[abstract] WORK OF BREATHING IMPOSED BY DIFFERENT VENTILATORS UNDER HYPERBARIC CONDITIONS.

Abstract

BACKGROUND: The continuous increase in gas density caused by compression is likely to affect the work of spontaneous breathing (WOB) under hyperbaric conditions. In intubated patients breathing spontaneously through demand flow ventilator systems WOB is additionally influenced by the WOB and WOBimp of different ventlators under hyperbaric conditions. METHODS: Spontaneous breathing was simulated by the electromechanical lung model LS 1500 (Drager AG, Germany). Lung model setting were: spontaneous tidal volume (VT) = 500 ml/cm H20 amd resistance (R) = 5 cm H20 s/l. EVITA-4, Microvent, Oxylog 2000 HBO (Dragerwerk AG, Germany) and Servo Airway Pressure (CPAP, O cm H20) and Pressure Support Ventilation (PSV, 5 and 10 cm H20 over CPAP except of the Oxylog 2000 HBO that do not provide a PSV-mode) under 5 (1, 1.3, 1.6, 1.9 and 2.8 ATA, EVITA-4 and Oxylog 2000 HBO) or 6 (additionally 6 ATA, Servo ventilator 900 C and Microvent) different pressure conditions respectively. The lung driving electrical signal used a pleural pressure (Ppl), the displacement of the bellow as flow (V) signal. Airway pressure (Paw) was measured inside the bellows. WOB and WOBimp were calculated by integration of the inspiratory Ppl and Paw drop over V respectively. (see UHMS Supplement, Vol.25, p. 21, 1998 for charted graphs) CONCLUSION: WOB and WOBimp increased significantly with atmospheric pressure. The properties of each ventilator need to be known in order to assess the impact on WOB. ACKNOWLEDGEMENT: We thank Drager AG, Germany for kindly providing the LS 1500.