The pattern of breathing and the ventilatory response to breathing through a tube and to physical exercise in sport divers.

Well-trained divers can be expected to differ from healthy controls in their ventilatory response to breathing through a tube and to physical exercise. Therefore, we measured their minute ventilation (VE) at rest and during breathing through a tube combined with two levels of physical exercise (1 or 2 W.kg body weight-1). For breathing through a tube an additional dead space of 600 ml was used. All divers were trained in the breath-hold technique and in the use of the breathing apparatus. Their mean period of training as divers was 9 +/- 6 years. The approximate age of the subjects was 25 years. The pattern of breathing and the oxygen uptake were measured by spirometer, the end-tidal concentration of CO2 was measured and all experiments were carried out above sea level. The ventilation of the divers at rest was comparable to that of the controls. During physical exercise it was smaller whether during breathing through a tube or not. The inadequate increase of VE during exercise in divers was associated with hypercapnia only at a higher physical work intensity (of 2 W.kg-1). This finding is interpreted as a lower chemoregulatory response to the combined stimuli of hypercapnia, hypoxia and physical exercise. In some situations significant bradypnoea and higher tidal volumes were found in the divers.