Ventilation-perfusion relationships in children with heart disease and diminished pulmonary blood flow

Pulmonary function of infants and children with diminished pulmonary blood flow was studied by measurement of alveolar ventilation and alveolar-arterial gas tension differences of O2, CO2, and N2. The increased ventilation of these subjects was found to be effective in CO2 elimination (arterial CO2 tension, 31 mm Hg), but there was evidence of considerable unevenness of distribution of ventilation/perfusion ratios (VAQ). A measure of the degree of VA/Q unevenness was obtained by use of the urine-alveolar nitrogen tension difference. It is likely, under the prevailing conditions of hyperventilation and hypoperfusion, that maldistribution of perfusion is the major abnormality. Uneven distribution of perfusion is most probably due to the effects of gravity enhanced by low pulmonary artery pressure and blood flow—an exaggenation of the normal physiologic relative overperfusion of the lower-most parts of the lung.