Changes in the human electrocardiogram on breathing oxygen under pressure and their relationship to a compensating pressure applied externally to the body (vector analysis)

Summary

Two series of observations were made in which the atmospheric pressure was reduced to a value corresponding to an altitude of 20,000 m. In the first, a study was made of the effects of a counter pressure applied externally to the body; in the second series the pressures were applied to separate areas of the body. When the excess pressure in the lung reached 136 mm Hg, and when an equal counter pressure was applied externally, the electrical axis and cardiac vectors deviated to the right. Variations of the external pressure up to 50 mm Hg applied while the intrapulmonary pressure is held constant, do not by themselves cause any significant changes in the ECG. When the pressure applied to the abdomen and thighs is insufficient, the cardiac vectors diminish, and circulatory disturbances occur. Vector analysis of the ECG shows that during respiration under increased pressure, the first changes occur in the right heart.