Arterial Stiffness Alterations during Hemodialysis: The Role of Dialysate Calcium

The impact of low and high dialysate calcium concentrations on cardiovascular disease and death in patients undergoing maintenance hemodialysis: a systematic review and meta-analysis

BACKGROUND

The optimal dialysate calcium (Ca) concentration for patients undergoing hemodialysis remains inconclusive, particularly concerning cardiovascular protection.

METHODS

We conducted a systematic review of 19 randomized controlled trials (RCTs) and a meta-analysis of eight RCTs to determine the optimal dialysate Ca concentration for cardiovascular protection. We compared outcomes in patients receiving maintenance hemodialysis treated with either a low-Ca dialysate (LCD) (1.125 or 1.25 mmol/L) or a high-Ca dialysate (HCD) (1.5 or 1.75 mmol/L). The outcomes were coronary artery calcification score (CACS), all-cause and cardiovascular death, cardiovascular function and structure, and serum biochemical parameters.

RESULTS

There was no significant difference between LCD and HCD concerning CACS (standardized mean difference [SMD] = -0.16, 95% confidence interval [CI]: [-0.38, 0.07]), the risk of all-cause death, and cardiovascular death in patients treated with chronic maintenance hemodialysis. Conversely, LCD was associated with a significantly lower intima-media thickness (SMD = -0.49, 95% CI [-0.94, -0.05]) and pulse wave velocity than HCD (SMD = -0.86, 95% CI [-1.21, -0.51]). Furthermore, LCD significantly decreased serum Ca levels (mean difference [MD] = 0.52 mg/dL, 95% CI [0.19, 0.85]) and increased serum parathyroid hormone levels (MD = 44.8 pg/mL, 95% CI [16.2, 73.3]) compared with HCD. Notably, most RCTs examined in our analysis did not include patients receiving calcimimetics.

CONCLUSIONS

Our meta-analysis showed no significant differences in cardiovascular calcification and death between LCD and HCD and revealed a paucity of RCTs on dialysate Ca concentrations, including those involving patients on calcimimetics, indicating the urgent need for further studies.

Can we reverse arterial stiffness by intervening on CKD-MBD biomarkers?

The increased cardiovascular risk of chronic kidney disease may in part be the consequence of arterial stiffness, a typical feature of kidney failure. Deranged homeostasis of minerals and hormones involved (CKD-MBD), are also strongly associated with this increased risk. It is well established that CKD-MBD is a main driver of vascular calcification, which in turn worsens arterial stiffness. However, there are other contributors to arterial stiffness in CKD than calcification. An overlooked possibility is that CKD-MBD may have detrimental effects on this potentially better modifiable component of arterial stiffness. In this review, the individual contributions of short-term changes in calcium, phosphate, PTH, vitamin D, magnesium, and FGF23 to arterial stiffness, in most studies assessed as pulse wave velocity, is summarized. Indeed, there is evidence from both observational studies and interventional trials that higher calcium concentrations can worsen arterial stiffness. This, however, has not been shown for phosphate, and it seems unlikely that, apart from being a contributor to vascular calcification and having effects on the microcirculation, phosphate has no acute effect on large artery stiffness. Several interventional studies, both by infusing PTH and by abrupt lowering PTH by calcimimetics or surgery, virtually ruled out direct effects on large artery stiffness. A well-designed trial using both active and nutritional vitamin D as intervention found a beneficial effect for the latter. Unfortunately, the study had a baseline imbalance and other studies did not support its finding. Both magnesium and FGF23 do not seem do modify central arterial stiffness.

Why is Intradialytic Hypotension the Commonest Complication of Outpatient Dialysis Treatments?

