Changes in visual evoked potentials on acute induction to high altitude.

BACKGROUND & OBJECTIVES: Induction to high altitude leads to altered central nervous system (CNS) functions induced by hypobaric hypoxia. The sensory systems like visual and auditory systems are reported to be affected by hypoxia. The present study was undertaken to assess the effects of hypobaric hypoxia on visual evoked potentials (VEPs) at 3200 m and 4300 m. METHODS: The VEP of 30 human volunteers were recorded at sea level (SL) and then at high altitude (HA) of 3200 m (HA I) and 4300 m (HA II) in eastern Himalayas and on return to sea level (RSL). The absolute latencies and amplitude of positive and negative waves were recorded. RESULTS: High altitude of 3200 m did not alter the latency of major wave N1, P1 and N2 of the VEPs. At HA II (4300 m), there was a statistically significant increase (P < 0.01) in the latency of NI wave as compared to the SL value and HA I (3200 m) in both left and right eye. There was a slight increase in latenty of P1 wave in both left and right eye at HA II. INTERPRETATION & CONCLUSION: From these results it may be concluded that induction to HA causes increase in latency of N1 wave at 4300 m which is still within physiological limits. This increase in wave latency of N1 wave in both eyes may be due to synaptic delay and/or altered neuronal processing at HA.

Effect of high altitude on human auditory brainstem responses.

The effect of hypobaric hypoxia on Brain Stem Auditory evoked potentials (BAERs) were studied. BAERs were recorded in 30 volunteers at sea level (SL) and then at high altitude (HA) of 3200 m (HA I) and 4300 m (HA II) in Eastern Himalayas and on return to sea level (RSL). The BAERs were recorded using Nicolet Compact - 4 (USA) in response to monaural auditory stimuli consisting of clicks of 100 ps square pulse at a rate of 15/sec. The BAERs were recorded on day 4 of their stay at 3200 m and 4300 m respectively. Findings indicated an increase in absolute peak latencies of wave V at 3200 m, which was statistically significant. On further ascent to 4300 m there was an increase in absolute peak latencies of wave I and III indicating delay in sensory conduction at the medullo-pontine auditory pathways.

Energy cost and cardiorespiratory changes during the practice of Surya Namaskar.

Surya Namaskar (SN), a group of Yogic exercise consists of a set of twelve postures which is practiced by some of the yoga practitioners. The present study was undertaken to observe critically the energy cost and different cardiorespiratory changes during the practice of SN. Twenty-one male volunteers from the Indian Army practiced selected Yogic exercises for six days in a week for three months duration. The Yogic practice schedule consisted of Hatha Yogic Asanas (28 min), Pranayama (10.5 min) and Meditation (5 min). In the Yogic practice schedule 1st they practiced Kapal Bhathi (breathing maneuvers) for 2 min then Yogamudra (yogic postural exercise) for 2 min, after that they took rest until oxygen consumption and heart rate (HR) came to resting value. Subsequently subjects performed SN for 3 min 40 seconds on an average. After three months of training at the beginning of the fourth month subjects performed entire Yogic practice schedule in the laboratory as they practiced during their training session and experiments were carried out. Their pulmonary ventilation, carbondioxide output, Oxygen consumption, HR and other cardiorespiratory parameters were measured during the actual practice of SN. Oxygen consumption was highest in the eighth posture (1.22+/-0.073 1 min(-1)) and lowest in the first posture (0.35+/-0.02 1 min(-1)). Total energy cost throughout the practice of SN was 13.91 kcal and at an average of 3.79 kcal/min. During its practice highest HR was 101+/-13.5 b.p.m. As an aerobic exercise SN seemed to be ideal as it involves both static stretching and slow dynamic component of exercise with optimal stress on the cardiorespiratory system.

Brainstem auditory evoked responses in young urban and rural boys--a comparison.

Brainstem auditory evoked responses (BAER) were studied in a total of 194 boys in the age group between 10-15 yrs taken from a busy metropolitan city and also from a relatively quiet town in order to compare their values and to look into the probable cause of the difference between them, if any. BAER were tested with the help of Compact-4 (Nicolet, USA) instrument using the standard technique. In general, the BAER values of the two sample populations were found to be almost similar with no gross differences in terms of peak latency and inter peak latencies. The values were found to be comparable to adult male values as reported earlier.

