Source: Annual Congress 2010 - Acute respiratory failure
Disease area: Pulmonary vascular diseases

Abstract

We assessed the acute effects of hemorrhage on respiratory mechanical parameters, in relation to pulmonary and systemic haemodynamics. Forced oscillations were used to measure airway resistance (Raw), respiratory tissue damping (G) and elastance (H) at baseline and after stepwise 1 ml blood withdrawals up to -5 ml total in 6 Sprague-Dawley rats followed by stepwise reinjection up to full volume restoration. Mean systemic (MAP) and Pulmonary arterial pressures (MPAP), aortic blood flow (Qao) were measured at each step.
Blood volume depletion decreased Raw (65.6±18.8 vs. 48.4±20.0 cmH2O·s/l with -5 ml, p<0.001), MAP and Qao. In contrast, G increased significantly (1099±224 vs. 1196±165, p=0.009 with -5 ml) while H did not change. Changes in Raw were fully reversible with volume restoration. The MPAP/Qao ratio (indicating changes in pulmonary vascular resistance) increased significantly with volume loss (30.3±11.1 vs. 115.5±46.0 mmHg·s/ml with -5 ml VL, p<0.001), while no significant changes were detected in systemic vascular resistance (SVR: estimated from MAP/Qao). The drop in Raw showed a significant correlation with MAP (R=0.95) and Qao (R=0.95) but not with MPAP (R=-0.36).
Our data suggest that Raw significantly and reversibly decreases with acute blood volume depletion in anaesthetized rat. This phenomenon may be related to a reduction in pulmonary vascular and blood volume leading to increased tethering forces, or to a reduction in bronchial submucosal blood vessel volume. These results highlight the close relation between airway conductance and the lung vascular compartment volume in hemorrhagic shock.
Supported by SNSF grant 3200B0-118231 and the Conseil Régional de Picardie grant REG 08009.

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S. Layachi, G. Albu, F. Petàk, W. Habre, S. Bayat (Amiens, France; Geneva, Switzerland; Szeged, Hungary). Acute hemorrhagic shock reversibly decreases airway resistance in anaesthetized rat. Eur Respir J 2010; 36: Suppl. 54, 2301

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