Factors influencing serial measurements of cardiac volumes by count-based methods: effects of elevated catecholamines, position, and exercise on technetium-99m-blood radioactivity concentration.

Most radionuclide methods for measuring cardiac volume require a determination of the blood radioactivity concentration. Thus, changes in blood radioactivity over time or during interventions might lead to spurious volume estimates unless blood radioactivity is serially measured. The effects of elevated epinephrine, posture and exercise on 99mTc-labeled blood radioactivity concentration were studied in 15 young (mean age = 28 yr) and 14 older (mean age = 68 yr) healthy males. An epinephrine infusion of 50 ng/kg/min resulted in a 4.1% +/- 1.0% increase in 99mTc-blood radioactivity (p less than or equal to 0.001) compared to baseline. Sitting increased blood radioactivity concentration by 12.3% +/- 3.0% (p less than 0.0002) compared to the supine position and peak supine bicycle exercise caused an 11.0% +/- 1.7% increase (p less than or equal to 0.0001) compared to supine rest. There was a significantly greater increase during peak supine exercise in the young compared to the older subjects (15.0% +/- 2.3% versus 6.3% +/- 2.0%, p less than or equal to 0.01). The mechanism of the increase in blood radioactivity concentration is uncertain, but presumably reflects the addition of hemoconcentrated red blood cells from the spleen and/or the loss of plasma volume. Failure to correct for the increased blood radioactivity concentration during exercise or pharmacological interventions will result in a significant error in serial measurements of cardiac volumes by methods requiring RBC radioactivity measurements.     

The effect of the referring dialysis center on renal transplant results

Between 1/1/76 and 12/31/86, 448 patients underwent transplantation (360 first transplants). Of these, 286 (230 first) were referred by 5 dialysis centers, each referring more than 40 recipients. The remainder were referred by a large number of centers. Using our 5 largest referral centers, we studied the effect of dialysis center on graft and patient survival. There was no difference between dialysis centers in patient survival. Actuarial graft survival differed significantly for all cadaver transplants and for first cadaver transplants (P less than 105). Significant differences persisted when groups were subdivided by type of immunosuppression (azathioprine vs cyclosporine). Demographic (age, race, cause of renal disease) and immunologic (transfusions, PRA, matching) differences between groups did not explain the difference in graft survival. We conclude that referring dialysis center is a previously unrecognized factor affecting transplant outcome. Further studies with larger numbers will be required to determine the underlying reasons for ths phenomenon.