Intradialytic hypotension (IDH) is the most frequent complication of hemodialysis (HD) treatments with a frequency of 10% to 12% for patients with chronic kidney disease attending for outpatient treatments and is associated with both temporary ischemic stress to vital organs, including the heart and brain, and increased patient mortality. Although there have been many different definitions of IDH over the years, an absolute nadir systolic blood pressure (SBP) has the strongest association with patient outcomes. The unifying pathophysiology is one of reduced effective blood volume, resulting in lower plasma tonicity, and if this cannot be adequately compensated for by activation of neurohumeral systems, then arteriolar tone and blood pressure fall. The risk factors for developing IDH are numerous, ranging from patient-related factors, including age and comorbidity with reduced cardiac reserve, to patient compliance with dietary and lifestyle advice, to reactions with the extracorporeal circuit and medications, choice of dialysate composition and temperature, setting of postdialysis target weight, ultrafiltration rate, and profiling. Advances in dialysis machine technology by providing real time estimates of the effective circulating volume and adjusting dialysate composition to maintain vascular tonicity are being developed, but currently require more sophisticated biofeedback loops to be clinically effective in preventing IDH. While awaiting advances in artificial intelligence, the clinician continues to rely on patient education to limit interdialytic weight gains, frequent assessment of the postdialysis target weight, adjusting dialysate composition and temperature, introducing convective therapies to increase thermal losses, and altering dialysis session duration and frequency to reduce ultrafiltration rate requirements.

Citric-acid dialysate improves the calcification propensity of hemodialysis patients: A multicenter prospective randomized cross-over trial

INTRODUCTION

The concentration of dialysate calcium (dCa) has been suggested to affect vascular calcification, but evidence is scarce. Calcification propensity reflects the intrinsic capacity of serum to prevent calcium and phosphate to precipitate. The use of citric-acid dialysate may have a beneficial effect on the calcification propensity due to the chelating effect on calcium and magnesium. The aim of this study was to compare the intradialytic and short-term effects of haemodialysis with either standard acetic-acid dialysate with dCa1.50 (A1.5) or dCa1.25 (A1.25), as well as citric-acid dialysate with dCa1.50 (C1.5) in bicarbonate dialysis on the calcification propensity of serum.

METHODS

Chronic stable hemodialysis patients were included. This multicenter randomized cross-over study consisted out of a baseline week (A1.5), followed by the randomized sequence of A1.25 or C1.5 for one week after which the alternate treatment was provided after a washout week with A1.5. Calcification propensity of serum was assessed by time-resolved nephelometry where the T50 reflects the transition time between formation of primary and secondary calciprotein particles.

RESULTS

Eighteen patients (median age 70 years) completed the study. Intradialytic change in T50 was increased with C1.5 (121 [90-152]min) compared to A1.25 (83 [43-108]min, p<0.001) and A1.5 (66 [18-102]min, p<0.001). During the treatment week, predialysis T50 increased significantly from the first to the third session with C1.5 (271 [234-291] to 280 [262-339]min, p = 0.002) and with A1.25 (274 [213-308] to 307 [256-337]min, p<0.001), but not with A1.5 (284 [235-346] to 300 [247-335]min, p = 0.33).

CONCLUSION

Calcification propensity, as measured by the change in T50, improved significantly during treatment in C1.5 compared to A1.25 and A1.5. Long-term studies are needed to investigate the effects of different dialysate compositions concentrations on vascular calcification and bone mineral disorders.

High Dialysate Calcium Concentration is Associated with Worsening Left Ventricular Function

Dialysate calcium concentration (d[Ca]) might have a cardiovascular impact in patients on haemodialysis (HD) since a higher d[Ca] determines better hemodynamic tolerability. We have assessed the influence of d[Ca] on global longitudinal strain (GLS) by two-dimensional echocardiography using speckle-tracking imaging before and in the last hour of HD. This is an observational crossover study using d[Ca] 1.75 mmol/L and 1.25 mmol/L. Ultrafiltration was the same between interventions; patients aged 44 ± 13 years (N = 19). The 1.75 mmol/L d[Ca] was associated with lighter drop of blood pressure. Post HD serum total calcium was higher with d[Ca] 1.75 than with 1.25 mmol/L (11.5 ± 0.8 vs. 9.1 ± 0.5 mg/dL, respectively, p < 0.01). In almost all segments strain values were significantly worse in the peak HD with 1.75 mmol/L d[Ca] than with 1.25 mmol/L d[Ca]. GLS decreased from −19.8 ± 3.7% at baseline to −17.3 ± 2.9% and −16.1 ± 2.6% with 1.25 d[Ca] and 1.75 d[Ca] mmol/L, respectively (p < 0.05 for both d[Ca] vs. baseline and 1.25 d[Ca] vs. 1.75 d[Ca] mmol/L). Factors associated with a worse GLS included transferrin, C-reactive protein, weight lost, and post dialysis serum total calcium. We concluded that d[Ca] of 1.75 mmol/L was associated with higher post dialysis serum calcium, which contributed to a worse ventricular performance. Whether this finding would lead to myocardial stunning needs further investigation.

