Relationship of pulmonary diffusing capacity (D _L ) and cardiac output ($\dot Q_c$) in exercise

Abstract

The present study was designed to investigate the interrelationships of pulmonary diffusing capacity for CO ($D_{L_{{\text{CO}}} }$), pulmonary capillary blood flow ($\dot Q_c$), oxygen uptake ($\dot V_{{\text{O}}_{\text{2}} }$), and related functions in exercise. Six young adult men were tested on a bicycle ergometer on 9–20 occasions at various intensities of exercise up to the maximal level that could be sustained for 5 min. Measurements at each exercise level included work load (kgm/min), heart rate (HR), minute ventilation (V _I ), $\dot Q_c$, $D_{L_{{\text{CO}}} }$, and $\dot V_{{\text{O}}_{\text{2}} }$. Using regression analysis, it was established that $\dot Q_c$ and D _{L CO} increased linearly with $\dot V_{{\text{O}}_{\text{2}} }$ throughout the work range in each subject and no tendency toward a plateau was observed. While the maximal value varied from subject to subject, there was no difference between individuals in the coefffcient describing the relationship of D _L and $\dot Q_c$ to $\dot V_{{\text{O}}_{\text{2}} }$. Combining all subjects, D _L was found to increase linearly with $\dot Q_c$ the regression equation being:

$$D_L = 26.4 + 1.03{\text{ }}\dot Q_c ,{\text{ }}r = .79$$

These results suggest that high-intensity short-duration exercise (5 min) is probably not limited by either of these functions in normals.