EXERCISE STIMULUS INCREASES VENTILATION FROM MAXIMAL TO SUPRAMAXIMAL INTENSITY

This study investigated the influence of an exercise stimulus on pulmo nary ventilation (V-E) during severe levels of exercise in a group of ten athletes. The altered ventilation was assessed in relation to its effect on blood gas status, in particular to the incidence and severit y of exercise induced hypoxaemia. Direct measurements of arterial bloo d were made at rest and during the last 15 s of two intense periods of cycling; once at an intensity found to elicit maximal oxygen uptake ( VO2(max); MAX) and once at an intensity established to require 115% of VO2max (SMAX). Oxygen uptake (VO2) and ventilatory markers were conti nually recorded during the exercise and respiratory flow-volume loops were measured at rest and during the final 30 s of each minute for bot h exercise intensities. When compared to MAX exercise, the subjects ha d higher ventilation and partial pressure of arterial oxygen (PaO2) du ring the SMAX intensity. Regression analysis for both conditions indic ated the levels of PaO2 and oxygen saturation of arterial blood (SaO2) were positively correlated with relative levels of ventilation during exercise. It was apparent that mechanical constraints to ventilate fu rther were not present during the MAX test since the subjects were abl e to elevate V-E during SMAX and attenuate the level of hypoxaemia. Th is was also confirmed by analysis of the flow volume recordings. These data support the conclusions firstly, that overwhelming mechanical co nstraints on V-E were not present during the MAX exercise, secondly, t he subjects exhibiting the most severe hypoxaemia had no consistent re lationship with any measure of expiratory flow limitation, and thirdly , ventilatory patterns during intense exercise are strong predictors o f blood gas status.