White blood cell concentrations during lower body negative pressure and blood loss in humans

What is the central question of this study? Is lower body negative pressure a useful surrogate to study white blood cell responses to haemorrhage in humans? What is the main finding and its importance? We found that lower body negative pressure appears to be a useful surrogate to study the early white blood cell mobilization response during blood loss. Hypovolaemia has been associated with an immune response that might be secondary to sympathoexcitation. We tested the hypothesis that simulated hypovolaemia using lower body negative pressure (LBNP) and real hypovolaemia induced via experimental blood loss (BL) cause similar increases in the white blood cell concentration ([WBC]). We measured [WBC] and catecholamine concentrations in 12 men who underwent an LBNP and a BL protocol in a randomized order. We compared 45 mmHg of LBNP with 1000 ml of BL; therefore, [WBC] and catecholamine concentrations were plotted against central venous pressure to obtain stimulus-response relationships using the linear regression line slopes for both protocols. Mean regression line slopes were similar for total [WBC] (LBNP 183 ± 4 μl^-1  mmHg^-1 versus BL 155 ± 109 μl^-1  mmHg^-1 , P = 0.15), neutrophils (LBNP 110 ± 2 μl^-1  mmHg^-1 versus BL 96 ± 72 μl^-1  mmHg^-1 , P = 0.15) and lymphocytes (LBNP 65 ± 21 μl^-1  mmHg^-1  versus BL 59 ± 38 μl^-1  mmHg^-1 , P = 0.90). Mean regression line slopes for adrenaline were similar (LBNP 15 ± 5 pg ml^-1  mmHg^-1 versus BL 16 ± 4 pg ml^-1  mmHg^-1 , P = 0.84) and were steeper during LBNP for noradrenaline (LBNP 28 ± 6 pg ml^-1  mmHg^-1 versus BL 9 ± 6 pg ml^-1  mmHg^-1 , P = 0.01). These data indicate that central hypovolaemia elicits a relative leucocytosis with a predominantly neutrophil-based response. Additionally, our results indicate that LBNP models the stimulus-response relationship between central venous pressure and [WBC] observed during BL.