Adaptation of the inert gas FRC technique for use in heavy exercise

Abstract

We automated the inert gas rebreathe technique for measurement of end-expiratory lung volume (EELV) during heavy exercise. We also assessed the use of two gas tracers (He and N2) vs. a single gas tracer (He) for measurement of this lung volume and compared the two-tracer EELV to changes in the inspiratory capacity (defined with transpulmonary pressure) and shifts in the end-expiratory pressure from rest through heavy exercise. A computer program switched a pneumatic valve when flow crossed zero at end expiration and defined points in the He and N2 traces for calculation of EELV. An inherent delay of the rebreathing valve (50 ms) caused virtually no error at rest and during light exercise and an error of 74 +/- 9 ml in the EELV at peak inspiratory flow rates of 4 l/s. The measurement of EELV by the two gas tracers was closely correlated to the single-gas tracer measurement (r = 0.97) but was consistently higher (120 +/- 10 ml) than when He was used alone. This difference was accentuated with increased work rates (2-5% error in the EELV, rest to heavy exercise) and as rebreathe time increased (2-7% error in the EELV with rebreathe times of 5-20 s for all work loads combined). The double-gas tracer measurement of EELV agreed quite well with the thoracic gas volume at rest (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Expiratory threshold loading impairs cardiovascular function in health and chronic heart failure during submaximal exercise

“…In the present investigation, the application of an expiratory load resulted in progressive dynamic hyperinflation, as evidenced by increases in the transpulmonary pressure at end expiration (i.e., zero airflow conditions) (14). Thus we cannot rule out the possibility that these increases in lung volume impaired cardiac filling because of reductions in the size and compliance of the cardiac fossa (17).…”

Emerging Concepts in the Evaluation of Ventilatory Limitation During Exercise

“…24 -26 On the other hand, a drop in EELV that is too great will cause expiratory-flow limitation near EELV due to the fall in maximal available air flow as lung volume decreases. In most normal subjects (average fitness; Ͻ 35 years old; no disease), EELV decreases with exercise, and expiratory airflow limitation generally averages Ͻ 25% of the Vt at peak exercise workloads 5,27 and generally occurs only over the lower lung volumes, near EELV.…”

Exercise‐induced diaphragmatic fatigue in healthy humans.

“…The open-circuit system for breath-by-breath measurement of inspiratory and expiratory flow rates, volumes, pressures, end-tidal P.P, P.0 and end-expiratory lung volume (EELV) during exercise has been described in detail (Henke et al 1988;Johnson, Seow, Pegelow & Dempsey, 1990). To determine how close subjects came to reaching expiratory flow limitation, tidal exercise flow: volume loops were measured, averaged over twenty to thirty breaths, and plotted within a maximal volitional flow: volume envelope (MFVL) using a measured EELV (Johnson, Reddan, Seow & Dempsey, 1991).…”