The effects of passive CO2 removal on breathing pattern in humans

To determine the effects of nonventilatory CO2 transfer on breathing pattern, we monitored breathing in 7 patients with renal failure undergoing hemodialysis. A respiratory inductance plethysmograph was used to record ventilation before and during dialysis. The duration of inspiration (TI), the duration of each breath (TTot) and the duty cycle (TI/TTot) did not differ for the pre-dialysis and the dialysis periods. In contrast, for each patient the mean tidal volume (VT) fell significantly during dialysis (p less than 0.05), accounting for the reduction in minute ventilation (p less than 0.005). The mean inspiratory flow rate (VT/TI) also fell (p less than 0.01), demonstrating that nonventilatory CO2 loss via the dialysis bath is associated with reduced respiratory drive.