Validity and reliability of measuring resting muscle sympathetic nerve activity using short sampling durations in healthy humans

Abstract

Resting muscle sympathetic nerve activity (MSNA) demonstrates high intraindividual reproducibility when sampled over 5-30 min epochs, although shorter sampling durations are commonly used before and during a stress to quantify sympathetic responsiveness. The purpose of the present study was to examine the intratest validity and reliability of MSNA sampled over 2 and 1 min and 30 and 15 s epoch durations. We retrospectively analyzed 68 resting fibular nerve microneurographic recordings obtained from 53 young, healthy participants (37 men; 23 ± 6 yr of age). From a stable 7-min resting baseline, MSNA (burst frequency and incidence, normalized mean burst amplitude, total burst area) was compared among each epoch duration and a standard 5-min control. Bland-Altman plots were used to determine agreement and bias. Three sequential MSNA measurements were collected using each sampling duration to calculate absolute and relative reliability (coefficients of variation and intraclass correlation coefficients). MSNA values were similar among each sampling duration and the 5-min control (all P > 0.05), highly correlated (r = 0.69-0.93; all P < 0.001), and demonstrated no evidence of fixed bias (all P > 0.05). A consistent proportional bias (P < 0.05) was present for MSNA burst frequency (all sampling durations) and incidence (1 min and 30 and 15 s), such that participants with low and high average MSNA underestimated and overestimated the true value, respectively. Reliability decreased progressively using the 30- and 15-s sampling durations. In conclusion, short 2 and 1 min and 30 s sampling durations can provide valid and reliable measures of MSNA, although increased sample size may be required for epochs ≤30 s, due to poorer reliability.

Evidence for Pressure‐Independent Sympathetic Modulation of Central Pulse Wave Velocity

“…Immediately following discrete brachial blood pressure measurements, cf‐PWV was measured at minute 7 and minute 9 during both baselines and at minute 9 and 11 during each pressure stimulus. In a subset of participants, continuous measures of MSNA were also collected over the entire duration of study to provide a direct marker of peripheral sympathetic activity 34, 35. To permit all variables to return to baseline levels, participants were given at least 8 minutes of quiet rest before repeating the protocol with the alternate pressure stimulus.…”

“…To confirm that the electrode site did not alter throughout the recording periods, the neural signal was monitored both audibly and visually. Custom semiautomated LabView software (National Instruments, Austin, TX) was used to quantify MSNA burst frequency (bursts/min), and total MSNA (AU/min) 34, 35. Total MSNA was calculated as the product of mean burst area × burst frequency; as each participant acted as their own control, we did not normalize the mean burst area data.…”

Cutaneous Mechanoreceptor Feedback from the Hand and Foot Can Modulate Muscle Sympathetic Nerve Activity

“…Efferent postganglionic multi-unit MSNA was recorded from the right fibular nerve as previously described (Millar et al, 2013; Notay et al, 2016). Briefly, the path of the fibular nerve, posterior to the fibular head, was marked using palpation and transdermal electrical simulation (Grass Technologies, Warwick, RI).…”

“…The integrated neurogram was analyzed using custom LabView software (Millar et al, 2013, 2015; Notarius et al, 2014; Notay et al, 2016) and reported as MSNA burst frequency (bursts/min), burst incidence (bursts/100 heartbeats), and normalized mean burst amplitude (% of maximum) and area (% of maximum). As MSNA burst amplitude and area are influenced by the proximity of the recording electrode to the discharging fibers, we normalized the data as a percentage of the largest burst amplitude and area, respectively, within each 4 min trial.…”

“…Similar short epochs have been used to assess the rapid MSNA response to the onset of exercise (Greaney et al, 2014). Our group recently published data on the validity and reliability of measuring MSNA using short epochs and recommended the reporting of absolute burst count to reduce the risk of magnifying the error in such measurements (Notay et al, 2016). Paired t -tests were used similarly to analyze the MSNA burst count, burst frequency, burst incidence, and normalized mean burst amplitude and area between baseline and first 10 s of vibration.…”