Ventilatory patterns during steady state and progressive exercise.

This study was conducted to differentiate the ventilatory and metabolic response to supine exercise at low levels (VO2 less than 1000 ml/min) from the well-documented response to high level upright exercise. Further, the respiratory cycle during exercise is analysed in terms of inspiratory time, flow and expiratory time as well as tidal volume and frequency. Using a canopy system for non-invasive measurement of breathing patterns and gas exchange, nine male subjects were studied while performing steady state (SSE) and progressive exercise (PRE). Work loads were: SSE 1-5 Kgm/sec for 17 min; PRE 1.5, 2.5, 3.75 and 5.0 Kgm/sec with 2 min increments. Total work was the same (1548 Kg . m) in both types of exercise. With SSE tidal volume (Vt) and respiratory rate (integral of) rose 70% and 30%, respectively. Minute ventilation (Ve) rose 113%. With PRE, integral of rose during the first work level, then remained stable, while Vt and Ve rose with each incremental exercise level. In both cases a decrease in expiratory time accounted for the major component of the decrease in total cycle time. With the onset of exercise, the rate of increase of inspiratory time and respiratory frequency exceeded that of tidal volume and inspiratory flow. This would suggest that these two groups of parameters are controlled by separate mechanisms, possibly, timing being under neurogenic control and flow determined by humoral factors. The respiratory quotient decreased with both forms of exercise and remained low throughout the exercise period.