A review on wearable photoplethysmography sensors and their potential future applications in health care

Photoplethysmography (PPG) is an uncomplicated and inexpensive optical measurement method that is often used for heart rate monitoring purposes. PPG is a non-invasive technology that uses a light source and a photodetector at the surface of skin to measure the volumetric variations of blood circulation. Recently, there has been much interest from numerous researchers around the globe to extract further valuable information from the PPG signal in addition to heart rate estimation and pulse oxymetry readings. PPG signal’s second derivative wave contains important health-related information. Thus, analysis of this waveform can help researchers and clinicians to evaluate various cardiovascular-related diseases such as atherosclerosis and arterial stiffness. Moreover, investigating the second derivative wave of PPG signal can also assist in early detection and diagnosis of various cardiovascular illnesses that may possibly appear later in life. For early recognition and analysis of such illnesses, continuous and real-time monitoring is an important approach that has been enabled by the latest technological advances in sensor technology and wireless communications. The aim of this article is to briefly consider some of the current developments and challenges of wearable PPG-based monitoring technologies and then to discuss some of the potential applications of this technology in clinical settings.

Impact of Dialysate Calcium Concentration on Clinical Outcomes in Incident Hemodialysis Patients

The association between dialysate calcium (DCa) concentration and mortality in hemodialysis (HD) patients is controversial. In this study, we evaluated the impact of DCa concentration on mortality in incident HD patient. Incident HD patients were selected from the Clinical Research Center registry-a prospective cohort study on dialysis patients in Korea. Patients were categorized into 3 groups according to the prescribed DCa concentration at the time of enrollment. High DCa was defined as a concentration of 3.5 mEq/L, mid-DCa as 3.0 mEq/L, and low DCa as 2.5 to 2.6 mEq/L. The primary outcome was all-cause mortality and secondary outcomes were cardiovascular or infection-related hospitalization. A total of 1182 patients with incident HD were included. The number of patients in each group was 182 (15.4%) in high DCa group, 701 (59.3%) in the mid-DCa group, and 299 (25.3%) in the low DCa group. The median follow-up period was 16 months. The high DCa group had a significantly higher risk of all-cause mortality compared with the mid-DCa group (hazard ratio [HR] 2.23, 95% confidence interval [CI] 1.28-3.90, P = 0.005) and the low DCa group (HR 3.67, 95% CI 1.78-7.55, P < 0.001) after adjustment for clinical variables. The high DCa group was associated with higher risk of cardiovascular and infection-related hospitalization compared with the low DCa group (HR 3.25, 95% CI 1.53-6.89, P = 0.002; and HR 2.77, 95% CI 1.29-5.94, P =  .009, respectively). Of these 1182 patients, 163 patients from each group were matched by propensity scores. In the propensity score matched analysis, the high DCa group had a significantly higher risk of all-cause mortality compared with the mid-DCa group (HR 2.52, 95% CI 1.04-6.07, P = 0.04) and the low DCa group (HR 4.25, 95% CI 1.64-11.03, P = 0.003) after adjustment for clinical variables. Our data showed that HD using a high DCa was a significant risk factor for all-cause mortality and cardiovascular or infection-related hospitalization in incident HD patients.

Dialysate Calcium Concentration, Mineral Metabolism Disorders, and Cardiovascular Disease: Deciding the Hemodialysis Bath

Patients with end-stage kidney disease treated with dialysis are at increased risk to experience fractures and cardiovascular events than similar-aged people from the general population. The enhanced risk for these outcomes in dialysis patients is not completely explained by traditional risk factors for osteoporosis and cardiovascular disease. Mineral metabolism abnormalities are almost universal by the time patients require dialysis therapy, with most patients having some type of renal osteodystrophy and vascular calcification. These abnormalities have been linked to adverse skeletal and cardiovascular events. However, it has become clear that the treatment regimens used to modify the serum calcium, phosphate, and parathyroid hormone levels almost certainly contribute to the poor outcomes for dialysis patients. In this article, we focus on one aspect of mineral metabolism management; dialysate calcium concentration and the relationships among dialysate calcium concentrations, mineral and bone disorder, and cardiovascular disease in hemodialysis patients.

