We demonstrate noninvasive near-infrared diffuse optical spectroscopy (DOS) measurements of tissue
hemoglobin contents that can track progressive reductions in central blood volume in human volunteers. Measurements of mean arterial blood pressure (MAP), heart rate (HR), stroke volume (SV), and cardiac output (Q) are obtained in ten healthy human subjects during baseline supine rest and exposure to progressive reductions of central blood volume produced by application of
lower body negative pressure (
LBNP). Simultaneous quantitative noninvasive measurements of tissue
oxyhemoglobin (OHb),
deoxyhemoglobin (RHb), total
hemoglobin concentration (THb), and tissue
hemoglobin oxygen saturation (S(t)O(2)) are performed throughout
LBNP application using broadband DOS. As progressively increasing amounts of
LBNP are applied, HR increases, and MAP, SV, and Q decrease (p<0.001). OHb, S(t)O(2), and THb decrease (p<0.001) in correlation with progressive increases in
LBNP, while tissue RHb remained relatively constant (p=0.378). The average fractional changes from baseline values in DOS OHb (fOHb) correlate closely with independently measured changes in SV (r(2)=0.95) and Q (r(2)=0.98) during
LBNP. Quantitative noninvasive broadband DOS measurements of tissue
hemoglobin parameters of peripheral perfusion are capable of detecting progressive reductions in central blood volume, and appear to be sensitive markers of early hypoperfusion associated with
hemorrhage as simulated by
LBNP.