Spontaneous Baroreflex Control of Muscle Sympathetic Nerve Activity in Humans: Standardizing Analysis Procedures

Seth W. Holwerda; Jason R. Carter; Huan Yang; Gary L. Pierce; Paul J. Fadel

doi:10.1096/fasebj.2018.32.1_supplement.595.8

Beat‐to‐beat variations in muscle sympathetic nerve activity (MSNA) are strongly related to diastolic blood pressure (DBP) fluctuations, and the use of spontaneous occurring bursts of MSNA at rest to determine sympathetic baroreflex sensitivity has become more prevalent. However, published results using spontaneous sympathetic baroreflex sensitivity have lacked standard methodology for analysis. Indeed, there have been variations in the duration of the recording used, the size of the DBP bins (1‐, 2‐, 3‐mmHg), and strength of the linear regression r‐values accepted. Thus, we sought to comprehensively examine the influence of these varying analysis procedures on spontaneous sympathetic baroreflex sensitivity. Our goal was to provide a standardized procedure that would allow for consistent and comparable results across laboratories. In a collective group of subjects (n=150), weighted linear regression analysis between MSNA and DBP was performed with MSNA expressed as either burst incidence (bursts/100heartbeats) or total MSNA (summation of MSNA burst amplitude relative to number of cardiac cycles). Resting MSNA was analyzed over a 10‐min baseline period, and subsequently segregated into separate 5‐, 2‐, and 1‐min segments to examine the influence of baseline duration on the weighted linear regression. MSNA was averaged over 1‐, 2‐, or 3‐mmHg DBP ranges (bins) to examine the influence of bin size. Also, in a subset of subjects (n=35), the modified Oxford technique (intravenous infusion of sodium nitroprusside followed by phenylephrine) was performed for comparison. The average slope of the linear regressions for resting MSNA burst incidence and total MSNA progressively increased as the baseline duration decreased with 1‐min duration being significantly greater than 10 min (P<0.05); however, correlation coefficients were reduced with the shorter durations. Indeed, the 10‐min baseline durations most frequently yielded statistically significant probability values for linear regressions (P<0.05), which closely reflected the p‐values obtained during the modified Oxford. Interestingly, although bin size (1‐, 2‐, 3‐mmHg) had no major influence on the average slope of the regressions (P>0.05), correlation coefficients progressively increased with bin size such that the highest correlation coefficients were observed for the 3‐mmHg bin size for each time duration segment. Overall, the 10‐min durations and 3‐mmHg bin size yielded the highest correlation coefficients. Collectively, these findings suggest that the duration of the recording used for analysis impacts the statistical validity of the r‐values defining the slopes for spontaneous sympathetic baroreflex sensitivity, whereas larger bin size improves the r‐value but has less influence on the p‐value. This is from the Experimental Biology 2018 Meeting. There is no full text article associated with this published in The FASEB Journal.

Spontaneous Baroreflex Control of Muscle Sympathetic Nerve Activity in Humans: Standardizing Analysis Procedures

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