The Diffusing Characteristics and Pressure-volume Relationships of the Pulmonary Capillary Bed in Mitral Valve Disease.

In 1957, Forster, Roughton, and their associates reported a method of estimating pulmonary capillary blood volume (Vc) and diffusing capacity of the alveolar-capillary membrane (DM) by measuring the diffusing capacity of the lung for carbon monoxide (DL) at varying levels of alveolar oxygen tension (1, 2).1 Since then there hlave been a number of reports on the behavior of membrane diffusion and pulmonary capillary blood volume under physiological and pharmacological stresses (3-7) and in certain disease states (8-17). The purpose of this study was to measure the pulmonary capillary blood volume in normal subjects and in patients with mitral valve disease and to relate the findings to intravascular pressure and flows^ data obtained by cardiac catheteri-zation. Most of the studies relating membrane diffusion and pulmonary capillary blood volume to hemody-namic data (5, 10, 11) have used a breath-holding method of estimating diffusing capacity of carbon monoxide (18). The physiological situation within the pulmonary circulation during the breath-holding maneuver differs from that in the resting steady state. For this reason, the steady-state method described in this report was designed to measure Vc so that the volume of blood in the pulmonary capillary bed could be compared with the pressure and flow relationships under the same physiological conditions. 1 The symbols DL, DM, and Vc, used in the original report (2) and in nearly all subsequent reports on this topic, have been retained here. Methods Two groups were studied: 1) The control group consisted of 18 normal subjects, nine of whom were laboratory personnel with no evidence of cardiorespiratory disease; nine were patients with systolic murmurs in whom no other abnormality was detected by physical examination, ECG, and chest X ray, or at cardiac catheterization. 2) The abnormal group comprised 18 patients with mitral valve disease, 15 of whom had pure mitral stenosis and three who had dominant mitral incompetence. Cardiac catheterization was performed by standard procedures (19) in the 18 patients with mitral valve disease and in the nine normal subjects who had systolic murmurs. In the normal subjects, catheterization of the right heart only was performed, and pulmonary arterial wedge pressure was obtained as an estimate of left atrial pressure. Left heart catheterization was also performed in all the patients with mitral valve disease, by the transeptal approach (20), and left atrial pressure was recorded directly. Cardiac output was measured by indicator dilution techniques (21); injections of cardio-green dye were …