Changes in pulse character and mental status are late responses to central hypovolemia.

OBJECTIVE Manual assessment of radial arterial pulse character remains an important determinant of physiological status in military and civilian casualties. This study hypothesized that changes in radial pulse character and mental 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, and diastolic blood pressure were measured continuously during baseline supine rest and during 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 and SBP were well-maintained. Although both radial pulse character and SBP decreased with subsequent increases in LBNP, these changes occurred only after an approximate 55% reduction in SV and were 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 and was highly correlated with decreases in SBP. In support of our hypothesis, changes in pulse character, SBP, and mental status occurred only after significant reductions in SV, suggesting that these standard vital signs may not be early indicators of central hypovolemia.