Myocardial texture characterization in uremics by ultrasonic videodensitometric analysis: a review.

Many studies have demonstrated that left ventricular hypertrophy is the most frequent cardiac alteration in patients on chronic hemodialysis. Autopsy studies have shown that hypertrophic hearts of uremic patients have peculiar characteristics, namely deposition of calcium salts, intermyocytic fibrosis, sometimes amyloid. None of the parameters obtainable from conventional echocardiografic images provides information on myocardial tissue structure. Analysis of "texture" originated as analysis of images sent by satellites for military or agricultural purposes and subsequently was applied to medicine for studying various organs like mainly and widely heart. Videodensitometry is a method for in vivo analysis of myocardial structure using computer-assisted quantitative assessment of grey levels of conventional echocardiographic images. In dialysis patients quantitative ultrasonic analysis of myocardial texture appears a promising technique for an observer-independent assessment of myocardial tissue characteristics. Although it may be hampered by many potentially confounding factors, quantitative echocardiography may offer useful parameters for the follow-up of myocardial structural changes in chronic uremia. Further studies are ongoing to completely understand the prognostic significance of myocardial ultrasonic textural alterations in dialysis population.

Isothermic dialysis for hypotension-prone patients.

Standard hemodialysis (dialysate temperature >or=37 degrees C) induces an increase in body temperature capable of eliciting circulatory adjustments dictated by the maintenance of thermal homeostasis. These adjustments oppose, and can overcome, those elicited by the hypovolemia caused by the ultrafiltration process, and thus predispose patients to develop hypotensive crises during the treatment. Hemodynamic studies in hypotension-prone patients treated with standard hemodialysis showed that during the hypotensive crisis the peripheral vascular resistances decrease, while the stroke volume decreases proportionally more than the blood volume, suggesting cardiac underfilling due to blood volume redistribution. On the other hand, removal of the body heat surplus by cool dialysis helped the same patients to sustain their peripheral vasoconstriction and cardiac filling. To prevent the increase in body temperature, dialysate temperature should be regulated in such a way as to remove through the dialyzer the heat surplus accumulated in the body as a result of the ultrafiltration process. The amount of heat removal should be tailored to each patient because there are wide interindividual and intraindividual variations in baseline body temperature and ultrafiltration requirements. This can be accomplished by the use of a device that can adjust the dialysate temperature automatically in order to keep the body temperature of the patient unchanged (isothermic hemodialysis). Isothermic hemodialysis reduced from 50% to 25% the incidence of treatments complicated by episodes of symptomatic hypotension in a large randomized clinical trial involving 95 high-risk patients. The thermoregulated treatment results in better patient tolerance because the cold stress inherent in this procedure is lower than that inflicted by the use of a fixed low temperature as was done in the past. Overall, the available evidence supports the Gotch hypothesis that the increase in body temperature during hemodialysis is due to the ultrafiltration process eliciting peripheral vasoconstriction and heat accumulation in the body. Heat accumulation brings into play the thermal homeostatic mechanisms endangering cardiovascular tolerance to ultrafiltration.

The effects of control of thermal balance on vascular stability in hemodialysis patients: results of the European randomized clinical trial.

BACKGROUND: Many reports note that the use of cool dialysate has a protective effect on blood pressure during hemodialysis (HD) treatments. However, formal clinical trials in which dialysate temperature is tailored to the body temperature of appropriately selected hypotension-prone patients are lacking. METHODS: We investigated the effect of thermal control of dialysate on hemodynamic stability in hypotension-prone patients selected from 27 centers in nine European countries. Patients were eligible for the study if they had symptomatic hypotensive episodes in 25% or more of their HD sessions, assessed during a prospective screening phase over 1 month. The study is designed as a randomized crossover trial with two phases and two treatment arms, each phase lasting 4 weeks. We used a device allowing the regulation of thermal balance (Blood Temperature Monitor; Fresenius Medical Care, Bad Homberg, Germany), by which we compared a procedure aimed at preventing any transfer of thermal energy between dialysate and extracorporeal blood (thermoneutral dialysis) with a procedure aimed at keeping body temperature unchanged (isothermic dialysis). RESULTS: One hundred sixteen HD patients were enrolled, and 95 patients completed the study. During thermoneutral dialysis (energy flow rate: DeltaE = -0.22 +/- 0.29 kJ/kg x h), 6 of 12 treatments (median) were complicated by hypotension, whereas during isothermic dialysis (energy flow rate: DeltaE = -0.90 +/- 0.35 kJ/kg x h), the median decreased to 3 of 12 treatments (P < 0.001). Systolic and diastolic blood pressures and heart rate were more stable during the latter procedure. Isothermic dialysis was well tolerated by patients. CONCLUSION: Results show that active control of body temperature can significantly improve intradialytic tolerance in hypotension-prone patients.