Relative and combined effects of heat and noise exposure on sleep in humans.

In a counter-balanced design, the effects of daytime and/or nighttime exposure to heat and/or traffic noise on night sleep were studied in eight healthy young men. During the day, the subjects were exposed to baseline condition (ambient temperature = 20 degrees C; no noise) or to both heat (35 degrees C) and noise. The duration of the daytime exposure was 8 h ending 5 h before sleep onset. The following nights, the subjects slept either in undisturbed (20 degrees C; no noise) or in noise, heat, or noise plus heat-disturbed environments. During the day, the various types of traffic noise were distributed at a rate of 48/h with peak intensities ranging between 79 and 86 dB(A). The background noise level was at 45 dB(A). At night, the peak intensities were reduced by 15 dB(A), the rate was diminished to 9/h, and the background noise was at 30 dB(A). Electrophysiological measures of sleep and esophageal and mean skin temperatures were continuously recorded. The results showed that both objective and subjective measures of sleep were more disturbed by heat than by noise. The thermal load had a larger impact on sleep quality than on sleep architecture. In the nocturnal hot condition, total sleep time decreased while duration of wakefulness, number of sleep stage changes, stage 1 episodes, number of awakenings, and transitions toward waking increased. An increase in the frequency of transient activation phases was also found in slow-wave sleep and in stage 2. In the nocturnal noise condition, only total number of sleep stage changes, changes to waking, and number of stage 1 episodes increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Nocturnal plasma thyrotropin variations are related to slow-wave sleep.

The thyrotropin (TSH) nycthemeral pattern is known to be strongly influenced by sleep, but previous studies have failed to demonstrate any link between sleep structure and TSH variations. Using 10-min blood sampling, nocturnal TSH profiles were analysed in 24 young healthy subjects during normal sleep. Six of the subjects then underwent a partial sleep deprivation experiment, sleep was permitted from 03.00 hours to 07.00 hours. Descending slopes of TSH values were observed for the first 20 minutes of SWS episodes, whereas no significant trend was found for other sleep stages. During the period of sleep deprivation, nocturnal TSH levels increased and then declined immediately after sleep onset; however, the association between SWS and descending TSH slopes persisted. This temporal concordance suggests that some particular mechanisms associated with SWS may modulate TSH release, or conversely that increasing TSH levels prevent the occurrence of SWS.

Mental task-induced strain and its after-effect assessed through variations in plasma cortisol levels.

Plasma cortisol levels were measured in 20 healthy men while they carried out mental tasks in intermittent noise. Half the subjects performed a serial short-term memory task and, later on, a multiple-choice task, whereas the other half performed only the multiple-choice task. The aim of the experiment was to determine whether enhanced cortisol release, due to a centrally mediated arousal reaction, depressed the cortisol level when the subjects had to cope with a new task situation. In a previous study, such a regulatory after-effect was revealed in the midday meal-related cortisol peak, but not in a subsequent exercise-induced cortisol peak, although cortisol release in both cases could be related to metabolic changes. The results showed that the second mental task still induced a pronounced rise in cortisol levels. No changes in task performances were found. It is concluded that different regulatory mechanisms are involved in adrenocortical secretion, depending on the origin of the stimulation, and that cortisol responses are closely related to individual coping abilities and strategies.

Plasma catecholamines and pituitary adrenal hormones related to mental task demand under quiet and noise conditions.

Plasma levels of catecholamines and pituitary adrenal hormones were measured in 20 min samples from eight subjects, in one control session and two experimental sessions, while they performed a short-term memory task under quiet of noise conditions. Performing the task led to significant increase in the plasma levels of cortisol, adrenaline and noradrenaline, whereas no variations in growth hormone and dopamine were observed. Similarly, significant changes occurred in urinary catecholamine excretion. A significant correlation was found between individual plasma cortisol increments and error-rates assessed from an accuracy of recall variable. For adrenaline and noradrenaline, an early response apparently linked with an anticipatory process preceded the task. Exposure to noise did slightly amplify cortisol response to the task, but during the first experimental session, with or without noise, the task elicited greater cortisol increases in all subjects than during the second session. These results provide evidence for a relationship between sympathoadrenocortical activity and attentional demand, whereas cortisol increments seem to be more specifically related to better coping with the task. Frequent hormone level measurements during a prolonged mental task might clarify the complex relationship between time-related bodily hormonal changes, performance and subjective feelings.

