THE INSPIRATORY TO END-TIDAL OXYGEN DIFFERENCE DURING EXERCISE

Objective. Fast paramagnetic oxygen analyzers have made it possible to measure inspiratory to end-tidal oxygen concentration difference (P(I -ET)O-2) breath-by-breath. It is now frequently displayed on monitors during routine anesthesia. We wanted to study the effects of major cha nges in metabolism, ventilation and circulation on P(I-ET)O-2. Methods . Ten healthy male volunteers were studied under exercise. P(I-ET)O-2 was measured with a fast-response paramagnetic differential oxygen sen sor. Cardiac output was measured with non-invasive transthoracic elect rical bioimpedance. Metabolism was measured with indirect calorimetry and ventilation with a side stream spirometer. After a rest period, th e subjects cycled at 30W and 60W, 6 minutes on each work load and were then observed during 10 minutes of rest. Results. P(I-ET)O-2 correspo nded well to (V)over dot O-2/(V)over dot A (the oxygen uptake to alveo lar ventilation quotient) correlation showed r = 0.79. P(I-ET)O-2 was influenced by changes in cardiac output which occurred primarily at th e start and at the end of exercise. Expired minute ventilation ((V)ove r dot E) multiplied by P(I-ET)O-2 was related to cardiac output with a high intrapersonal correlation. Conclusion. P(I-ET)O-2 is a good meas ure of adequate ventilation in relation to the oxygen consumption leve l and multiplied by (V)over dot E it might offer a non-invasive bedsid e parameter indicating changes in cardiac output.