Lung volume recruitment in lambs during high-frequency oscillatory ventilation using respiratory inductive plethysmography

Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. We measured Δ changes in lung volume above end-expiratory volume (VRIP) during HFOV and studied whether changes in VRIP parallel changes in mean airway pressure. Calibration of the plethysmograph was made by serial injections of a known gas volume in six term (140 d gestation) and eight preterm (125 d gestation) lambs. Linear regression analysis of the relationship between injected gas volume and VRIP showed strong correlation (r2 = 0.93-1.00 term animals, r2 = 0.86-1.00 preterm animals). The pressure volume curves from the calibration with the injected gas volumes also correlated well with the pressure volume curves extrapolated from changes in VRIP. Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.