Pulmonary blood volume and haemodynamic changes with legs raised in chronic lung disease patients

The aim was determine the early effect of a posture change from supine (S) to legs raised 30 degrees above the table plane (LR) on haemodynamics in patients with chronic lung disease.

Right heart catheterization was performed as part of a routine evaluation. Pulmonary arterial, pulmonary wedge, right atrial, and systemic arterial pressure were monitored at rest supine and during 8 min (steady values) after LR. Pulmonary blood volume was measured by double dye dilution, at rest S and after 1 and 8 minutes LR, in 14 patients; cardiac output was measured by thermodilution in the remaining 15 subjects, during S and 1, 4, and 8 minutes LR.

29 patients with chronic pulmonary disease of various types, mainly chronic bronchitis and emphysema, were studied when in a stable clinical condition, with no signs of heart failure.

Raising the legs produced a sharp increase in all the pressures measured, with a subsequent decline towards a steady value slightly higher than during S. Pulmonary blood volume increased in all patients initially, but stayed elevated only in the normocapnic patients; in the patients with hypercapnia it decreased from 1 to 8 min LR. The pulmonary blood volume change showed a significant correlation with PaCO2 (p less than 0.01), and with the VD/VT ratio (p less than 0.01). The relation between the pulmonary blood volume and the distending pressure changes from S to 1 and 8 min LR was linear in the normocapnic group, but not in the hypercapnic group, where it showed a hysteresis.

In patients with chronic lung disease who are hypercapnic, the volume/pressure relation following leg raising cannot be expressed by a single distensibility coefficient.