Gravitational effects on volume distribution in a model of partial and total liquid ventilation

To estimate regional lung volume during ventilation with liquids (e.g. perf luorochemicals, PFC) we developed a multi-compartment mathematical model of a lung and thorax. The height of the fluid column and the fluid's density determine alveolar pressure (PA). The weight of thoracic contents above any given gravitational plane influences pleural pressure (PPL). Transpulmonar y pressure (PTP = PA - PPL) and compliance of the lung and chest wall permi t estimation of volumes. The results indicate the lung inflates almost unif ormly during total liquid ventilation despite a substantial vertical PA gra dient. Inflation uniformity is due to the offsetting vertical PPL gradient created by the added weight of the PFC and sustained by the relative rigidi ty of the chest wall. During partial liquid ventilation our model indicates that the combination of uniform PA with a large vertical gradient in PPL l eads to a vertical PTP gradient and therefore relative over-inflation of th e top of the lung. This effect increases with increasing PFC dose and with lung height. (C) 2000 Elsevier Science B.V. All rights reserved.