| Approximately 50% to 90% of patients on maintenance hemodialysis (MHD) had hypertension, with only few of them achieved satisfactory blood pressure (BP) control. Hypertension in MHD patients may enhance the cardiac afterload, which results in left ventricular hypertrophy and myocardial remodeling, and thus greatly increase the risk of cardiovascular events. Moreover, it may also expose the patients to higher risk of stroke. Similarly, renal damage could be further exacerbated and remnant kidney function subsequently compromised. As such, there might be an elevated admission and mortality rate in patients on MHD.The most common type of hypertension in patients on MHD is that of increased volume, usually manifested as higher pre-dialysis BP which returns to normal after ultrafiltration and relief of water-sodium retention and rises again before next dialysis session. Another type of hypertension is unaccompanied by increased volume, frequently exhibiting as refractory one that, by ultrafiltration, could not be relieved and might contrarily elevate or remain in an elevated state. It may be poorly responsive to the joint use of multiple antihypertensive agents. Currently there is no universally accepted definition of the intradialytic hypertension and the nomenclature is thereby less clear: it is referred as hypertension in hemodialysis patients, hemodialysis-associated hypertension, interdialytic hypertension and intradialytic hypertension. Unanimous understanding of its mechanism and therapy is not available.The present study aimed to explore the mechanism of intradialytic hypertension as well as new approaches for its prevention and management, by investigating the effects of single hemodialysis on cardiovascular function in the pertinent patients and the variation of vasoactive substances. Part I: Effects of single hemodialysis on the cardiovascular function in patients with intradialytic hypertensionObjective: Role of varied cardiovascular function in the onset of intradialytic hypertension was studied, with regard to providing theoretical basis for its prevention and management. For this purpose, we examined the pre- and post-dialysis heart rate (HR), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), parameters functionally reflecting the cardiovascular system.Methods: 18 patients, who underwent MHD for more than 3 months in the blood purification center of the 4th hospital of HeBei medical university, were registered. They were in consistent with the diagnosis criteria of K/DOQI (kidney Disease Outcome Quality Initiative) for chronic kidney disease stage five. The hemodialysis regimen was: 2-3 sessions weekly with 4-4.5 hours each, CT-190 dialyzer, blood flow rate between 200-280 ml/min, dry weight (as estimated by clinical and bioelectrical impedance assessment) achieved and Kt/V higher than 1.2 reached after each session. The patients were then subdivided into 2 groups: 10 cases of intradialytic hypertension (MAP rise≥15 mmHg at the late stage or the end of the hemodialysis); 8 cases of stable BP during hemodialysis (MAP change < 15 mmHg at the late stage or the end of the hemodialysis). All the patients were allowed to rest for 10 minutes before hemodialysis and heart rate and BP of each individual were taken at pre-dialysis, 1, 2, 3 hour after the initiation of, and the end of dialysis. The BP was measured at the brachial artery on the arm without fistula. SV and CO were determined by Doppler ultrasonic sound at pre- and post-dialysis, SVR was defined as SVR=MAP/CO, and variation rate (X) of SVR and CO were calculated as X=(pre-dialysis value– post-dialysis value)/pre-dialysis value. Statistical analysis was performed by using the SPSS 16.0 package. Numerous data were given as means±SD. Inter-group difference was tested by independent t-test, pre-and post-dialysis values were compared by paired t-test. P<0.05 was considered statistically significant.Results:1 There was no inter-group difference in the pre-dialysis values of age, vintage of dialysis, dry weight and height (P>0.05). Neither were those of serum albumin, hemoglobin, calcium and potassium. Pre-dialysis values of the MAP, HR, SV, CO and SVR were statistically comparable between the groups.2 In the group with stable BP, post-dialysis values of SV, HR and MAP were not significantly different from those of pre-dialysis ones (P>0.05). CO and SVR showed remarkable decrease and increase, respectively, after the hemodialysis (P<0.05). In the group with intradialytic hypertension, only the SVR increased significantly after hemodialysis (P<0.05) and the rest of variables were otherwise unchanged.3 In the group with intradialytic hypertension and with regard to the variation rate, SVR and MAP were significantly higher than (P<0.05), CO was significantly lower than (P<0.05), SV and HR were similar to (P>0.05), the corresponding values of the group with stable BP.Summary:Single hemodialysis session could increase the SVR in patients achieving post-dialysis dry weight. However, patients with intradialytic hypertension had greater increase in SVR and less decrease in CO against those with stable BP, indicating single hemodialysis may affect intradialytic BP by influencing SVR and CO.Part II: Effects of single hemodialysis on vasoactive substances in patients with intradialytic hypertensionObjective: our purpose was to explore the role of vasoactive substances in the onset of intradialytic hypertension and, by doing so, provide theoretical basis for the prevention and therapy. And for this purpose we examined the pre- and post-dialysis values of serum adrenalin (Ad), noradrenalin (NAd), plasma renin activity (PRA), endothelin-1 (ET-1) and nitric oxide (NO) in the pertinent patients.Methods: Case selection and division were identical to those of part I, in which blood samples were taken before and after the hemodialysis session. Ad, NAd, PRA, ET-1 were assayed by the ELISA method, NO was determined by the nitric acid reductase method. Statistical analysis was performed by using the SPSS 16 package. Numerous data were given as means±SD. Inter-group difference was tested by independent t-test, pre-and post-dialysis values were compared by paired t-test. P<0.05 was considered statistically significant.Results:1 There was no inter-group difference in the pre-dialysis values of Ad, NAd, PRA, ET-1, NO, ET-1/NO (P>0.05).2 Post-dialysis values of Ad, NAd and PRA were comparable to those of pre-dialysis in both groups (P>0.05).3 In the group with intradialytic hypertension, post-dialysis values of the NO was significantly lower, whereas ET-1 and ET-1/NO were higher than those of the pre-dialysis (P<0.05).4 In the group with stable BP, post-dialysis values of the NO was significantly lower (P<0.05), whereas ET-1/NO was higher than (P<0.05)and ET-1 was similar to, those of the pre-dialysis (P>0.05).5 In the group with intradialytic hypertension and concering the variation rate, that of NO did not differ significantly (P>0.05), ET-1 and ET-1/NO showed markedly elevation (P<0.05).Summary:1 The lack of difference between the pre- and post-dialysis values of Ad, NAd and PRA in both groups indicated that these substances were not subject to the influence of single hemodialysis.2 In both groups, post-dialysis values of NO was significantly lower, ET-1/NO was significantly higher, than those of the pre-dialysis. The variation rate of ET-1/NO was significantly increased in accompany with a rise in the post-dialysis ET-1, indicating the participation of these two variables in the pathogenesis of intradialytic hypertension. Conclusion:1 Single hemodialysis can affect the blood pressure of the patients who are going through Hemodialysis by changing cardiac output and SVR.2 Single hemodialysis can lead to the increasing of SVR by changing ET-1,NO.3 Endothelial dysfunction leads to the change of ET-1 /No, which can make the increase of SVR. It is probablly the main mechanism of the pathogenesis of intradialytic hypertension.
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