Association of Intradialytic Hypertension with Left Ventricular Mass in Hypertensive Hemodialysis Patients Enrolled in the Blood Pressure in Dialysis (BID) Study

BACKGROUND/AIMS

Intradialytic hypertension (IDH), or paradoxical rise in blood pressure (BP) during hemodialysis (HD) is associated with increased morbidity and mortality. The association between IDH and increased left ventricular mass (LVM), a well-known risk factor for adverse cardiovascular outcomes in HD patients, has not been studied. The aim of our study is to evaluate the cross-sectional association of intradialytic change in BP with cardiac structure and function measured by cardiac MRI in hypertensive HD patients enrolled in the multi-center Blood Pressure in Dialysis (BID) clinical trial.

METHODS

Participants in the BID study were categorized into 3 groups based on average change (Δ) in systolic blood pressure (SBP) (post-HD SBP minus pre-HD SBP) during HD over a 1 month period: group 1 - patients with an increase in SBP ≥ 10mm Hg during HD (IDH); group 2 -patients with SBP decrease of greater ≥10mm Hg during HD; group 3 - patients with SBP increase or decrease by < 10mm Hg during HD. LVM index (LVMI) was measured using cardiac MRI, which were centrally read. Baseline characteristics were compared in the 3 groups and multivariable regression models were fitted for the adjusted association of IDH with LVMI.

RESULTS

Among the 80 participants, 7 (8.8%) had IDH and had average Δ SBP 17.0 ± 10.1 mmHg during HD. Patients with IDH were less likely to be diabetic, had lower pre-dialysis SBP and lower percent interdialytic weight gain as compared to the other 2 groups (p=0.02, p< 0.001 and p=0.02 respectively). In multivariable regression analyses, IDH was significantly associated with LVMI (adjusted mean difference relative to SBP decreased group [95% confidence interval (CI)] = 12.5 [3.6, 21.5], p=0.01) after adjusting for age, sex, diabetes, IDWG%, pre-HD SBP and beta blocker use. Every 1 mm rise in ΔSBP during HD was associated with 0.2 g/m2 increase in LVMI in adjusted models (p=0.04).

CONCLUSION

IDH is independently associated with higher LVMI in hypertensive HD patients and may contribute to increased cardiovascular events.

BP Control and Long-Term Risk of ESRD and Mortality

We recently showed an association between strict BP control and lower mortality risk during two decades of follow-up of prior participants in the Modification of Diet in Renal Disease (MDRD) trial. Here, we determined the risk of ESRD and mortality during extended follow-up of the African American Study of Kidney Disease and Hypertension (AASK) trial. We linked 1067 former AASK participants with CKD previously randomized to strict or usual BP control (mean arterial pressure ≤92 mmHg or 102-107 mmHg, respectively) to the US Renal Data System and Social Security Death Index; 397 patients had ESRD and 475 deaths occurred during a median follow-up of 14.4 years from 1995 to 2012. Compared with the usual BP arm, the strict BP arm had unadjusted and adjusted relative risks of ESRD of 0.92 (95% confidence interval [95% CI], 0.75 to 1.12) and 0.95 (95% CI, 0.78 to 1.16; P=0.64), respectively, and unadjusted and adjusted relative risks of death of 0.92 (95% CI, 0.77 to 1.10) and 0.81 (95% CI, 0.68 to 0.98; P=0.03), respectively. In meta-analyses of individual-level data from the MDRD and the AASK trials, unadjusted relative risk of ESRD was 0.88 (95% CI, 0.78 to 1.00) and unadjusted relative risk of death was 0.87 (95% CI, 0.76 to 0.99) for strict versus usual BP arms. Our findings suggest that, during long-term follow-up, strict BP control does not delay the onset of ESRD but may reduce the relative risk of death in CKD.

Developing a Screening Algorithm for Type II Diabetes Mellitus in the Resource-Limited Setting of Rural Tanzania

BACKGROUND

Noncommunicable diseases are on pace to outnumber infectious disease as the leading cause of death in sub-Saharan Africa, yet many questions remain unanswered with concern toward effective methods of screening for type II diabetes mellitus (DM) in this resource-limited setting. We aim to design a screening algorithm for type II DM that optimizes sensitivity and specificity of identifying individuals with undiagnosed DM, as well as affordability to health systems and individuals.

METHODS

Baseline demographic and clinical data, including hemoglobin A1c (HbA1c), were collected from 713 participants using probability sampling of the general population. We used these data, along with model parameters obtained from the literature, to mathematically model 8 purposed DM screening algorithms, while optimizing the sensitivity and specificity using Monte Carlo and Latin Hypercube simulation.

RESULTS

An algorithm that combines risk assessment and measurement of fasting blood glucose was found to be superior for the most resource-limited settings (sensitivity 68%, sensitivity 99% and cost per patient having DM identified as $2.94). Incorporating HbA1c testing improves the sensitivity to 75.62%, but raises the cost per DM case identified to $6.04. The preferred algorithms are heavily biased to diagnose those with more severe cases of DM.

CONCLUSIONS

Using basic risk assessment tools and fasting blood sugar testing in lieu of HbA1c testing in resource-limited settings could allow for significantly more feasible DM screening programs with reasonable sensitivity and specificity.

