We investigated whether near infrared spectroscopy could be used to monitor regional tissue oxygenation during uncompensated hemorrhage in man. A Somanetics INVOS 4100 oximeter was used to measure regional hemoglobin oxygen saturation in the cerebral cortex (CsO2, left frontal area) and from the left calf muscle (PsO2) in 40 volunteers donating 470 mL of the whole blood. A Critikon 2001 Cerebral Redox Instrument was used to monitor total (tHb), oxygenated (O2Hb), and deoxygenated (HHb) hemoglobin in the right calf muscle. The oxygenation index, [HbD] = [O2Hb] - [HHb] was derived. CsO2 decreased by a mean (95% CI) of 2 (1-3.3%) (P < 0.001), PsO2 decreased by a mean (95% CI) of 3.2 (1.7-4.6%) (P < 0.001), and HbD decreased by a median (95% CI) of 6.4 (2.65-10.16) delta microM/cm (P < 0.001) during blood collection. There was an inverse correlation between blood loss and CsO2 (R = -0.59, P < 0.001), PsO2 (R = -0.61, P < 0.001), and HbD (R = -0.5, P < 0.001). Regional tissue oxygenation decreases in proportion to uncompensated blood loss. Near infrared spectroscopy may potentially be developed into a transfusion trigger.

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Hemoglobin desaturation in exercising calf muscle is profound in patients with claudication, considerably greater even than that induced with three minutes of tourniquet occlusion. Further studies are necessary to investigate the relationship between the inflammatory response and near-infrared spectroscopy during exercise in patients with claudication.

The Cassini Propulsion Module Subsystem (PMS) has performed excellently throughout the first four years of mission operations. The PMS is the most complex interplanetary propulsion subsystem ever flown, with separate monopropellant and bipropellant propulsion modules, each replete with many redundant components. Propulsion system performance has generally been exemplary, with the apparent exception of large leakage through the primary hard-seat regulator. Maneuver performance has been excellent, and the spacecraft has flown a complex, Venus-Venus-Earth-Jupiter gravity assist trajectory virtually trouble flee. There is no early evidence for pressure transducer drift, in contrast with the Galileo, Voyager, and TOPEX-Poseidon missions. PMS system health checks based on helium mass calculations (helium mass budgets) have demonstrated no discernible helium pressurant or propellant leakage to date. An extensive, in-flight assessment of 0.9-N monopropellant hydrazine thruster performance during pulse-mode operation has been undertaken. Main engine and hydrazine thruster performance has been within specification. Propellant and consumable usage have generally been lower than predicted, and the prospect for a highly successful, multi-year scientific investigation of the Saturnian system remains excellent.