Nuclear magnetic resonance spectroscopy of rat ventricles following chronic hypoxia: A model of right ventricular hypertrophy

Nuclear magnetic resonance spectroscopy was used to study the effect of chronic hypoxia on both right (RV) and left ventricular and septal (LV + S) muscle. Rats in the hypoxic group, kept in a hypobaric chamber at $\text{1}\text{2}$ atm pressure for 2 weeks, developed right, but not left, ventricular hypertrophy (p < 0.001). Tissues were studied within 2.5 h of return to air. T₁ and T₂ relaxation times of RV, LV + S and thigh muscle (Th) from hypoxic and control rats were compared. The T₂ value distinguished hypoxic from control RV (p < 0.002), but not hypoxic from control LV + S or Th, indicating that the change in relaxation time reflects cellular hypertrophy, and not hypoxemia. For hypoxic rats only the T₂ value distinguished each muscle type: RV from LV + S (p < 0.009), RV from Th (p < 0.001) and LV + S from Th (p < 0001). The T₁ value did not identify either the hypoxic or control group or the type of muscle. Percent water content was similar for all tissues. For hypoxic RV, T₂ correlated with the percent water content (r = 0.89; p < 0.01). The sensitivity of T₂ to the cellular changes associated with hypoxic RV hypertrophy could provide a means of detecting right ventricular hypertrophy.     

A comparative study of diffusion samplers for the determination of hexavalent chromium by sequential injection spectrophotometry

A method is described for determining hexavalent chromium in high particulate-containing surface waters by sequential injection (SI). The relative performance of two membrane-based methods for sampling is compared. The first membrane approach is based on a commercial design known as the ‘supported capillary membrane sampler (SCMS)’ (Wolcott, D.K., US Pat. 5 317 932 (1995)) that uses tubular membranes; the second approach is based on a conventional parallel-plate dialyzer (PPD) design that uses planar membranes. The membranes are evaluated using the well-known colorimetric method for the determination of hexavalent chromium by complexation with 1,5-diphenylcarbazide (DPC). Thin-walled (∼200 μm) microporous (pore size ∼0.2 μm) polypropylene membranes are equilibrated with DPC during each sampling period. Formation of the DPC-Cr(VI) complex allows for efficient membrane transport; without the membrane, Cr(VI) transport decreases ∼90%. Factors optimized included reagent concentrations, sampling time, flow rate, and spectrophotometric conditions. Optimal conditions were 2.00 mM DPC and 0.100 M nitric acid for the reagent, and 600 and 900 s sampling times for the planar and tubular designs, respectively. The planar (PPD) design increased the sensitivity relative to the tubular (SCMS) design by ∼225%. The PPD-SI method was applied to the determination of dissolved Cr(VI) in high particulate-containing surface water samples. Figures of merit included a detection limit of <20 μg/l, precision of 1.1% R.S.D. at 100 μg/l (n=4), and selectivity for dissolved Cr(VI) in several surface water samples with high levels of particulate matter.