Changes in Pulse Character andMental Status Are Late Responses to Central Hypovolemia

Abstract

Objective. Manual assessment of radial arterial pulse character remains an important determinant of physiological status in military andcivilian casualties. This study hypothesized that changes in radial pulse character andmental status (presyncopal symptoms) in humans occur only during the later stages of progressive reductions in central blood volume in close association with systolic blood pressure (SBP). Methods. Pulse character (i.e., normal, weak, absent), estimated stroke volume (SV), SBP, anddiastolic blood pressure were measured continuously during baseline supine rest andduring progressive reductions of central blood volume to cardiovascular collapse with application of lower body negative pressure (LBNP) in 19 healthy human volunteer subjects. Results. LBNP resulted in a progressive reduction in SV. At early stages of LBNP, both radial pulse character andSBP were well-maintained. Although both radial pulse character andSBP decreased with subsequent increases in LBNP, these changes occurred only after an approximate 55% reduction in SV andwere associated with the onset of presyncopal symptoms. Changes in mental status did not occur until the point of cardiovascular collapse. Conclusions. In this model of progressive central hypovolemia secondary to application of LBNP in humans, radial pulse character score decreased in concert andwas highly correlated with decreases in SBP. In support of our hypothesis, changes in pulse character, SBP, andmental status occurred only after significant reductions in SV, suggesting that these standard vital signs may not be early indicators of central hypovolemia.

Key words:

• hemorrhagic shock
• lower body negative pressure
• cardiovascular collapse