STUDIES OF THE PULMONARY CIRCULATION. I. THE CIRCULATION TIME FROM THE PULMONARY ARTERY TO THE FEMORAL ARTERY AND THE QUANTITY OF BLOOD IN THE LUNGS IN NORMAL INDIVIDUALS

Factors contributing to the reversible pulmonary hypertension of patients with acute respiratory failure studies by serial observations during recovery

Eight patients with acute respiratory failure secondary to chronic bronchitis were studied for up to 5 consecutive days following admission; cardiac output and intravascular pressures, blood volume, arterial blood gas tensions, and body weight were measured. These observations were also compared with further measurements made some weeks later just before the patient was discharged. The effects of oxygen and acetylcholine on the pulmonary circulation were also studied. Pulmonary arterial pressure was raised in all patients during their acute illness and had fallen substantially after recovery. The pulmonary arterial pressure throughout the study correlated directly with the arterial carbon dioxide and inversely with the arterial oxygen tensions. The inhalation of 24% and 28% oxygen and the infusion of acetylcholine into the pulmonary artery resulted in a fall in pulmonary arterial pressure, often to levels close to those subsequently seen after recovery from the acute illness. No significant change in cardiac output was observed. It is suggested that the acute pulmonary hypertension seen in these patients is due primarily to pulmonary vasoconstriction resulting from hypoxia.

Hemodynamic studies on cholera. Effects of hypovolemia and acidosis

The hemodynamic effects of hypovolemia and acidosis were studied in 23 patients with cholera. Studies were made before and during fluid replacement and administration of alkali.

The major hemodynamic abnormalities encountered before rehydration can be ascribed to a reduction in circulating blood volume. Hypovolemia was associated with a reduction in cardiac output, blood pressures, and central blood volume. Restoration of blood volume returned these variables toward normal.

The chief effect of acidosis appeared to be a redistribution of blood from the peripheral to the central circulation; consequently, central blood volume, lesser circulation pressures, and cardiac output were relatively well maintained despite hypovolemia. Fluid administration without correction of acidosis favored a disproportionate increase in central blood volume, while reduction in hydrogen ion concentration attending fluid replacement resulted in a more even distribution of the circulating blood volume and reduced the possibility of engorgement of the pulmonary bed.

It is postulated that this redistribution of blood stems from peripheral venoconstriction and a reduction in the capacity of venous reservoirs induced by acidosis.

Hemodynamic Effects of Cerebral Arteriovenous Aneurysms

The hemodynamic alterations produced by large cerebral arteriovenous aneurysms are qualitatively similar to those caused by arteriovenous aneurysms elsewhere in the body. Congestive heart failure was not observed in our eight patients; it appears to be unusual in adult cases.

By comparing cardiac outputs with a control group the mean aneurysm blood flow in six patients was estimated to be 2,804 ml. per minute at rest. Isoproterenol increased cardiac output relatively more than the estimated aneurysm flow.

Implications of the present data with respect to the concept of "central" blood volume are discussed.

Progressive mental and neurologic deterioration is the rule with large cerebral arteriovenous aneurysms. Repeated bleeding episodes, which may not be obvious clinically, appear to be partially responsible.

Respiratory burns with special reference to pulmonary edema and congestion

The functional changes in respiration, circulation, blood composition and blood temperature were investigated in anesthetized dogs that were subjected to the inhalation of steam. The pathogenesis of the accompanying pulmonary congestion and edema was analyzed by measurements of: (a) pulmonary blood flow, (b) pressures in pulmonary artery and vein, (c) pulmonary blood (P 32 ) volume, (d) electrical (AC) resistance of the lungs, and (e) edema fluid of the excised lung. The peculiarities of the pulmonary circulation that were demonstrated by bleeding and blood infusion explain the difficulties of correcting the congestion that regularly preceded thermal edema.

The Pulmonary Vascular Responses to Short-Term Hypoxia in Human Subjects

Using the catheter technic, the acute circulatory reactions to a brief period of hypoxia have been studied. It was found that when a normal person breathed a gas mixture containing only 10 per cent oxygen, the pulmonary arterial pressure rose but the pulmonary capillary pressure remained unchanged. This indicated pulmonary vasoconstriction, thought to be due to a direct effect on the pulmonary vascular tree. No demonstrable change in so-called pulmonary blood volume could be detected. In an additional group of patients with cardiopulmonary disease the reactions were more erratic but not significantly different in type.

Cardiac Asthma

Cardiac asthma may be defined as the clinical syndrome induced by acute passive congestion and edema of the lungs. It occurs when the left side of the heart suffers from a sudden disproportion between work load and work capacity. It may result, therefore: (1) from disorders which cause rapid impairment of the myocardium, the load being constant (for example, myocardial infarction); (2) from disorders which suddenly increase the resistance or pressure load (such as paroxysmal hypertension consequent to an adrenal medullary tumor); (3) from disorders which markedly elevate the inflow or venous load without impairing the myocardium (such as strenuous exertion in a person with mitral stenosis); or (4) from a combination of these factors. The most common cause is increased venous return in a recumbent subject with left ventricular strain consequent to hypertension. Of the numerous conditions which may produce increased venous return, nocturnal reabsorption of extracellular fluid from dependent parts is probably the most common. The therapeutic implications are obvious.

Cardiac asthma must be differentiated from the various primary diseases of the lungs which cause paroxysms of wheezing or panting. The differentiation is usually readily made by simple clinical measures; in doubtful instances measurements of circulation time may be of crucial value.

The management of cardiac asthma involves chiefly three therapeutic principles: (1) Control of precipitating factors (and especially treatment of latent edema and control of nocturnal cough); (2) measures aimed at reducing the inflow load (sitting position, morphine, venesection, tourniquets on extremities, positive pressure breathing); (3) attempts to reduce the amount of residual blood in the left ventricle (rapid digitalization, use of oxygen, and aminophyllin).

A severe attack of cardiac asthma associated with rapidly developing pulmonary edema constitutes one of the commonest and gravest of all medical emergencies. There are few conditions in the broad domain of internal medicine in which prompt and energetic therapy, based on an understanding of the mechanism of the disorder, can produce such immediate and gratifying benefit.

The Fourth Walter Wile Hamburger Memorial Lecture, Institute of Medicine of Chicago

A review of present day knowledge of the pulmonary circulation in man is presented. In particular the state of the lesser circulation in normal man at rest and under conditions of exercise and acute anoxia is defined in detail in order to provide the physiologic background against which to present the accumulated data in patients with certain types of chronic cardiopulmonary diseases.