Sequential modulation of cardiac autonomic control induced by cardiopulmonary and arterial baroreflex mechanisms

• Published in: Circulation (New York, N.Y.) Vol. 104; no. 24; pp. 2932 - 2937
• Main Authors: Furlan, R., Jacob, G., Palazzolo, L., Rimoldi, A., Diedrich, A., Harris, P. A., Porta, A., Malliani, A., Mosqueda-Garcia, R., Robertson, D.
• Format: Journal Article
• Language: English
• Published: Legacy CDMS Lippincott Williams & Wilkins 11.12.2001; American Heart Association, Inc
• Subjects: Adult; Aerospace Medicine; Arteries - physiology; Autonomic Nervous System - physiology; Baroreflex - physiology; Biological and medical sciences; Blood Pressure - physiology; Female; Fundamental and applied biological sciences. Psychology; Heart - innervation; Heart - physiology; Heart Rate - physiology; Hemodynamics. Rheology; Humans; Lower Body Negative Pressure - methods; Lung - physiology; Male; Respiratory Mechanics - physiology; Supine Position - physiology; Vertebrates: cardiovascular system; Human; Blood Pressure/physiology; Heart Rate/physiology; Supine Position/physiology; Clinical Trial; Lower Body Negative Pressure/methods; Non-Nasa Center; Heart/innervation/physiology; Respiratory Mechanics/physiology; Male; Controlled Clinical Trial; Lung/physiology; Nasa Discipline Regulatory Physiology; Arteries/physiology; Female; Adult; Autonomic Nervous System/physiology; Baroreflex/physiology; Heart rate; Baroreflex; Cardiopulmonary; Physiology; Circulatory system; Hemodynamics; Sympathetic nervous system; Artery; NASA Discipline Regulatory Physiology; Non-NASA Center
• DOI: 10.1161/hc4901.100360
• ISSN: 0009-7322; 1524-4539

BACKGROUND: Nonhypotensive lower body negative pressure (LBNP) induces a reflex increase in forearm vascular resistance and muscle sympathetic neural discharge without affecting mean heart rate. We tested the hypothesis that a reflex change of the autonomic modulation of heartbeat might arise during low intensity LBNP without changes of mean heart rate. METHODS AND RESULTS: Ten healthy volunteers underwent plasma catecholamine evaluation and a continuous recording of ECG, finger blood pressure, respiratory activity, and central venous pressure (CVP) during increasing levels of LBNP up to -40 mm Hg. Spectrum and cross-spectrum analyses assessed the changes in the spontaneous variability of R-R interval, respiration, systolic arterial pressure (SAP), and CVP and in the gain (alpha(LF)) of arterial baroreflex control of heart rate. Baroreceptor sensitivity was also evaluated by the SAP/R-R spontaneous sequences technique. LBNP began decreasing significantly: CVP at -10, R-R interval at -20, SAP at -40, and the indexes alpha(LF) and baroreceptor sensitivity at -30 and -20 mm Hg, compared with baseline conditions. Plasma norepinephrine increased significantly at -20 mm Hg. The normalized low-frequency component of R-R variability (LF(R-R)) progressively increased and was significantly higher than in the control condition at -15 mm Hg. CONCLUSIONS: Nonhypotensive LBNP elicits a reflex increase of cardiac sympathetic modulation, as evaluated by LF(R-R), which precedes the changes in the hemodynamics and in the indexes of arterial baroreflex control.