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Time Course of Compensatory Physiological Responses to Central Hypovolemia Varies with Tolerance
Author(s) -
Ryan Kathy L,
Rickards Caroline A,
Hinojosa-Laborde Carmen,
Convertino Victor A
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.1080.5
Subject(s) - hypovolemia , medicine , decompensation , presyncope , heart rate , hemodynamics , cardiology , blood pressure , vasodilation , anesthesia
While it is known that human subjects with high tolerance (HT) to central hypovolemia induced by lower body negative pressure (LBNP) have a greater ability to increase total peripheral resistance (TPR) and heart rate (HR) than low tolerant (LT) subjects, the time course of these compensatory events is unknown. We hypothesized that the rate of increase in HR and TPR would be greater in LT subjects. Subjects were instrumented to record beat‐by‐ beat arterial pressure, TPR and HR (Finometer) during a progressive LBNP protocol taken to the point of tolerance (presyncope). Subjects were classified as HT (n=113) if they completed at least the −60 mmHg level and LT (n=59) if they did not complete this level. LT reached maximal TPR (24.3 ± 0.9 mmHg*min/L) in 756 ± 31 s, while HT reached a higher (p=0.003) maximal TPR (27.7 ± 0.7 mmHg*min/L) in 1265 ± 37 s (p<0.001); rates of change from baseline did not differ statistically (p=0.17). Similar results were obtained for HR (max HR, LT: = 111 ± 2 bpm at 923 ± 27 s; HT: 130 ± 2 bpm at 1489 ± 23 s; both p<0.001); again, rates of change were comparable (P=0.20). LT subjects therefore vasoconstrict and increase HR at similar rates as HT subjects during central hypovolemia, but their ability to continue these compensatory responses is limited. A relative vasodilation occurs in both groups before maximal HR is attained, which may contribute to eventual hemodynamic decompensation. (Funded by US Army MRMC)