Aortic blood pressure is decreasing approximately exponentially during diastole and the time constant of the decay is supposed to hold information about total arterial compliance and peripheral resistance. However, it is unclear if the pressure would drop to zero without further excitations from the heart or if it would reach an asymptotic pressure level Pinf. The aim of this work was to examine the fitting performance of an exponential decay with and without Pinf in invasive aortic pressure readings with prolonged diastoles caused by missing heartbeats.

A total number of 35 pressure signals (5F Millar SPC-454D catheters) from 5 different subjects were examined. For the fitting procedure, the squared error between measured data and analytical function was minimized with Pinf ranging from 0 to 100% (5% steps) of the diastolic blood pressure DBP. The data was fitted over the duration of both, the regular and the prolonged diastole.

The irregular heartbeats were on average 1.7 (0.3 SD) times longer than the preceding beats. In all settings, mean root mean squared error RMSE between measured and calculated pressure drop was lowest for Pinf=0.7*DBP. For Pinf=0, the deviation was more than two times higher than for Pinf=0.7*DBP, regardless of the chosen part for fitting (mean RMSE: 1.8 (0.6 SD) and 5.2 (2.6 SD) with and without Pinf respectively when fitted to the first part).

The results indicate that an asymptotic pressure level exists, which is, at least for the observed timescales, maintained by the vascular system even without ejection from the heart.