Breath-by-breath determination of inspiratory occlusion pressure

Summary. In order to determine the influence of breath-by-breath measurement of inspiratory occlusion pressure (P_0.1) on the pulmonary ventilation, the respiratory timing and the central inspiratory activity as reflected by P_0.1per 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 P_0.1 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 P_0.1 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 P_0.1. We conclude that breath-by-breath measurement of P_0.1 is a feasible technique, and that the slightly shortened inspiratory duration and the increased P_0.1 with increased threshold pressure may not necessarily be expressions of a true stimulation of the central inspiratory activity.