Study of the pituitary-thyroid functions at high altitude in man.

The alterations in serum levels of T3, T4, TSH and TBG, TSH response to 100 mug iv TRH, and urinary excretion of T3 and T4 were studied in 8 healthy men at sea level (SL), on days 1, 2, 4, 8 and 16 after arrival by air at high altitude (3,700 m, HA), and during days 5 to 7 after their return to SL. No significant alterations in serum levels of TSH and TBG or TSH response to TRH were observed during exposure to HA or on return to SL. There was, however, an acute elevation in both serum total T3 and T4. Serum total T3 from a mean basal+/-SE value of 128+/-13 ng/dl increased to 320+/-18 on day 1 and remained significantly elevated at 225+/-48 up to day 8 after arrival at high altitude. Similarly serum total T4 increased from basal level of 9+/-0.92 mug/dl to 15.2+/-1.2 and remained elevated till day 16 and it was 11+/-1.19 mug/dl during days 5 to 7 after return to SL. The urinary excretion of both T3 and T4 was decreased. These changes perhaps were the result of complex physiologic adjustments on acute exposure to high altitude, like shrinkage of the T3 and T4 distribution pools, altered binding capacities of thyroid hormones binding proteins, and a reduction in clearance of thyroid hormones from the plasma compartment; and were probably not suggestive of an enhanced thyroid activity. Their actual significance in high altitude adaptation in man is not clearly understood.

Exercise in an hypoxic environment as a screening test for ischaemic heart disease.

Submaximal and maximal exercise testing have been used to predict coronary events but these tests do not give reliable information regarding employability of subjects with abnormal electrocardiogram. In 30 subjects with stabilized ischaemic heart disease (Group A) and 70 subjects with abnormal resting electrocardiogram (Group B), resting electrocardiograms--at ground level and at a simulated height of 4592 m (15000 ft)--after 40-min exposures were recorded. The double Master's two-step exercise test (DM) was performed at ground level as well as at stimulated height (DMH). In the ischaemic group, exercise combined with hypoxia did not yield better results than exercise alone; but among the asymptomatic subjects, exercise in an hypoxic environment gave significantly better results than exercise alone (p less than 0.005) or hypoxia alone (p less than 0.01). Those with negative responses to the test have been employed on strenous duties, including employment at high altitude for the last 3 years. None of them have manifested any objective or subjective evidence of ischaemic heart disease. DM exercise testing in an hypoxic environment is a reliable method to assess subjects with abnormal electrocardiogram and evaluate their functional status.