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A Comparison of Protocols for Simulating Hemorrhage in Humans: Step vs. Ramp Lower Body Negative Pressure
Author(s) -
Rosenberg Alexander A.J.,
Kay Victoria L,
Anderson Garen K,
Sprick Justin D,
Rickards Caroline A
Publication year - 2019
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.2019.33.1_supplement.838.22
Subject(s) - presyncope , hypovolemia , medicine , blood pressure , anesthesia , hemodynamics , heart rate , cardiology , mean arterial pressure , stroke volume
Lower body negative pressure (LBNP) elicits central hypovolemia, and has been used to characterize the cardiovascular and cerebrovascular responses to simulated hemorrhage in humans. LBNP protocols traditionally employ a progressive stepwise reduction in pressure that is maintained for specific time periods. More recently, however, continuous ramp LBNP protocols have been utilized to simulate the continuous nature of most bleeding injuries. The aim of this study was to compare tolerance and hemodynamic responses between a step LBNP protocol and a continuous ramp LBNP protocol until the onset of presyncope. Methods Healthy human subjects (N=20; 8F, 12M) participated in two LBNP protocols to presyncope: 1) Step Protocol, where chamber pressure decreased every 5‐min to −15, −30, −45, −60, −70, −80, −90 and −100 mmHg, and, 2) Ramp Protocol, where chamber pressure decreased 3 mmHg/min. Heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), middle and posterior cerebral artery velocity (MCAv and PCAv), muscle and cerebral oxygen saturation (SmO 2 and ScO 2 ), and endtidal CO 2 (etCO 2 ) were measured continuously. Time to presyncope, the cumulative stress index (CSI; summation of chamber pressure*time at each pressure), and hemodynamic responses were compared between the two protocols. Results Time to presyncope (Step: 1611.8 ± 80.5 s vs. Ramp: 1675.4 ± 68.3 s; P=0.17), and the ensuing magnitude of central hypovolemia (%Δ SV, Step: −54.3 ± 2.5 % vs. Ramp: −51.9 ± 2.7 %; P=0.31) were similar between protocols, despite a higher CSI for the step protocol (Step: 946.5 ± 98.4 mmHg*min vs. Ramp: 836.7 ± 81.6 mmHg*min; P=0.06). While there were no differences at presyncope between protocols for the maximum change in HR, MCAv, or SmO 2 (P≥0.21), the reduction in MAP was slightly less (Step: −17.1 ± 1.8 % vs. Ramp: −20.0 ± 1.4 %; P=0.02) and the reductions in PCAv, ScO 2 , and etCO 2 (P≤0.08) were slightly greater for the step protocol compared to the ramp protocol. Conclusion These results suggest that step and continuous ramp LBNP protocols elicit relatively similar tolerance times, reductions in central blood volume, and subsequent reflex hemodynamic responses, despite a greater cumulative stress in young healthy adults. Support or Funding Information Funding for this study was provided by the U.S. Army MRMC Combat Casualty Care Research Program Grant # W81XWH‐11‐2‐0137. The content is solely the responsibility of the authors and does not necessarily represent the official views the US Department of Defense. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .