The effect of hydration on the dose to the urinary bladder wall during technetium-99m diethylene triamine penta-acetic acid renography.

A spherical bladder dynamic model for the estimates of the radiation dose to the bladder walls from intravenously injected radionuclides was implemented to investigate in theory the effect of hydration on the reduction of the bladder dose in technetium-99m diethylene triamine penta-acetic acid (99mTc) DTPA renography. This model gives due consideration to the variation with time of the urine flow rate to the bladder, following a known fluid load. According to the model, the estimated dose depends on the renal function, the fluid load, the time elapsed from the fluid load to the i.v. DTPA injection, the micturition volume and the residual urine volume. Experimental data concerning the values of these parameters for normal individuals were obtained from the literature. Calculations cover the time period from i.v. injection up to the time of the ninth postinjection void. Results show that the patient's condition of hydration is critical for the radiation protection of the bladder. It is shown that optimum combinations of the values of the parameters involved in the calculations exist, which minimize the radiation dose. On the basis of these results, a general protocol is proposed, referring to the hydration conditions under which the renal dynamic study may be normally carried out, with a minimal absorbed dose to the bladder walls (less than 0.045 mGy/MBq).

The effect of blood transfusion on 51Cr-red blood cells surface-counting data in homozygous beta-thalassaemia.

The effect of blood transfusion on 51Cr-red blood cells surface-counting patterns was studied in 22 patients with homozygous beta-thalassaemia being transfused during erythrocyte survival study. Surface-counting patterns of 15 thalassaemics who had not been submitted to blood transfusion during the erythrocyte survival study were served as controls. In 17 of the transfused patients (group A), spleen excess counts (SEC) appeared decreasing after blood transfusion, reaching a minimum (about 50% of the initial value) 3-4 days later, and increasing thereafter to reach again their initial value on 8th to 10th posttransfusion day. The SEC pattern of the remaining 5 transfused patients (group B) presented a continuously ascending curve. Corresponding changes were observed in excess liver counts and heart counts patterns. As a result of these changes spleen/liver ratio (S/L) was found significantly affected by blood transfusion in the majority of thalassaemic patients which were transfused during the erythrocyte survival study. Furthermore, the mean age of group A patients (12.1 +/- 5.5 years) has been found to be significantly lower than that of group B (21.8 +/- 3.3 years). On the contrary, in the control group the SEC pattern appeared permanently increasing and the S/L was found unaltered during the whole duration of the erythrocyte survival study. In conclusion, as far as the surface-counting data represent indexes for splenectomy in thalassaemic patients, the results of this study signify that the influence of blood transfusion on these has to be taken into account.

Kinetics of heat-damaged homologous erythrocytes. A five-compartmental analysis.

A new theoretical five-compartmental model (5CM) was developed for analysis of the clearance of heat-damaged erythroctes (HDE) labelled with chromium 51. Besides the HDE-spleen interaction, this new model also takes into account the interaction between extrasplenic reticuloendothelial (RES) sites and HDE, i.e. the hepatic clearance of fragmented erythrocytes (FE). Accordingly, HDE clearance curves are analysed into three exponential components, the fastest of which describes the RES-FE interaction, whereas the others describe the splenic clearance of spherocytes. Therefore, an estimation of the effective liver blood flow for HDE (ELBF) was achieved, along with a series of parameters describing splenic function. The 5CM proved to be more efficient than a previously proposed three-compartmental model (3CM) in the mathematical description of HDE clearance. Comparison was made by applying both models to 37 experimental curves obtained from 20 patients with congenital hemolytic anemias. The values for the splenic function parameters calculated by 5CM analysis and the strong correlations observed among them offer evidence that this model provides an adequate approximation to the real conditions under which HDE clearance takes place. Furthermore, a detailed quantitative analysis of the pooling of spherocytes within the spleen was attempted in this work, and this phenomenon was found to compete with splenic irreversible spherocyte trapping. The ELBF proved to be closely correlated with the hemodynamic splenic parameters, following first-order kinetics, as do low-dose colloids.

Function of reticuloendothelial system in splenectomised thalassemics.

The activity of reticuloendothelial system (RES) was estimated in 19 patients with beta-thalassemia major, 20 +/- 4 years old, who had undergone successful splenectomy 6 +/- 5 years previously. The kinetics of 125I denatured human serum albumin in low and large doses was applied for this purpose and the parameters derived (effective RES blood flow-ERBF- and maximum phagocytic capacity-PCmax) were compared to those of nonsplenectomized thalassemics, detected in previous works, as well as to those of 13 healthy controls. In splenectomised thalassemics both parameters of RES activity were found significantly lower than those of nonsplenectomized patients (p less than 0.001). Compared to those of healthy controls, PCmax of splenectomised thalassemics was found not to be significantly different, while ERBF was significantly lower (p less than 0.001). No correlation was noted between the above parameters of RES function and the age of the patients, the age at which splenectomy was performed, the time lapsed since the operation, the amount of blood transfused to the patients after splenectomy or their serum ferritin levels. A pilot study performed in 6 out of the 19 splenectomised patients did not reveal any effect of blood transfusion on RES function parameters, by contrast to observations in nonsplenectomized thalassemics. The results of this study suggest that in splenectomised thalassemics the remaining RES reacts to the continuing hemolytic stimulus in a manner different than that of splenic RES of nonsplenectomized patients and account for, at least in part, the predisposition of the former group to infections.