Effect of high altitude (HA) on event related brain potentials.

Event Related brain potentials (ERPs) were recorded in 15 subjects using standard auditory odd ball paradigm, in which subjects were presented a sequence of two distinguishable sound stimuli of that occurred frequently (frequently (frequent stimulus-non target) and the other infrequently (rare stimulus-target). These recordings were made at sea level (SL) and then the subjects were air lifted to 3500 m altitude (HA), where they stayed for 3 weeks. Their ERPs were recorded during the first and third week of stay at HA and on return to sea level (RSL). Data indicated impairment in cognitive function as a result of exposure to HA as depicted by increase in the latency of P3 which was significant during the 1st week of stay at HA compared to sea level. The P3 wave latency during the 3rd week of stay at HA showed an increase compared to SL but was not statistically significant. From the results it may be concluded that high altitude hypoxia induced slow processing of stimulus evaluation, may be responsible for increase in P3 latency. The difference in the latent period of P3 waves during the first and third week of stay at HA may be due to continuous stay at HA which might lead to the time dependent adaptive processes occurring with increasing duration of exposure to HA which may induce learning effects.

Oxygen saturation response to exercise VO2 at 2100 m and 4350 m in women mountaineering trainees.

Human work performances decreases at high altitude (HA). This decrement does not appear to be similar for every individual, may be due to variety of factors like elevation, mode of induction, work intensity, physical condition and specificity of the subjects. The purpose of the study was to evaluate the effects of alteration in responses of oxygen saturation (SaO2) and oxygen consumption (VO2) to a standard exercise in women mountaineering trainees under hypobaric hypoxia. Experiments were conducted in 2 groups (10 each) of females and compared the difference in responses of native women of moderate altitude with those of the plains/low altitude. A standard exercise test (Modified Harvard Step-Test for women) was performed on a 30 cm stool with 24 cycles/min for 5 min, initially at 2100 m and then at 4350 m. The exercise VO2 values for plains dwelling women achieved apparently VO2max level at both altitude locations with significant reduction in SaO2 during standard exercise. Exercise VO2 values decreased on exposure to 4350 m with further reduction in SaO2. Whereas with same work intensity, under same situation the exercise VO2 values of the moderate altitude women did not appear to have reached VO2max. They also maintained comparatively higher level of SaO2. It may be concluded that hypoxic exposure along with mountaineering training, the moderate altitude women maintained a higher level of SaO2 during standard exercise at both altitude locations, compared to low altitude women who might have lost a compensatory reserve to defend the hypoxic stress to exercise. Thus, moderate altitude women are proved to be better fit for hypoxic tolerance/HA performance.

Immediate treatment of frostbite using rapid rewarming in tea decoction followed by combined therapy of pentoxifylline, aspirin & vitamin C.

BACKGROUND & OBJECTIVES: Frostbite, the severest form of cold injury is a serious medical problem for our Armed Forces operating in the snow bound areas at high altitude. Effects of treatment by rapid rewarming in tea decoction followed by combined therapy of pentoxifylline, aspirin and vitamin C were evaluated in amelioration of tissue damage due to experimentally induced frostbite in rats. METHODS: Experiments were conducted in 2 groups (25 each) of albino rats (control i.e., untreated and experimental i.e., treated). Frostbite was produced experimentally in all the animals by exposing one of the hind limbs at -12 +/- 1 degree C with wind flow 25-30 lit/min for 30 min in a freezing-machine, with simultaneous recordings of rectal and ambient temperatures. The degree of tissue damage was assessed after 10 days. Following cold exposure, neither external thawing nor any medication was given to the animals of the control group; while the exposed limb of the experimental animals was rewarmed in tea decoction maintained at 37-39 degrees C for 30 min immediately after cold exposure, with simultaneous oral ingestion of warm tea decoction. These animals were also given pentoxifylline (40 mg/kg), aspirin (5 mg/kg) and vitamin C (50 mg/kg) twice daily orally for the next 7 days. RESULTS: In the control group, 68 per cent animals suffered from severe (56%) to very severe (12%) frostbite, while the remaining 32 per cent had moderate frostbite. No animals of this group could escape injury or suffered anything less than moderate frostbite; whereas 52 per cent of experimental animals escaped injury (no frostbite) and 32 and 16 per cent suffered only with primary and moderate degree of injury, respectively. None from this group suffered from severe or very severe frostbite. INTERPRETATION & CONCLUSION: It is evident from the study that this combined therapy resulted in significant improvement in the degree of tissue preservation and proved to be highly beneficial as an immediate treatment of frostbite in rats. The combined pharmacological properties of these drugs might have altered the haemorrheologic status of blood and produced curative beneficial effect in improving tissue survival. Clinical studies are required for confirmation of these beneficial effects in humans, which has already been taken up.

