Vascular calcification is associated with impaired microcirculatory function in chronic haemodialysis patients

Spatial-Temporal Oxygenation Mapping Using a Near-Infrared Optical Scanner: Towards Peripheral Vascular Imaging

Near-infrared spectroscopy (NIRS)-based peripheral perfusion, or microcirculation, can be used to assess the severity of peripheral vascular dysfunction. A low-cost, portable non-contact near-infrared optical scanner (NIROS) was developed for spatio-temporal mapping of tissue oxygenation and perfusion in tissues. In vivo validation studies were carried out on control subjects (n = 3) to assess the ability of NIROS to measure real-time oxygenation changes in response to an occlusion paradigm on the dorsum of the hand. NIROS captured real-time tissue oxygenation changes with 95% correlation when compared to a commercial device. A feasibility peripheral imaging study was performed in a mouse model (n = 5) of chronic kidney disease (CKD) induced vascular calcification to assess differences in microcirculatory peripheral tissue oxygenation. The tissue oxygenation (in terms of oxy-, deoxy-, and total hemoglobin changes) due to the occlusion paradigm was distinctly different prior to (week-6) and after the onset of vascular calcification (week-12) in the murine tails. Future work will involve extensive studies to correlate these microcirculatory tissue oxygenation changes in the peripheral tail to the vascular calcification in the heart.

Calcification detection on upper extremity arteries: a comparison of ultrasonic and X-ray methods

Background

Vascular calcification (VC) has been observed in patients with hemodialysis, whereas few studies have investigated calcification in the upper extremity vasculature. Both ultrasound and X-ray are used to investigate the calcification of arteries in patients. However, there is a lack of data on the consistency between these two methods. The aim of this study was to investigate the occurrence of VC in the radial and ulnar arteries of hemodialysis patients and investigate the detection consistency in VC between ultrasound and X-ray.

Methods

Ultrasound and X-ray examinations were performed in the radial and ulnar arteries of both the left and right upper extremities of 40 patients on hemodialysis. The calcification status of arteries was evaluated by the calcification index from ultrasound and X-ray respectively. Clinical variables of patients were collected from all the involved patients.

Results

Of the 40 patients, VC was detected in 31 patients by ultrasound, while X-ray detected VC in 22 patients. Compared to ultrasound assessment, X-ray assessment was 73.21% sensitive but only 66.35% specific with a positive predictive value of 53.95% for detecting calcifications in the radial or ulnar artery. The level of agreement between ultrasound and X-ray results was fair. In addition, our data showed that more ulnar arteries had VCs than the corresponding radial arteries.

Conclusion

Ultrasound is more sensitive in detecting the presence of calcified atherosclerotic lesions. Ultrasound and X-ray exhibited fair consistency. Ultrasound screening for upper extremity radial and ulnar arteries in hemodialysis patients may deserve attention to explore its clinical significance.

Elastin haploinsufficiency accelerates age-related structural and functional changes in the renal microvasculature and impairment of renal hemodynamics in female mice

Age-related decline in functional elastin is associated with increased arterial stiffness, a known risk factor for developing cardiovascular disease. While the contribution of elastin insufficiency to the stiffening of conduit arteries is well described, little is known about the impact on the structure and function of the resistance vasculature, which contributes to total peripheral resistance and the regulation of organ perfusion. In this study, we determined how elastin insufficiency impinges on age-related changes in the structure and biomechanical properties of the renal microvasculature, altering renal hemodynamics and the response of the renal vascular bed to changes in renal perfusion pressure (RPP) in female mice. Using Doppler ultrasonography, we found that resistive index and pulsatility index were elevated in young Eln +/- and aged mice. Histological examination showed thinner internal and external elastic laminae, accompanied by increased elastin fragmentation in the medial layer without any calcium deposits in the small intrarenal arteries of kidneys from young Eln +/- and aged mice. Pressure myography of interlobar arteries showed that vessels from young Eln +/- and aged mice had a slight decrease in distensibility during pressure loading but a substantial decline in vascular recoil efficiency upon pressure unloading. To examine whether structural changes in the renal microvasculature influenced renal hemodynamics, we clamped neurohumoral input and increased renal perfusion pressure by simultaneously occluding the superior mesenteric and celiac arteries. Increased renal perfusion pressure caused robust changes in blood pressure in all groups; however, changes in renal vascular resistance and renal blood flow (RBF) were blunted in young Eln +/- and aged mice, accompanied by decreased autoregulatory index, indicating greater impairment of renal autoregulation. Finally, increased pulse pressure in aged Eln +/- mice positively correlated with high renal blood flow. Together, our data show that the loss of elastin negatively affects the structural and functional integrity of the renal microvasculature, ultimately worsening age-related decline in kidney function.

