Circadian rhythm of heart rate, urinary cortisol excretion, and sleep in civil air traffic controllers.

The examination of Air Traffic Controllers (ATCs) from the Warsaw Airport (Poland) included 24-hr ECG monitoring. The participants were 10 civil ATCs, 9 males and 1 woman. The study was carried out on a group of 19 ATCs during their duty periods, 14 of them working 12-hr shifts and 5 performing 24-hr duties. The participants collected urine every 4 hrs, and cortisol concentration was determined. Further, the survey included the quality and duration of sleep, and subjective fatigue in the 62 participants. In ATCs, shift work modifies natural rhythms of the circulatory system and decreases the ability for intensified mental work at night. In consequence ATCs experience frequent sleep disorders.

Heart rate variability in exposure to high altitude hypoxia of short duration.

The objective of the presented studies is to attempt an evaluation of heart rate (HR) and heart rate variability (HRV) regulatory mechanisms in the presence of autonomous nervous system (ANS) components in transient exposure to high altitude hypoxia. During 24 hrs including a stay in hypobaria, the participants had their HR continuously recorded using the Holter method. The following parameters were calculated at rest and during the stay in a thermobarochamber: spectral power in low frequency bands (LF) 0.04-0. 15 Hz and high frequency bands (HF) 0.15-0.5 Hz, and the sympathetic-parasympathetic balance index LF/HF. Under hypobaric conditions, a decrease in mean spectral power of R-R intervals was noted within both frequency ranges, compared with the study performed in normobaria. The observed differences were larger at daytime.

Heart rate variability during centrifuge (+Gz) and lower body negative pressure (LBNP) in pilot candidates.

NASA: Electrocardiograms were recorded in healthy men undergoing centrifugation and lower body negative pressure. Heart rate variability was studied in conjunction with acceleration tolerance. Specific results allowed the authors to conclude that there was significantly lower sympathetic nervous system activity in individuals with high acceleration tolerance.^ieng

Comparison of the circadian rhythm in cell proliferation in corneal epithelium of male rats studied under normal and hypobaric (hypoxic) conditions.

Groups of 20-45-day-old rats maintained on a light (0600-1800)/dark (1800-0600) regimen with food and water available ad libitum were studied for the effect of hypoxic hypoxia on the circadian rhythm of corneal epithelial mitosis and thymidine incorporation. In experiments conducted during the months of September and November, hypoxic hypoxia was accomplished by the exposure of rats to a simulated altitude of 7500 m in one series of experiments, or to a gaseous mixture of 8% oxygen and 92% nitrogen at sea level atmospheric pressure (760 mmHg) in another series of experiments. Controls were included as well. Statistically significant (P less than 0.05) circadian rhythmicity in the corneal mitotic index was substantiated in the control animals with mesor (M) = 12.4%, amplitude (A) = 9.6% and acrophase (phi) of 0911. In the hypoxic hypoxia situation, the mesor and amplitude were depressed to 8.6 and 5.9%, respectively. In control groups, thymidine incorporation was circadian rhythmic with M = 38.5 and A = 11.3 cpm/microns DNA and acrophase of 2255. In the hypoxic hypoxia situation, the mesor was similar to the controls; whereas the amplitude was suppressed to 6.1% and acrophase was phase advanced by about 7 hr. Changes in the circadian rhythm of corneal mitosis and in thymidine incorporation under hypoxic hypoxia can be explained by programmed-in-time energy requirements during the corneal cell regeneration cycle.

Circadian rhythms of glucose, triiodothyronine and insulin in relation to composition of diet and meal-timing in rats.

A possible role of nutrition as a synchronizer has been recently emphasized, particularly the effect of controlled diet composition of circadian variations of many functions of the organism. The aim of the study was to determine whether diet composition (low or high fat diet) could be a synchronizer of circadian rhythms of glucose, insulin and triiodothyronine. The effect of diet composition on diurnal changes in glucose tolerance was also tested. After 24 h starvation period the biochemical parameters in the serum were measured every 4 hours i.e. 600, 1000, 1400, 1800, 2200, 200. Glucose tolerance was tested between 500-700, 1100-1300, 1700-1900 and 2300-100. The circadian variations of glucose and insulin levels were observed in animals fed both diets. An increase of glucose level was noted during reduced activity of the animals and the acrophase was recorded at 1659 h (low fat diet) and 1514 h (high fat diet). The acrophase of insulin level was observed at 526 h (low fat diet) and 352 hrs (high fat diet) in the period of activity of the animals. Circadian changes of triiodothyronine level were noted in animals fed the low fat diet only, the acrophase appeared at 1447. Simultaneously, no variations occurred in animals fed the high fat diet. A consequence of the high fat diet was also a disappearance of diurnal variations in glucose tolerance test at 60, 90 and 120 min.

