White Blood Cell Counts during Lower Body Negative Pressure vs. Blood Loss in Humans

Abstract

Hypovolemia‐induced sympathoexcitation might initiate an immune response through an increase in circulating epinephrine and splenic demargination. We tested the hypothesis that lower body negative pressure (LBNP) and blood loss (BL) result in comparable increases in white blood cell counts (WBCs). We determined WBCs and epinephrine levels 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). Blood draws were performed at baseline and after the last stage of each protocol. LBNP to −45mmHg was a greater central hypovolemic stimulus vs. BL, therefore WBCs and epinephrine concentrations were plotted against central venous pressure (CVP) to obtain stimulus‐response relationships using the linear regression line slopes for both protocols. Paired tests were used to determine if the slopes of these regression lines fell on similar trajectories for each protocol. Mean regression line slopes fell on similar trajectories for total WBC (LBNP 183±46 vs. BL 155±109 mcL−1 *mmHg−1, p=0.15), neutrophils (LBNP 110±29 vs. BL 96±72 mcL−1 *mmHg−1, p=0.15) and lymphocytes (LBNP 65±21 vs. BL 59±38 mcL−1 *mmHg−1, p=0.90). Mean regression line slopes for epinephrine were similar as well (LBNP 15±5 vs. BL 16±4 pg *mL−1 *mmHg−1, p=0.84). Our results indicate that LBNP models the stimulus‐response relationship between CVP and WBCs observed during BL. Central hypovolemia, induced by LBNP or BL, elicits a relative leukocytosis with a predominantly neutrophil‐based response.Support or Funding InformationUS Army MRMC Combat Casualty Care Research Program Grant # W81XWH‐11‐1‐0823