Assessment of cardiac function using resaturation curves.

Abstract

A reproducible, objective measure of lung-to-ear circulation time has been made during exercise. Alveolar Po2 is lowered to about 50 mm Hg and abruptly raised to about 350 mm Hg by having the subject take a breath of Na followed by a breath of O2. Changes in arterial O2 saturation are recorded with an ear oximeter. The rise in arterial saturation after the breath of O2 is exponential during exercise and its time constant ([tau]) is measured. 1/[tau] represents the ratio Q/V where Q is the pulmonary blood flow and V is related to the volume of the dominant mixing chamber in the left heart. Values for Q/V have been arbitrarily expressed in l./min./300 ml left heart mixing volume. Exercise tests in 28 normal subjects and 38 patients with rheumatic heart disease indicate that Q/V increases with exercise. The increase in Q/V in patients with heart disease is less than normal. The method is not applicable in patients with gross abnormalities of distribution of ventilation.