Validation of a novel method to determine non-invasively the rate of central aortic pressure changes

One of the most sensitive indices of myocardial contractility is represented by the rate of increase of intraventricular pressure during isovolumetric contraction (dP/dt) and (dP/dt(ejc)), which represents the rate of change of pressure during ejection. Today these parameters can be obtained only by invasive catheterization methods. We developed a novel technique that leads to the non-invasive reconstruction of the central aortic pressure. The technique is based on the concept of applying multiple successive occlusive pressures on the brachial artery from peak systole to diastole using an inflatable cuff and plotting the values against time intervals. The hypothesis is that the time intervals required for the aortic pressure wave to overcome a given occlusive brachial pressure applied by a sphyngomanometer on the arm are equal to time needed to reach the same pressure in the central aorta plus the propagation time to the brachial point, which is constant in the same patient throughout the measurements.

We tested the hypothesis using an animal experiment. The new non-invasive device was mounted on the left forelimb of the animal. A Millar pressure transducer catheter was inserted to the aorta and the aorta pressure was recorded at time intervals of 1 ms. A second catheter was inserted into the coronary arteries and used to create controlled occlusion of the arteries using a balloon inflated to 10 atm. Measurements were obtained before the intervention was started, and throughout the sequence of repeated occlusions and deflations. At the end of the sequence, IV dobutamine was administered and results were monitored for 10 min while the heart rate and blood pressure were rising. Non-invasive dP/dt(ejc) was reduced typically by 20% in response to balloon inflation. In long occlusion periods, stabilization and sometimes recovery of dP/dt(ejc) is observed. By plotting dP/dt(ejc) measured by the new non-invasive device versus catheter measurements a correlation factor of 0.843 was found.

A newly developed method of non-invasive measurement of central dP/dt has been found to correlate to invasive measurements in an animal model.