Validation of speed-resolved laser Doppler perfusion in a multimodal optical system using a blood-flow phantom.

The PeriFlux 6000 EPOS system combines diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) for the assessment of oxygen saturation (expressed in percentage), red blood cell (RBC) tissue fraction (expressed as volume fraction, %RBC), and perfusion (%RBC × mm / s) in the microcirculation. It also allows the possibility of separating the perfusion into three speed regions (0 to 1, 1 to 10, and >10 mm / s). We evaluate the speed-resolved perfusion components, i.e., the relative amount of perfusion within each speed region, using a blood-flow phantom. Human blood was pumped through microtubes with an inner diameter of 0.15 mm. Measured DRS and LDF spectra were compared to Monte Carlo-simulated spectra in an optimization routine, giving the best-fit parameters describing the measured spectra. The root-mean-square error for each of the three speed components (0 to 1, 1 to 10, and >10 mm / s, respectively) when describing the blood-flow speed in the microtubes was 2.9%, 8.1%, and 7.7%. The presented results show that the system can accurately discriminate blood perfusion originating from different blood-flow speeds, which may enable improved measurement of healthy and dysfunctional microcirculatory flow.

A blinded randomized assessment of laser Doppler flowmetry efficacy in standardizing outcome from intraluminal filament MCAO in the rat.

BACKGROUND: Laser Doppler flowmetry (LDF) is widely used for estimating cerebral blood flow changes during intraluminal middle cerebral artery occlusion (MCAO). No investigation has systematically examined LDF efficacy in standardizing outcome. We examined MCAO histologic and behavioral outcome as a function of LDF measurement. MATERIALS AND METHODS: Rats were subjected to 90min MCAO by 4 surgeons having different levels of MCAO surgical experience. LDF was measured in all rats during ischemia. By random assignment, LDF values were (Assisted) or were not (Blinded) made available to each surgeon during MCAO (n=12-17 per group). Neurologic and histologic outcomes were measured 7 days post-MCAO. A second study examined LDF effects on 1-day post-MCAO outcome. RESULTS: Pooled across surgeons, intra-ischemic %LDF change (P=0.12), neurologic scores (Assisted vs. Blinded=14±6 vs. 13±7, P=0.61, mean±standard deviation) and cerebral infarct volume (162±63mm(3)vs. 143±86mm(3), P=0.24) were not different between groups. Only for one surgeon (novice) did LDF use alter infarct volume (145±28mm(3)vs. 98±61mm(3), P=0.03). LDF use decreased infarct volume coefficient of variation (COV) by 35% (P=0.02), but had no effect on neurologic score COV. COMPARISON WITH EXISTING METHODS: We compared intraluminal MCAO outcome as a function of LDF use. CONCLUSIONS: LDF measurement altered neither neurologic nor histologic MCAO outcome. LDF did not decrease neurologic deficit COV, but did decrease infarct volume COV. LDF may allow use of fewer animals if infarct volume is the primary dependent variable, but is unlikely to impact requisite sample sizes if neurologic function is of primary interest.

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.

A comparison between laser-doppler imaging and colorimetry in the assessment of scarring: "a pilot study".

BACKGROUND: This cross-sectional pilot-study investigated the reproducibility of the LDI (Moor-LDI-B2; Moor Instruments) and the chromameter (Minolta chromameter CR-300) when used in scar assessment. METHODS: Twenty-seven scars in 14 subjects were included between January and June 2003. One observer performed two times both measurements with 10 min apart. The intra-observer agreement is quantified by means of the intra-class correlations (ICC) and the standard errors of measurement (SEM) for both the LDI and the chromameter. RESULTS: Ignoring one outlier, the ICC of the LDI = 0.856 and the SEM = 34.56. The chromameter shows a better reproducibility with an ICC of 0.93 and a SEM of 0.79. CONCLUSION: This pilot-study with a limited number of measurements shows a moderate reproducibility of the LDI compared to the chromameter measurements, in the assessment of respectively flux and redness in scars.

Reduced cost of extremity free flap monitoring.

We analyzed the results and cost-effectiveness of our protocol for free flap monitoring in extremity patients. Of 70 consecutive free flaps to the upper and lower extremity that were monitored by laser Doppler flowmeter, 62 were managed on the hospital ward immediately after recovery from general anesthesia. The duration of laser Doppler monitoring was 5 days. Perfusion compromise occurred in three flaps, two of which occurred in the recovery room and were initially detected by the laser Doppler and successfully salvaged by early exploration. The average equipment cost for the use of the laser Doppler flowmeter for 5 days was significantly less than the cost of an intensive care unit bed for a single day. Our experience confirms that monitoring free flaps with laser Doppler is cost-effective and indicates that a specialized care bed after the recovery room is not necessary in routine extremity cases. Since no vascular complication occurred beyond the second postoperative day, this study suggests that the duration of laser Doppler monitoring can be discontinued on the third postoperative day.