Pressure-Diameter Relation of the Human Aorta

Abstract

Background Pressure-diameter relation of the aorta provides important information about the elastic properties of the vessel. However, owing to methodological limitations, data regarding this relation are limited in conscious humans. In the present study, we assessed a new method for the direct estimation of the elastic properties of the aorta in conscious humans by simultaneous acquisition of instantaneous aortic pressure and diameter. Methods and Results With this method, instantaneous diameter of the thoracic aorta was acquired by a newly designed intravascular catheter developed in our institution that incorporates an ultrasonic displacement meter at its distal end. Instantaneous aortic pressure was acquired simultaneously at the same aortic level with a catheter-tip micromanometer. Aortic pressure-diameter loops were derived from computer analysis of data. After in vitro and animal testing, elastic properties of the aorta were investigated in coronary artery disease (CAD) patients (n=15) and compared with those of control subjects (n=10). Aortic distensibility was less in the CAD group than in the control group (1.73±0.33 versus 3.95±1.09×10 −6 ×cm 2 ×dyne −1 , P <.001). Compared with control subjects, the mean value of the slope of the pressure-diameter loops was significantly greater in the CAD group (38.89±8.75 versus 19.62±5.46 mm Hg · mm −1 , P <.001), whereas the mean value of the intercept was lower in this latter group of patients (−785.60±177.55 versus −313.43±126.41 mm Hg, P <.001). An excellent correlation was found between the slope of pressure-diameter loop and age in the group of control subjects ( r =.827). Ninety-three percent of the patients with CAD had values above the upper 95% confidence limits of the control subjects ( P <.001). In a third group of patients (n=16) in whom assessment of pulse wave velocity was also included in the study of the elastic properties of the aorta, pulse wave velocity had a strong inverse correlation with aortic distensibility ( r =−.95) and a strong positive correlation with the slope of the pressure-diameter loop ( r =.97). Conclusions This new method of determination of pressure-diameter of the aorta enables an accurate and reliable evaluation of the elastic properties of the aorta in conscious humans and may be useful for a profound study of human aorta mechanics.