Relationship Between Spectral Components of Cardiovascular Variabilities and Direct Measures of Muscle Sympathetic Nerve Activity in Humans

TLDR

Spectral analysis of RR interval and systolic arterial pressure variabilities can serve as indirect markers of sympathetic‑vagal balance in cardiovascular control. The study aimed to assess how spectral power of RR interval, systolic arterial pressure, and MSNA relate across varying blood pressures. Eight healthy volunteers underwent simultaneous recording of MSNA, RR interval, intra‑arterial pressure, and respiration while blood pressure was lowered with nitroprusside and raised with phenylephrine. The study found that MSNA variability contains distinct LF and HF components that shift with sympathetic activity, with the LF component tightly correlated with LF power of RR interval and systolic arterial pressure and the HF component correlated with their HF power, indicating that sympathetic activation favors LF oscillations while inhibition favors HF, and that these patterns are best observed when spectral components are normalized, suggesting shared central control of sympathetic and parasympathetic cardiovascular modulation.

Abstract

Spectral analysis of RR interval and systolic arterial pressure variabilities may provide indirect markers of the balance between sympathetic and vagal cardiovascular control.We examined the relationship between power spectral measurements of variabilities in RR interval, systolic arterial pressure, and muscle sympathetic nerve activity (MSNA) obtained by microneurography over a range of blood pressures. In eight healthy human volunteers, MSNA, RR interval, intra-arterial pressure, and respiration were measured during blood pressure reductions induced by nitroprusside and during blood pressure increases induced by phenylephrine. Both low-frequency (LF; 0.10 +/- 0.01 Hz) and high-frequency (HF; 0.23 +/- 0.01 Hz) components were detected in MSNA variability. Increasing levels of MSNA were associated with a shift of the spectral power toward its LF component. Decreasing levels of MSNA were associated with a shift of MSNA spectral power toward the HF component. Over the range of pressure changes, the LF component of MSNA variability was positively and tightly correlated with LF components of RR interval (in normalized units; P < 10(-6)) and of systolic arterial pressure variability (both in millimeters of mercury squared and normalized units; P < 5 x 10(-5) and P < 5 x 10(-6), respectively). The HF component of MSNA variability was positively and tightly correlated with the HF component (in normalized units) of RR-interval variability (P < 3 x 10(-4)) and of systolic arterial pressure variability (P < .01).During sympathetic activation in normal humans, there is a predominance in the LF oscillation of blood pressure, RR interval, and sympathetic nerve activity. During sympathetic inhibition, the HF component of cardiovascular variability predominates. This relationship is best seen when power spectral components are normalized for total power. Synchronous changes in the LF and HF rhythms of both RR interval and MSNA during different levels of sympathetic drive are suggestive of common central mechanisms governing both parasympathetic and sympathetic cardiovascular modulation.