Performance assessment of an opto-fluidic phantom mimicking porcine liver parenchyma.

An implantable, optical oxygenation and perfusion sensor to monitor liver transplants during the two-week period following the transplant procedure is currently being developed. In order to minimize the number of animal experiments required for this research, a phantom that mimics the optical, anatomical, and physiologic flow properties of liver parenchyma is being developed as well. In this work, the suitability of this phantom for liver parenchyma perfusion research was evaluated by direct comparison of phantom perfusion data with data collected from in vivo porcine studies, both using the same prototype perfusion sensor. In vitro perfusion and occlusion experiments were performed on a single-layer and on a three-layer phantom perfused with a dye solution possessing the absorption properties of oxygenated hemoglobin. While both phantoms exhibited response patterns similar to the liver parenchyma, the signal measured from the multilayer phantom was three times higher than the single layer phantom and approximately 21 percent more sensitive to in vitro changes in perfusion. Although the multilayer phantom replicated the in vivo flow patterns more closely, the data suggests that both phantoms can be used in vitro to facilitate sensor design.

Photodynamic therapy of actinic keratosis at varying fluence rates: assessment of photobleaching, pain and primary clinical outcome.

BACKGROUND: Although photodynamic therapy (PDT) is becoming an important treatment method for skin lesions such as actinic keratosis (AK) and superficial basal cell carcinoma, there are still discussions about which fluence rate and light dose are preferable. Recent studies in rodents have shown that a low fluence rate is preferable due to depletion of oxygen at high fluence rates. However, these results have not yet been verified in humans. OBJECTIVES: The objective was to investigate the impact of fluence rate and spectral range on primary treatment outcome and bleaching rate in AK using aminolaevulinic acid PDT. In addition, the pain experienced by the patients has been monitored during treatment. PATIENTS/METHODS: Thirty-seven patients (mean age 71 years) with AK located on the head, neck and upper chest were treated with PDT, randomly allocated to four groups: two groups with narrow filter (580-650 nm) and fluence rates of 30 or 45 mW cm(-2), and two groups with broad filter (580-690 nm) and fluence rates of 50 or 75 mW cm(-2). The total cumulative light dose was 100 J cm(-2) in all treatments. Photobleaching was monitored by fluorescence imaging, and pain experienced by the patients was registered by using a visual analogue scale graded from 0 (no pain) to 10 (unbearable pain). The primary treatment outcome was evaluated at a follow-up visit after 7 weeks. RESULTS: Our data showed a significant correlation between fluence rate and initial treatment outcome, where lower fluence rate resulted in favourable treatment response. Moreover, the photobleaching dose (1/e) was found to be related to fluence rate, ranging from 4.5 +/- 1.0 J cm(-2) at 30 mW cm(-2), to 7.3 +/- 0.7 J cm(-2) at 75 mW cm(-2), indicating higher oxygen levels in tissue at lower fluence rates. After a cumulative light dose of 40 J cm(-2) no further photobleaching took place, implying that higher doses are excessive. No significant difference in pain experienced by the patients during PDT was observed in varying the fluence rate from 30 to 75 mW cm(-2). However, the pain was found to be most intense up to a cumulative light dose of 20 J cm(-2). CONCLUSIONS: Our results imply that the photobleaching rate and primary treatment outcome are dependent on fluence rate, and that a low fluence rate (30 mW cm(-2)) seems preferable when performing PDT of AK using noncoherent light sources.

Heart rate variability in long-term risk assessment in middle-aged women with coronary heart disease: The Stockholm Female Coronary Risk Study.

OBJECTIVES: Low heart rate variability (HRV) is associated with poor prognosis after acute coronary events in men. In women, the prognostic impact is not well documented. The objective of this study was to assess the long-term predictive power of HRV on mortality amongst middle-aged women with coronary heart disease (CHD). DESIGN, SETTINGS AND SUBJECTS: Consecutive women below 65 years hospitalized for an acute coronary syndrome during a 3-year period in Stockholm were examined for cardiovascular prognostic factors including HRV, and followed for a median of 9 years. An ambulatory 24-h electrocardiograph was recorded during normal activities, 3-6 months after hospitalization. SDNN index (mean of the standard deviations of all normal to normal intervals for all 5-min segments of the entire recording) and the following frequency domain parameters were assessed: total power, high-frequency (HF) power, low-frequency (LF) power, very-low frequency (VLF) power and LF/HF ratio. Using Cox proportional hazards regression, the hazard ratios (HR) for each 25% decrease of the HRV parameters were assessed. RESULTS: After controlling for the independent, significant predictors of mortality amongst the clinical variables, the following HRV parameters were found to be significant predictors of all-cause mortality: SDNN index [HR 1.56, 95% confidence intervals (CI) 1.19-2.05], total power (HR 1.21, 95% CI 1.08-1.35), VLF power (HR 1.22, 95% CI 1.09-1.36), LF power (HR 1.18 95%, CI 1.07-1.30) and HF power (HR 1.18, 95% CI 1.05-1.33). The results were essentially the same when cardiovascular mortality was used as end-points. The HRV parameters were stronger predictors of mortality in the first 5 years following the index event. CONCLUSION: Low HRV is a predictor of long-term mortality amongst middle-aged women with CHD when measured 3-6 months after hospitalization for an acute coronary syndrome, even after controlling for established clinical prognostic markers.

Assessment of jet pilots' upper trapezius load calibrated to maximal voluntary contraction and a standardized load.

Electromyographic (EMG) recording of the myoelectrical activity level in the trapezius muscle is often used as one method of assessing neck and shoulder muscle workload. To analyse how the normalization value influences interpretation of upper trapezius load during a work task, two different reference values for normalization were applied - one obtained during a maximum voluntary contraction (MVE) and the other during a standardized muscular load (RVE). Nine jet pilots (ages 30-48 yr) flew two sorties in a 37 Viggen aircraft using either of two types of head garment while 3-D acceleration and muscular activity were recorded. In each sortie twice in the programme a steep left turn at 5-6 +G(Z) was performed. The highest activity level (MVE) obtained during shoulder elevation combined with an isometric heavy resistance (maximum) against arm flexion/abduction was used as one normalization value. Before, between, and after the two flights, 15 s EMG recordings (RVE) during a dumbbell test in the same arm position were also taken. The muscular activity in the upper trapezius during a given task varied a great deal between individuals, but the reliability of the amplitude levels on different occasions during a work day was good, given the same electrode location and application. If muscular activity during a standardized loading force (e.g. dumbbell test) is used to normalize the recordings for workload assessments related to utilized muscular capacity, a subject with high muscular strength and comparatively low workload might in some situations be assessed as having the same workload as, or a higher load than a subject with less strength and a comparatively high workload. While normalization using a standardized force can be used to assess changes in workload, for assessing workload related to the individual's capacity recording the myoelectrical activity during maximal contraction is preferable.