Sympathetic transduction of blood pressure during graded lower body negative pressure in young healthy adults

Sympathetic transduction of blood pressure (BP) is correlated negatively with resting muscle sympathetic nerve activity (MSNA) in crosssectional data, but the acute effects of increasing MSNA are unclear. Sixteen (4 female) healthy adults (26??3 years) underwent continuous measurement of heart rate, BP, and MSNA at rest and during graded lower body negative pressure (LBNP) at -10, -20, and -30 mmHg. Sympathetic transduction of BP was quantified in the time (signal averaging) and frequency (MSNA-BP gain) domains. The proportions of MSNA bursts firing within each tertile of BP were calculated. As expected, LBNP increased MSNA burst frequency (P < 0.01) and burst amplitude (P 0.02), although the proportions of MSNA bursts firing across each BP tertile remained stable (all P 0.44). The MSNA-diastolic BP low-frequency transfer function gain (P = 0.25) was unchanged during LBNP; the spectral coherence was increased (P = 0.03). Signal-averaged sympathetic transduction of diastolic BP was unchanged (from 2.1??1.0 at rest to 2.4?? 1.5, 2.2?? 1.3, and 2.3??1.4 mmHg; P = 0.43) during LBNP, but diastolic BP responses following nonburst cardiac cycles progressively decreased (from-0.8 ?? 0.4 at rest to -1.0 ?? 0.6, -1.2 ?? 0.6, and -1.6 ?? 0.9 mmHg; P < 0.01). As a result, the difference between MSNA burst and nonburst diastolic BP responses was increased (from 2.9??1.4 at rest to 3.4?? 1.9, 3.4?? 1.9, and 3.9??2.1 mmHg; P < 0.01). In conclusion, acute increases in MSNA using LBNP did not alter traditional signal-averaged or frequency-domain measures of sympathetic transduction of BP or the proportion of MSNA bursts firing at different BP levels. The factors that determine changes in the firing of MSNA bursts relative to oscillations in BP require further investigation.

Automated summary

The sympathetic transduction of blood pressure is negatively correlated with resting muscle sympathetic nerve activity. The acute effects of increasing sympathetic nerve activity on blood pressure are still unclear. This study used lower body negative pressure to increase sympathetic nerve activity and found that it did not alter the traditional measures of sympathetic transduction of blood pressure. Further research is needed to determine the factors that affect the firing of sympathetic nerve activity in relation to blood pressure oscillations.