H S Nayar’s research while affiliated with INHS Asvini and other places

Studies were carried out to ascertain the role of sympatho-parasympathetic responses in the process of adaptation to altitude. The assessment of status of autonomic balance was carried out in a group of 20 young male subjects by recording their resting heart rate, blood pressure, oral temperature, mean skin temperature, extremity temperatures, pupillary diameter, cold pressor response, oxygen consumption, cardioacceleration during orthostasis and urinary excretion of catecholamines; in a thermoneutral laboratory. The same parameters were repeated on day 3 and at weekly intervals for a period of 3 weeks, after exposing them to 3,500 m; and also after return to sea level. At altitude, similar studies were carried out in a group of 10 acclimatized lowlanders, 10 high altitude natives and 6 patients who had recently recovered from high altitude pulmonary oedema. In another phase, similar studies were done in two groups of subjects, one representing 15 subjects who had stayed at altitude (3,500–4,000 m) without any ill effects and the other comprising of 10 subjects who had either suffered from high altitude pulmonary oedema (HAPO) or acute mountain sickness (AMS). The results revealed sympathetic overactivity on acute induction to altitude which showed gradual recovery on prolonged stay, the high altitude natives had preponderance to parasympathetic system. Sympathetic preponderance may not be an essential etiological factor for the causation of maladaptation syndromes.

Studies were carried out in a group of 20 young male subjects to investigate the changes in chemoreceptor sensitivity during acclimatization to altitude. Their hypoxic sensitivity and carbon dioxide sensitivity were studied at Delhi, during acclimatization at 3500 m, and on return to sea level. Similar studies were also done in a group of 10 acclimatized lowlanders who stayed at 3500-4000 m for 12-14 months, and also on 10 high-altitude natives. The results showed no significant alteration in the hypoxic sensitivity of the lowlanders; but CO2 sensitivity was markedly elevated at altitude, both in sojourners and acclimatized lowlanders. The high-altitude natives showed less sensitivity to hypoxia, whereas the CO2 sensitivity was normal.

Studies were carried out to find out the role of chemoreceptor sensitivity in the causation of maladaptation syndromes on acute exposure to altitude. The experiments were done in two phases. In phase I, the responses in chemoreceptor sensitivity were studied in altitude acclimatized subjects and compared with those who suffered from either High Altitude Pulmonary Oedema (HAPO) or Acute Mountain Sickness (AMS). In Phase II, a similar comparison was done in two groups of subjects, one representing normal sojourners at 3,500 m and the other being subjects who had just recovered from HAPO. The first phase was done at Delhi; and the second at an altitude of 3,500 m. Parameters of assessment were hypoxic sensitivity, carbon dioxide sensitivity, ventilation ($\dot V$ E), respiratory frequency (Rf), forced vital capacity (FVC), forced expiratory volume at the first second (FEV1), heart rate (HR), blood pressure (BP), and oral temperature (Tor). The results showed significantly lower sensitivity to both hypoxia and carbon dioxide in maladapted subjects, as compared to those who were well acclimatized in both the categories suggesting thereby that reduced chemoreceptor sensitivity might be an initiating factor in the causation of maladaptation syndromes at altitude.

Boyd height and weight are found to contribute significantly in linear regression equations established to estimate lean body weight, body density and leg muscle volume from anthropometric measurements. To ascertain whether other body measurements could also be predicted by body weight and height at sea level and high altitude situations, 15 measurements including height and weight were taken using standard anthropometric techniques. These anthropometric data were obtained on two simple random samples consisting of 120 and 101 human male subjects staying at sea level and at high altitude situations, respectively. Separate multiple linear regression equations have been constructed for each body measurement using height and weight as predictors. The equality of these multiple linear regression equations was tested and it was found that most of these equations differ significantly from each other. Thus, the present paper provides various multiple linear regression equations for predicting 13 important body measurements from height and weight of an individual at two locations.

Physiological parameters have been compared in 75 normal healthy individuals exposed to occupational noise of 88–107 dB (A) (6–8h/day) for 10–15 years and in 36 normal non-exposed subjects. Blood pressure, both systolic (P<0.01) and diastolic (P<0.001), and heart rate (P<0.05) were found to be significantly higher in the exposed subjects. Irregularity in cardiac rhythm, both in amplitude and duration, was found in 18% of the exposed subjects as against 6% in the non-exposed group. Variation in the heart rate during acute noise exposure of 90 dB (A) has been shown to be related with the preponderance of tonicity of sympathetics and parasympathetics. Measurement of hand blood flow during the same exposure showed a lesser degree of vasoconstriction and a slower recovery rate in the exposed group. Altered observations in the exposed group could be attributed to changes in the mechanical property of blood vessels.

Gompertz curve has been successfully used to estimate mortality intensities, recovery and relapse rates for human beings suffering from specific diseases. Perhaps, no attempt has yet been made to describe statistically the phenomenon of thermoregulation efficiency of man. This paper deals with the statistical approach for describing the above mentioned phenomenon. For this purpose, Gompertz curve has been fitted to the data of recovery palm skin temperature of human subjects, which was collected after removing the hand of a subject dipped for two minutes in cold water maintained at 10 +/- 1 degree C on seven environmental situations including altitude. The coefficients of correlation between observed and estimated palm skin temperature expressed logarithmically were close to 0.99 for each situation indicating the high precision of the fitted curve. The average rates of recovery of palms skin temperature have also been compared between these seven environmental situations using analysis of covariance technique. It is concluded that recovery of palm skin temperature of sea level residents during stay at plains is much faster than their recovery at high altitude situations.

Studies were conducted on 15 healthy young soldiers to evaluate the effect of a cold acclimatization schedule on the thermoregulatory and metabolic activity on exposure to acute cold stress. These men were exposed to cold (10C) for 4 h daily wearing only shorts for 21 days, in a cold chamber. They were subjected to a standard cold test at 10 1C the day 1, 6, 11 and 21. The subjects were made to relax in a thermoneutral room (26–28C) for 1 h and their heart rate, blood pressure, oxygen consumption, oral temperature, mean skin temperature, mean body temperature, peripheral temperatures, and shivering activity were recorded. Then they were exposed to 10C and measurements were repeated at 30 min intervals, for 2 h. The cold induced vasodilatation (CIVD), cold pressor response and thermoregulatory efficiency tests were measured initially and at the end of acclimatization schedule. The data show that the procedure resulted in elevated resting metabolism, less fall in body temperature during acute cold stress, reduction in shivering, improvement in CIVD and thermoregulatory efficiency and less rise in BP and HR during cold pressor response. The data suggest the possibility of cold acclimatization in man by repeated exposure to moderately severe cold stress.

A study was carried out on 10 healthy subjects to evaluate the effect of yogic training on some autonomic responses and biochemical indices. Yogic training was performed daily in the morning hours for one hour under the supervision of qualified yoga instructors. Physiological and biochemical responses were assessed before and after 3 months of training. A significant decrease in heart rate, blood pressure and elevation of mean skin temperature and alpha index of EEG were recorded, followed by reduction in blood glucose and plasma cholesterol level. Changes in the dopamine-β-hydroxylase activity, monoamine oxidase and adrenal steroids along with the physiological parameters indicated a shift in the autonomic balance towards relative parasympathodominance.