Serum and urinary cation changes on acute induction to high altitude (3200 and 3771 metres).

Twenty subjects each were rapidly inducted by road to 3200 ad 3771 m. Serum and urinary sodium, potassium, calcium, and magnesium were measured during 10 d at high altitude. At 3200 m, only serum potassium increased significantly on the 10th day. At 3771 m, serum potassium did not increase. Serum sodium generally remained low, serum magnesium increased, while calcium decreased significantly. Urinary volume over 24 h decreased more and for longer duration at 3771 m than at 3200 m. Urinary cations did not change significantly at 3200 m. At 3771 m, sodium and potassium excretion decreased on days 1 and 3 later returned towards preinduction levels. Magnesium and calcium decreased throughout the high-altitude stay. Significant changes were noticed in serum and urinary cations on exposure to high altitude when adequate caloric intakes were not ensured.

Platelet count, platelet aggregation and fibrinogen levels following acute induction to high altitude (3200 and 3771 metres).

Two groups of 20 subjects each were separately exposed to altitudes of 3200 m and 3771 m for 10 days by rapid induction requiring 14 and 16 hours respectively to reach high altitude camps. A statistically significant fall in platelet counts was observed from day 2 at 3200 m and day 3 at 3771 m and counts remained decreased. Platelet aggregation was also decreased initially at both altitudes. Blood fibrinogen decreased only on day 2 at 3771 m with a significant increase over control values by day 10 at both altitudes.

Platelet adhesiveness in permanent residents of high altitude.

Platelet adhesiveness (PA) has been studied in 43 permanent residents of high altitude (highlanders) and in an equal number of age matched low landers for comparison. The importance of our findings in the light of our earlier observations in young low landers developing ischaemic cerebral stroke at high altitude and the development of ill effects of high altitude induction in fresh unacclimatised inductees is discussed.

Urinary catecholamine excretion in temporary residents of high altitude.

Urinary catecholamine excretion was estimated in 50 lowlanders temporarily staying at altitudes above 3,000 m. They were divided in subgroups according to the length of their continuous stay. For comparison, 25 highlanders who were born and brought up at high altitude and 50 lowlanders who had never been to altitudes of more than 1,000 m were also studied. High catecholamine excretion was noted in temporary residents staying at high altitude for up to 30 days as compared to that in lowlanders (P greater than 0.01). The excretion rate gradually returned to basal values thereafter. Catecholamines were essentially similar in lowlanders and highlanders. The significance of these findings is discussed regarding the possible pathogenetic role of the sympathoadrenal system in the development of ill effects in respone to high-altitude exposure.

Effect of high-altitude exposure for 10 days on stroke volume and cardiac output.

Resting stroke volume and cardiac output of 50 normal healthy sea-level residents (group A) were estimated by the noninvasive technique of electrical impedance plethysmography. They were then airlifted to an altitude of 3,658 m and serial estimations carried out at 0-4 h and 5-8 h and on the 2nd, 3rd, 4th, 5th, and 10th days. The subjects were brought back to sea level and studied for up to 5 days. Thirty permanent residents of high altitude (group B) and sixteen lowlanders temporarily resident at high altitude (group C) were also subjected to similar studies. It was found that resting stroke volume and cardiac output of group A started falling immediately on arrival at high altitude, reached the minimum on the 3rd day and tended to improved on the 4th and 5th day, but showed a secondary fall on the 10th day. The reduction in stroke volume in this group was not fully compensated by tachycardia. On return to sea level the cardiac output normalized immediately, the stroke volume on the 2nd day. At sea level goup A had values similar to group B and at high altitude to group C.

Urinary catecholamine excretion on induction to high altitude (3,658 m) by air and road.

In a preliminary pilot study we had reported a significant difference in urinary catecholamine excretion between symptomatic and asymptomatic individuals inducted to high altitude by air. The present study covers slower induction by road; 25 lowlanders ascended from 1,800 to 3,658 m in 50 h and 33 similar subjects covered the journey in 6 h. They were studied according to the protocal used in the initial study. None of the 58 subjects inducted by road developed symptoms of high-altitude illness. Their urinary catecholamine excretion remained normal during the 10 days' stay at high altitude. These findings lend support to our earlier contention that there might be a relationship between increased sympathoadrenal activity and high-altitude illnesses.

Changes in transthoracic electrical impedance at high altitude.

Mean transthoracic electrical impedance (impedance) which is inversely related to intrathoracic extravascular fluid volume was measured in 121 normal healthy volunteers at sea-level and at 3658 metres altitude. Fifty (group A) reached the high altitude location after an hour's journey in a pressurised aircraft. Twenty-five (group D) underwent slow road ascent including acclimatisation en route. Thirty permanent residents (group B) and 16 temporary residents at high altitude (group C) were also studied. Serial studies in the 30 subjects of group A who developed symptoms of high altidue sickness showed a significant decrease of impedance up to the fourth day of exposure to high altitude which later returned to normal. The 4 volunteers who developed severe symptoms showed the largest drop in impedance. A case of acute pulmonary oedema developing at 4300 metres showed an impedance value of 24-1 ohms on admission. After effective treatment the impedance increased by 11-9 to 36-0 ohms. Twenty asymptomatic subjects of group A and 25 of group D showed a small average increase in impedance values at high altitude. These obstructions suggest that measurement of transthoracic electrical impedance may be a valuable means of detecting incipient high altitude pulmonary oedema.

Urinary catecholamine excretion on acute induction to high altitide (3,658 m).

Fifty healthy male volunteers, 21-34 yr of age, normally resident at altitudes less than 1,000 m, were airlifted to 3,658 m. Urinary excretion of catecholamines was measured at sea level (198 m) and on the 1st, 2nd, 4th, and 10th day of a stay at high altitude. The symptoms observed on exposure to high altitude were assigned arbitrary scores. The volunteers could, on this basis, be divided into "symptomatic" and "asymptomatic" groups. The two groups showed a markedly different pattern of urinary catecholamines excretion on exposure to high altitude and on return to sea level. Significant increase in the catecholamine excretion was observed in the symptomatic group only. A possible role for enhanced sympathoadrenal activity in the etiopathogenesis of high-altitude illnesses is postulated.