Peyman Mirtaheri

Electrode polarization impedance in weak NaCl aqueous solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10/sup -2/-10/sup 3/ Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance R/sub p/ and capacitance C/sub p/ as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.

Non-invasive measurements of post-mortem changes in dielectric properties of haddock muscle - a pilot study

Significant changes can be measured in the electrical properties of organs and muscle during ischemia. This will undoubtedly form the basis of new diagnostic tools and tools for assessing food quality in the future. In this paper, we present measurements of the electrical properties of haddock muscle from 1 Hz to 100 kHz as a function of time after the fish was sacrificed. Clear alpha and beta dispersions were found. Most of the alpha dispersion disappeared after a few hours. The low frequency resistance of the beta dispersion increased during the first 5 h as the fish went into rigor, and then decreased as cell destruction developed.

Detection of organ ischemia during hemorrhagic shock.

Background:  In a porcine hemorrhagic shock model we aimed to determine: (a) whether blood flow to the intestine and kidney was more reduced than cardiac output; (b) whether parameters of anaerobic metabolism correlated with regional blood flow; and (c) whether metabolic parameters in intestine, kidney and skeletal muscles detected a compromized metabolic state at an earlier stage than did systemic parameters.

Effect of three‐dimensional culture and incubator gas concentration on phenotype and differentiation capability of human mesenchymal stem cells

To obtain sufficient numbers of cells for tissue engineering applications, human bone marrow‐derived mesenchymal stem cells (hBM‐MSC) are commonly cultured as monolayers in incubators containing room air. In this study, we investigated whether three‐dimensional (3D) culture conditions and incubator gas concentrations more similar to those observed in vivo impacted on cell expansion, differentiation capability, or phenotype of hBM‐MSC. We found that 3D culture alone increased the expression of some molecules involved in osteogenic and adipogenic differentiation. In contrast, 3D culture did not induce chondrogenic differentiation, but enhanced the response to the chondrogenic differentiation medium. Changing the oxygen concentration to 6% and the carbon dioxide concentration to 7.5% did not impact on the results of any of our assays, showing that the hyperoxia of room air is not detrimental to hBM‐MSC proliferation, differentiation, or phenotype. J. Cell. Biochem. 112: 684–693, 2011.

A new biomedical sensor for measuring PCO2

Measuring PCO2 (partial pressure of carbon dioxide) in an organ can enable early detection of ischemia. However, there are few clinical applicable solutions for measuring PCO2. Based upon the requirement for clinical applications, a conductivity based PCO2 sensor is proposed. A conductivity based PCO2 sensor measures conductance in an aqueous solution separated from the measured object by a gas-permeable membrane. A bridge design with two cavities is favored for such a sensor. A planar and a cylindrical macro prototype based upon the bridge design were studied. The design criteria were based on the contribution from the electrode polarization, stray capacitances, contact area with the sample and design ability to miniaturize the sensor. The cylindrical sensor is favored because of its large contact area and advantages for miniaturization. Further investigation has to be done to confirm the functionality of such a design in a miniaturized form and its clinical performance.

Miniaturization of a biomedical gas sensor

In a previous study, we concluded that a conductivity based PCO2 sensor is an attractive solution for early detection of ischemia and presented two design geometries. For organ surface measurements, the planar design was suitable but it was difficult to insert the sensor into the tissue. A cylindrical design solution was favored for insertion due to the large membrane contact area and easy placement in a medical catheter. Since the previous cylindrical prototype was large and could damage the tissue, a more miniaturized sensor was needed. In the current paper, we present a miniaturized sensor with an outer diameter of 1 mm. The applied technology for manufacturing the sensor was a combination of mechanical turning, excimer laser drilling and conventional molding technique. The materials applied were PEEK (polyetherether ketone), PI (polyimide) with gold layers and polysiloxane. The membrane had to be gas permeable while acting as a barrier for ion transport, and was made of polysiloxane and had a thickness of 100-150 microm. The miniaturized sensor was tested for calibration, response time, drifting and pressure sensitivity. The results show that the miniaturized PCO2 sensor is capable of rapid and stable measurements both in vitro and ex vivo. The result from this study will be applied for the industrial manufacturing of such a biomedical sensor as a clinical product.

A Review of the Role of the Partial Pressure of Carbon Dioxide in Mechanically Loaded Tissues: The Canary in the Cage Singing in Tune with the Pressure Ulcer Mantra

Pressure ulcers (PUs) can occur in any situations where people are subjected to non-uniform distribution of pressure over a prolonged period. They can have devastating effects on the patients’ well-being and in extreme conditions can prove fatal. In addition to traditional wisdom implicating mechanically induced ischaemia, there is strong evidence that other mechanisms play a role in the cascade of events which can initiate the PU damage process at the cellular level. Some of these refer to a metabolic imbalance with compromised delivery of nutrients and accumulation of waste products in the local environment of the cells. The approach of much research has focused on the measure of oxygen in compressed tissues as a means of predicting early damage. However, the present review adopting a hierarchical approach, using length scales ranging from cells through to human models, has revealed compelling evidence which highlights the importance of carbon dioxide levels and associated concentration of other metabolites, such as lactate and purines. The temporal profiles of these metabolites have been monitored in the various models subjected to periods of mechanical-induced loading where the localized cells have converted to anaerobic metabolism. They reveal threshold levels of carbon dioxide which might be indicative of early tissue damage during both mechanical-induced ischaemia and subsequent reperfusion and an appropriate sensor could be used in a similar manner to the long-standing “canary in a cage” method to detect toxic gasses in enclosed mines.

