Daytime noise and subsequent night sleep in man

The effects of daytime noise on recovery processes during subsequent undisturbed night sleep were studied in six healthy men (21-27 years), exposed to 80 dB (A) pink noise 8 h per day for 2 days. Sleep EEG, ECG, and respiration were recorded in the laboratory for five consecutive nights: two baseline nights, two nights following noise stimulation, and again one baseline night. Additionally questionnaire data were collected, reflecting a subjective impairment of the recovery function of sleep after noise exposure. EEG sleep data of the first post-noise night showed an increase in slow wave sleep with a simultaneous decrease in stage 2 sleep. During the second post-noise night these changes were less prominent. Three subjects additionally showed an instability in the sleep course coinciding with elevated heart and respiration rates. However, altogether the autonomic parameters were not clearly affected by the noise exposure. The findings support the assumption that strong daytime noise may interfere with subsequent sleep processes.     

Cardiovascular changes associated with obstructive sleep apnea syndrome.

Five men free of lung or cardiovascular diseases and with severe obstructive sleep apnea participated in a study on the impact of sleep states on cardiovascular variables during sleep apneas. A total of 128 obstructive apneas [72 from stage 2 non-rapid-eye-movement (NREM) sleep and 56 from rapid-eye-movement (REM) sleep] were analyzed. Each apnea was comprised of an obstructive period (OP) followed by a hyperventilation period, which was normally associated with an arousal. Heart rate (HR), stroke volume (SV), cardiac output (CO) (determined with an electrical impedance system), radial artery blood pressures (BP), esophageal pressure nadir, and arterial O2 saturation during each OP and hyperventilation period were calculated for NREM and REM sleep. During stage 2 NREM sleep, the lowest HR always occurred during the first third of the OP, and the highest was always seen during the last third. In contrast, during REM sleep the lowest HR was always noted during the last third of the OP. There was an inverse correlation when the percentage of change in HR over the percentage of change in SV during an OP was considered. The HR and SV changes during NREM sleep allowed maintenance of a near-stable CO during OPs. During REM sleep, absence of a compensatory change in SV led to a significant drop in CO. Systolic, diastolic, and mean BP always increased during the studied OPs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preterm birth in lambs: sleep patterns and cardio-respiratory changes.

Cardio-respiratory physiology in sleep was examined in eight preterm lambs born at 133-135 (134 +/- 1, mean SEM) days of gestation after 3-5 days of pulsatile ACTH/TRH infusion, and contrasted with eight lambs born at term (147 +/- 1 days). Lambs were instrumented with electrodes for recording electrocorticogram, electro-oculogram and nuchal electromyogram to define behavioural states, as well as carotid arterial catheters for determination of arterial pressure, heart rate and arterial blood gases. Compared to full-term lambs, the preterm lambs exhibited extended active sleep times, elevated PaCO2 and faster heart rate in all behavioural states than full-term lambs; with increasing postnatal age, sleep times and heart rate declined. As similar differences are found in preterm human infants, the preterm lamb will be a useful model to study the underlying physiology of these cardio-respiratory alterations.     

Cold-induced bradycardia in man during sleep in Arctic winter nights

Two young male Caucasians volunteered for a study on the effects of cold exposure during night sleep in winter in the Arctic. The 14-day experiment was divided in three consecutive periods, baseline (2 nights), cold exposure (10 night) and recovery (2 nights). Both baseline and recovery data were obtained in neutral thermal conditions in a laboratory. The subjects slept in a sleeping bag under an unheated tent during the cold exposure. Apart from polysomnographic and body temperature recordings, electrocardiograms were taken through a telemetric system for safety purposes. Heart rates were noted at 5-min intervals and averaged hourly. In both environmental conditions, heart rate decreased within the first two hours of sleep. Comparison of the data obtained during cold exposure vs. thermal neutrality revealed lower values of heart rate in the cold, while body temperatures remained within normal range. This cold-induced bradycardia supervening during night sleep is discussed in terms of the occurrence of a vagal reflex preventing central blood pressure to rise.     

Direct measurement of immunoreactive renin during changes of posture in man.

For several years, it has been possible to determine renin by a direct RIA. In the present study, plasma active renin concentration (PRC) was related to plasma renin activity (PRA) and aldosterone as a function of a standardized posture test. Using PRC, our target was to define the shortest necessary test duration. The three parameters were examined in 10 healthy male subjects (22-34 years old). Salt balance was determined in 24-hour urine, and plasma potassium and sodium were measured. Volunteers were hospitalized for 1 night, and at 8 a.m. the next morning they were subjected to the following postural changes: 3 h active orthostasis and 3 h recumbency. Frequent blood samples were taken. Orthostasis induced a significant rise in PRC, PRA and aldosterone already after 15 min. PRC and PRA reached a maximum level after 90 min of orthostasis and remained relatively stable, while aldosterone reached its highest level already after 30 min and then gradually decreased. Significant correlations were found between PRA and PRC (p < 0.001), between PRC and aldosterone (p < 0.001), and between PRA and aldosterone (p < 0.001). The PRC/PRA ratio changed during the course of the test, especially in supine subjects. When subjects returned to the supine position, all the parameters measured began a continual decrease. There were no significant changes in serum potassium and sodium levels throughout the duration of the test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Memory facilitation by auditory stimulation during paradoxal sleep in man

REM sleep involvement in memory processes was demonstrated in animals and humans. Learning sessions are followed by modifications of REM sleep patterns. Furthermore, one can modify sleep patterns by applying auditory stimulation during REM sleep oculomotor activity. We show that such a procedure facilitates the retention of Morse code learning.     

Sweat gland response to local heating during sleep in man

In order to assess whether the fluctuations in the sweating response occurring during sleep are related to changes in central drive or in peripheral sweat gland reactivity, 4 healthy male subjects spent 6 non-consecutive nights in a climatic chamber. Air temperature was 25 degrees C, dew-point temperature was 10 degrees C and air velocity was 0.3 m X s-1, while wall temperature was either 38 degrees C, 46 degrees C or 48.7 degrees C giving 3 levels of operative temperature (To = 30, 33 or 34 degrees C). During the whole night, 2 local sweating rates on the right and the left sides of the upper chest were continuously recorded from 12 cm2 area capsules using a dew-point hygrometer technique, while applying local thermal clamps, a constant 2 degrees C difference in local skin temperatures being imposed between the two symmetrical skin areas. Continuous measurements were made of rectal temperature, 10 local skin temperatures, 2 EEGs, 2 EOGs, 1 EMG and 1 ECG. Results show that the multiplicative relationship between the peripheral influence of local skin temperature and the central drive for sweating described in waking subjects, is still valid in sleeping subjects. No peripheral change appears in sweat gland reactivity between the different sleep stages. Changes in the sensitivity of the thermoregulatory system occurring during sleep cannot be explained by a local factor acting at the sweat gland level.