Sleep and performance--recent trends.

Sleep and sleep deprivation are intimately related to performance. Sleep management of people working in different sectors of the society like multi shift workers, nurses, doctors, students in professional schools and the armed forces has a great bearing on performance, health and safety of the subject population. The detrimental effects of sleep deprivation on psychological performance are indicated as increased lapsing, cognitive slowing, memory impairment, decrease in vigilance and sustained attention and shift in optimum response capability. Its effects on physical performance are manifested as decline in ability to perform maximal exercise, self-selected walking pace and increase in perceived exertion. Sleep deprivation appears to have no effect in respect of muscle contractile properties and maximum anaerobic power. At high altitude (HA), there is a reduction in NREM sleep with frequent awakening due to hypoxia as a physiological adaptive measure to prevent accentuation of hypoxemia due to sleep-hypoventilation. Total sleep deprivation for 48 hours at high altitude can affect the acclimatization status, thermoregulation efficiency and cognitive functions. The concept of 'sleepiness' has also been studied, as it is an emerging concept for better understanding of the effects of sleep deprivation and its effects on performance. A special mention of sustained operations in the armed forces has been made keeping in mind its uniqueness in challenging the normal sleep-work schedule and its deployment in extreme environment and operational condition. This article reviews in detail the functions of sleep, its requirement and the effects of sleep deprivation on human performance.

Aerobic capacity & perceived exertion after practice of Hatha yogic exercises.

BACKGROUND & OBJECTIVES: Reports on the effect of yogic exercises on aerobic capacity are few. There is also no literature available on the effect of yogic exercise on perceived exertion (PE) after maximal exercise. In this study the effect of training in Hatha yogic exercises on aerobic capacity and PE after maximal exercise was observed. METHODS: Forty men from the Indian army (aged 19-23 yr) were administered maximal exercise on a bicycle ergometer in a graded work load protocol. The oxygen consumption, carbon dioxide output, pulmonary ventilation, respiratory rate, heart rate (HR) etc., at maximal exercise and PE score immediately thereafter were recorded. The subjects were divided into two equal groups. Twelve subjects dropped out during the course of study. One group (yoga, n = 17) practiced Hatha yogic exercises for 1 h every morning (6 days in a week) for six months. The other group (PT, n = 11) underwent conventional physical exercise training during the same period. Both groups participated daily in different games for 1 h in the afternoon. In the 7th month, tests for maximal oxygen consumption (VO2Max) and PE were repeated on both groups of subjects. RESULTS: Absolute value of VO2Max increased significantly (P < 0.05) in the yoga group after 6 months of training. The PE score after maximal exercise decreased significantly (P < 0.001) in the yoga group after 6 months but the PT group showed no change. INTERPRETATION & CONCLUSION: The practice of Hatha yogic exercises along with games helps to improve aerobic capacity like the practice of conventional exercises (PT) along with games. The yoga group performed better than the PT group in terms of lower PE after exhaustive exercise.

Effect of yogic exercises on physical and mental health of young fellowship course trainees.

