• Babs R Soller, Kathy L Ryan, Caroline A Rickards, William H Cooke, Ye Yang, Olusola O Soyemi, Bruce A Crookes, Stephen O Heard, and Victor A Convertino.
• Department of Anesthesiology, University of Massachusetts Medical School, Worcester, MA, USA. babs.soller@umassmed.edu
• Crit. Care Med. 2008 Jan 1;36(1):176-82.

ObjectiveTo compare the responses of noninvasively measured tissue oxygen saturation (StO2) and calculated muscle oxygen tension (PmO2) to standard hemodynamic variables for early detection of imminent hemodynamic instability during progressive central hypovolemia in humans.DesignProspective study.SettingResearch laboratory.SubjectsSixteen healthy human volunteers.InterventionsProgressive lower body negative pressure (LBNP) to onset of cardiovascular collapse.Measurements And Main ResultsNoninvasive measurements of blood pressures, heart rate, and stroke volume were obtained during progressive LBNP with simultaneous assessments of StO2, PmO2, and muscle oxygen saturation (SmO2). Forearm SmO2 and PmO2 were determined with a novel near infrared spectroscopic measurement device (UMMS) and compared with thenar StO2 measured by a commercial device (HT). All values were normalized to the duration of LBNP exposure required for cardiovascular collapse in each subject (i.e., LBNP maximum). Stroke volume was significantly decreased at 25% of LBNP maximum, whereas blood pressure was a late indicator of imminent cardiovascular collapse. PmO2 (UMMS) was significantly decreased at 50% of maximum LBNP while SmO2 (UMMS) decreased at 75% of maximum LBNP. Thenar StO2 (HT) showed no statistical change throughout the entire LBNP protocol.ConclusionsSpectroscopic assessment of forearm muscle PO2 and SmO2 provides noninvasive and continuous measures that are early indicators of impending cardiovascular collapse resulting from progressive reductions in central blood volume.

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