P122: Calculating Reservoir Pressure with or Without Flow Information: Similarity and Algorithmic Sensitivity At Radial Artery

• Published in: Artery research Vol. 20; no. 1; pp. 78 - 79
• Main Authors: Ebner, Michael, Parker, Kim, Vercauteren, Tom, Ourselin, Sébastien, Wassertheurer, Siegfried, Hughes, Alun, Hametner, Bernhard
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.12.2017; Springer Nature B.V; BMC
• Subjects: Algorithms; ARTERY 17 Poster Presentation abstracts; Blood pressure; Flow velocity; Veins & arteries
• ISSN: 1872-9312; 1876-4401; 1876-4401
• DOI: 10.1016/j.artres.2017.10.104

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. Table 1 Quantification of reservoir pressures p res 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, A p 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. Radial artery p res (F) p res (P1) p res (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* A p [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 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.