CARDIOGENIC MIXING IN THE PULMONARY CONDUCTING AIRWAYS OF MAN

The increase in dispersion of a bolus of He or SF6 was used as a direct, noninvasive measure of pulmonary gas mixing in the conducting airways of 1 female and 2 male subjects. Mixing was compared for matched respiratory maneuvers at rest and during bicycle ergometer exercise at 35-50% .ovrhdot.VO2 max [maximum O2 uptake] (tidal volume of 2 l, inspiratory flow rate .gtoreq. 1.5 l/s, mean expiratory flow rate of 2.8 l/s and bolus penetrations of 30, 90, 150 and 180 ml). No enhancement of mixing occurred when the heart rate was increased 53% by bycycle exercise. Apparently, cardiogenic mixing in the upper and central airways is unresponsive to normal changes in the heart rate.