Continuous positive airway pressure treatment. Effects on growth hormone, insulin and glucose profiles in obstructive sleep apnea patients.

The principal nocturnal GH peak normally coincides with the first episode of slow wave sleep (SWS). Obstructive sleep apnea (OSA) patients have low nocturnal GH levels which may be explained by their poor quality fragmented sleep but other factors are possibly involved. Obesity is frequently associated with OSA, and obese patients also manifest reduced GH secretion. The mechanisms reducing GH levels in obese subjects are not understood, but hyperinsulinaemia is a suggested factor. In this study nocturnal plasma and secretory GH profiles of OSA patients were examined in relation to the quality and quantity of sleep, together with plasma glucose and insulin levels. Eight OSA patients, (BMI 32.7 +/- 2.3 kg/m2), underwent 2 night studies. For one night no treatment was given and for the other continuous positive airway pressure (CPAP) treatment was administered for the first time. Blood was collected continuously throughout each night and plasma GH, insulin and glucose profiles established in 10 min interval samples. From the plasma data a deconvolution model was used to calculate GH secretion rates. Sleep was recorded during the studies. For the non-treatment night GH levels were low and increased significantly with treatment, p = 0.008 for plasma levels and p = 0.02 for secretion rates. Treatment significantly decreased the cumulative apnea duration and increased the quantity of SWS and Rapid Eye Movement (REM) sleep (p = 0.008), but the mean insulin and glucose profiles did not differ between the two nights. Individual GH plasma and secretion rates, on treatment, showed a tendency to correlate with the amount of SWS (p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular responses and electroencephalogram disturbances to intermittent noises: effects of nocturnal heat and daytime exposure.

During sleep, in thermoneutral conditions, the noise of a passing vehicle induces a biphasic cardiac response, a transient peripheral vasoconstriction and sleep disturbances. The present study was performed to determine whether or not the physiological responses were modified in a hot environment or after daytime exposure to both heat and noise. Eight young men were exposed to a nocturnal thermoneutral (20 degrees C) or hot (35 degrees C) environment disturbed by traffic noise. During the night, the peak intensities were of 71 dB(A) for trucks, 67 dB(A) for motorbikes and 64 dB(A) for cars. The background noise level (pink noise) was set at 30 dB(A). The noises were randomly distributed at a rate of 9.h-1. Nights were equally preceded by daytime exposure to combined heat and noise or to no disturbance. During the day, the noises as well as the background noise levels were increased by 15 dB(A) and the rate was 48.h-1. Electroencephalogram (EEG) measures of sleep, electrocardiograms and finger pulse amplitudes were continuously recorded. Regardless of the day condition, when compared with undisturbed nights, the nocturnal increase in the level of heart rate induced by heat exposure disappeared when noise was added. Percentages, delays, magnitudes and costs of cardiac and vascular responses as well as EEG events such as transient activation phases (TAP) due to noise were not affected by nocturnal thermal load or by the preceding daytime exposure to disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Training effects on the hydromineral endocrine responses of cardiac transplant patients.

