Pulmonary arterial pressure at high pulmonary flow.

Abstract

The relationship between pulmonary arterial pressure and pulmonary blood flow has been studied by a number of investigators in anesthetized animals (1), in man after pneumonectomy or unilateral pulmonary arterial occlusion (2, 3), and in normal man during exercise (4-7). With a few exceptions (1) these studies have agreed that doubling or trebling the pulmonary arterial flow does not produce a comparable increase of pulmonary arterial pressure. Sloan, Morris, Figley, and Lee (2) and Brofman (3) found in human subjects only a very slight rise of pulmonary arterial pressure during balloon occlusion of one main pulmonary artery branch when cardiovascular dynamics were normal. However, the relationship between pulmonary arterial pressure and pulmonary arterial blood flow at higher rates of flow has been examined by only a few investigators.In 1950, Cournand, Riley, Himmelstein, and Austrian (8) published studies of pulmonary blood pressure in normal physicians at rest and during exercise and in patients who had had a pneumonectomy with a normal remaining lung. These investigators concluded that pulmonary blood flow in man can increase to approximately three times the normal before the pulmonary arterial pressure will rise above normal limits. Lategola studied pulmonary pressure and flow relationships at high flow levels achieved by occluding 50% or more of the pulmonary circulation in anesthetized dogs (9). Lategola also found that when pulmonary blood flow was increased to approximately 250 to 300% above normal, the pressure rose sharply. * Submitted for publication March 15, 1965; accepted September 16, 1965. Supported by U. S. Public Health Service grants HE-06307 and HE-5445. Unlike Cournand, he found some increment of pulmonary arterial pressure even when pulmonary blood flow was increased less than 100% above the normal.In the foregoing studies of high pulmonary blood flow, the methods used for measuring pulmonary blood flow were necessarily indirect, and left atrial pressure was not measured. Thus the effect of pulmonary blood flow upon pulmonary vascular resistance could not be accurately computed. The purpose of the present study is to examine in anesthetized dogs the effect of increase of pulmonary blood flow under circumstances that permitted direct measurement of pulmonary blood flow and left atrial pressure. The pulmonary blood flows were measured at levels from 50% to 500% of normal,' and left atrial pressures were held constant in some experiments. MethodsThe experiments were performed upon 19 mongrel dogs that were in three groups.Group 1 consisted of nine dogs. The experimental design for equal perfusion of the systemic and pulmonary circulations with a roller pump is described in detail elsewhere (10) and is only summarized here. Three animals were anesthetized with pentobarbital sodium, 30 mg per kg, intravenously. Six received morphine sulfate, 5 mg per kg, intramuscularly followed by intravenous chloralose in amounts required to maintain anesthesia. The animals received heparin, 5 mg per kg, ...

Microvascular Pressures in Isolated Perfused Immature Lamb Lungs: Effects of Flow Rate, Left Atrial Pressure and Surfactant Therapy

“…The relationship between blood flow, vas cular pressures and resistances in the lung has been reported by several investigators [5][6][7], In the adult lung, flow can be increased three fold before any appreciable change in pulmo nary artery pressure is detected; however, when the lung is already fully recruited, in creases in blood flow result in large increases in pulmonary artery and venous pressures [8], When the total vascular surface area is re duced, an increase in flow will also markedly increase vascular pressures in the lung [ IV collagen, laminin, heparin sulfate, proteoglycansand clastin. Type-IV collagen is the ele ment in basement membranes which imparts strength to it.…”

Pulmonary Circulation at Exercise

“…A similar sharp rise in Ppa m at flows above 350 % of normal was reported a few years later in isolated perfused lungs (120). However, subsequent studies repeatedly reported a linear increase in Ppa m as a function of flow in isolated perfused lungs (59,236) as well as in intact human beings studied using the unilateral balloon occlusion technique (to double the flow in the contralateral lung) and/or exercise (18,44). There has been a recent report of a “take-off” pattern of Ppa m -Q relationships in normal subjects at exercise (216) reminiscent of the pioneering work of Cournand.…”

Pulmonary Vasodilator Responses to Nitroprusside and Nitroglycerin in the Dog

“…The lobe was perfused by means of a roller pump (model 3500, Sarns, Inc., Ann Arbor, Mich.) and the pumping rate was adjusted so that mean pressures in the lobar artery and main pulmonary artery were similar. The pumping rate was 293±12 ml/min (mean± SE, n = 20) 30, 100, and 300 Ag. All doses were administered in a random order and enough time was permitted between injections for hemodynamic variables to return to base-line levels.…”