, causing a reduction in diaphragm electromyogram amplitude until apnea/periodic breathing occurred. We used the reduction in PET(CO2) below spontaneous breathing required to produce apnea (DeltaPET(CO2)) as an index of the susceptibility to apnea. DeltaPET(CO2) was -5 mm Hg in control animals and changed in proportion to background ventilatory drive, increasing with metabolic acidosis (-6.7 mm Hg) and nonhypoxic peripheral chemoreceptor stimulation (almitrine; -5.9 mm Hg) and decreasing with metabolic alkalosis (-3.7 mm Hg). Hypoxia was the exception; DeltaPET(CO2) narrowed (-4.1 mm Hg) despite the accompanying hyperventilation. Thus, hyperventilation and hypocapnia, per se, widened the DeltaPET(CO2) thereby protecting against apnea and hypopnea, whereas reduced ventilatory drive and hypoventilation narrowed the DeltaPET(CO2) and increased the susceptibility to apnea. Hypoxia sensitized the ventilatory responsiveness to CO2 below eupnea and narrowed the DeltaPET(CO2); this effect of hypoxia was not attributable to an imbalance between peripheral and central chemoreceptor stimulation, per se. We conclude that the DeltaPET(CO2) and the ventilatory sensitivity to CO2 between eupnea and the apneic threshold are changeable in the face of variations in the magnitude, direction, and/or type of ventilatory stimulus, thereby altering the susceptibility for apnea, hypopnea, and periodic breathing in sleep.

Sleep unmasks a highly sensitive hypocapnia-induced apnoeic threshold, whereby apnoea is initiated by small transient reductions in arterial CO 2 pressure (P aCO 2 ) below eupnoea and respiratory rhythm is not restored until P aCO 2 has risen significantly above eupnoeic levels. We propose that the 'CO 2 reserve' (i.e. the difference in P aCO 2 between eupnoea and the apnoeic threshold (AT)), when combined with 'plant gain' (or the ventilatory increase required for a given reduction in P aCO 2 ) and 'controller gain' (ventilatory responsiveness to CO 2 above eupnoea) are the key determinants of breathing instability in sleep. The CO 2 reserve varies inversely with both plant gain and the slope of the ventilatory response to reduced CO 2 below eupnoea; it is highly labile in non-random eye movement (NREM) sleep. With many types of increases or decreases in background ventilatory drive and P aCO 2 , the slope of the ventilatory response to reduced P aCO 2 below eupnoea remains unchanged from control. Thus, the CO 2 reserve varies inversely with plant gain, i.e. it is widened with hyperventilation and narrowed with hypoventilation, regardless of the stimulus and whether it acts primarily at the peripheral or central chemoreceptors. However, there are notable exceptions, such as hypoxia, heart failure, or increased pulmonary vascular pressures, which all increase the slope of the CO 2 response below eupnoea and narrow the CO 2 reserve despite an accompanying hyperventilation and reduced plant gain. Finally, we review growing evidence that chemoreceptor-induced instability in respiratory motor output during sleep contributes significantly to the major clinical problem of cyclical obstructive sleep apnoea.

Patients with OSAS (obstructive sleep apnoea syndrome) demonstrate renal signs such as proteinuria, glomerular hypertrophy and focal glomerular sclerosis. We performed a clinical study to investigate the glomerular function in OSAS patients and the short-term effect of CPAP (continuous positive airway pressure) on it. OSAS patients underwent a sodium thiosulphate and p-aminohippurate double clearance test, polysomnography and ambulatory blood pressure monitoring before and a week after the induction of CPAP. Twenty-seven consecutive patients (24 males) with moderate-to-severe OSAS admitted to our hospital for the induction of CPAP, and 32 healthy donors for renal transplantation as controls participated in the study. Before treatment, the glomerular filtration rate, estimated by the sodium thiosulphate clearance test, was within normal range, and the renal plasma flow was significantly lower than normal in the OSAS patients, thus the FF (filtration fraction) value was much higher than normal. FF before CPAP was not significantly correlated with age, body mass index or blood pressure; however, indices of increased hypoxaemia correlated with increased FF values. Polysomnographic variables after CPAP showed significant improvements in all patients, and only the nocturnal blood pressures were slightly lower than before CPAP. In 21 patients who underwent the clearance test after CPAP, FF significantly decreased from 0.26 +/- 0.04 to 0.23 +/- 0.03 (P < 0.001). OSAS patients were generally in a glomerular-hyperfiltrating condition that appeared to cause the renal findings associated with OSAS. CPAP might prevent nephropathy by ameliorating the glomerular hyperfiltration in OSAS patients.

