Influence of work rate on ventilatory and gas exchange kinetics

Abstract

A linear system has the property that the kinetics of response do not depend on the stimulus amplitude. We sought to determine whether the responses of O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) in the transition between loadless pedaling and higher work rates are linear in this respect. Four healthy subjects performed a total of 158 cycle ergometer tests in which 10 min of exercise followed unloaded pedaling. Each subject performed three to nine tests at each of seven work rates, spaced evenly below the maximum the subject could sustain. VO2, VCO2, and VE were measured breath by breath, and studies at the same work rate were time aligned and averaged. Computerized nonlinear regression techniques were used to fit a single exponential and two more complex expressions to each response time course. End-exercise blood lactate was determined at each work rate. Both VE and VO2 kinetics were markedly slower at work rates associated with sustained blood lactate elevations. A tendency was also detected for VO2 (but not VE) kinetics to be slower as work rate increased for exercise intensities not associated with lactic acidosis (P less than 0.01). VO2 kinetics at high work rates were well characterized by the addition of a slower exponential component to the faster component, which was seen at lower work rates. In contrast, VCO2 kinetics did not slow at the higher exercise intensities; this may be the result of the coincident influence of several sources of CO2 related to lactic acidosis. These findings provide guidance for interpretation of ventilatory and gas exchange kinetics.

Peak and kinetic cardiorespiratory responses during arm and leg exercise in patients with spinal cord injury

“…First, we sacri®ced the ability to describe the Vo 2 kinetics in more detail than with summary statistics (ie, MRT). However, as previously reported, 28,29 inordinately long overall kinetics as described here are associated with elevated blood lactate levels and emergence of a secondary, slow rise in Vo 2 which projects above the anticipated Vo 2 cost for the work rate performed. Thus, this current analysis approach yields conclusions regarding exer-cise intensity which are very similar to those derived in able-bodied subjects from more discriminative techniques.…”

Kinetics of Pulmonary Gas Exchange During and While Recovering From Exercise in Patients After Anterior Myocardial Infarction

“…6,26 The reason of the discrepancy between these findings in normal subjects and our present findings in cardiac patients is not well understood.…”

“…3,[7][8][9][10][11][12][13] If the work rate is mild to moderate, gas exchange kinetics can be characterized by a single exponential equation. 5,26 During high-intensity exercise, these kinetics become more complex, and a multiexponential fitting equation may be more suitable for analyzing kinetics. 26,27 However, we used a single exponential equation to characterize the overall kinetics of V • O2, V • CO2, V • E, and HR during exercise and recovery for both low-and high-intensity tests in the present study.…”

“…5,26 During high-intensity exercise, these kinetics become more complex, and a multiexponential fitting equation may be more suitable for analyzing kinetics. 26,27 However, we used a single exponential equation to characterize the overall kinetics of V • O2, V • CO2, V • E, and HR during exercise and recovery for both low-and high-intensity tests in the present study. The methodology involved in the use of a multiexponential equation would be too complex for use in obtaining the clinical parameters of exercise capacity.…”

Oxygen Uptake Kinetics During Exercise

“…1). [4,6,13,18,21] The occurrence of the slow component is closely associated with the onset of lactate accumulation. The greater the increase in lactate, the greater the magnitude of the slower component.…”