Arterial pulse pressure and its association with reduced stroke volume during progressive central hypovolemia

Background: The reduction of stroke volume (SV) during hemorrhage reflects the degree of blood loss, but accurate assessment of SV in bleeding patients in the field currently is not possible. In a previous pilot study, we reported that arterial pulse pressure and estimated sympathetic nerve activity (SNA) in trauma patients who died of hemorrhagic injuries was significantly lower than that observed in patients who did not die. For the current study, we measured mean arterial blood pressure (MAP), pulse pressure (PP), SV, and muscle sympathetic nerve activity (MSNA) in human subjects during progressive lower body negative pressure (LBNP) to test the hypothesis that a reduction in PP tracks the reduction of SV and change in MSNA during graded central hypovolemia in humans. Methods: After a 12-minute baseline data collection period, 13 men were exposed to LBNP at -15 mm Hg for 12 minutes followed by continuous stepwise increments to -30, -45, and -60 nun Hg for 12 minutes each. Results: Comparing baseline to -60 mm Hg chamber decompression, systolic blood pressure (SBP) decreased (from 129 +/- 3.0 to 111 +/- 6.1 mm Hg; p = 0.005) and diastolic pressure was unchanged (78 +/- 3.0 versus 81 +/- 4.0 min Hg; p = 0.55). Pulse pressure decreased (from 50 +/- 2.5 to 29 +/- 4.0 mm Hg; p = 0.0001). LBNP caused linear reductions in PP and SV (from 125 +/- 9.2 to 47 +/- 6.4; r(2) = 0.99), and increases in MSNA (from 14 +/- 3.5 to 36 +/- 4.6 bursts/min(-1); r(2) = 0.96) without a significant change in MAP (r(2) = 0.28). PP was inversely correlated with MSNA (r(2) = 0.88) and positively correlated with SV (r(2) = 0.91). Conclusions: Reduced PP resulting from progressive central hypovolemia is a marker of reductions in SV and elevations in SNA. Therefore, when SBP is > 90 min Hg, PP may allow for early, noninvasive identification of volume loss because of hemorrhage and more accurate and timely triage.