Effects of acute blood volume expansion on respiratory mechanics in the rat.

BACKGROUNDS The effects of acute blood volume expansion (BVE) on the respiratory mechanics of normal animals have been not extensively studied. The subject is of both theoretical and practical interest since BVE is a frequent medical intervention, and the associated increase in cardiac output may occur in different physiopathological situations. OBJECTIVES To describe the changes in the parameters of respiratory mechanics occurring as an effect of acute BVE and the related increase in cardiac output. METHODS We applied the end-inflation occlusion method in normal, positive pressure-ventilated rats to measure the respiratory mechanics under control and BVE conditions. RESULTS Under BVE conditions, we found a statistically significant increase in static respiratory system elastance (E(st,rs)), ohmic airway resistance plus resistance of respiratory system tissues to movement (R(min,rs)), and overall resistance including pendelluft and stress relaxation effects (R(max,rs)). Under BVE conditions, the resistive component due to sole stress relaxation and pendelluft (R(visc,rs)) increased almost significantly while a significant increment in mean respiratory system hysteresis surface area (Hy(rs)) was also found. CONCLUSIONS Increasing pulmonary blood flow by BVE increases the mechanical work of breathing because of the effects on E(st,rs), R(min,rs) and R(max,rs), and because of the increase in Hy(rs).