A study was undertaken to observe any beneficial effect of yogic practices during training period on the young trainees. 54 trainees of 20-25 years age group were divided randomly in two groups i.e. yoga and control group. Yoga group (23 males and 5 females) was administered yogic practices for the first five months of the course while control group (21 males and 5 females) did not perform yogic exercises during this period. From the 6th to 10th month of training both the groups performed the yogic practices. Physiological parameters like heart rate, blood pressure, oral temperature, skin temperature in resting condition, responses to maximal and submaximal exercise, body flexibility were recorded. Psychological parameters like personality, learning, arithmetic and psychomotor ability, mental well being were also recorded. Various parameters were taken before and during the 5th and 10th month of training period. Initially there was relatively higher sympathetic activity in both the groups due to the new work/training environment but gradually it subsided. Later on at the 5th and 10th month, yoga group had relatively lower sympathetic activity than the control group. There was improvement in performance at submaximal level of exercise and in anaerobic threshold in the yoga group. Shoulder, hip, trunk and neck flexibility improved in the yoga group. There was improvement in various psychological parameters like reduction in anxiety and depression and a better mental function after yogic practices.

Effect of sojourn at altitude of 3,500 m on auditory evoked potential in man.

Auditory evoked potentials were studied on 27 male subjects to evaluate the effect of sojourn at high altitude (HA). They were initially studied at Delhi (260 m) for their auditory evoked potentials and were then flown to an altitude of 3,500 m. During their stay at HA the same parameter was tested twice, once on the second day of arrival at HA and another on 21st day of stay. Then they were flown back to sea level (SL) and were retested on the third day of return. The results showed a significant delay in the peak latency of wave I of both the right and left ears on the second day of arrival at HA with a persistent delay in wave V even after 3 days of return to SL. The results suggest that HA stress caused a delay in sensory conduction at the cochlear level during the first week of induction, which was normalised during further stay.

Suggested predictive indices for high altitude pulmonary oedema.

A study was conducted to evaluate the responses of chemoreceptors and pulmonary vascular bed to hypoxia, on two groups of soldiers exposed to similar altitudes, one group which did not suffer from high altitude (HA) maladies (Gp A) and the other when exposed to similar altitudes suffered from HA maladies (Gp B high altitude pulmonary edema--susceptible group (HAPE-S). Aim of this study was to find out whether these two tests could be used as a screening test for soldiers and sojourners proceeding to HA. Chemoreceptor responses were evaluated by hypoxic ventilatory response (HVR) test and the pulmonary vascular responses were studied by recording pulmonary artery pressure (PAP) changes under simulated hypoxia by breathing hypoxic gas mixtures (HGM) in both the groups. It was observed that HAPE-S subjects showed a reduced HVR response and an increase in PAP (systolic, diastolic, and mean). While Gp A subjects showed an increase in ventilation of 11.39 +/- 3.36 L, the same in Gp B subjects was 3.51 +/- 2.65 L. Thus, the comparison of increase in ventilation following HVR test between the two groups was highly significant. Under hypoxic gas mixture (HGM) breathing, systolic pressure of 28.2 +/- 6.9 and 52.6 +/- 11.0 mm Hg; diastolic pressure of 11.4 +/- 3.8 and 23.6 +/- 5.8 mm Hg and mean pressure of 17.6 +/- 4.3 and 35.0 +/- 7.4 mm Hg were recorded in pulmonary arteries in Gp A and Gp B subjects, respectively. Gp B subjects showed a highly significant increase in all the three pulmonary pressures under HGM breathing.

Physiological and psychological effects of ageing in man.

A cross-sectional study involving men in various age groups was carried out to evaluate some of the physiological and psychological correlates responsible for functional alteration with advancement of age. Each group consisted of 20 soldiers. Their resting physiological variables, lung function parameters, psychophysiological tests, and different mental functions were studied in thermoneutral laboratory. The results revealed the age related decline in various physiological and psychological functions.

Efficacy of pentoxifylline with aspirin in the treatment of frostbite in rats.

