Relation between pressure and diameter in main pulmonary artery of man

The pressure-diameter relationship in the main pulmonary artery of man was estimated in 11 patients undergoing open-heart surgery. The diameter was measured with a recording caliper sutured to the vessel wall. The lateral intravascular pressure was measured with a 20-gauge needle connected directly to a Statham P23Db strain gauge. In the eight patients with normal pulmonary artery pressure the results indicate: 1) the shapes of the pressure and diameter curves are similar; 2) the mean value for the ratio of change in radius to change in pressure (ΔR/ΔP) x 103 was 8.77 cm/cm H2O (±sd 2.10); 3) the mean value for the pressure-strain elastic modulus (Ep) was 159.0 g/cm2 (±sd 26.0); and 4) the mean change in cross-sectional area during an average cardiac cycle was 22.9% of the diastolic value. In three patients with pulmonary hypertension the value of both ΔR/ΔP and the pressure-strain elastic modulus was lower.