No abstract

Pulmonary function and oxygen transfer was studied in five patients with cirrhosis of the liver and different degrees of portasystemic encephalopathy. Four patients were restudied after a change in CNS function. The contribution of various parameters of pulmonary gas exchange to the unsaturation found was evaluated employing the graphic analysis described by King and Briscoe. The following results were obtained: (1) there was no inequality of ventilation as judged by a nitrogen washout study; (2) a large true venous admixture was found in all patients; (3) in four patients studied twice venous admixture was larger when mean EEG frequency was lower; (4) besides the true venous admixture a low overall D/Q ratio was an important factor contributing to unsaturation in most cases; (5) in some cases a decreased overall V/Q ratio contributed to the unsaturation. This decreased V/Q ratio appeared to be due to an increase in pulmonary perfusion without a concomitant rise in ventilation. Changes in pulmonary perfusion pathways are suggested as the most likely cause of the defect in oxygen transfer found in patients with cirrhosis.

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Patients with cirrhosis of the liver frequently have an increased cardiac output *l and diminished systemic vascular ~e s i s t a n c e .~~~~~~~ This hyperkinetic circulatory state probably represents a response to a decrease in systemic vascular resistance. The existence of a circulating vasodilating substance has been suggested as a possible cause. The available evidence would indicate that it must be affecting the vascular system at various sites. It could be responsible for an admixture of venous to arterial blood since arterial oxygen unsaturation was found in about one-third of patients with hepaticThe possibility of anastomoses between the pulmonary veins and either the pulmonary artery or the portal venous system has been discussed repeatedly. To investigate further the relationships between portal hypertension and pulmonary circulation as the possible basis for arterial oxygen unsaturation, we have done some studies during the administration of histamine which is known to be a potent vasoactive material. Special InvestigationsStudy 1

In 5 patients with liver cirrhosis the measured pulmonary diffusing capacity for oxygen (D_LO2) was related to the diffusing capacity of the pulmonary membrane (D_M) and to the volume of blood in the pulmonary capillary bed (V_c) as estimated from the measured pulmonary blood flow (Q_c) and the value of the presumptive transit time. D_L and D_M were found to be diminished in 4 of the 5 cases, D_M being only once 1,7 times greater than D_L. The relationship between the resistance of the red blood cells to diffusion and the resistance of the pulmonary membrane to diffusion (1/ΘV_C/1/D_M)ranged between 5 and 35 % indicating that the resistance of the pulmonary membrane to the uptake of O₂ was of greater importance than the resistance of the red cells. A correlation was found to exist between D/Q and D_M/ΘVc (diffusing capacity/blood flow and membrane diffusing capacity/diffusing capacity of the red cells in the pulmonary capillary bed). The possible site and nature of the diffusion defect is discussed.