Cardiorespiratory Adaptations at the Start of Exercise in Normal Subjects and in Patients with Chronic Obstructive Bronchitis

Abstract

1. The time-courses of the respiratory changes at the start of exercise were assesse in twenty middle-aged normal men and in twenty patients with chronic obstructive bronchitis with a moderate reduction in forced expiratory volume in 1 s (FEV₁) (group M: mean 1.451; range 1.0–2.2 1) and in twenty patients with a more severe reduction in FEV₁ (group S: mean 0.62 1; range 0.2–0.9 1). All subjects exercised at a constant work rate for 6 min, starting abruptly from a steady resting state. Cardiac frequency (fH), ventilation (V̇E), oxygen uptake (V̇o₂) and carbon dioxide output (Vco₂) were measured at the end of each minute and the rates of adaptation of these variables determined.

2. When the normal middle-aged men exercised at a low work rate [mean V̇o₂ = 44.7 mmol (1.0 1 STPD) min⁻¹] the increases by the end of the first minute were in the order: f H > V̇E > V̇o₂ > V̇co₂. At a work rate of 50% of their working capacity [V̇o₂ = 67.1 mmol (1.5 1 STPD) min⁻¹] the pattern of adaptation in the normal subjects was fH > V̇o₂ > V̇E > V̇co₂. In the patients working at 50% of their working capacity [V̇o₂ approximately 44.6 mmol (1.01 STPD) min⁻¹], the rates of adaptation were in the order: fH > V̇o₂ >V̇E > V̇co₂, but all adapted significantly more slowly than in the normal subjects exercising at the same work rate.

3. A reduced ventilatory capacity does not appear to be associated with any special influence on the time-course of the ventilatory adaptation at the start of exercise. The rate of adaptation of V̇E at the start of exercise is (in common with that of fH, V̇o₂ and V̇co₂) reduced in proportion to the overall reduction in working capacity.