Tube breathing as a new potential method to perform respiratory muscle training: safety in healthy volunteers.

Summary Normocapnic hyperpnea has been established as a method of respiratory muscle endurance training (RMET). This technique has not been applied on a large scale because complicated and expensive equipment is needed to maintain CO 2 -homeostasis during hyperpnea. This CO 2 -homeostasis can be preserved during hyperpnea by enlarging the dead space of the ventilatory system. One of the possibilities to enlarge dead space is breathing through a tube. If tube breathing is safe and feasible, it may be a new and inexpensive method for RMET, enabling its widespread use. The aim of this study was to evaluate the safety of tube breathing and investigate the effect on CO 2 -homeostasis in healthy subjects. A total of 20 healthy volunteers performed 10min of tube breathing (dead space 60% of vital capacity). Oxygen-saturation, P aCO 2 , respiratory muscle function, hypercapnic ventilatory response and dyspnea (Borg-score) were measured. Tube breathing did not lead to severe complaints, adverse events or oxygen desaturations. A total of 14 out of 20 subjects became hypercapnic ( P aCO 2 >6.0kPa) during tube breathing. There were no significant correlations between P aCO 2 and respiratory muscle function or hypercapnic ventilatory responses. The normocapnic versus hypercapnic subjects showed no significant differences between decrease in oxygen saturation (–0.7% versus –0.2%, respectively, P = 0.6 ), Borg score (4.3 versus 4.7, P = 0.9 ), respiratory muscle function nor hypercapnic ventilatory responses. Our results show that tube breathing is well tolerated amongst healthy subjects. No complaints, nor desaturations occurred. Hypercapnia developed in a substantial number of subjects. When tube breathing will be applied as respiratory muscle training modality, this potential development of hypercapnia must be considered.