Cardiorespiratory responses to slight expiratory resistive loading during strenuous exercise at sea level

Abstract

At sea level we determined the cardiorespiratory and performance effects of a slight expiratory resistive load (ERL) which, at mild altitude, had been effective in mitigating exercise-induced hypoxemia (EIH). Paired VO2max bicycle ergometer tests, (ERL vs control) were performed by 28 highly-fit (VO2max = 63.4 ±. 1.36) athletes (age = 33.5 ± 7.3). There was significant EIH in both control and ERL tests at 75, 80, 85. and 90% maximum power output (POmax) and at VO2max when compared to resting SaO2; but no difference in SaO2 between control and ERL at any level of intensity. Peak-expiratory mouth pressures (Pao) were greater (p≤0.05) with ERL at 75, 80, 85, 90 % POmax and VO2max: with ERL, Pao was increased compared to control by 0.20, 0.35, 0.41, 0.49, and 0.73 cm H2O, respectively. Concomitantly, minute ventilation (VE) was greater with ERL vs control (p≤0.05) by 4.1, 4.9, 4.5, and 5.8 L min^-1 at 80, 85, 90 % POmax and VO2max. The increase in VE was largely due to a trend toward increased tidal volume (.1 ml = 121, 198, 154, and 103, from 75 to 90 % POmax). There was a small, non-significant increase in VO2 (averaging 3.0 ml kg^-1-sec^-1) with ERL from 75-90 % POmax. With ERL, heart rate (HR) was consistently lower (≥ 2.0 BPM) throughout, although not significantly so. However, O2 pulse (VO2/ HR) was significantly greater with ERL by 9.5, 9.0, 7.9, 7.1 and 7.0 % at 75, 80, 85, 90 % POmax and V02max. With ERL, athletes attained greater (p ≤ 0.05) POmax 352.0 ±. 9.9 vs 345.7 ±. 9.5 watts, and higher (p ≤ 0.05) VO2max = 63.4 ±. 1.36 vs 60.3 ±. 1.26 ml kg^-l min^-1. Subsequently, in a subset (n =12), FRC was determined by He-dilution during steady-state 75 % POmax. With ERL, Pao VE, and VT/Te were greater (p<0.05) and FRC was elevated (p≤0.05) 0.67 ±. 0.29 L. End-inspiratory lung volume (EILV) with ERL was greater than control (p≤0.05), 82.2 ±. 1.1 vs 72.5 ±. 1.3 % of TLC, respectively. We conclude that during heavy to intense exercise, surprisingly small ERL (ranging from 1.27 to 2.94 cm H2O) may cause VT to increase and FRG to shift upward, reducing the potential for air flow limitation. That O2 pulse was higher with ERL at workloads identical to that of control, would suggest that venous return was augmented, perhaps in response to reduced pulmonary vascular resistance associated with increased FRG. The significantly improved VO2max with ERL may be due in part to the increased inspiratory work of breathing that exercising at elevated FRCs may entail; however, it would appear that some fraction of the increased VO2max observed with ERL was delivered to the working skeletal muscle which produced significantly greater POmax. We conclude that during strenuous exercise, slight expiratory resistive loading enhances performance in highly-trained athletes.