Re‐Examining the Measurement of Sympathetic Baroreflex Sensitivity at Rest and During Stress

Abstract

The sympathetic arterial baroreflex regulates blood pressure through negative feedback changes in vasoconstrictor muscle sympathetic nerve activity (MSNA). Spontaneous sympathetic baroreflex sensitivity (BRS) is quantified using a weighted linear regression relating absolute diastolic blood pressure (DBP) with occurrence (burst incidence [BI]) or strength (burst amplitude [BA]) of a multi‐unit MSNA burst. Such as assessment generally produces strong negative linear relationships between DBP and MSNA at rest, but are often weakened or absent during sympathoexcitatory stimuli, such as exercise or mental stress. We hypothesized that sympathetic BRS would be better represented during stress by using the change in DBP between two subsequent cardiac cycles (DBP change) rather than the absolute DBP value (absolute DBP). We retrospectively examined 64 participants whom underwent continuous recordings of heart (ECG), blood pressure (Finometer), and MSNA (microneurography). Each participant completed a 2–5 min resting baseline followed by one or more of the following protocols: rhythmic handgrip (RHG; n=24; 3 min at 40% maximal voluntary contraction [MVC]), static handgrip (SHG; n=16; 2 min at 30% MVC), mental stress (MS; n=28; 2 min serial subtraction). At rest, we observed a similar number of strong negative linear relationships (r>0.6) with BI (52/64 vs. 59/64, p=0.12) and BA (41/64 vs. 49/64, p=0.18) using the absolute and change methods. In participants possessing strong relationships across both methods (BI: n=49; BA: n=32), we observed differences in sympathetic BRS of BI (−4.7±1.8 bursts/100 heartbeats/mmHg vs. −5.4±2.0 bursts/100 heartbeats/ΔmmHg, p=0.03) and BA (−2.9±1.0 AU/mmHg vs. −2.5±1.3 AU/ΔmmHg, p=0.06), and modest correlations between methods for BRS of BI (r=0.32) and for BRS of BA (r=0.42). During stress, the absolute and change methods yielded a similar proportion of strong negative linear relationships with BI during RHG (6/24 vs. 10/24, p=0.36), but a higher number using the DBP change method during SHG (7/16 vs. 15/16, p=0.006) and MS (16/28 vs. 24/28, p=0.04). Similarly, the change method identified a greater proportion of strong negative linear relationships with BA during RHG (0/24 vs. 12/24, p<0.001), SHG (0/16 vs. 14/16, p<0.001), and MS (9/28 vs. 20/28, p=0.007). The DBP change method more consistently identified strong negative linear relationships with MSNA BI and BA. The modest relationships between methods at rest may highlight the importance of beat‐to‐beat DBP changes in arterial baroreflex regulation of muscle sympathetic outflow.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada (NSERC); NSERC Discovery Grant; Canada Foundation for InnovationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.