[The function of respiratory muscles in healthy persons during tube breathing]

Tube breathing (added dead space of 600 ml) stimulates ventilation by hypercapnia and is proposed as a new test of respiratory chemosensitivity. In this study the increase of respiratory work during tube breathing was evaluated by two methods.

In the first one respiratory values were measured and the rate of respiratory work was calculated according Otis, Crosfill and Widdicombe. In the second one the increase was indicated by changes in oxygen consumption at various levels of ventilation. The control rate of total respiratory work in healthy subjects was 0.07 +/- 0.04 W, during the test it was 0.18 +/- 0.07 W. The control oxygen consumption was e.g. 0.28 +/- 0.09 l.min-1 and during the test 0.32 +/- 0.06 l.min-1.

The increase of work of breathing during the test is relatively small and is related especially to higher minute ventilation. The new test of respiratory chemosensitivity could be therefore accepted even for patients with respiratory disease.