Haemodialysis-induced pulmonary granulocyte sequestration in rabbits is organ specific

Intravital microscopic observation of the microvasculature during hemodialysis in healthy rats

Hemodialysis (HD) provides life-saving treatment for kidney failure. Patient mortality is extremely high, with cardiovascular disease (CVD) being the leading cause of death. This results from both a high underlying burden of cardiovascular disease, as well as additional physiological stress from the HD procedure itself. Clinical observations indicate that HD is associated with microvascular dysfunction (MD), underlining the need for a fundamental pathophysiological assessment of the microcirculatory consequences of HD. We therefore successfully developed an experimental small animal model, that allows for a simultaneous real-time assessment of the microvasculature. Using in-house built ultra-low surface area dialyzers and miniaturized extracorporeal circuit, we successfully dialyzed male Wistar Kyoto rats and combined this with a simultaneous intravital microscopic observation of the EDL microvasculature. Our results show that even in healthy animals, a euvolemic HD procedure can induce a significant systemic hemodynamic disturbance and induce disruption of microvascular perfusion (as evidence by a reduction in the proportion of the observed microcirculation receiving blood flow). This study, using a new small animal hemodialysis model, has allowed direct demonstration that microvascular blood flow in tissue in skeletal muscle is acutely reduced during HD, potentially in concert with other microvascular beds. It shows that preclinical small animal models can be used to further investigate HD-induced ischemic organ injury and allow rapid throughput of putative interventions directed at reducing HD-induced multi-organ ischemic injury.

Effect of isolated ultrafiltration and isovolemic dialysis on myocardial perfusion and left ventricular function assessed with 13N-NH3 positron emission tomography and echocardiography

Hemodialysis is associated with a fall in myocardial perfusion and may induce regional left ventricular (LV) systolic dysfunction. The pathophysiology of this entity is incompletely understood, and the contribution of ultrafiltration and diffusive dialysis has not been studied. We investigated the effect of isolated ultrafiltration and isovolemic dialysis on myocardial perfusion and LV function. Eight patients (7 male, aged 55 ± 18 yr) underwent 60 min of isolated ultrafiltration and 60 min of isovolemic dialysis in randomized order. Myocardial perfusion was assessed by ¹³N-NH₃ positron emission tomography before and at the end of treatment. LV systolic function was assessed by echocardiography. Regional LV systolic dysfunction was defined as an increase in wall motion score in ≥2 segments. Isolated ultrafiltration (ultrafiltration rate 13.6 ± 3.9 ml·kg^-1·h^-1) induced hypovolemia, whereas isovolemic dialysis did not (blood volume change -6.4 ± 2.2 vs. +1.3 ± 3.6%). Courses of blood pressure, heart rate, and tympanic temperature were comparable for both treatments. Global and regional myocardial perfusion did not change significantly during either isolated ultrafiltration or isovolemic dialysis and did not differ between treatments. LV ejection fraction and the wall motion score index did not change significantly during either treatment. Regional LV systolic dysfunction developed in one patient during isolated ultrafiltration and in three patients during isovolemic dialysis. In conclusion, global and regional myocardial perfusion was not compromised by 60 min of isolated ultrafiltration or isovolemic dialysis. Regional LV systolic dysfunction developed during isolated ultrafiltration and isovolemic dialysis, suggesting that, besides hypovolemia, dialysis-associated factors may be involved in the pathogenesis of hemodialysis-induced regional LV dysfunction.

Exercise and leukocyte interchange among central circulation, lung, spleen, and muscle

Circulating leukocytes increase rapidly with exercise then quickly decrease when the exercise ends. We tested whether exercise acutely led to bidirectional interchange of leukocytes between the circulation and the lung, spleen, and active skeletal muscle. To accomplish this it was necessary to label a large number of immune cells (granulocytes, monocytes, and lymphocytes) in a way that resulted in minimal perturbation of cell function. Rats were injected intravenously with a single bolus of carboxyfluorescein diacetate succinamidyl ester (CFSE) dye which is rapidly and irreversibly taken up by circulating cells. The time course of the disappearance of labeled cells and their reappearance in the circulation following exercise was determined via flow cytometry. The majority of circulating leukocytes were labeled at 4h. post-injection and this proportion slowly declined out to 120 h. At both 24 and 120 h, running resulted in an increase in the proportion of labeled leukocytes in the circulation. Analysis of the skeletal muscle, spleen and lung indicated that labeled leukocytes had accumulated in those tissues and were mobilized to the circulation in response to exercise. This indicates that there is an ongoing exchange of leukocytes between the circulation and tissues and that exercise can stimulate their redistribution. Exchange was slower with muscle than with spleen and lung, but in all cases, influenced by exercise. Exercise bouts redistribute leukocytes between the circulation and the lung, spleen and muscle. The modulatory effects of exercise on the immune system may be regulated in part by the systemic redistribution of immune cells.

Acute effects of intermittent hemodialysis and sustained low-efficiency hemodialysis (SLED) on the pulmonary function of patients under mechanical ventilation

The effects of hemodialysis (HD) on pulmonary function are still controversial. The objective of this study was to evaluate the effect of intermittent hemodialysis (IHD) and sustained low-efficiency dialysis (SLED) on the respiratory mechanics of ICU patients under invasive mechanical ventilation. We prospectively studied 31 patients. Laboratory and respiratory evaluation (static and dynamic compliance and resistance) was performed pre- and post-HD. Forty HD sessions were studied and grouped in: SLED (n = 17; Qa = 200-250 mL/min, Qd = 300 mL/min) and IHD (n = 23; Qa = 250-300 mL/min, Qd = 500 mL/min). There was no difference between the groups according to age, gender, comorbidities, APACHE II, and cause of mechanical ventilation, but pre-HD, patients in the IHD group had higher levels of plasma creatinine (5.4 +/- 2.0 vs. 4.2 +/- 1.3 mg/dL, p = 0.048) and platelets (286 +/- 186 vs. 174 +/- 95 10(3)/mm(2), p = 0.032) and lower arterial pH (7.37 +/- 0.07 vs. 7.42 +/- 0.05, p = 0.02). The efficiency of the treatment was similar (p > 0.05) with both types of HD regarding fluid removal, urea reduction rate, and decrease in plasma creatinine. Pre-HD, the ventilatory conditions of both groups were similar (p > 0.05) except for pressure support ventilation and airflow resistance. There were no changes (pre- versus post-HD p > 0.05) induced either by IHD or SLED in the ratio PaO(2)/FiO(2) or in any measured ventilatory parameter. In conclusion, neither IHD nor SLED modifies the pulmonary function of patients under mechanical ventilation.