Do higher dialysate calcium concentrations increase vascular stiffness in haemodialysis patients as measured by aortic pulse wave velocity?

Background

Haemodialysis patients have an increased prevalence of hypertension and risk of cardiovascular mortality and stroke. Higher dialysate calcium concentrations have been reported to cause both an acute and chronic increase in arterial stiffness. We therefore looked at changes in arterial stiffness in established haemodialysis patients to determine whether there was a threshold effect of dialysate calcium concentration linked to change in arterial stiffness.

Methods

We performed pulse wave velocity measurements six months apart in patients dialysing with calcium concentrations of 1.0, 1.25, 1.35 and ≥1.5 mmol/l.

Results

289 patients, 62.2% male, mean age 65.5 ± 15.7 years, weight body mass index 25.8 ± 5.4 kg/m² ,47.9% diabetic were studied. Systolic blood pressure (SBP) was 148.4 ± 28.6 mmHg and diastolic blood pressure (DBP) 80.2 ± 15.5 mmHg. Mean pulse wave velocity increased over time (9.66 ± 2.0 vs 10.13 ± 2.16 m/s; p < 0.001), but there was no change in aortic augmentation index (38.7 ± 16.3 vs 39.8 ± 15.6%) or central aortic pressure (149.6 ± 33.3 vs 150.4 ± 31.9 mmHg).

Pulse wave velocity did not differ between the four groups either at start or end of the study, but increased both in the groups dialysing with a calcium concentration of 1.0 mmol/l (9.64 ± 1.94 vs 10.45 ± 1.98 m/s, p = 0.0028) and also with 1.35 mmol/l (9.75 ± 1.96 vs 10.21 ± 2.18 m/s, p = 0.02).

Conclusions

Pulse wave velocity increased over the six months study. As pulse wave velocity increased in the group dialysing using the lowest dialysate calcium, it is likely that factors, other than simple net calcium influx and efflux during dialysis according to dialysate calcium concentration are involved with vascular stiffening.

Low calcium dialysate combined with CaCO3 in hyperphosphatemia in hemodialysis patients

This aim of this study was to observe the effects of the application of low calcium dialysate (LCD) combined with oral administration of CaCO3 in the treatment of hyperphosphatemia, as well as blood Ca2+, calcium-phosphate product (CPP), parathyroid hormone (PTH) and blood pressure in patients undergoing hemodialysis. Thirty-one maintenance hemodialysis (MHD) patients with hyperphosphatemia, but normal blood Ca2+, underwent dialysis with an initial dialy-sate Ca2+ concentration (DCa) of 1.50 mmol/l for six months and then with 1.25 mmol/l for six months. The patients who underwent dialysis with a DCa of 1.25 mmol/l were treated orally with 0.3 g CaCO3 tablets three times a day. In the third and sixth months [observation end point (OEP)] of the dialysis, the concentrations of Ca2+, phosphorus and intact PTH (iPTH) were measured; blood pressure and side-effects prior to and following dialysis were also observed. The Ca2+, CPP and iPTH levels increased (P<0.05) in the sixth month of treatment with a DCa of 1.50 mmol/l. However, the Ca2+ concentration declined to a certain degree, CPPs decreased significantly (P<0.05) and the iPTH concentration increased following treatment with a DCa of 1.25 mmol/l for six months. The incidence rate of adverse effects of LCD was 12.9% (4/31); the effects were mainly muscle spasms, hypotension and elevated PTH. The periodic application of LCD combined with the oral administration of CaCO3 effectively reduced serum phosphorus and CPPs among MHD patients with hyperphosphatemia, indicating that the treatment may be used clinically.

