Relationship between repeated measures of hemodynamics, muscle sympathetic nerve activity, and their spectral oscillations

Abstract

Background: We determined the intraclass correlation coefficients (ICC) of repeated measures of the mean levels and variability of RR and muscle sympathetic nerve activity (MSNA) in 7 normal subjects. We examined whether spontaneous fluctuations in RR and MSNA over repeated measurements were mirrored by changes in spectral components of RR and MSNA. Methods and Results: Twenty-minute recordings of respiration, RR, blood pressure (BP), and MSNA were performed at day 1, 1 week, 1 month, and 3 months and divided into two 10-minute periods for the analysis of short-term reliability. Comparison between these recordings also determined the long-term reliability. Linear regressions examined the relationship between changes in these measurements and changes in spectral components of RR and MSNA. All analyses were carried out blinded to subject and session. Short-term ICC of RR, BP, MSNA and of the variabilities of RR and MSNA (in % of total power) ranged between .98 and .70 and indicated a good short-term reliability. The long-term reliability of RR variability was comparable to MSNA variability (range of ICC, .34 to .52). Spontaneous decreases in RR during the repeated recordings were accompanied by increases in sympathetic drive, as evidenced by increases in the ratio of low-frequency to high-frequency variability (LF/HF ratio) of RR interval (r=-.43, P