Transient respiratory sensitivity to small mechanical stimuli assessed by spontaneously breathing on a ventilator

Respiratory response to repeated sequences of mild negative inspiratory pressure (NIP) was investigated. Ten healthy male subjects were spontaneously breathing on a Siemens Servo Ventilator. The ventilator delivered the NIP loading (-2 cm H₂O during 30 seconds at 1 min interval) and was also used as a measuring device. Six transient response sequences were ensemble-averaged to discern changes in the same order as normal variation of breathing at rest. Analysis of variance showed that NIP caused a moderate reduction in ventilation (V_I), that was not compensated by increased respiratory activity (P_0.1). The intra-individual coefficient of variation of these two breathing parameters decreased markedly (p<0.05), in a way that resembles restrictive lung disease. NIP loading might be an alternative test for clinical assessment of the lung; and respiratory function. It is simple and with repeated measurements, the sensitivity can be adjusted to interfere minimally with the patient.