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ABSTRACT: It is well known that red blood cell scattering has an impact on whole blood oximetry as well as in vivo retinal oxygen saturation measurements. The goal of this study was to quantify the impact of small angle forward scatter on whole blood oximetry for scattering angles found in retinal oximetry light paths. Transmittance spectra of whole blood were measured in two different experimental setups: one that included small angle scatter in the transmitted signal and one that measured the transmitted signal only, at absorbance path lengths of 25, 50, 100, 250 and 500 µm. Oxygen saturation was determined by multiple linear regression in the 520-600 nm wavelength range and compared between path lengths and experimental setups. Mean calculated oxygen saturation differences between setups were greater than 10% at every absorbance path length. The deviations to the Beer-Lambert absorbance model had different spectral dependences between experimental setups, with the highest deviations found in the 520-540 nm range when scatter was added to the transmitted signal. These results are consistent with other models of forward scatter that predict different spectral dependences of the red blood cell scattering cross-section and haemoglobin extinction coefficients in this wavelength range.
The Analyst 02/2011; 136(8):1637-43. · 4.23 Impact Factor
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ABSTRACT: The incidence of congestive heart failure is 3-fold greater than that of acute coronary syndrome in haemodialysis (HD) patients. The purpose of this study was to determine if blood flow through an arteriovenous (AV) access contributes to an increase in left ventricular mass (LVM) that may increase the risk of congestive heart failure.
We conducted a 1-year prospective cohort study at two Canadian centres of HD patients at high risk for congestive heart failure who had a first AV access created. Patients underwent echocardiography and measurement of plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) levels before and 1-year post-AV access creation. Access flows were measured within the first month of access maturation and 1-year post-access creation. Data were analysed using descriptive statistics, Student's t-test, correlation coefficients and regression.
One-year post-AV access creation, LVM increased by 12.2 +/- 32% (P = 0.025) and plasma NT-proBNP levels increased by 170 +/- 465% (P = 0.02). The average AV access blood flow did not correlate with an increase in LVM or NT-proBNP levels.
In patients on chronic HD after 1 year, AV access flow does not correlate with increases in LVM by echocardiography or plasma levels of NT-proBNP.
Nephrology Dialysis Transplantation 02/2010; 25(8):2656-61. · 3.40 Impact Factor
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ABSTRACT: [(11)C]Methyl-candesartan and its desethyl derivative ([(11)C]TH4) were developed as potential radiotracers for imaging angiotensin II (Ang II) type 1 (AT(1)) receptors. These compounds were synthesized via methylation of tetrazole-protected candesartan using [(11)C]methyl iodide followed by deprotection through HCl hydrolysis at 65 degrees C to produce [(11)C]methyl-candesartan, and 90 degrees C for [(11)C]TH4. Ex vivo biodistribution and competition studies were carried out for both [(11)C]methyl-candesartan and [(11)C]TH4 to assess tissue retention time course and binding selectivity. Besides the liver, [(11)C]methyl-candesartan and [(11)C]TH4 displayed highest tissue retention in the AT(1) receptor-rich renal cortex and outer medulla. At tracer doses 15 min post-injection, [(11)C]methyl-candesartan demonstrated higher specific binding proportion for AT(1) receptors, and selectivity for AT(1) over Ang II AT(2), Mas, beta-adrenergic, and alpha(2)-adrenergic receptors in rat kidneys compared to [(11)C]TH4. This study indicates that [(11)C]methyl-candesartan has potential for in vivo imaging renal AT(1) receptors selectively using positron emission tomography.
Bioorganic & medicinal chemistry 12/2009; 17(23):7971-7. · 2.82 Impact Factor
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ABSTRACT: Visible and near infrared transmission and diffuse reflection spectroscopy were used to monitor changes in whole blood resulting from hemodialysis treatment for end-stage renal disease. Blood samples from 8 patients on chronic hemodialysis therapy were measured in the 500- to 1700-nm wavelength range immediately before and after a single treatment. Principal component scores characteristic of each spectrum were derived, and mean pre- and posttreatment scores of the first principal component indicated a significant treatment-dependent change in both optical transmission (P = 0.004) and diffuse reflection (P < 0.001). Significant treatment-induced change persisted (P < 0.05) when the first four principal components were used to account for >97% of the treatment-dependent spectral variation. Some blood spectral changes expressed in terms of difference spectra (posttreatment - pretreatment) were consistent with standard clinical indicators of weight reduction, urea reduction, and potassium change, with probable origins at a molecular level. The results indicate the feasibility of using optical transmission and diffuse reflection spectroscopy to characterize clinically relevant blood changes for the future development of more comprehensive indicators of hemodialysis efficacy and long-term clinical outcomes. Moreover, the optical techniques employed are adaptable for potential online monitoring of blood changes during the hemodialysis treatment.
Journal of Biomedical Optics 11(5):054003. · 3.16 Impact Factor