Abstract P632: The Blood Pressure in Dialysis (BID) Pilot Study

Background: The optimal blood pressure (BP) target for hypertensive hemodialysis (HD) patients is unknown. Current KDOQI guidelines have been extrapolated from data in the general population. The BID pilot, funded by NIDDK and DCI, is the first trial to randomize hypertensive HD patients to intensive (110-140 mm Hg) vs. usual (155-165 mm Hg) control of systolic blood pressure (SBP). The study’s goal is to assess the feasibility of conducting a full-scale trial.

Methods: BID consortium consists of 5 clinical centers, a cardiac MRI reading center and a data coordinating center. Standardized predialysis SBP, measured in the dialysis unit in accord with AHA recommendations (SDUSBP), guide therapy. To be eligible for randomization patients needed a 2-week running mean SDUSBP ≥ 155 mm Hg. Home BP measurements (HBPM) are obtained twice on the day after the midweek dialysis. Ambulatory Blood Pressure Monitoring (ABPM) during a 44h interdialytic period is obtained quarterly. We compared SDUSBP, HBPM and ABPM.

Results: We enrolled 281 and randomized 126 participants. Major reasons for drop out during the baseline period were 2-week mean SDUSBP < 155 mm Hg (40.6%), no cardiac MRI (13.0%) and perception of protocol as burdensome (11.2%). Adherence with prescribed SDUSBP was satisfactory. The percent of patients with ≥ 4, ≥ 8 and ≥12 SBP per month were 96, 88 and 57% in month 1 and 78, 68 and 37% in month 12. In a constant cohort of participants followed ≥ 330 days 2-week mean SDUSBP were 144 ± 17.4 and 156 ± 15.2 mm Hg in the intensive and usual arms, respectively. Major reasons that participants in the intensive arm did not achieve target SBP included large interdialytic weight gain (27.2%), non-adherence with medications or dialysis prescription (40.9%), and intradialytic hypotension (31.9%). Differences between the SDUSBP and both HBPM and ABPM were often ≥ 10 mm Hg. Optimal control of BP requires measurements in and out of the dialysis unit. Rates of adverse events were similar to those in other NIDDK funded ESRD studies.

Conclusion: The difference in BP between arms was achieved and maintained throughout the study. It is feasible to conduct a full-scale clinical trial of intensive vs. usual treatment of hypertension in HD patients.

Tubuloglomerular feedback-mediated decreases in glomerular pressure in Munich-Wistar rats

These experiments were performed to evaluate directly measured glomerular capillary pressure and single nephron glomerular filtration rate (SNGFR) tubuloglomerular feedback responses in Munich-Wistar rats during increased distal flow rate achieved by infusing an isotonic electrolyte solution into unblocked late proximal tubules. Arterial pressure averaged 114 +/- 2 mmHg and proximal tubule pressure was 14 +/- 1 mmHg. In eight tubules, control SNGFR based on distal tubular fluid collections averaged 22 +/- 3 nl/min, decreased to 15 +/- 2.3 nl/min when 10-12 nl/min of perfusate was infused into the late proximal tubule, and further decreased to 9 +/- 1.7 nl/min at an infusion of 20-24 nl/min. In 22 tubules, control glomerular capillary pressure was 55 +/- 1.6 mmHg, decreased to 43 +/- 2.5 mmHg with addition of perfusate into a late proximal tubule at a rate of 24 nl/min, and returned to 53 +/- 3.1 mmHg when perfusion was stopped. In eight nephrons, glomerular capillary pressure was shown to be responsive to smaller increments in the late proximal infusion rate and was reduced by 4 +/- 0.5 and 7 +/- 1.1 mmHg at the intermediate rates of 10 and 15 nl/min, respectively. These results demonstrate that glomerular pressure decreases during increased distal delivery even when the tubule is not blocked. They are consistent with the hypothesis that increases in afferent arteriolar resistance are primarily responsible for feedback-mediated reductions in glomerular filtration rate.

Role of dietary potassium in the treatment of hypertension

This review summarizes the historical development and recent resurgence of interest in dietary potassium as a factor in hypertension. Some epidemiologic evidence has suggested that potassium intake by humans may be inversely related to the level of arterial blood pressure. Other studies have suggested that a marked reduction in the Na+/K+ ratio of the human diet reduces the blood pressure of normotensives. Further, the administration of high potassium diets has resulted in a lowering of blood pressure in some animal models of hypertension. Several possible mechanisms for this putative antihypertensive effect are evident. Some observations suggest that potassium could act as a diuretic agent and thereby reduce extracellular fluid volume, which in turn could result in decreased blood pressure. An alternative mechanism of action is that potassium may alter the activity of the renin-angiotensin system and reduce angiotensin influences on vascular, adrenal, or renal receptors. Other evidence supports the possibility that potassium modifies central or the peripheral neural mechanisms that regulate blood pressure. In addition, high potassium diets could reduce blood pressure by relaxing vascular smooth muscle and reducing peripheral vascular resistance directly. Although diets high in potassium content do appear to modify arterial blood pressure under some circumstances, particularly in salt-dependent hypertension, a high potassium intake has not always attenuated blood pressure in all models examined. Further, evaluation of these data do not allow definite conclusions regarding a common mechanism through which potassium exerts these effects.