{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,16]],"date-time":"2026-10-16T20:17:02Z","timestamp":1792181822033,"version":"4.4.0"},"reference-count":51,"publisher":"American Physiological Society","issue":"4","funder":[{"name":"US Army Medical Research & Materiel Command","award":["W81XWH-11-2-0137"],"award-info":[{"award-number":["W81XWH-11-2-0137"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["American Journal of Physiology-Regulatory, Integrative and Comparative Physiology"],"published-print":{"date-parts":[[2016,2,15]]},"abstract":"<jats:p> Tolerance to central hypovolemia is highly variable, and accumulating evidence suggests that protection of anterior cerebral blood flow (CBF) is not an underlying mechanism. We hypothesized that individuals with high tolerance to central hypovolemia would exhibit protection of cerebral oxygenation (ScO<jats:sub>2<\/jats:sub>), and prolonged preservation of CBF in the posterior vs. anterior cerebral circulation. Eighteen subjects (7 male\/11 female) completed a presyncope-limited lower body negative pressure (LBNP) protocol (3 mmHg\/min onset rate). ScO<jats:sub>2<\/jats:sub> (via near-infrared spectroscopy), middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv) (both via transcranial Doppler ultrasound), and arterial pressure (via finger photoplethysmography) were measured continuously. Subjects who completed \u226570 mmHg LBNP were classified as high tolerant (HT; n = 7) and low tolerant (LT; n = 11) if they completed \u226460 mmHg LBNP. The minimum difference in LBNP tolerance between groups was 193 s (LT = 1,243 \u00b1 185 s vs. HT = 1,996 \u00b1 212 s; P &lt; 0.001; Cohen's d = 3.8). Despite similar reductions in mean MCAv in both groups, ScO<jats:sub>2<\/jats:sub> decreased in LT subjects from \u221215 mmHg LBNP ( P = 0.002; Cohen's d=1.8), but was maintained at baseline values until \u221275 mmHg LBNP in HT subjects ( P &lt; 0.001; Cohen's d = 2.2); ScO<jats:sub>2<\/jats:sub> was lower at \u221230 and \u221245 mmHg LBNP in LT subjects ( P \u2264 0.02; Cohen's d \u2265 1.1). Similarly, mean PCAv decreased below baseline from \u221230 mmHg LBNP in LT subjects ( P = 0.004; Cohen's d = 1.0), but remained unchanged from baseline in HT subjects until \u221275 mmHg ( P = 0.006; Cohen's d = 2.0); PCAv was lower at \u221230 and \u221245 mmHg LBNP in LT subjects ( P \u2264 0.01; Cohen's d \u2265 0.94). Individuals with higher tolerance to central hypovolemia exhibit prolonged preservation of CBF in the posterior cerebral circulation and sustained cerebral tissue oxygenation, both associated with a delay in the onset of presyncope. <\/jats:p>","DOI":"10.1152\/ajpregu.00367.2015","type":"journal-article","created":{"date-parts":[[2015,12,16]],"date-time":"2015-12-16T23:48:30Z","timestamp":1450309710000},"page":"R375-R383","source":"Crossref","is-referenced-by-count":42,"title":["The role of cerebral oxygenation and regional cerebral blood flow on tolerance to central hypovolemia"],"prefix":"10.1152","volume":"310","author":[{"given":"Victoria L.","family":"Kay","sequence":"first","affiliation":[{"name":"Institute for Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Caroline A.","family":"Rickards","sequence":"additional","affiliation":[{"name":"Institute for 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