Mechanical work of breathing during maximal voluntary ventilation.

With the use of the esophageal balloon technique, the working capacity of the respiratory muscles was assessed in four normal subjects by measuring the work per breath (W) and respiratory power (W) during maximal voluntary ventilation with imposed respiratory frequencies (f) ranging from 20 to 273 cycles/min. Measurements were made in a body plethysmograph to assess the work wasted as a result of alveolar gas compressibility (Wg'). In line with other types of human voluntary muscle activity, W decreased with increasing f, whereas W exhibited a maximum at f of approximately 100 cycles/min. Up to this f value, Wg' was small relative to W. With further increase in f, the Wg'/W ratio increased progressively, amounting to 8-22% of W at f of 200 cycles/min.