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 (VI), that was not compensated by increased respiratory activity (P0.1). 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.