A study of cardiopulmonary function and working capacity of sojourners acutely exposed to different altitude levels in Ethiopia

Abstract

Forced vital capacity (fvc, L/sec), forced expiratory volume (fev1, L/sec), fev1%, forced expiratory flow rate (fef 200—1200 ml,. L/sec), forced mid-expiratory flow rate (fmf 25—75 %, L/sec), peak expiratory flow rate (pefr, L/min), minute ventilation (ve, L/min), oxygen saturation of arterial blood (SaO2%), working capacity (Kgm/min/m2 body surface area), pulse rate (beats/min) and arterial blood pressure (mmHg) were studied in eight male sojourners descending to 1370—490 m and ascending to 2550—3300 m from their altitude of residence (2440 m). Of the lung function indices, mean fef 200—1200 ml increased from 6.54 L/sec at 2440 m to 7.18 L/sec and 8.33 L/sec, respectively, at 2550 m and 3100 m. It was not measured at 3300 m for lack of electric power supply. Mean values of fef 200—1200 ml were found to be correlated to the altitudes of investigation significantly (r=0.7316). The increase in fef 200—1200 ml probably reflects that large airways tend to open up more widely perhaps concomitant with enlargement of alveolar spaces at 2550 m and above to compensate for the reduced pao2 and reduced O2 uptake. Mean ve showed a 4—5-fold increase with exercise essentially at all levels of altitude. Acute altitudinal effect became quite evident at 3300 m. At rest, ve increased from 5.62 L/min at 2440 m to 7.78 L/min at 3300 m. During exercise, increase in ve with ascent apparently protects the low O2 saturation (91.9% at rest and 86.9% in this study). Although the mean of exercise ve was markedly increased only at 3300 m, its overall correlation with altitude (r=0.6698) and mean working capacity (r=-0.6426) was quite significant (two-tailed P=0.0236). SaO2% was found to be correlated with mean (r=0.7955) and individual measurements (r=0.7628) of working capacity. Mean working capacity was reduced by about 20% with ascent and increased by about 9% with descent. It was negatively correlated with ascent (r=-0.9101). This signifies that physical performance is quite limited by hypoxia with ascent. Mean pulse rate, which was 75 beats /min at 2440 m increased to 82 beats/min at 490 m. It decreased to 72 beats/min at 3300 m. This is probably attributable to the decrease in ambient temperature and relative humidity with ascent and to the increase with descent. Arterial blood pressure (mean systolic/diastolic) was found to be 100.1 / 62.13 mmHg at 2440 m, 93.1/59.4 mm Hg at 490 m, 99.6/59.4 at 1370 m and 101.46—102.5/62.5—63.1 mmHg at 2550–3300 m. This pattern of change seems to be attributable to changes in peripheral vascular resistance which is apparently secondary to changes in ambient temperature and relative humidity. One of the sojourners experienced only generalised fatigue. This suggests that physiological alterations occurring at 3300 m cannot apparently induce acute mountain sickness in residents of medium altitude.


Key words/phrases: Cardiopulmonary functions, high altitude, Sojourners, working capacity


SINET: Ethiopian Journal of Science Vol.25(1) 2002: 71-82