Compression garments do not alter cerebrovascular responses to orthostatic stress after mild passive heating S. A. Morrison 1,2 , P. N. Ainslie 3 , R. A. I. Lucas 1 , S. S. Cheung 4 , J. D. Cotter 1 1 School of Physical Education, University of Otago, Dunedin, New Zealand, 2 Jozef Stefan Institute, Ljubljana, Slovenia, 3 School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada, 4 Department of Kinesiology, Brock University, St. Catharines, ON, Canada Corresponding author: Shawnda A. Morrison, PhD., Jozef Stefan Institute, Department of Automation, Biocybernetics and Robotics, Jamova 39, SI-1000 Ljubljana, Slovenia. Tel: +386 1477 37 77, Fax: +386 1477 31 54, E-mail:shawnda.morrison@ijs.si Accepted for publication 14 August 2012 Whole-body heating increases the likelihood of syncope, whereas utilizing lower-body compression garments may reduce syncope risk. We hypothesized that graded com- pression garments would reduce the typically observed large postural reductions in arterial blood pressure and middle cerebral artery velocity, in normothermia and especially once passively heat stressed. Fifteen men (age: 27  4 years, aerobic fitness range: 30–75 mL/kg / min) completed a supine-to-stand orthostatic challenge for 3 min at normothermia and after passive heating (esoph- ageal temperature, +0.5 °C from baseline) on two occa- sions (> 7 days): once wearing commercially available compression trousers and once wearing low-compression placebo trousers (randomized order). Blood flow velocity in the middle cerebral artery (transcranial Doppler), mean arterial blood pressure (mean BP: Finometer) and end-tidal carbon dioxide pressure were measured con- tinuously. During normothermia, compression, garments did not alter the magnitude of the postural changes in mean BP or middle cerebral artery velocity. After passive heating, although the magnitudes of these changes were exaggerated, they were not significantly affected by com- pression garments. Compression garments did not attenuate the initial or sustained orthostatic hypotension associated with posture change, either during normoth- ermia or following passive heat stress. The act of moving from a supine to a standing posture is a significant orthostatic stress on the human body, reduc- ing central venous pressure and venous return as blood pools in the lower extremities immediately after the pos- tural changes. Following a chronotropically mediated increase in cardiac output ( ɺ Q) (Sjostrand, 1952), the displacement of blood away from the heart can decrease ventricular filling pressure, stroke volume (SV) and mean arterial blood pressure (MAP), potentially attenu- ating cerebral perfusion (Van Lieshout et al., 2003). When heat and orthostatic stressors are combined, greater reductions in orthostatic tolerance have been observed (Lind et al., 1968; Wilson et al., 2002; Crandall et al., 2003; Cui et al., 2004; Carter et al., 2006; Wilson et al., 2006). Lower orthostatic tolerance observed when heat stressed presumably reflects an elevated vascular compliance, reduced cardiac and vascular baroreflex (Cui et al., 2004), hyperthemic-induced hyperventila- tion, and related hypocapnic-induced reductions in cere- bral perfusion (Fan et al., 2008; Nelson et al., 2011). One non-pharmacological means of limiting the orthostatic stress of standing could be graduated com- pression garments. In this way, increasing peripheral vascular resistance and minimizing venous pooling may provide a better method to maintain MAP. This approach has been used as a mechanical method for reducing the incidence of deep-vein thrombosis by potentially increasing mean deep venous velocity and improving venous return (O’Donnell et al., 1979; Lawrence & Kakkar, 1980; Gandhi et al., 1984; Byrne, 2001). More recently, lower limb and abdominal compression ban- dages have proven effective in attenuating the decrease in systolic blood pressure (SBP) (~20 mm Hg) during progressive orthostatic hypotension from 60° passive tilt (Podoleanu et al., 2006) in elderly persons, and reducing edema in the ankles and lower legs during 8 h of stand- ing on a hard surface (Kraemer et al., 2000), although neither study investigated these observations with respect to their influence on cerebral perfusion. Com- pression garments have also been shown to maintain MAP via an increase in total peripheral resistance (TPR) in older adults when moving from a supine to a standing posture (Lucas et al., 2012), although changes in middle cerebral artery velocity (MCAv) were minimal. Privett et al. (2010) have reported lower incidences of orthos- tatic intolerance to standing in athletes who wore com- pression garments after a bout of maximal exercise. The six athletes recruited for that study were previously diag- nosed with vasovagal syncope. However, only slight increases in heart rate and SBP were observed in the Scand J Med Sci Sports 2012: ••: ••–•• doi: 10.1111/sms.12001 © 2012 John Wiley & Sons A/S 1