Membrane Bioincompatibility and Ultrafiltration Effects on Pulse Wave Analysis during Haemodialysis

Membrane bioincompatibility was demonstrated by successive white blood cell counts and C3a generation. Pulse wave analysis was obtained by applanation tonometry (SphygmoCor) in a sequential way: basal, after 30 minutes with nul ultrafiltration, and after a complete dialysis with ultrafiltration. At 15 minutes of haemodialysis, significant decrease in leukocyte count occurred: 6801 ± 1186 versus 4412 ± 1333 (P < 0.001), while C3a levels sharply increased from 427 ± 269 to 3501 ± 1638 ng/mL (P < 0.000). No changes were observed in augmentation index without ultrafiltration: 26.1 ± 11.1 versus 26.6 ± 12.4. Only aortic systolic blood pressure was lower at 15 minutes: 120.1 ± 17.7 versus 110.4 ± 25.8 mmHg (P = 0.009), in agreement with a reduction in brachial systolic blood pressure: 135.1 ± 18.1 versus 122.7 ± 27.4 mmHg (P = 0.01), without changes in aortic or brachial diastolic blood pressure. Important changes in pulse wave analysis were observed after a complete haemodialysis session: augmentation index 29.9 ± 10.1 versus 18.6 ± 15.0, aortic systolic blood pressure 139.8 ± 25.5 versus 119.4 ± 28.5 mmHg (P < 0.00), without changes in aortic diastolic blood pressure. In summary, haemodialysis with cellulose diacetate acutely induced a transient state of immunoactivation due to bioincompatibility, this phenomenon was nondetectable by pulse wave analysis. Complete haemodialysis session led to important changes in pulse wave analysis.

Effects of lowering dialysate calcium concentrations on arterial stiffness in patients undergoing hemodialysis

BACKGROUND/AIMS

We assessed changes in hemodynamic and arterial stiffness parameters following reductions of dialysate calcium concentrations in patients undergoing hemodialysis.

METHODS

In this prospective study, 20 patients on maintenance hemodialysis (10 females, 10 males) with dialysate calcium concentrations of 1.75 mmol/L were enrolled. At the start of the study, the dialysate calcium level was lowered to 1.50 mmol/L. Serial changes in biochemical, hemodynamic, and arterial stiffness parameters, including pulse wave velocity (PWV) and augmentation index (AIx), were assessed every 2 months for 6 months. We also examined changes in the calcification-inhibitory protein, serum fetuin-A.

RESULTS

During the 6-month study period, serum total calcium and ionized calcium decreased consistently (9.5 ± 1.0 to 9.0 ± 0.7, p = 0.002 vs. 1.3 ± 0.1 to 1.1 ± 0.1, p = 0.035). Although no apparent changes in blood pressure were observed, heart-femoral PWW (hf-PWV) and AIx showed significant improvement (p = 0.012, 0.043, respectively). Repeated-measures ANOVA indicated a significant effect of lowering dialysate calcium on hf-PWV (F = 4.58, p = 0.004) and AIx (F = 2.55, p = 0.049). Accompanying the change in serum calcium, serum fetuin-A levels significantly increased (95.8 ± 45.8 pmol/mL at baseline to 124.9 ± 82.2 pmol/mL at 6 months, p = 0.043).

CONCLUSIONS

Lowering dialysate calcium concentration significantly improved arterial stiffness parameters, which may have been associated with upregulation of serum fetuin-A.

Cardiovascular effects of calcium supplementation

Trials in normal older women and in patients with renal impairment suggest that calcium supplements increase the risk of cardiovascular disease. To further assess their safety, we recently conducted a meta-analysis of trials of calcium supplements, and found a 27-31% increase in risk of myocardial infarction and a 12-20% increase in risk of stroke. These findings are robust because they are based on pre-specified analyses of randomized, placebo-controlled trials and show consistent risk across the trials. The fact that cardiovascular events were not primary endpoints of any of these studies will introduce noise but not bias into the data. A recent re-analysis of the Women's Health Initiative suggests that co-administration of vitamin D with calcium does not lessen these adverse effects. The increased cardiovascular risk with calcium supplements is consistent with epidemiological data relating higher circulating calcium concentrations to cardiovascular disease in normal populations. There are several possible pathophysiological mechanisms for these effects, including effects on vascular calcification, on the function of vascular cells, and on blood coagulation. Calcium-sensing receptors might mediate some of these effects. Because calcium supplements produce small reductions in fracture risk and a small increase in cardiovascular risk, there may be no net benefit from their use. Food sources of calcium appear to produce similar benefits on bone density, although their effects on fracture are unclear. Since food sources have not been associated with adverse cardiovascular effects, they may be preferable. Available evidence suggests that other osteoporosis treatments are still effective without calcium co-administration.

