Breath-by-breath determination of inspiratory occlusion pressure

In order to determine the influence of breath-by-breath measurement of inspiratory occlusion pressure (P0.1) on the pulmonary ventilation, the respiratory timing and the central inspiratory activity as reflected by P0.1 per se, nine healthy males were studied as they breathed in a valve assembly including an externally controlled occlusion valve. A new technique was used, terminating occlusions at a preset inspiratory threshold pressure and determining P0.1 from linear regression of the mouth pressure curve. Subjects were studied at rest and during light exercise, with the occluding function (threshold pressure) on or off during alternating periods. Breath-by-breath variability of P0.1 was of the order of 30%. We found no detectable influence of breath-by-breath short-lasting inspiratory occlusions on tidal volume and ventilation. However, mean inspiratory flow was slightly increased due to a shortened inspiratory duration at rest and during light exercise. Also, raising the threshold pressure for occlusions from 69 to 147 Pa (0.7 to 1.5 cm H2O) resulted in a 20% increase of P0.1. We conclude that breath-by-breath measurement of P0.1 is a feasible technique, and that the slightly shortened inspiratory duration and the increased P0.1 with increased threshold pressure may not necessarily be expressions of a true stimulation of the central inspiratory activity.