Fall in skin temperature during initial muscular work was investigated in ten healthy men. Bicycle exercise was performed at workloads of 50-150 W in a climatic chamber at ambient temperatures of 10-40'C (relative humidity 45-55%). Skin temperatures at seven or eight points over the body surface were measured using thermography and thermocouple recording systems. Sweat rates were significantly higher at 400C than at 30'C, whereas the fall in skin temperature was almost equal. The reduction of skin temperature during exercise was the same throughout the year, although sweat rate was significantly higher in summer than in winter. In coloured thermographics of the skin temperature distribution during exercise of both 50 and 150 W at 10 or 20'C, the skin temperature began to dedine immediately at the onset of the exercise. Increased work intensities reduced skin temperature. The results suggest that fall in skin temperature during initial exercise was not due to increased evaporative cooling but to vasoconstriction, probably caused by non-thermal factors.

Background: The mechanism underlying nocturnal sudden death in patients with MSA remains unclear. It may be explained by upper airway obstruction, such as vocal cord abductor paralysis; an impairment of the respiratory center, such as Cheyne-Stokes respiration; or an impaired hypoxemic ventilatory response. Objective: To investigate the mechanism of sleepdisordered breathing in multiple system atrophy (MSA) Design: We recruited 21 patients with probable MSA who were admitted sequentially to our hospital, and performed daytime blood gas analysis, pulmonary function tests, polysomnography, and fiberoptic laryngoscopy during wakefulness and with the patient under anesthesia. Results: A decrease in arterial oxygen pressure and an increase in alveolar-arterial oxygen gradient significantly correlated with disease duration (P=.045 and .046, respectively). Polysomnography demonstrated Cheyne-Stokes respiration in 3 (15%) of 20 patients. Fiberoptic laryngoscopy during wakefulness showed that 3 (14%)

We studied the quality of life of obesity hypoventilation syndrome (OHS) by comparing it with age- and body mass index-matched patients without hypoventilation and age-matched obstructive sleep apnea (OSA) patients with body mass index (BMI) under 30, and the efficacy of nasal continuous positive airway pressure (CPAP) therapy for 3 to 6 months on the quality of life in these patients. Prospectively recruited patients from six sleep laboratories in Japan were administered assessments of the general health status by the Short-Form 36 Health Survey (SF-36) and subjective sleepiness by the Epworth Sleepiness Scale (ESS). Compared with matched healthy subjects, OHS and OSA patients not yet treated had worse results on the ESS scores and the SF-36 subscales for physical functioning, role limitations due to physical problems, general health perception, energy/vitality, role limitations due to emotional problems, and social functioning. The ESS scores of OHS patients were worse than those of the OSA groups including the age- and BMI-matched OSA patients. In the SF-36 subscales of OHS patients, only the subscale of social functioning showed worse results compared with that of BMI-matched OSA patients. After 3 to 6 months of treatment, ESS scores and these SF-36 subscales in all three patient groups improved to the normal level. These results suggested that the quality of life of OHS before nasal CPAP was significantly impaired and that nasal CPAP for OHS improved the quality of life associated with the improvement of daytime sleepiness to the level of the other OSA patients.

Sudden death has been reported in patients with multiple system atrophy (MSA), although the frequency of this event has not been well delineated. We investigated the frequency and potential causes of sudden death in patients with MSA. During the 5-year observation period, 10 of 45 patients with probable MSA died. The causes of death included sudden death of unknown etiology (seven patients), aspiration pneumonia (one patient), asphyxia after vomiting (one patient), and lung cancer (one patient). The mean survival time of patients with sudden death was 63.0 +/- 24.7 months (range, 39-116 months). Among seven patients who experienced sudden death, six were found to have died during sleep. Among these patients, two had been treated with tracheostomy and three with continuous positive airway pressure (CPAP) or noninvasive positive pressure ventilation (NPPV) during sleep, suggesting that these treatments do not always prevent sudden death in patients with MSA. Nocturnal sudden death should be recognized as the most common mechanism of death in patients with MSA.

. Carotid body denervation eliminates apnea in response to transient hypocapnia.