Relationship Between Repeated Measures of Hemodynamics, Muscle Sympathetic Nerve Activity, and Their Spectral Oscillations

• Published in: Circulation (New York, N.Y.) Vol. 96; no. 12; pp. 4326 - 4332
• Main Authors: van de Borne, Philippe, Montano, Nicola, Zimmerman, Bridget, Pagani, Massimo, Somers, Virend K.
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 16.12.1997; American Heart Association, Inc
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Electrocardiography; Electrophysiology; Female; Fundamental and applied biological sciences. Psychology; Hemodynamics - physiology; Hemodynamics. Rheology; Humans; Male; Middle Aged; Muscles - innervation; Oscillometry; Respiration - physiology; Sympathetic Nervous System - physiology; Time Factors; Vertebrates: cardiovascular system; Human; Heart rate; Exploration; Arterial pressure; Circulatory system; Hemodynamics; Striated muscle; Sympathetic nervous system; Spectral analysis
• ISSN: 0009-7322; 1524-4539
• DOI: 10.1161/01.CIR.96.12.4326

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 <.01) and by increases in MSNA ( r =−.36, P =.01). The changes in the LF/HF ratio of RR were mirrored by parallel changes in the LF/HF ratio of MSNA ( r =+.30, P <.05). Spontaneous decreases in BP were accompanied by increases in the LF/HF ratio of MSNA ( r =−.52; P =.0001). Conclusions Heart rate, MSNA, and their variability are stable in the short-term, but less so over the long term. Spontaneous changes in repeated measurements of RR interval and blood pressure over the long term are accompanied by parallel changes in the normalized spectral components of RR and MSNA variability. Thus even over an extended period, there is a synchrony between changes in absolute cardiovascular measures and changes in their spectral components.