The efficacy of pentoxifylline--a haemorrheologic agent along with aspirin--an analgesic agent was evaluated in the amelioration of the tissue damage due to experimentally induced frostbite in 5 groups (20 each) of rats with body weights ranging between 175 and 200 g. Frostbite was produced experimentally in the hind limbs by exposing the animals to -15 +/- 1 degrees C for 1 h using the harness technique, with simultaneous recording of rectal and environmental temperatures. The degree of tissue damage was assessed on the basis of tissue necrosis after 15 days. Administration of pentoxifylline (40 mg/kg bw) 30 min before and 30 min after the cold exposure followed by two doses of the same daily for the next 5 days along with aspirin (5 mg/kg bw) twice daily for the same duration only after cold exposure, resulted in significant improvement in the degree of tissue preservation. The findings of this preliminary study have brought to light the potential usefulness of these drugs in the treatment of frostbite. The combined pharmacological properties of these two drugs might have altered the haemorrheologic status of blood and produced the curative beneficial effect in improving tissue survival following experimentally induced frostbite in rats.

A new physiological approach to control essential hypertension.

This study was conducted on 20 male patients of Essential Hypertension (EH) in order to explore the possible role of baroreflex mechanism in the etiology of EH and also to find out whether by restoration of baroreflex sensitivity to normal level either by postural tilt stimulus on a tilt table or by the equivalent yogic postural exercise (Yogic asanas), the EH could be cured or controlled. Patients on therapeutic regime were gradually withdrawn from drug therapy, and later divided into two groups of 10 each. Group-I (age 34 +/- 1.7 years) was subjected to a 3 week course of 70 degrees head-up tilt for 30 min daily, while in group-II (age 50 +/- 3.3 years), specific yogic exercises equivalent to head-up or head-down tilt were administered for the same duration. The progressive autonomic readjustments were assessed by a battery of tests including cardiovascular responses to head up tilt, cold pressor response at 4 degrees C water (CPR), alpha index of EEG (AI), level of blood catecholamines (CA) and plasma renin activity (PRA). At the end of 3 weeks, there was a significant reduction (P < 0.001) in blood pressure in both the groups. Progressive changes in BP and HR response to tilt during 3 weeks course of tilt and yogic exercise clearly indicated gradual improvement in baroreflex sensitivity. Likewise, changes in other indices like CPR, AI, CA and PRA indicated progressive attenuation of sypatho-adrenal and renin-angiotensin activity. All these changes together with the reduction in BP strongly suggest a close link between the etiology of EH and baroreflexes on the one hand and controlling influence of the latter on sympatho-adrenal and renin-angiotensin systems on the other. It also throws light on the physiological mechanism underlying the effects of selected yogic exercises in the treatment of EH.

Physiological, biochemical and histological changes due to physostigmine in monkeys.

Physostigmine (Phy), a short-acting reversible anticholinesterase agent is considered to be a potent prophylactic antidote for the highly toxic organophosphorous (OP) compounds. The toxic effects, if any, of the probable prophylactic doses of Phy have been evaluated by studying its physiological, biochemical and histological effects in monkeys. Phy only at 100 micrograms/kg resulted in certain cholinergic signs such as salivation, lacrymation and muscular faciculations; physiological changes such as mild tachycardia, tachypnea, higher amplitude in electrical activity of the brain, clinico-chemical effects like fall in PO2, PCO2 and alkalosis and histologically an inflammatory reaction in the lungs. On the other hand, the lower dose, i.e. 50 micrograms/kg appeared to be devoid of cholinergic signs and symptoms. However, we observed a significant inhibition of both plasma and erythrocyte ChE and increase in the rectal temperature in both the Phy treated groups. From this study, Phy at a dose of 50 micrograms/kg could be inferred as a safe, sign free intramuscular dose and may probably be used in pretreatment regimen against nerve agents.

Involvement of a protease in tert-butylhydroperoxide-mediated activation of Ca2+ ATPase in microsomes of pulmonary smooth muscle.