Arterial stiffness and dialysis calcium concentration

Arterial stiffness is the major determinant of isolated systolic hypertension and increased pulse pressure. Aortic stiffness is also associated with increased cardiovascular morbidity and mortality in patients with chronic kidney disease, hypertension, and general population. Hemodynamically, arterial stiffness results in earlier aortic pulse wave reflection leading to increased cardiac workload and decreased myocardial perfusion. Although the clinical consequence of aortic stiffness has been clearly established, its pathophysiology in various clinical conditions still remains poorly understood. The aim of the present paper is to review the studies that have looked at the impact of dialysis calcium concentration on arterial stiffness. Overall, the results of small short-term studies suggest that higher dialysis calcium is associated with a transient but significant increase in arterial stiffness. This calcium dependant increase in arterial stiffness is potentially explained by increased vascular smooth muscle tone of the conduit arteries and is not solely explained by changes in mean blood pressure. However, the optimal DCa remains to be determined, and long term studies are required to evaluate its impact on the progression of arterial stiffness.

Intradialytic hypertension: a less-recognized cardiovascular complication of hemodialysis

Intradialytic hypertension, defined as an increase in blood pressure during or immediately after hemodialysis that results in postdialysis hypertension, has long been recognized to complicate the hemodialysis procedure, yet often is largely ignored. In light of recent investigations suggesting that intradialytic hypertension is associated with adverse outcomes, this review broadly covers the epidemiologic characteristics, prognostic significance, potential pathogenic mechanisms, prevention, and possible treatment of intradialytic hypertension. Intradialytic hypertension affects up to 15% of hemodialysis patients and occurs more frequently in patients who are older, have lower dry weights, are prescribed more antihypertensive medications, and have lower serum creatinine levels. Recent studies associated intradialytic hypertension independently with higher hospitalization rates and decreased survival. Although the pathophysiologic mechanisms of intradialytic hypertension are uncertain, it likely is multifactorial and includes subclinical volume overload, sympathetic overactivity, activation of the renin-angiotensin system, endothelial cell dysfunction, and specific dialytic techniques. Prevention and treatment of intradialytic hypertension may include careful attention to dry weight, avoidance of dialyzable antihypertensive medications, limiting the use of high-calcium dialysate, achieving adequate sodium solute removal during hemodialysis, and using medications that inhibit the renin-angiotensin-aldosterone system or decrease endothelin 1 levels. In summary, although intradialytic hypertension often is underappreciated, recent studies suggest that it should not be ignored. However, further work is necessary to elucidate the pathophysiologic mechanisms of intradialytic hypertension and its appropriate management and determine whether treatment of intradialytic hypertension can improve clinical outcomes.

The growing problem of intradialytic hypertension

Intradialytic hypertension is not a rare complication of dialysis, with a prevalence of 5-15% among hemodialysis patients, and it seems to be associated with adverse outcomes. This complex phenomenon is not well understood, and many uncertainties exist regarding its pathophysiologic mechanisms and appropriate treatment strategies. Mechanisms that might be involved in the pathogenesis of intradialytic hypertension include extracellular volume overload, increased cardiac output, changes in electrolyte levels (particularly sodium), activation of the renin-angiotensin-aldosterone system, overactivity of the sympathetic nervous system, and endothelial cell dysfunction. Most current treatment strategies are based only on expert opinion and not on the results of randomized clinical trials, as very little data on the therapy of intradialytic hypertension are available. The most important treatment is adequate sodium and water removal, but reducing sympathetic hyperactivity and reducing endothelin-1 levels should also be considered. Well-designed, randomized clinical trials are urgently needed to better understand the pathophysiologic mechanisms of this complex phenomenon and to improve its diagnosis, prognosis and treatment.

Effects of acute variation of dialysate calcium concentrations on arterial stiffness and aortic pressure waveform

BACKGROUND

Abnormal mineral metabolism in chronic kidney disease plays a critical role in vascular calcification and arterial stiffness. The impact of presently used dialysis calcium concentration (D(Ca)) on arterial stiffness and aortic pressure waveform has never been studied. The aim of the present study is to evaluate, in haemodialysis (HD) patients, the impact of acute modification of D(Ca) on arterial stiffness and central pulse wave profile (cPWP). Method. A randomized Latin square cross-over study was used to evaluate the three different concentrations of D(Ca) (1.00, 1.25 and 1.50 mmol/L) during the second HD of the week for 3 consecutive weeks. Subjects returned to their baseline D(Ca) for the following two treatments, allowing for a 7-day washout period between each experimental HD. cPWP, carotido-radial (c-r) and carotido-femoral (c-f) pulse wave velocities (PWV), plasma level of ionized calcium (iCa) and intact parathyroid hormone (PTH) were measured prior to and immediately after each experimental HD session. Data were analysed by the general linear model for repeated measures and by the general linear mixed model.

