The effect of hypoxic hypoxia and low barometric pressure on the human electrocardiogram

Summary

One hundred and twenty observations were made of the effect of a short stay in an altitude chamber on the ECG of healthy subjects at an effective “altitude” of 5,000 m while breathing either air, which induced hypoxia, or at an equivalent height of 10,000 m while breathing oxygen. In subjects who tolerated the hypoxia there was a combined swing to the left of the AP and AQRS-T vectors without any definite cardiac displacement. When the hypoxia was not well tolerated, after about 20–25 min at the reduced pressure there was a relative swing to the right of the cardiac vectors, indicating an increased load on the right heart. When no adverse effects resulted, the shift of the cardiac vectors to the left was accompanied by signs of increased left ventricular activity. When the subject's condition deteriorated, an ECG of the S₁-Q₃ type developed, and the AP and often the AQRS vector swung to the right while the R/T and R/P indices rose, which also indicated an increased load on the right heart. Therefore an ECG indicating such an increased right heart load constitutes also an objective sign of a deterioration of the physical condition.