Relation Between Pressure and Diameter in the Ascending Aorta of Man

The pressure-diameter relationship in the ascending aorta of man was estimated directly in 10 patients undergoing open-heart surgery. The diameter was measured by means of an electrical strain-gauge caliper sutured to the vessel wall. The lateral intravascular pressure was measured using a 22-gauge needle connected directly to a Statham P23Db strain gauge. The results indicate: (1) a gross similarity between the pressure and diameter curves; (2) the mean value for ratio of change in radius to change in pressure (ΔR/ΔP) was 1.82 x 10 -3 cm. per cm. H 2 O (± S.D. 0.80); (3) the mean value for circumferential extensibility was 0.14 per cent change in radius per cm. H 2 O (± S.D. 0.06); and (4) the change in cross sectional area during an average cardiac cycle was 11 per cent of the diastolic value.