Utilization of glucose during exercise in relation of meal-timing.

The effect of glucose administration was studied on its utilization during exercise carried out in the hours 500-700, 1100-1300, 1700-1900, 2300-100. The control group comprised animals at rest which had one or two glucose loads. Circadian variability of blood glucose level was observed in response to glycaemic stimulation in control animals. In the animals during exercise the circadian changes of glucose level depended on the time after glucose administration and the duration of exercise. Glucose utilization during exercise was not identical at various times of the 24-hour period. The greatest fall of blood glucose was observed at 1800 after one as well as after two glucose loads. Glucose administration after one hour of exercise prevented hypoglycaemia development.

Biological time-related changes in tolerance of male rats to hypoxia--I. Survival rate and carbohydrate metabolism.

Investigations were carried out on male Wistar rats, synchronized in standard conditions to a light-dark regiment (LD 12:12 with L from 0600 to 1800). Rats exposed to hypoxia equivalent to 10,500m at a clock-hour of 1000 had a survival time twice as long as that of animals exposed at 2200. Data from this study indicate the ability to mobilize energy stores through the conversion of liver glycogen to glucose along with circadian differences in hormonal response (e.g. corticosterone and insulin) contributes to the tolerance to hypoxia being greater during diurnal rest than nocturnal activity in rats.

Biological time-related changes in tolerance of male mice to hypoxia--II. Circadian rhythm of lysosomal susceptibility to hypoxia.

Circadian variations of mouse liver, brain and heart lysosomal susceptibility to hypoxia were investigated. Lysosomal disruption during hypoxia was estimated on the basis of the following measurements: changes in percentage free activity of beta-galactosidase and acid phosphatase, tissue loss of both lysosomal enzymes and accumulation of serum beta-galactosidase. When exposure to hypoxia took place at the end of the rest phase or at the beginning of the active phase, it was accompanied by maximum increase of percent free activity. This, presumably represents a diffusion of enzymes from lysosomes due to altered membrane permeability. However, hypoxia when occurring during the second part of the active phase and first part of the rest phase resulted in tissues loss of lysosomal enzymes and accumulation of serum lysosomal enzymes. This is believed to represent the release of lysosomal enzymes in bulk from damaged or ruptured lysosomal membranes.

Circannual rhythms of physical fitness and tolerance of hypoxic hypoxia.

Presence of a circannual rhythm of physical fitness and tolerance of hypoxia was demonstrated. The rhythm of physical fitness had two peaks, in April and September. Using cosinor analysis the acrophase of the circannual rhythm was found to be on Aug. 10 with a 95% confidence limit (May 30-October 16), and the amplitude of the rhythm was 1.6 ml O2/kg/min with a 95% confidence limit (0.22-2.96 ml/kg/min). The circannual rhythm of hypoxia tolerance showed a similar pattern of changes. The maximum value of this rhythm was observed also in April and in autumn, its acrophase was calculated to occur on Aug. 26 with a 95% confidence limit (May 10-October 2), and its amplitude was 33.4 sec with a 95% confidence limit (10.4-56.4 sec.). An analysis of the results of physical fitness tests carried out in training camps confirmed these circannual fluctuations of physical fitness.

Response of Aspergillus nidulans and Physarum polycephalum to microwave irradiation.

The influence of microwaves on genetic processes in Aspergillus nidulans and Physarum polycephalum was investigated. Suspensions of organisms were exposed in the far zone to 2450-MHz waves at 10 mW/cm2 for one hour in both CW and pulsed (1 microsecond, 600 pps) fields. Spores of A. nidulans were irradiated before and during germination. No changes in survival rate or in frequency of morphological mutation were found. Polycephalum under the influence of CW microwaves incorporated 3H-Thymine into DNA at a rate five times that of controls and twice that of thermal controls. The accelerated synthesis may reflect more efficient volume heating by microwaves, or in the presence of microthermal gradients in suspensions, or field-specific influences in concern with focal or volume heating.