3.4 RESERVOIR PRESSURE SEPARATION AT BRACHIAL, CAROTID AND RADIAL ARTERIES: A QUANTITATIVE COMPARISON AND EVALUATION

Abstract

Background: At present, reservoir pressure parameters are derived from arterial pressure waveforms regardless of the location of measurement. However, a comparison between sites has not been made, and site-related differences may affect interpretation. In this study, we computed reservoir pressure waveform separations on hypertensive individuals where brachial, carotid and radial pressure measurements were available and quantitatively assessed their results. Methods: 95 participants in the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) had sequential measurements of pressure and flow velocity waveforms from carotid, brachial and radial arteries [1]. Pre-processing was performed to impose identical diastolic and mean blood pressures at all three arterial locations. Using pressure information only, reservoir pressure separation was performed [2, 3]. Systolic durations were estimated based on minimum pressure waveform derivatives. Reservoir curves characterized by physiologically implausible parameters, i.e. a rate constant b < 0 or an asymptotic pressure P∞ < 0, were discarded, leaving 74 subjects with valid reservoir pressure waveforms at all three arterial locations. Results: Estimated reservoir parameters are shown in Table 1. We observed significant differences between arteries in almost all parameters. A high correlation was observed between reservoir pulse pressure and reservoir pressure area at all locations, and the correlation between brachial and radial arteries was stronger for all parameter. Reservoir Brachial Artery(B) Carotid Artery(C) Radial Artery(R) r(B,C) r(B,R) r(C,R) PP [mmHg] 37.1 ± 8.6 41.6 ± 9.0 36.1 ± 8.4 0.84* 0.95* 0.84* Ap [mmHg s] 16.7 ± 5.0 19.0 ± 4.4 16.0 ± 4.3 0.91* 0.96* 0.91* P∞ [mmHg] 61.6 ± 14.2 66.6 ± 12.8 66.2 ± 11.2 0.50* 0.51* 0.46* A [1/s] 8.3 ± 3.7 11.4 ± 2.7 7.0 ± 2.7 0.11* 0.91* 0.18* B [1/s] 1.8 ± 0.6 2.2 ± 0.9 2.1 ± z0.7 0.30* 0.62* 0.40* Table 1Quantification of reservoir pressures at three arterial locations in the format of mean ± standard deviation based on 74 subjects whereby PP denotes the reservoir pulse pressure, Ap the area of reservoir pressure above diastolic blood pressure, P∞ the asymptotic blood pressure and a, b = 1/τ the rate constants with the time constant τ describing the diastolic pressure decay. The correlation coefficient r is computer between relevant arterial locations. The statistical significance of the differences between locations was based on a paired t-test with * indicating p < 0.05. Conclusions: The results of this study indicate differences in parameters derived from reservoir pressure separation at different arterial locations. This suggests that interpretations cannot be made agnostic to the location of measurement.