Microsomes isolated from bovine pulmonary artery smooth muscle tissue treated with the oxidant t-buOOH stimulated Ca2+ ATPase activity dose-dependently as also protease activity when tested with a synthetic substrate N-benzoyl-DL-arginine p-nitroanilide. At 300 microM, t-buOOH optimally stimulated these activities. Treatment of the microsomes with t-buOOH stimulated ATP dependent Ca2+ uptake while Na+ dependent Ca2+ uptake was inhibited by t-buOOH. Pretreatment of the microsomes with vitamin E (1 mM) and aprotinin (1 mg/ml) prevented t-buOOH caused stimulation of protease activity and Ca2+ ATPase activity, and also stimulation of ATP dependent Ca2+ uptake while t-buOOH caused inhibition of Na+ dependent Ca2+ uptake was reversed by vitamin E and aprotinin. Treatment of the microsomes with trypsin (1 microgram/ml) stimulated Ca2+ ATPase and ATP dependent Ca2+ uptake while Na+ dependent Ca2+ uptake was inhibited. Pretreatment of the microsomes with aprotinin prevented trypsin caused stimulation of Ca2+ ATPase and ATP dependent Ca2+ uptake, while trypsin caused inhibition of Na+ dependent Ca2+ uptake was reversed by aprotinin.

Clinical observations on tropical men during their sojourn over the Arctic region.

In the present study, besides a detailed clinical evaluation, roentgenographic changes in cardio-respiratory system in Indian soldiers (IS) during their 60 days stay at the arctic have been observed. These results have been compared with the responses at Delhi (before cold acclimatisation) and on return to Delhi (deacclimatisation). An attempt has also been made to compare the same physiological variables with those of Russian Migrants (RM) and Russian Natives (RN) in the arctic region to review significant differences if any. Heart Rate (HR) did not show much change; there was a tendency to increase in both systolic and diastolic blood pressure; and Kerdo's index inclined towards increased sympathetic activity in IS. X-ray chest (PA View) did not show any appreciable change in the lungs in the three groups. One subject amongst IS showed cardiac enlargement and RN subjects showed prominence of pulmonary artery and pulmonary vascular markings. All these physiological changes aim at increasing the cardiac output to overcome the ill effects of cold. Pneumopathy, a clinical condition of increased pulmonary haemodynamics could have resulted in the prominence of pulmonary artery and pulmonary blood flow in the RN. Most of the physiological changes reverted to the baseline value on return to Delhi thus proving that there were no permanent changes during short stay at extreme cold conditions.

Effect of Sahaja yoga practice on seizure control & EEG changes in patients of epilepsy.

The effect of Sahaja yoga meditation on seizure control and electroencephalographic alterations was assessed in 32 patients of idiopathic epilepsy. The subjects were randomly divided into 3 groups. Group I (n = 10) practised Sahaja yoga for 6 months, Group II (n = 10) practised exercises mimicking Sahaja yoga for 6 months and Group III (n = 12) served as the epileptic control group. Group I subjects reported a 62 per cent decrease in seizure frequency at 3 months and a further decrease of 86 per cent at 6 months of intervention. Power spectral analysis of EEG showed a shift in frequency from 0-8 Hz towards 8-20 Hz. The ratios of EEG powers in delta (D), theta (T), alpha (A) and beta (B) bands i.e., A/D, A/D + T, A/T and A + B/D + T were increased. Per cent D power decreased and per cent A increased. No significant changes in any of the parameters were found in Groups II and III, indicating that Sahaja yoga practice brings about seizure reduction and EEG changes. Sahaja yoga could prove to be beneficial in the management of patients of epilepsy.

Effect of Sahaja yoga practice on stress management in patients of epilepsy.

An attempt was made to evaluate the effect of Sahaja yoga meditation in stress management in patients of epilepsy. The study was carried out on 32 patients of epilepsy who were rendomly divided into 3 groups: group I subjects practised Sahaja yoga meditation for 6 months, group II subjects practised postural exercises mimicking Sahaja yoga and group III served as the epileptic control group. Galvanic skin resistance (GSR), blood lactate and urinary vinyl mandelic acid (U-VMA) were recorded at 0, 3 and 6 months. There were significant changes at 3 & 6 months as compared to 0 month values in GSR, blood lactate and U-VMA levels in group I subjects, but not in group II and group III subjects. The results indicate that reduction in stress following Sahaja yoga practice may be responsible for clinical improvement which had been earlier reported in patients who practised Sahaja yoga.