Cardiac oscillations in expired gas tensions, and regional pulmonary blood flow

Abstract

Oscillations in expired gas tensions synchronous with the heartbeat were studied in detail following a tidal inspiration of a gas mixture containing 20.9% oxygen, 20% argon, and the rest nitrogen. A respiratory mass spectrometer continuously analyzed expired gas for argon, oxygen, and carbon dioxide. Simultaneous recordings of expiratory flow rate, expired volume, and electrocardiogram were made where necessary. The gas tension oscillations reflected pulsatile changes in gas flow from regions of different ventilations, blood flows, and V_a/Q_c ratios. An explanation for the oscillations was developed on the basis of cardiac-induced variations in relative gas flows from upper and lower zones of the lungs. This allowed the identification of these zones with the regions of different V_a/Q_c ratios, and the calculation of minimum differences in ventilation and blood flow between upper and lower lung zones. Blood flow in the upper lung zones of erect normal subjects was found to be very low, rising considerably on lying down. Three patients with raised left auricular pressures showed high upper zone blood flow in the erect position. Submitted on February 27, 1961