van Helmond N, Johnson BD, Curry TB, Cap AP, Convertino VA, Joyner MJ. Coagulation changes during lower body negative pressure and blood loss in humans. Am J Physiol Heart Circ Physiol 309: H1591-H1597, 2015. First published September 9, 2015; doi:10.1152/ajpheart.00435.2015.-We tested the hypothesis that markers of coagulation activation are greater during lower body negative pressure (LBNP) than those obtained during blood loss (BL). We assessed coagulation using both standard clinical tests and thrombelastography (TEG) in 12 men who performed a LBNP and BL protocol in a randomized order. LBNP consisted of 5-min stages at 0, Ϫ15, Ϫ30, and Ϫ45 mmHg of suction. BL included 5 min at baseline and following three stages of 333 ml of blood removal (up to 1,000 ml total). Arterial blood draws were performed at baseline and after the last stage of each protocol. We found that LBNP to Ϫ45 mmHg is a greater central hypovolemic stimulus versus 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 whether the slopes of these regression lines fell on similar trajectories for each protocol. Mean regression line slopes for coagulation markers versus CVP fell on similar trajectories during both protocols, except for TEG ␣°angle (Ϫ0.42 Ϯ 0.96 during LBNP vs. Ϫ2.41 Ϯ 1.13°/mmHg during BL; P Ͻ 0.05). During both LBNP and BL, coagulation was accelerated as evidenced by shortened R-times (LBNP, 9.9 Ϯ 2.4 to 6.2 Ϯ 1.1; BL, 8.7 Ϯ 1.3 to 6.4 Ϯ 0.4 min; both P Ͻ 0.05). Our results indicate that LBNP models the general changes in coagulation markers observed during BL. blood coagulation; hemorrhage; lower body negative pressure; blood coagulation tests; humans; central hypovolemia
NEW & NOTEWORTHYOur study provides noteworthy data that directly compare blood coagulation activation induced by lower body negative pressure to those observed during blood loss in conscious humans.HEMORRHAGE IS ONE OF THE LEADING causes of accidental death (1) and is the leading cause of death on the battlefield (8, 9). Activation of the coagulation system is vital following a hemorrhagic injury to reduce the risk of exsanguination. Consequently, studying the activation of the coagulation system during blood loss (BL) is of upmost importance so new therapies and treatment algorithms, such as fluid resuscitation, can be developed. However, using invasive methods to experimentally induce BL is challenging to perform in humans.Lower body negative pressure (LBNP) is a technique that is used as a noninvasive surrogate to study many of the physiological responses to BL (4, 15, 18). LBNP sequesters circulating blood in the lower body, thereby reducing central blood volume and mimicking hemodynamic responses generated during BL (4,15,18). However, it is unclear if markers of coagulation system activation respond similarly during these protocols. Reductions in central blood volume by LBNP (38) ...