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

Study Objective: 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.

Study Design: 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.

Subjects: 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.

Measurements And Main Results: 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.

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