A mathematical model for the prediction of solute kinetics, osmolarity and fluid volume changes during hemodiafiltration with on-line regeneration of ultrafiltrate (HFR).

Hemodiafiltration with on-line regeneration of ultrafiltrate (HFR) is a technique indicated for the treatment of dialysis patients affected by inflammatory syndrome and malnutrition. In the present work, a mathematical model, which describes intradialytic fluid and solute kinetics during standard diffusive dialysis, has been adapted to analyze solutes and fluid dynamics during HFR. The model is an improved version of our previous ones, and represents a good compromise between simplicity and reliability. It considers the intradialytic kinetics of sodium, potassium and urea, and two body fluid compartments: intracellular and extracellular. Moreover, the model includes simple equations to predict the intradialytic time pattern of osmolarity. The model has been experimentally validated by using 9 HFR sessions on 9 patients (one per each patient), comparing the time course of plasma solutes and osmolarity measured every 30 minutes during HFR, with those predicted by the model. Predictions are performed a priori, i.e., without any parameter adjustment, but just starting from knowledge of a few quantities (plasma sodium, potassium, urea, osmolarity and body weight) at the beginning of the session. The average deviations between model and real data (sodium: 1.9 mEq/L; potassium: 0.32 mEq/L; urea: 1.04 mmol/L; osmolarity: 5.02 mosm/L) are of the same order as measurement errors and similar to those obtained using our previous models in standard and profiled hemodialysis. Moreover, the prediction on sodium concentration only scarcely worsens (from 1.9 to 2.02 mEq/L) if default values are used for the initial value of other solutes in blood (i.e., if the algorithm uses only initial body weight and initial sodium concentration in plasma). The results confirm the good predictive capacity of the model in HFR, and suggest its possible innovative use to optimize sodium balance in HFR, from knowledge of only the sodium concentration in the ultrafiltrate.

Reliability of power output during intermittent high-intensity cycling.

PURPOSE: We determined the number of trials on consecutive days required to establish high reliability of an intermittent high-intensity cycling test in subjects unfamiliar with multiple-sprint exercise. We also examined the extent to which this reliability could be maintained for 6 d. METHODS: Five untrained men performed a multiple-sprint test (10 x 7 s, with each sprint separated by 30 s) on each of four consecutive days (days 1-4), then rested for 6 d, and finally performed two additional tests on consecutive days (days 11 and 12). For statistical comparisons (analyses of variance), mean power outputs during sprints 8, 9, and 10 (MP8-10) on each test day were calculated for each of the 4th, 5th, and 6th seconds of the sprints, i.e., MP8-10(4th), MP8-10(5th), and MP8-10(6th). Peak power during each sprint was also examined. RESULTS: For days 3 and 4, values for MP8-10(4th), MP8-10(5th), and MP8-10(6th) were greater than on day 1 (P < 0.05). MP8-10(6th) on day 2 was also greater than on day 1 (P < 0.05). There were no differences in MP8-10 among days 2, 3, 4, 11, and 12. Also, peak power on day 1 was lower (P < 0.05) than peak power for all other days, which were not different from one another. The coefficients of variation (CV) for MP8-10 on day 3 versus day 4 were 3.3%, 2.5%, and 2.9% for MP8-10(4th), MP8-10(5th), and MP8-10(6th), respectively. The CV for MP8-10(4th), MP8-10(5th), and MP8-10(6th) on days 4, 11, and 12 ranged from 2.1 to 3.9%, with an overall mean of 3.1%. The greatest CV for MP8-10 was 5.2% for MP8-10(6th) on days 2 versus 3 and 2 versus 4. The mean CV for peak power for all pairwise combinations of days 4, 11, and 12 was 2.8%. CONCLUSIONS: In conclusion, satisfactory reliability of intermittent cycling tests is achieved after two familiarization sessions identical to the tests, and that reliability can be maintained for 6 d.