P122 CALCULATING RESERVOIR PRESSURE WITH OR WITHOUT FLOW INFORMATION: SIMILARITY AND ALGORITHMIC SENSITIVITY AT RADIAL ARTERY

Abstract

Background: Reservoir pressure is typically estimated from the pressure waveform information only. Comparability with estimates made using pressure and flow depend on assumptions, e.g. a proportional relationship between excess pressure and flow [1]. In this study, we compared (i) results using flow and pressure versus pressure-only at the radial artery, and (ii) two different algorithms used in the literature for pressure- only analysis. Methods: Reservoir pressure separations were performed on 95 hypertensive individuals where radial pressure and flow velocity waveform measurements were available [2]. Algorithm (F) used flow and pressure information [3]. Algorithms (P1) and (P2) refer to the two different pressure-only implementations as used in [4, 5], and [1, 6], respectively. Reservoir curves characterized by physiologically implausible parameters, i.e. a rate constant b < 0 or an asymptotic pressure P∞ < 0, were discarded, leaving 63 subjects with valid reservoir pressure data. Results: Estimated reservoir parameters are shown in Table 1. Algorithm (F) showed statistically significant differences in most of the parameters compared to (P1) and (P2), although, except time constant τ and asymptotic pressure P∞, there was a strong correlation between methods. Significant differences were observed in reservoir pulse pressure and area estimates between (P1) and (P2) despite their, in general, high correlation. Radial artery pres (F) pres (P1) pres (P2) r(F,P1) r(F,P2) r(P1,P2) PP [mmHg] 41.5±10.0 36.3±7.2 35.7±7.0 0.82* 0.82* 0.96* Ap [mmHg s] 17.5±4.3 15.6±3.7 15.5±3.7 0.94* 0.94* 1.00* τ [S] 0.3±0.1 0.6±0.4 0.6±0.3 0.36* 0.42* 0.88 P∞ [mmHg] 65.7±10.3 63.9±15.2 64.8±12.6 0.45 0.53 0.79 a [1/s] – 8.1±5.2 7.4±2.7 – – 0.93 b [1/s] – 2.2±1.1 2.1±0.8 – – 0.84 R [mmHg s/m] 419.0±188.8 453.7±348.2 436.7±302.6 0.68 0.75 0.92 C [mm/mmHg] 0.8±0.3 1.7±1.0 1.7±1.0 0.70* 0.70* 1.00 Table 1.Quantification of reservoir pressures pres obtained by methods (F), (P1) and (P2) at radial artery in the format of mean±standard deviation based on 63 subjects whereby PP denotes the reservoir pulse pressure, Ap the area of reservoir pressure above diastolic blood pressure, τ the time constant describing the diastolic pressure decay, P∞ the asymptotic blood pressure and a,b = 1/τ the rate constants. Peripheral (area) resistance and compliance, i.e. R and C, were estimated from the rate constants a and b for (P1) and (P2) using flow information. The correlation coefficient r was computed between relevant methods. The statistical significance of the differences between methods was based on a paired t-test with * indicating p < 0.05. Conclusions: The discrepancies between (F) and (P1), (P2) raise concerns about the validity of the implicit assumptions in pressure-only reservoir pressure separation at the radial artery. Differences in (P1) and (P2) indicate some sensitivity of derived parameters to the algorithm employed.