A prospective and follow up study of renal tubular and glomerular function in 11 children receiving ifosfamide treatment was con-

SUMMARY. An isocratic high-performance liquid chromatography (HPLC) method is described using the natural fluorescence of phenylalanine and tyrosine compared with that of an internal standard N-methyl phenylalanine. Plasma precipitated with 6% perchloric acid was separated isocratically using a base-deactivated CIS column with 5% acetonitrile in water as the mobile phase. Fluorescent measurements at an excitation wavelength of 215 nm and emission 283 nm showed only three peaks for tyrosine, phenylalanine and the internal standard eluting within 9 min. Inter-batch coefficients of variation for phenylalanine were 2·9% and 1·8% at levels of 70 and 567 J.Lmol/L, respectively, and 2·9% at a level of 63 J.Lmol/L for tyrosine. The results for phenylalanine for this method showed a small mean positive bias (II J.Lmol/L) when compared with the target all-method means for UK National External Quality Assessment Scheme samples (n = 31). The results for tyrosine showed a small positive mean bias (10 J.Lmol/L) when compared with an ion-exchange chromatographic method (n = 40). This method provides a quick and simple alternative to those using HPLC with pre-or post-column derivatization for monitoring patients with phenylketonuria. It is also less subject to interferences than HPLC methods using ultraviolet detection, particularly for the early eluting tyrosine peak.

A prospective and follow up study of renal tubular and glomerular function in 11 children receiving ifosfamide treatment was con-

Background Exercise‐based cardiac rehabilitation (CR) is known to reduce morbidity and mortality for patients with cardiac conditions. Sociodemographic disparities in accessing CR persist and could be related to the distance between where patients live and where CR facilities are located. Our objective is to determine the association between sociodemographic characteristics and geographic proximity to CR facilities. Methods and Results We identified actively operating CR facilities across Los Angeles County and used multivariable Poisson regression to examine the association between sociodemographic characteristics of residential proximity to the nearest CR facility. We also calculated the proportion of residents per area lacking geographic proximity to CR facilities across sociodemographic characteristics, from which we calculated prevalence ratios. We found that racial and ethnic minorities, compared with non‐Hispanic White individuals, more frequently live ≥5 miles from a CR facility. The greatest geographic disparity was seen for non‐Hispanic Black individuals, with a 2.73 (95% CI, 2.66–2.79) prevalence ratio of living at least 5 miles from a CR facility. Notably, the municipal region with the largest proportion of census tracts comprising mostly non‐White residents (those identifying as Hispanic or a race other than White), with median annual household income <$60 000, contained no CR facilities despite ranking among the county's highest in population density. Conclusions Racial, ethnic, and socioeconomic characteristics are significantly associated with lack of geographic proximity to a CR facility. Interventions targeting geographic as well as nongeographic factors may be needed to reduce disparities in access to exercise‐based CR programs. Such interventions could increase the potential of CR to benefit patients at high risk for developing adverse cardiovascular outcomes.

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