Assessment of microcirculatory function during hemodialysis

PURPOSE OF REVIEW

Patients with chronic kidney disease characteristically exhibit microcirculatory dysfunction, in combination with vascular damage. Hemodialysis superimposes additional circulatory stress to the microvasculature (repetitive ischemic insults/cumulative damage) resulting in high mortality. Intradialytic monitoring and hemodialysis delivery is currently limited to macrovascular/systemic assessment and detection of intradialytic systemic hypotension. Monitoring of the microcirculation has the potential to provide valuable information on hemodialysis-induced circulatory stress likely to result in end-organ ischemia (with/without systemic hypotension) generating an opportunity to intervene before tissue injury occurs.

RECENT FINDINGS

Various noninvasive technologies have been used assessing the microcirculation in hemodialysis patients at rest. Some technologies have also been applied during hemodialysis studying the effects of treatment on the microcirculation. Despite the approach used, results are consistent. Hemodialysis patients have impaired microcirculations with treatment adding additional stress to inadequately regulated vascular beds. Utility/practicality/clinical relevance vary significantly between methodologies.

SUMMARY

Intradialytic monitoring of the microcirculation can provide additional insights into a patient's individual response to treatment. However, this valuable perspective has not been adopted into clinical practice. A microcirculatory view could provide a window of opportunity to enable a precision medicine approach to treatment delivery improving current woefully poor subjective and objective clinical outcomes.

Relationship between serum alkaline phosphatase and poor 3-month prognosis in acute ischemic stroke patients with preserved renal function: results from Xi'an Stroke Registry Study of China

Background

In recent years, alkaline phosphatase (ALP) has been considered as one of the independent risk factors of acute ischemic stroke (AIS) and leads to worse clinical outcomes in patients with renal failure. In this study, we aim to investigate whether serum ALP level is associated with poor early-term prognosis in relationship of AIS patients with preserved renal function.

Methods

A prospectively collected database of AIS patients hospitalized in the Xi’an district of China from January to December, 2015 was analyzed. The demographics, serum ALP levels and stroke outcomes of all patients at 3 months were reviewed. Patients were routinely followed-up for 3 months. Serum ALP level was analyzed as a continuous variable and quintiles (Q1-Q5). Multivariate logistic regression model and a two-piecewise linear regression model were used to investigate the relationship and to determine the threshold effect regarding serum ALP levels and poor 3-month prognosis of AIS patients with preserved renal function.

Results

Overall, 1922 AIS patients were enrolled with 62.3% of them being men. The risk of having a poor 3-month prognosis was significantly increased in Q1, Q2, Q3 and Q5, when compared to that in Q4 being as the reference. The highest risk was noted in Q5 (odds ratio 2.21, 95% confidence interval: 1.32–3.73, P = 0.003) after being adjusted for confounders. Further analysis revealed a J-shaped curvilinear relationship between ALP levels and a poor 3-month prognosis of strokes (optimal threshold ALP level = 90 U/L). The relationship between both parameters was not significantly affected by age, sex, drinking, hypertension and leukocyte count (stratified by 10 × 10⁹/L) (P for interaction > 0.05).

Conclusions

Serum ALP was noted as an independent risk factor for a poor 3-month prognosis of AIS patients with preserved renal function. ALP levels higher than 90 U/L could cause an increased risk of a poor 3-month prognosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02779-y.

The risk factors for calcification vary among the different sections of the lower extremity artery in patients with symptomatic peripheral arterial disease

BACKGROUND

Peripheral arterial disease (PAD) is associated with considerable mortality and morbidity worldwide. The present study explored the risk factors for arterial calcification among the different sections of the lower extremity in patients with PAD and analyzed their correlations with the extent of arterial stenosis at the corresponding section.

METHODS

This study enrolled symptomatic PAD patients from our hospital from March 2017 to March 2018. The lower extremity arterial calcification score (LEACS) and lower extremity arterial stenosis index (LEASI), representing the extent of arterial stenosis, were measured on computed tomography (CT) and the correlations between them were analyzed using Spearman's correlation analysis. The relationships between risk factors and calcification were analyzed among the different sections of the lower extremity artery.

