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J Markham

Publications and source records attributed to J Markham.

67 records · Page 4Linked to original sources
PubMed1975

Metabolism in immunoreactive parathyroid hormone in the dog. The role of the kidney and the effects of chronic renal disease.

The role of the kidney in the metabolism of parathyroid hormone (PTH) was examined in the dog. Studies were performed in awake normal and uremic dogs after administration of bovine parathyroid hormone (b-PTH) or synthetic amino terminal tetratricontapeptide of b-PTH (syn b-PTH 1-34). The renal clearance of immunoreactive PTH was determined from the product of renal plasma flow and the percent extraction of PTH immunoreactivity by the kidney. Blood levels of circulating immunoreactive PTH were determined by radioimmunoassay. The normal dog kidney extracted 20 plus or minus 1% of the immunoreactive b-PTH delivered to it, and renal clearance (RC) of immunoreactivity was 60 ml/min. When RC was compared to an estimate of total metabolic clearance (MCR) of immunoreactivity, it accounted for 61% of the total. Both MCR and RC were markedly decreased in dogs with chronic renal disease. However, the percent extraction of immunoreactive PTH was unchanged in chronic renal disease, and the observed decrease in RC was due to changes in renal plasma flow. The largest portion of the reduction in total MCR was accounted for by the decrease in RC, and there was no compensation for the decrease in RC by extrarenal sites of PTH metabolism.

Animals↗
PubMed1975

The measurement of regional ventilation during tidal breathing: a comparison of two methods in healthy subjects, and patients with chronic obstructive lung disease.

Regional ventilation has been measured in 17 healthy volunteers, and 24 patients with chronic obstructive lung disease during tidal breathing using 133-Xe. The wash-in and wash-out of 133-Xe were recorded by a gamma camera interfaced to a small digital computer. Regional ventilation was calculated as the distribution of tidal volume per unit lung volume-a measure of relative ventilation--and from the wash-out curves as the fractional exchange of air per second. Determination of the regional fractional exchange of air showed a significant difference between the patients with chronic obstructive lung disease and normal subjects for all regions. The distribution of tidal volume per unit lung volume did not effect such a clear separation. Significant correlations were found between the whole-lung fractional exchange of air in the patients with chronic obstructive lung disease and their FEV1 r equal 0-70, MMFR r equal 0-70, FVC r equal 0-56 and FEV1/FVC r equal 0-57. It is suggested that measurement of regional ventilation as the fractional exchange of air is more realistic than methods that determine relative ventilation or only make use of the early part of the wash-out 133-Xe.

Adult↗
PubMed1974

[Community care].

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Community Health Services↗
PubMedDate not supplied

Quantitation of myocardial blood flow with H2 15O and positron emission tomography: assessment and error analysis of a mathematical approach.

Quantitation of regional myocardial blood flow (MBF) in absolute terms with positron emission tomography (PET) has been difficult to achieve in part because of errors induced by the relatively low spatial resolution of current tomographic instruments. We previously demonstrated that MBF could be accurately measured over a wide range of flows after intravenous administration of H2 15O when the arterial input function and myocardial radiotracer content were measured directly. To extend this quantitative approach for noninvasive estimates of MBF with PET. We recently developed and implemented a novel mathematical approach whereby partial volume and spillover effects were estimated along with flow within the operational one-compartment flow equation. Noninvasive estimates of flow correlated closely with flow measured directly with radiolabeled microspheres. In the present study, with the use of a commercially available cardiac phantom, we assessed our ability to obtain true time-activity curves from observed PET data contaminated by partial volume and spillover effects. Computer simulations demonstrated that the approach developed is relatively insensitive to most potential sources of error, but is sensitive to timing discrepancies between the arterial input function and the tissue time-activity curve. Implementation of this approach provides accurate quantitation of regional MBF in absolute terms and should be useful in noninvasive evaluation of the efficacy of treatments designed to enhance nutritional perfusion in human subjects.

Coronary Circulation↗