P129 Determination of the Diastolic Pressure Decay Constant (tau) from Radial Tonometry: Demographic and Hemodynamic Associations in Normal and Hypertensive Individuals

Introduction The feasibility of measuring the diastolic pressure-decay constant (tau) in normal and hypertensive humans is not established and the clinical and physiological relevance of tau is not known. Methods Studies were performed in the non-invasive cardiac laboratory in subjects who had been supine for at least 30 minutes. Measurements included standard oscillometric cuff BP, echocardiography (stroke volume [SV] and systemic vascular resistance [SVR]), pulse wave velocity (PWV, both aortic [heart-femoral] and peripheral [femoral-ankle]), and radial tonometry (Sphygmocor). Tau was estimated by photo-digitizing the pulse contour (Webplot digitizer) and modeling the terminal diastolic component according to the formula: P = A + (SBP-A)*exp(-(t-t0)/tau), where P is pressure, A is the modeled diastolic BP, and t0 is the start of the mono-exponential diastolic pressure decay. Results Full data were available In 76 individuals (mean age 55 years, weight 84 kg, BP 138/79 mmHg, resting HR 67; 45% female). Using simple Pearson correlations, tau was positively correlated with age, female gender and SVR, but negatively correlated with HR (all p < 0.05). Tau was unrelated to blood pressure (systolic, diastolic, mean or pulse pressure) or to peripheral or central PWV. In a forward stepwise multiple regression model of tau that included various hemodynamic indicators, only SVR survived, whereas BP, HR, SV, and PWV were excluded. Conclusions Tau can be estimated from radial tonometry and is most closely related to SVR, age, and female gender. Further application of tau (e.g. in the study of circulatory models) also seems feasible.