RESULTS

In total, 209 patients were included. The LEACSs of the total lower extremity, aortoiliac artery, and femoropopliteal and infrapopliteal arteries were correlated with the LEASI (all P < 0.05), but their correlation was relatively weak in the aortoiliac artery. Univariate analysis showed that hypertension was associated with the total (P = 0.019) and aortoiliac (P = 0.012) LEACSs. Diabetes was related to both femoropopliteal (P = 0.001) and infrapopliteal (P = 0.002) LEACSs. The infrapopliteal LEACS was higher in male patients (P = 0.011). After adjustment for age, the above relationships were maintained among the different sections, but not in the total lower extremity artery.

CONCLUSIONS

The LEACS is associated with the LEASI in all arterial sections, but that of the aortoiliac artery was relatively weak. Different factors have different effects on calcification among the various sections of the lower extremity artery.

The systemic microcirculation in dialysis populations

In a rapidly expanding population of patients with chronic kidney disease, including 2 million people requiring renal replacement therapy, cardiovascular mortality is 15 times greater than the general population. In addition to traditional cardiovascular risk factors, more poorly defined risks related to uremia and its treatments appear to contribute to this exaggerated risk. In this context, the microcirculation may play an important early role in cardiovascular disease associated with chronic kidney disease. Experimentally, the uremic environment and dialysis have been linked to multiple pathways causing microvascular dysfunction. Coronary microvascular dysfunction is reflected in remote and more easily studied vascular beds such as the skin. There is increasing evidence for a correlation between systemic microvascular dysfunction and adverse cardiovascular outcomes. Systemic microcirculatory changes have not been extensively investigated across the spectrum of chronic kidney disease. Recent advances in non-invasive techniques studying the microcirculation in vivo in man are increasing the data available particularly in patients on hemodialysis. Here, we review current knowledge of the systemic microcirculation in dialysis populations, explore whether non-invasive techniques to study its function could be used to detect early stage cardiovascular disease, address challenges faced in studying this patient cohort and identify potential future avenues for research.

Risk Factors Before Dialysis Predominate as Mortality Predictors in Diabetic Maintenance Dialysis patients

Diabetic patients undergoing maintenance dialysis (MD) have a particularly high mortality rate. Many of the risk factors for mortality have been identified in diabetics who die before reaching end stage renal disease (ESRD), i.e. before dialysis (BD). In addition, many risk factors for mortality have been identified in diabetics after dialysis onset (AD). However, whether in the BD period there are long-term risk factors for AD mortality in diabetics is unknown. We therefore investigated a new concept, i.e. that clinical and biochemical risk factors during the BD stage affect long-term AD mortality. We performed a population based retrospective cohort study, in diabetic CKD patients in a single center in south Israel who initiated MD between the years 2003 and 2015. Clinical and biochemical data 12 months BD and 6 months AD were collected and evaluated for association with mortality AD using Cox’s proportional-hazards model. BD parameters that were found to be significant were adjusted for significant parameters AD, thus generating a “combined” regression model in order to isolate the contribution of BD factors on long term mortality. Six hundred and fifty two diabetic MD patients were included in the final analysis. Four independent BD parameters were found in the multivariate model to significantly predict AD mortality: age, BMI (inversely), pulse pressure (U-shaped) and cardiovascular comorbidity. AD independent risk factors for mortality were age, BMI (inversely) and albumin (inversely). Of note, BD factors remained dominantly significant even after additionally adjusting for AD factors. No association was found between either BD HbA1C levels or BD proteinuria and AD mortality. In diabetics who reach ESRD, BD parameters can predict long term AD mortality. Thus, some of the factors affecting the poor survival of diabetic MD patients appear to begin already in the BD period.

