Voxel-based measurement sensitivity of spatially resolved near-infrared spectroscopy in layered tissues.

We quantitatively investigated the measurement sensitivity of spatially resolved spectroscopy (SRS) across six tissue models: cerebral tissue, a small animal brain, the forehead of a fetus, an adult brain, forearm muscle, and thigh muscle. The optical path length in the voxel of the model was analyzed using Monte Carlo simulations. It was found that the measurement sensitivity can be represented as the product of the change in the absorption coefficient and the difference in optical path length in two states with different source-detector distances. The results clarified the sensitivity ratio between the surface layer and the deep layer at each source-detector distance for each model and identified changes in the deep measurement area when one of the detectors was close to the light source. A comparison was made with the results from continuous-wave spectroscopy. The study also identified measurement challenges that arise when the surface layer is inhomogeneous. Findings on the measurement sensitivity of SRS at each voxel and in each layer can support the correct interpretation of measured values when near-infrared oximetry or functional near-infrared spectroscopy is used to investigate different tissue structures.

Effectiveness of laser Doppler perfusion monitoring in the assessment of microvascular function in patients undergoing on-pump coronary artery bypass grafting.

OBJECTIVES: To evaluate the effectiveness of single-point laser Doppler perfusion monitoring (LDPM) in the assessment of microvascular reactivity in the skin during cardiopulmonary bypass (CPB). DESIGN: Cross-sectional observational study. SETTING: Government-affiliated teaching hospital. PARTICIPANTS: Twenty male patients aged 60 ± 2 years who underwent coronary artery bypass grafting under CPB. INTERVENTIONS: The authors assessed the endothelium-dependent vasodilation of the skin microcirculation at the forehead and forearm using LDPM coupled with thermal hyperemia. This measurement was performed before and after the induction of anesthesia, during and after CPB, and 24 h after the end of the surgical procedure. RESULTS: The basal values of microvascular flow before the induction of anesthesia were significantly higher in the skin of the forehead compared with that of the forearm. There were no significant alterations in microvascular reactivity throughout the recording periods for both recording sites, as assessed by the vasodilation range expressed as cutaneous vascular conductance (arbitrary perfusion units/mean arterial pressure). CONCLUSIONS: Using LDPM, the authors showed that the microcirculatory bed of the skin of the forehead, which is readily accessible during cardiac surgery, is a suitable model for the study of microvascular reactivity and tissue perfusion in cardiovascular surgical procedures using CPB. This technique could, thus, be suitable for evaluating the effects of drugs or technical procedures on tissue perfusion during cardiac surgery under cardiopulmonary bypass.

Capillary refill time in term neonates: bedside assessment.

Capillary refill time (CRT) is yet to be established as a specific clinical sign of peripheral circulation in neonates. This study was conducted to assess the influence of four body sites used for measurement, interobserver variability, sex, birth weight, age at assessment and room temperature on CRT recorded in healthy term neonates, at bedside. Two observers measured CRT in four different body sites (forehead, chest, palm and heel) of each of 155 healthy term neonates. Significant differences occurred between the mean CRT recorded by the two observers in forehead (mean +/- SD: 2.62 +/- 0.8 s and 1.88 +/- 0.57 s; p < 0.001), palm (2.99 +/- 0.61 s and 2.75 +/- 1.12 s; p < 0.05) and heel (3.08 +/- 0.79 s and 4.24 +/- 1.84 s; p < 0.001). Only CRT in chest (2.7 +/- 0.42 s and 2.62 +/- 0.74 s) produced no significant differences in the means with a statistically significant and clinically fair, but not strong, interobserver agreement (r = 0.4; p < 0.001). No significant associations occurred between CRT and sex or birth weight. The associations of chest CRT with age at assessment (r = -0.23; p < 0.01) and room temperature (r = 0.27; p < 0.01) were clinically not important. In conclusion, CRT in neonates needs to be validated further before it can be useful as a specific clinical sign of peripheral circulation.