Blood Coagulation during Lower Body Negative Pressure vs. Blood Loss in Humans

Abstract

We tested the hypothesis that changes in markers of coagulation are greater during lower body negative pressure (LBNP) than those obtained during blood loss (BL). We assessed coagulation using both standard clinical tests corrected for changes in hemoconcentration and thrombelastography in 12 men who performed a LBNP and BL protocol in a randomized order. LBNP consisted of 5-minute stages at 0, -15, -30, and -45 mmHg of suction. BL included 5 minutes at baseline and following three stages of 333 mL of blood removal (up to 1000 mL total). Arterial blood draws were performed at baseline and after the last stage of each protocol. We found that LBNP to -45mmHg is a greater central hypovolemic stimulus vs. BL, therefore the coagulation markers were plotted against central venous pressure (CVP) to obtain stimulus-response relationships using the linear regression line slopes for both protocols. Paired t-tests were used to determine if the slopes of these regression lines fell on similar trajectories for each protocol. Mean regression line slopes for coagulation markers vs. CVP fell on similar trajectories during both protocols, except for hemoconcentration corrected prothrombin time (-0.18 ± 0.08 during LBNP vs. 0.08 ± 0.05 s/mmHg during BL, p=0.01) and TEG αº angle (-0.42 ± 0.96 during LBNP vs. -2.41 ± 1.13 °/mmHg during BL, p<0.05). Our results indicate that LBNP models the general changes in coagulation markers observed during BL. Hypovolemia during BL has a greater impact on activation of the extrinsic coagulation pathway and rate of clot formation than during LBNP. US Army MRMC Combat Casualty Care Grant W81XWH-11-1-0823