Assessment of splenic and RES function of patients with thalassemia major long after partial splenic embolization: in vivo clearance study.

The activity of the remaining reticuloendothelial system (RES) and the function of the splenic remnants was estimated in 5 thalassemic patients who had undergone successful partial splenic embolization (PSE) 6 yr previously. The kinetics of 125I-heat-denatured human albumin as well as that of 51Cr-heat-damaged homologous red blood cells were applied for this purpose and the parameters derived were compared to those of nonsplenectomized as well as splenectomized thalassemics with the following results: (a) The parameters of splenic function in embolized thalassemics were found to be within the limits observed in nonsplenectomized patients. (b) Their maximum phagocytic capacity was significantly lower, not only than that found in nonsplenectomized, but also than in thalassemic patients splenectomized at about the same time. It is concluded that, 6 yr after PSE has been performed, a reorientation of the altered circulatory dynamics has taken place in the splenic remnants allowing previously blockaded areas to gain normal function. It therefore seems that, despite the continuing hemolytic stimulus, RES hyperplasia is prevented, resulting in the stable, low-level transfusion requirements that have been observed in embolized thalassemics.

RES phagocytosis in children with homozygous beta-thalassemia in relation to blood transfusion.

In order to investigate the effect of blood transfusion on the RE cell function in thalassemia major, 14 children with homozygous beta thalassemia were studied prior to and 7 to 10 d following blood transfusion, when, according to previous studies, spleen reaches its minimum size. The denatured human albumin (DHA) low and large dose clearance techniques were used in order to estimate the maximum RES phagocytic capacity. It is shown that, despite the confirmed post-transfusion high hepatosplenic circulation, the RE cell phagocytic capacity is not significantly affected. Furthermore the RES phagocytic capacity of beta-thalassemics is shown to be significantly higher than that of normal controls, and this can probably be attributed to the RES hyperplasia accompanying the disease.

Kinetics of heat-damaged homologous red blood cells in patients with homozygous beta-thalassemia in relation to blood transfusion.

The kinetics of heat-damaged homologous red blood cells (HDE) was studied prior to and 7-10 d following blood transfusion in 14 patients with homozygous beta-thalassemia. On the basis of our results, beta-thalassemic patients were classified into two distinct groups. In the first group the pretransfusion HDE extraction efficiency of the spleen was significantly lower than that of the second group and it increased dramatically following blood transfusion. On the contrary, the relatively higher pretransfusion HDE extraction efficiency of the patients of the second group showed a significant decrease after blood transfusion. These differences between the two groups of beta-thalassemics might be attributed to the different qualitative as well as quantitative alterations of the splenic vascular bed occurring in these patients during the course of their disease. Furthermore, there was convincing evidence that part of the HDE mixture was extracted by RES sites outside the spleen, a function which is also affected by blood transfusion.

Fitting of radioactivity data to exponential functions by weighted least squares analysis.

The weighted least squares analysis ( WLS ) was compared with the commonly used least squares analysis in the fitting of radioactivity data to an exponential equation. The results show that the two methods present the same accuracy in estimating the parameters of exponential functions, while the WLS analysis offers a much higher reliability, permitting a considerable shortening of the sample counting time.

Effective RES blood flow changes in children with homozygous beta-thalassemia in relation to blood transfusion.

Denatured radioiodinated human serum albumin (DHA) clearance studies at a dose of 1 mg/kg body wt., were carried out in 16 thalassemic children, prior to and 7-10 days following blood transfusion, to investigate changes of the effective RES blood flow which might accompany the posttransfusion spleen size diminution. A statistically significant increase (P less than 0.001) of the DHA plasma clearance rate was observed 7-10 days following blood transfusion denoting an increase of the blood flow to the effective RES while at the same time the spleen diminished in size. It is suggested that changes in the effective RES blood flow in these patients are directly related to changes in the intrasplenic circulatory capacity.

Mathematical analysis of 51Cr-labelled red cell survival curves in congenital haemolytic anaemias.

The parameters of 51Cr labelled red cell survival curves were calculated in 33 patients with homozygous beta-thalassaemia, 8 with sickle-cell anaemia and 3 with s -- beta-thalassaemia, using a non-linear weighted least squares analysis computer program. In thalassaemic children the calculated parameters denote that the shortening of the mean cell life is due to early senescence alone, while there is some evidence that in thalassemic adults additional extracellular destruction mechanisms participate as well. Red cell survival curves from patients with sickle-cell anaemia and s -- beta-thalassaemia resemble each other, while their parameters indicate an initial rapid loss of radioactivity, early senescence and the presence of extracellular red cell destruction factors.

Colloid clearance rate changes in children with homozygous-beta-thalassemia in relation to blood transfusion.

The plasma clearance rate of heat denatured human serum albumin (DHAI-125, 5 mg/kg body weight) was studied in 20 children with homozygous-beta-thalassemia before and 7--10 days after blood transfusion. A significant increase of the DHAI-125 clearance rate (P less than 0.02) was found 7--10 days after blood transfusion while the spleen presented its minimum size. This finding may be relevant to the improved intrasplenic blood circulation after blood transfusion due to the release of the blood trapped within the spleen.