Aortic distensibility is reduced during intense lower body negative pressure and is related to low frequency power of sy
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ORIGINAL ARTICLE
Aortic distensibility is reduced during intense lower body negative pressure and is related to low frequency power of systolic blood pressure Aaron A. Phillips • Shannon S. D. Bredin • Anita T. Cote • C. Taylor Drury • Darren E. R. Warburton
Received: 3 May 2012 / Accepted: 29 August 2012 / Published online: 14 September 2012 Ó Springer-Verlag 2012
Abstract As sympathetic activity approximately doubles during intense lower body negative pressure (LBNP) of -60 mmHg or greater, we examined the relationship between surrogate markers of sympathetic activation and central arterial distensibility during severe LBNP. Eight participants were exposed to progressive 8-min stages of LBNP of increasing intensity (-20, -40, -60, and -80 mmHg), while recording carotid-femoral pulse wave velocity (cPWV), stroke volume (SV), heart rate, and beatby-beat blood pressure. The spectral power of low frequency oscillations in SBP (SBPLF) was used as a surrogate indicator of sympathetically modulated vasomotor modulation. Total arterial compliance (C) was calculated as C = SV/pulse pressure. Both cPWV and C were compared between baseline, 50 % of the maximally tolerated LBNP stage (LBNP50), and the maximum fully tolerated stage of LBNP (LBNPmax). No change in mean arterial pressure (MAP) occurred over LBNP. An increase in cPWV (6.5 ± 2.2; 7.2 ± 1.4; 9.0 ± 2.5 m/s; P = 0.004) occurred during LBNPmax. Over progressive LBNP, SBPLF increased (8.5 ± 4.6; 9.3 ± 5.8; 16.1 ± 12.9 mmHg2; P = 0.04) and C decreased significantly (18.3 ± 6.8; 14.3 ± 4.1; 11.6 ± Communicated by Massimo Pagani. A. A. Phillips (&) S. S. D. Bredin A. T. Cote C. T. Drury D. E. R. Warburton Cardiovascular Physiology and Rehabilitation Laboratory, Physical Activity and Chronic Disease Prevention Unit, University of British Columbia, Rm. 205, Unit II Osborne Centre, 6108 Thunderbird Blvd, Vancouver, BC V6T 1Z3, Canada e-mail: [email protected] A. A. Phillips C. T. Drury D. E. R. Warburton Faculty of Medicine, Experimental Medicine Program, University of British Columbia, Vancouver, Canada
4.8 ml/mmHg 9 10; P = 0.03). The mean correlation (r) between cPWV and SBPLF was 0.9 ± 0.03 (95 % CI 0.79–0.99). Severe LBNP increased central stiffness and reduced total arterial compliance. It appears that increased sympathetic vasomotor tone during LBNP is associated with reduced aortic distensibility in the absence of changes in MAP. Keywords Hypovolemia Pulse wave velocity Compliance Sympathetic nervous system
Introduction Mean arterial pressure (MAP) exerts an independent influence on central arterial stiffness (Nichols and O’Rourke 2005), however increased sympathetic nervous system (SNS) modulation of vasomotor tone is likely to also play a role (Boutouyrie et al. 1994). From a physiological perspective however, MAP is rarely increased without concomitant increases in SNS activity. Studies have shown increases in aortic stiffness after administration of caffeine (Mahmud and Feely 2001), cold pressor test (Liu et al. 2011), handgrip exer
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