COMPARATIVE EFFECTS OF PRESSURE SUPPORT VENTILATION AND INTERMITTENT POSITIVE PRESSURE BREATHING (IPPB) IN NONINTUBATED HEALTHY-SUBJECTS

We compared the efficacy of three devices delivering assisted noninvas ive ventilation with different working mechanisms, during room air bre athing and during CO2-induced hyperventilation, In seven healthy volun teers, breathing pattern, respiratory muscle activity and comfort were assessed: during unassisted spontaneous breathing through a mouthpiec e (SE); during assisted breathing with a device delivering inspiratory pressure support (IFS); and with two devices delivering intermittent positive pressure breathing (IPPB), the Monaghan 505 (IPPB1), and the CPU 1 ventilator (IPPB2), All three devices were set at 10 cmH(2)O of maximal pressure. During room air breathing, the work of breathing exp ressed as power, was significantly greater with the two IPPB devices t han with the two other modes (IPPB1 and IPPB2 7.3 +/- 5.2 and 7.2 +/- 6.2 J . min(-1), respectively, versus SE and IPS 2.4 +/- 0.7 and 2.3 /- 3.3 J . min(-1), respectively), The difference did not reach the st atistical significance for the pressure-time product (PTP), Discomfort was also greater during the IPPB modes, During CO2-induced hyperventi lation, considerable differences in power of breathing were found betw een the two IPPB devices and the other two modes, The PTP was also muc h higher with IPPB. Transdiaphragmatic pressure was significantly smal ler during IFS than during the three other modes (IFS 18 +/- 2.6 cmH(2 )O versus SB 22 +/- 2.6, IPPB1 32 +/- 5.2, and IPPB2: 28 +/- 5.2). Max imal discomfort was observed during the IPPB modes and was correlated with the magnitude of transdiaphragmatic pressure (r = -0.60), Despite similarities in their operational principles, IFS and IPPB had very d ifferent effects on respiratory muscle activity in healthy non-intubat ed subjects, IPPB machines not only failed to reduce patient's effort but also induced a significant level of extra work by comparison to sp ontaneous ventilation at ambient pressure, Great caution is, therefore , needed in the use of patient-triggered devices for nonintubated pati ents with acute respiratory failure.