The Pressure-Volume Relationship of the Normal Pulmonary Capillary Bed*

Abstract

The pressure-volume relationship of the normal pulmonary capillary bed was studied by relating breath holding diffusing capacity (DLCO) and pulmonary capillary blood volume (VC) to central vascular pressure over a range of right atrial pressure from 1.0 to 20.0 mm Hg. Both DLCO and VC reached a plateau after an increase of 6 mm Hg in pressure. Further increases in pressure produced no further increase in the instantaneous volume of blood available for carbon monoxide absorption. After maximal increases in DLCO been produced by pressure alone, muscular exercise increased DLCO even further. These data then demonstrate a limit to the increase in DLCO which can be produced by pressure alone and suggest that the greater increases which are produced during exercise are dependent upon factors other tnan increased intravascular pressure.