Hemodynamic Responses to Resistance Exercise in Patients with Coronary Artery Disease.

PURPOSE Investigate hemodynamic responses of resistance exercise (RE) with moderate load (i.e., international guidelines for RE of patients) versus RE with high load in patients with coronary artery disease (CAD). METHODS Medically stable male (n = 11) and female patients (n = 4) treated with PCI or percutaneous coronary intervention, or coronary artery bypass surgery a minimum of 6 months before this study, performed three sets of 15RM and 4RM RE in a randomized order on separate days. Beat-to-beat systolic (SBP), diastolic (DBP) blood pressure, heart rate (HR), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR) were monitored at preexercise, and continuously during RE. RESULTS Compared with preexercise, SBP and DBP (mean of three sets) increased by 12% to 13% (both; P < 0.001) and 35% to 40% after 15RM RE (both; P < 0.001). 15RM SBP and DBP were higher than 4RM SBP and DBP (both; P < 0.001). The SBP of the fourth repetition of 15 RM RE was similar to the SBP of the fourth repetition of 4RM RE. Compared with preexercise, SV increased moderately after 4RM and 15 RM RE, respectively (both, P < 0.001). HR increased more after 15RM compared with 4RM RE (P < 0.05); thus, higher CO after 15RM (compared with 4RM RE; P < 0.05) was mainly caused by higher HR. SVR decreased by 15% (P < 0.001) and 50% (P < 0.01) after 4RM and 15RM RE. CONCLUSIONS SBP and DBP increased significantly more during moderate load RE; thus, the magnitude of the external load is not the prime determinant of the pressure response during RE. If management of blood pressure is of concern, high load/low rep RE is preferable to medium load/high rep RE.

Detection of ischemia by PCO2 before adenosine triphosphate declines in skeletal muscle.

ObjectiveIschemia is a serious problem in clinical medicine, and effective methods are needed to detect ischemia before the injury becomes irreversible. In experimental studies on several organs, Pco2 was found to increase rapidly after the onset of supply-dependent anaerobic metabolism. A shortcoming of these studies was that Pco2 was not correlated with tissue concentrations of lactate and the energy status in the cell. Thus, in this study we have measured tissue concentrations of lactate, phosphocreatine, and adenosine triphosphate. We hypothesized that during ischemic conditions, Pco2 reflects lactate generation in the cell and not exhausted energy stores per se. If this is the case, Pco2 can be used to detect ischemia before the energy stores are depleted. Consequently, therapy can be instituted at a time when the organ is salvageable. DesignProspective laboratory study. SettingUniversity research laboratory. SubjectsSeven pigs. InterventionsIn a porcine model, gluteal skeletal muscles with no-flow ischemia were examined. Pco2 was measured both in situ and in vitro at increasing periods of time. Concomitantly, tissue lactate, adenosine triphosphate, and phosphocreatine were analyzed. Measurements and Main ResultsTissue surface CO2 tension (PtCO2) increased rapidly after onset of ischemia. From a baseline of 63 ± 3 torr (8.4 ± 1.2 kPa) under aerobic conditions, it increased to 157 ± 6 torr (21 ± 2.2 kPa) after 30 mins of ischemia and 386 ± 9 torr (51.5 ± 3 kPa) at 120 mins. The rapid increase of PtCO2 correlated well with increasing values of lactate (r2 > .9) in the tissue. Adenosine triphosphate was essentially unchanged for 45 mins after onset of ischemia, after which it declined. Phosphocreatine decreased earlier than adenosine triphosphate in accordance with the notion that high-energy phosphate groups are transferred from phosphocreatine to adenosine triphosphate. ConclusionIn this porcine model of skeletal muscle ischemia, PtCO2 correlates well with tissue lactate and increases long before the energy stores of phosphocreatine and most notably adenosine triphosphate are severely reduced. Thus, PtCO2 could be monitored to detect and treat earlier stages of ischemia.

Assessment of aerobic capacity and walking economy of unilateral transfemoral amputees

Background: Studies of the maximal oxygen uptake (VO2max) of transfemoral amputees have mostly used protocols that activate a relatively small muscle mass. Consequently, transfemoral amputee VO2max may be systematically underestimated, and the validity of these test protocols is questionable. Objectives: (1) Investigate validity and reliability of a VO2max walking protocol and (2) compare the VO2max of a transfemoral amputee group with a group of matching controls. Study design: (1) Randomized crossover study: walking versus running VO2max for the control group and (2) case-control study: transfemoral amputees versus control group VO2max. Methods: Twelve transfemoral amputees and control participants performed a walking VO2max test with increasing treadmill inclinations to voluntary exhaustion. The control group also completed a running (“gold-standard”) VO2max test. Results: Mean (standard deviation) control group VO2max following walking and running was similar, that is, 2.99 (0.6) L min−1 and 3.09 (0.7) L min−1, respectively. Mean (standard deviation) transfemoral amputee walking VO2max was 2.14 (0.8) L min−1 (compared to CON; p < 0.01). Mean intraclass correlation coefficient of repeated VO2 measurements was 0.97, and within-subjects standard deviation was 60 mL min−1. Conclusions: The walk protocol is valid. Walking VO2max of transfemoral amputees was 40% lower compared to control group. Reliability of the walking protocol is comparable to other walking protocols. Clinical relevance The design, alignment, and materials of prostheses are important for effective ambulation. Cardio-respiratory fitness is, however, also important in this regard, and a low fitness may compromise health and independent living. Hence, transfemoral amputees with low physical fitness should engage in regular physical activity to improve health, gait capacity, and independency.