Reliability of measuring resting spontaneous cardiac baroreflex sensitivity using short sampling durations in healthy humans: Impact of central blood volume mobilization
Authors: Sabino‐Carvalho Jeann L. , Melo Camilla , Teixeira André L. , Millar Philip J. , Vianna Lauro C. 
Published: May 2022

IntroductionCalculation of spontaneous cardiac baroreflex sensitivity (cBRS) is used commonly to quantify arterial baroreflex buffering of beat‐to‐beat changes in blood pressure (BP). Studies report large interindividual variability in resting cBRS, which may be exacerbated by the supine posture and the use of shorter sampling duration (1‐3 min). However, this has yet to be reported in humans. Therefore, the purpose of the present study was to examine the impact of sampling duration on the intratest reliability of resting cBRS in healthy subjects. To accomplish this, we sought to compare resting cBRS derived from a standard 10‐min epoch (control) with values sampled over 7, 5, 3, and 1 min epoch durations. In addition, we examined the impact of central blood volume (CBV) mobilization on intratest reliability of resting cBRS.MethodsIn 30 healthy subjects (28 men; 22±3yrs) beat‐to‐beat measurements of BP and heart rate were recorded for 10‐min during both sitting and supine position. The cBRS was derived by sequence technique. Randomly selected epochs of 1‐min, 3‐min, 5‐min and 7‐min were then compared to the 10‐min control. To calculate the relative and absolute reliability we analyzed the technical error of the measurement (TEM), the intraclass correlation coefficients (ICC), Bland‐Altman analysis and coefficient of variations (CV). To test the impact of CBV mobilization on resting cBRS, ten subjects were also randomized to a non‐hypotensive lower body negative pressure (LBNP) trial at ‐20mmHg.ResultscBRS was lower in the sitting position than in the supine position (P<0.01). All cBRS values were similar between each sampling duration compared to the 10‐min control (P>0.12). The ICC obtained for cBRS ranged from very good to excellent in the supine position, whereas in the sitting position values demonstrated excellent between‐sampling duration reliability. The absolute and relative TEM increased with a shorter sampling duration (Table 1). In the LBNP trial, no significant differences in cBRS were observed within sampling durations in the LBNP trial (P=0.27). No significant differences in cBRS were observed between supine LBNP, sitting and supine positions (P=0.17). During LBNP trial, TEM increased with shorter sampling durations [10 vs. 7‐min: 0.7 ms/mmHg (4%), 10 vs. 5‐min: 1.4 ms/mmHg (8%), 10 vs. 3‐min: 1.9 ms/mmHg (11%), 10 vs. 1‐min: 3.1 ms/mmHg (17%), which was similar to the sitting position when compared to the supine posture.ConclusionOur findings show that 1) reliability decreased progressively using the 3‐ and 1‐min sampling durations; 2) the sitting position provides more reliable measures than all epoch durations measured in the supine position and; 3) the increases in the limits of agreement with shorter durations were attenuated by supine LBNP, suggesting that a cardiopulmonary baroreflex mechanism may play a role in the level of variability in resting cBRS.