Abstract
Lower body negative pressure (LBNP) application simulates hemorrhage. We investigated how seasons affect coagulation values at rest and during LBNP. Healthy participants were tested in cold (November–April) and warm (May–October) months. Following a 30-min supine period, LBNP was started at −10 mmHg and increased by −10 mmHg every five minutes until a maximum of −40 mmHg. Recovery was for 10 min. Blood was collected at baseline, end of LBNP, and end of recovery. Hemostatic profiling included standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and thrombin formation markers. Seven men (25.0 ± 3.6 years, 79.7 ± 7.8 kg weight, 182.4 ± 3.3 cm height, and 23.8 ± 2.3 kg/m2 BMI) and six women (25.0 ± 2.4 years, 61.0 ± 8.4 kg weight, 167 ± 4.7 cm height, and 21.8 ± 2.4 kg/m2 BMI) participated. Baseline levels of prothrombin (FII), tissue factor (TF) and markers for thrombin generation F1+2 and the thrombin/antithrombin complex (TAT) were higher during summer. Factor VIII, prothrombin fragment 1+2 (F1+2), TAT and the coagulation time showed significant increases during LBNP in both seasons. Some calibrated automated thrombography variables (Calibrated automated thrombography (CAT): lag, time to peak (ttPeak), peak) shifted in a procoagulant direction during LBNP in summer. Red blood cell counts (RBC), hemoglobin and white blood cell counts (WBC) decreased during LBNP. LBNP application reduced prothrombin time in winter and activated partial thromboplastin time in summer. Greater levels of FII, TF, F1+2, and TAT—a more pronounced LBNP-induced procoagulative effect, especially in CAT parameters (lag time (LT), Peak, ttPeak, Velindex)—were seen in summer. These results could have substantial medical implications.
Highlights
Lower body negative pressure (LBNP) is a method that reduces central venous pressure by redistributing the blood towards the lower body via the use of a vacuum chamber that is sealed at the iliac crest [1,2]
This leads to increases in blood viscosity and plasma protein concentrations, and elevates interactions between procoagulant cellular factors and coagulation factors, creating a procoagulant environment [5] which is seen in both sexes [6,7,8]
LBNP suction caused a shortening of activated partial thromboplastin time (aPTT) during summer (p = 0.018) and prothrombin times (PTs) during winter (p = 0.028) (Table 1)
Summary
Lower body negative pressure (LBNP) is a method that reduces central venous pressure by redistributing the blood towards the lower body via the use of a vacuum chamber that is sealed at the iliac crest [1,2]. LBNP induces a reduction in cardiac preload that significantly lowers the stroke and end-diastolic volume in a linear relationship with the degree of negative pressure applied. The pressure gradient created by LBNP causes a migration of intravascular fluid to the lower body’s extravascular compartment, causing a rise in hemoconcentration. This leads to increases in blood viscosity and plasma protein concentrations, and elevates interactions between procoagulant cellular factors and coagulation factors, creating a procoagulant environment [5] which is seen in both sexes [6,7,8]. How seasonal variation in coagulation parameters occurs in both sexes and how they are influenced by LBNP have not yet well been researched
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