Cardiac transplant patients manifest several haemodynamic changes as well as altered peripheral responses to exercise which may disrupt body fluid regulation. This study examined the effect on an endurance training programme on the exercise-induced hydromineral endocrine responses of heart transplant patients. Seven patients underwent a square-wave exercise test before and after a 6-week training programme. The tests were performed at the same absolute intensity but, during training, the workload was increased to maintain the same relative exercise intensity. Pretraining results were compared to those obtained from age-matched controls. Training improved physical capacity, producing a significant increase in maximal tolerated power and workload between the first and last training session (P < 0.05, P < 0.001, respectively). Haematocrit and osmolality were increased in both groups at the end of exercise (P < 0.01) but changes observed post-training did not differ from pretraining values. Apart from atrial natriuretic peptide (ANP), which showed significantly higher concentrations at rest and during exercise (P < 0.01), the changes in hydromineral hormones of the patients resembled those of the controls. Basal plasma renin activity (PRA) was slightly raised prior to training (P < 0.07) compared to the controls and post-training. For both PRA and aldosterone, a significant training effect was revealed when both the exercise-stimulated increase and postexercise decline were considered (P < 0.05), possibly reflecting lower noradrenaline concentrations. Training had no effect on either basal or exercise stimulated ANP levels, which is compatible with the theory that ANP regulation is largely under mechanical rather than sympathetic nervous system control.(ABSTRACT TRUNCATED AT 250 WORDS)

Nycthemeral patterns of thyroid hormones and their relationships with thyrotropin variations and sleep structure.

In order to precise the relationships between TSH, FT3, and FT4 nycthemeral variations and the relationships between thyroid hormone variations and sleep, 8 healthy young males were studied twice, once during a 24-h experiment with normal nocturnal sleep, and once during a night of sleep deprivation. The subjects received continuous enteral nutrition and remained supine during the whole experiment. Blood was sampled every 10 min for TSH, FT3, and FT4 measurements. Thyroid hormones exhibited small oscillations which were not systematically related to TSH pulses, and there was no evidence of a nycthemeral rhythm. SWS was associated with TSH declining phases, whereas awakenings were strongly associated with ascending phases of TSH variations. There was no association between sleep structure or awakenings and thyroid hormones. Sleep deprivation led to increased TSH and FT3 levels, without any variation in FT4 levels. These results demonstrate that short-term thyroid hormone variations do not only depend on the effect of TSH on thyroid secretion but also on a possible role of TSH on peripheral FT4 to FT3 conversion. Conversely, the relationships between TSH and SWS or awakenings are not mediated by thyroid hormones.

Nocturnal prolactin pulses in relation to luteinizing hormone and thyrotropin.

The two hypothalamic releasing factors, luteinizing hormone releasing hormone (LHRH) and thyrotropin releasing hormone (TRH), have been shown to stimulate pituitary prolactin (PRL) release as well as their respective pituitary hormones, luteinizing hormone (LH) and thyrotropin (TSH). In this study the influence of LH and TSH regulatory mechanisms on nocturnal PRL secretion was investigated by evaluating whether the coincidence of PRL with LH and TSH pulses occurred more frequently than would be expected if the hormone generators were not coupled. Thirty night studies were conducted in twelve healthy male subjects. Six subjects underwent 3 studies and 6 subjects 2 studies. Blood was collected into aliquots at 10 min intervals throughout the night and plasma concentrations of PRL, TSH, and LH were determined. From the plasma profiles, hormone secretory rates were calculated using a method of deconvolution. Significant plasma and secretory hormone pulses were identified by a peak detection computer program. For statistical analysis the night studies of each subject were concatenated. Concomitance between the plasma pulses of both TSH and LH with PRL was insufficient to reject the null hypothesis of random coincidence. An increase in the number of subjects demonstrating significant coincidence between the hormone pulses was obtained when secretory pulses were analysed. Seven of the 12 and 10 of the 12 subjects showed significant concomitance between PRL and respectively TSH and LH. This proportion was sufficient to confirm copulsatility between PRL and LH. These results suggest that LH regulatory mechanisms are involved in the generation of the nocturnal pulsatile PRL profile, TRH may also play a role in the secretion of PRL at a central level, but was not reflected in the plasma or secretory profiles because of other overriding regulatory factors.