RESULTS

Eighteen patients with a mean age of 48.9 +/- 18 years and a median duration of HD of 8.7 months (range 1-87 months) completed the study. In post-HD, iCa decreased with D(Ca) of 1.00 mmol/L (-0.14 +/- 0.04 mmol/L, P < 0.001), increased with a D(Ca) of 1.50 mmol/L (0.10 +/- 0.06 mmol/L, P < 0.001) but did not change with a D(Ca) of 1.25 mmol/L. Tests of within-subject contrast showed a linear relationship between higher D(Ca) and a higher post-HD Deltac-f PWV, Deltac-r PWV and Deltamean BP (P < 0.001, P = 0.008 and P = 0.002, respectively). Heart rate-adjusted central augmentation index (AIx) decreased significantly after HD, but was not related to D(Ca). The timing of wave refection (Tr) occurred earlier after dialysis resulting in a linear relationship between higher D(Ca) and post-HD earlier Tr (P < 0.044). In a multivariate linear-mixed model for repeated measures, the percentage increase in c-f PWV and c-r PWV was significantly associated with the increasing level of iCa, whereas the increasing level of DeltaMBP was not significant. In contrast, the percentage decrease in Tr (earlier wave reflection) was determined by higher DeltaMBP and higher ultrafiltration, whereas the relative change in AIx was inversely determined by the variation in the heart rate and directly by DeltaMBP.

CONCLUSION

We conclude that D(ca) and acute changes in the serum iCa concentration, even within physiological range, are associated with detectable changes of arterial stiffness and cPWP. Long-term studies are necessary to evaluate the long-term effects of D(Ca) modulation on arterial stiffness.

The Influence of Dialysate Calcium on Progression of Arterial Stiffness in Peritoneal Dialysis Patients

Background

One of the origins of cardiovascular disease in dialysis patients is arterial stiffness. The aim of our study was to assess the relationship between the calcium content of peritoneal dialysis (PD) solution and arterial stiffness.

Patients and Methods

We enrolled into the study 49 PD patients who had been treated with the same PD solution for the preceding 6 months. The calcium content of the PD solution was 1.25 mmol/L in 34 patients (low-Ca group) and 1.75 mmol/L in 15 patients (high-Ca group). Study patients were followed for 6 months on the same PD prescription. Arterial stiffness was assessed by measurement of augmentation index (AI) and brachial pulse wave velocity (PWV) at baseline and at month 6 (SphygmoCor: Atcor Medical, West Ryde, NSW, Australia). Demographic data were recorded from patient charts.

Results

Mean age of the whole group was 51 ± 11 years, prevalence of diabetes was 14%, duration of PD was 43 ± 30 months, percentage of women was 45%, and percentage of patients using a cycler was 33%. We observed no differences between groups with regard to those variables or creatinine clearance, residual renal function, Ca, phosphorus, parathormone, C-reactive protein, lipid parameters, and use of phosphate binder with or without Ca content. Mean arterial pressure was higher in the high-Ca group, but the difference was not statistically significant (100 ± 22 mmHg vs 88 ± 18 mmHg, p = 0.06). At baseline, AI was significantly higher in the high-Ca group than in the low-Ca group (27% ± 10% vs 21% ± 9%, p < 0.05). Measurements of PWV were not different between the groups (8.4 ± 1.1 m/s vs 8.5 ± 1.7 m/s). Measurement of arterial stiffness parameters at month 6 revealed that PWV had increased in the high-Ca group (to 9.6 ± 2.3 m/s from 8.4 ± 1.1 m/s, p < 0.05), but had not changed in the low-Ca group (to 8.2 ± 1.9 m/s from 8.5 ± 1.7 m/s). The AI did not change in either group.

Conclusions

These data suggest that Ca exposure through PD solution plays a role in the progression of arterial stiffness, which may be related to increased vascular calcification.