Pulmonary mechanics during pregnancy.

Previously reported changes in static lung volumes during pregnancy have been confirmed. Measurements of lung compliance (C(L)) and total pulmonary resistance (R(L)) were made in 10 women in the last trimester of pregnancy and 2 months postpartum, employing an esophageal balloon and recording spirometer. C(L) was unaffected by pregnancy, but R(L) was 50% below normal during pregnancy. Measurements of airway conductance (C(A)) were made, employing the constant pressure body plethysmograph on 14 nonpregnant and 13 pregnant women. Specific airway conductance was increased during pregnancy. Serial measurements of C(A) indicated a progressive increase beginning at about 6 months of gestation and a return to normal by 2 months postpartum. The mechanism of the increased C(A) during pregnancy is not known. It may be related to changes in bronchial smooth muscle tone and conceivably explains the tolerance of certain patients with lung resections to pregnancy.

The determination of total body exchangeable O2 stores.

A method is described for the measurement of total body exchangeable oxygen stores (TBO(2)). It is based on the dilution of the stable oxygen isotope, (18)O(2), by the body exchangeable oxygen stores under circumstances in which (18)O(2) steady-state equilibrium was evaluated simultaneously for both arterial and venous blood compartments. After evaluation of several simplifying assumptions, TBO(2) values in dog, normal man, and anemic patients were measured. The magnitude of the exchangeable nonlung oxygen stores was 11.0 +/- 3.1 ml/kg (SD) in 5 dogs, 11.9 +/- 2.1 ml/kg in 10 normal subjects, and 7.0 +/- 1.6 ml/kg in 8 patients with severe anemia (hematocrits of 25% or less).