Blood pressure regulation in neurally intact human vs. acutely injured paraplegic and tetraplegic patients during passive tilt

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2007-03, Vol.292 (3), p.R1146-R1157
• Main Authors: Aslan, Sevda C, Randall, David C, Donohue, Kevin D, Knapp, Charles F, Patwardhan, Abhijit R, McDowell, Susan M, Taylor, Robert F, Evans, Joyce M
• Format: Article
• Language: English
• Subjects: Adult; Autonomic Nervous System - physiology; Baroreflex; Blood Pressure; Case-Control Studies; Female; Heart Rate; Humans; Male; Middle Aged; Paralysis; Paraplegia - physiopathology; Posture; Quadriplegia - physiopathology; Spinal cord injuries; Tilt-Table Test; Time Factors
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00225.2006

1 Center for Biomedical Engineering, Wenner-Gren Research Laboratory, University of Kentucky, Lexington; 2 Electrical and Computer Engineering, University of Kentucky, Lexington; 3 Department of Physiology, University of Kentucky College of Medicine, Lexington; 4 Department of Physical Medicine and Rehabilitation, University of Kentucky, Lexington; and 5 Cardinal Hill Rehabilitation Hospital, Lexington, Kentucky Submitted 30 March 2006 ; accepted in final form 12 October 2006 We investigated autonomic control of cardiovascular function in able-bodied (AB), paraplegic (PARA), and tetraplegic (TETRA) subjects in response to head-up tilt following spinal cord injury. We evaluated spectral power of blood pressure (BP), baroreflex sensitivity (BRS), baroreflex effectiveness index (BEI), occurrence of systolic blood pressure (SBP) ramps, baroreflex sequences, and cross-correlation of SBP with heart rate (HR) in low (0.04–0.15 Hz)- and high (0.15–0.4 Hz)-frequency regions. During tilt, AB and PARA effectively regulated BP and HR, but TETRA did not. The numbers of SBP ramps and percentages of heartbeats involved in SBP ramps and baroreflex sequences increased in AB, were unchanged in PARA, and declined in TETRA. BRS was lowest in PARA and declined with tilt in all groups. BEI was greatest in AB and declined with tilt in all groups. Low-frequency power of BP and the peak of the SBP/HR cross-correlation magnitude were greatest in AB, increased during tilt in AB, remained unchanged in PARA, and declined in TETRA. The peak cross-correlation magnitude in HF decreased with tilt in all groups. Our data indicate that spinal cord injury results in decreased stimulation of arterial baroreceptors and less engagement of feedback control as demonstrated by lower 1 ) spectral power of BP, 2 ) number (and percentages) of SBP ramps and barosequences, 3 ) cross-correlation magnitude of SBP/HR, 4 ) BEI, and 5 ) changes in delay between SBP/HR. Diminished vasomotion and impaired baroreflex regulation may be major contributors to decreased orthostatic tolerance following injury. orthostatic hypotension; baroreflex sensitivity; baroreflex effectiveness index; cross correlation; feedback Address for reprint requests and other correspondence: J. M. Evans, Center for Biomedical Engineering, Wenner-Gren Research Laboratory, Univ. of Kentucky, Lexington, KY 40506-0070 (e-mail: jevans1{at}pop.uky.edu )