Physiological influence of basic perturbations assessed by non-invasive optical techniques in humans.

New non-invasive techniques enabling frequent or continuous assessments of various pathophysiological conditions might be used to improve in-hospital outcome by enabling earlier and more reliable bedside detection of medical deterioration. In this preclinical study, three modern non-invasive optical techniques, laser Doppler imaging (LDI), near-infrared spectroscopy (NIRS), and tissue viability imaging (TVI), were all evaluated with respect to the influence of basic physiological perturbations (including local changes in arm positioning, skin temperature, and regional blood flow conditions) on quasi simultaneously obtained values of skin perfusion, muscle tissue oxygenation (StO₂), and skin blood volume, recorded in eighteen healthy volunteers. Skin perfusion measured by LDI responded prominently to changes in positioning of the arm, whereas muscle StO₂ measured by NIRS did not change significantly. Total haemoglobin count (HbT) measured by NIRS and blood volume estimated by TVI both increased significantly on lowering of the limb. On local cooling, the perfusion and blood volume were both found to increase considerably, while StO₂ and HbT did not change. Local heating induced a more than 10-fold increase in skin perfusion and a small increase in blood volume. On progressive venoarterial occlusion, the perfusion, StO₂, HbT, and blood volume values decreased, after transient increases in HbT and blood volume before full arterial occlusion occurred, and all values approached the baseline level on release of the occlusion with a slight overshoot of the StO₂. The results obtained have potential bearing on future utilization of these non-invasive techniques in the management of severely injured and (or) critically ill patients.