Alkaline phosphatase: a potential biomarker for stroke and implications for treatment

Stroke is the fifth leading cause of death in the U.S., with more than 100,000 deaths annually. There are a multitude of risks associated with stroke, including aging, cardiovascular disease, hypertension, Alzheimer's disease (AD), and immune suppression. One of the many challenges, which has so far proven to be unsuccessful, is the identification of a cost-effective diagnostic or prognostic biomarker for stroke. Alkaline phosphatase (AP), an enzyme first discovered in the 1920s, has been evaluated as a potential biomarker in many disorders, including many of the co-morbidities associated with stroke. This review will examine the basic biology of AP, and its most common isoenzyme, tissue nonspecific alkaline phosphatase (TNAP), with a specific focus on the central nervous system. It examines the preclinical and clinical evidence which supports a potential role for AP in stroke and suggests potential mechanism(s) of action for AP isoenzymes in stroke. Lastly, the review speculates on the clinical utility of AP isoenzymes as potential blood biomarkers for stroke or as AP-targeted treatments for stroke patients.

Blood pressure targets for hemodialysis patients

The association between blood pressure (BP) and mortality is unique in hemodialysis patients compared with that in the general population. This is because of an altered benefit-risk balance associated with BP reduction in these patients. An adequately designed study comparing BP targets in hemodialysis patients remains to be conducted. The current evidence available to guide dialysis providers regarding treatment strategies for managing hypertension in this population is limited to large observational studies and small randomized controlled trials. In this opinion article, we review these data and discuss the key points regarding BP management for hemodialysis patients. Our aim is to provide a practical opinion regarding BP targets that nephrologists can incorporate into clinical practice, with a focus on moving away from dialysis unit BPs and focusing on out-of-dialysis unit BPs.

Association of arterial calcification with chronic limb ischemia in patients with peripheral artery disease

OBJECTIVE

Arterial calcification is associated with an increased risk of limb events, including amputation. The association between calcification in lower extremity arteries and the severity of ischemia, however, has not been assessed. We thus sought to determine whether the extent of peripheral artery calcification (PAC) was correlated with Rutherford chronic ischemia categories and hypothesized that it could independently contribute to worsening limb status.

METHODS

We retrospectively reviewed all patients presenting with symptomatic peripheral artery disease who underwent evaluation by contrast and noncontrast computed tomography scan of the lower extremities as part of their assessment. Demographic and cardiovascular risk factors were recorded. Rutherford ischemia categories were determined based on history, physical examination, and noninvasive testing. PAC scores and the extent of occlusive disease were measured on noncontrast and contrast computed tomography scans, respectively. Spearman's correlation testing was used to assess the relationship between occlusive disease and calcification scores. Multivariable logistic regression was used to identify factors associated with increasing Rutherford ischemia categories.

RESULTS

There were 116 patients identified, including 75 with claudication and 41 with critical limb ischemia. In univariate regression, there was a significant association between increasing Rutherford ischemia category and age, diabetes duration, hypertension, the occlusion score, and PAC. There was a moderate correlation between the extent of occlusive disease and PAC scores (Spearman's R = 0.6). In multivariable analysis, only tobacco use (odds ratio [OR], 3.1; 95% confidence interval [CI], 1.2-8.3), diabetes duration (OR, 1.04; 95% CI, 1.01-1.08), and the calcification score (OR, 2.1; 95% CI, 1.4-3.2) maintained an association with increasing ischemia categories after adjusting for relevant cardiovascular risk factors and the extent of occlusive disease.

CONCLUSIONS

PAC is independently associated with increased ischemia categories in patients with peripheral artery disease. Further research aimed at understanding the relationship between arterial calcification and worsening limb ischemia is warranted.

Association between Serum Alkaline Phosphatase Level and Cerebral Small Vessel Disease

BACKGROUND

Serum alkaline phosphatase (ALP) is a marker of vascular calcification. A high serum ALP level is associated with an increase in cardiovascular events, and predicts poor functional outcome in patients with stroke. We investigated whether serum ALP was associated with cerebral small vessel disease (cSVD) and large cerebral artery stenosis (LCAS).

METHODS

We evaluated vascular risk factors, brain magnetic resonance images (MRIs), and MR angiograms from 1,011 neurologically healthy participants. The presence of silent lacunar infarction (SLI) and moderate-to-severe cerebral white matter hyperintensities (MS-cWMH) were evaluated as indices of cSVD on brain MRIs. Findings of extracranial arterial stenosis (ECAS) or intracranial arterial stenosis (ICAS) were considered to be indices of LCAS on MR angiograms.

RESULTS

Subjects with SLI (odds ratio [OR]: 2.09; 95% confidence interval [CI]: 1.27-3.42; p = 0.004) and MS-cWMH (OR: 1.48; 95% CI; 1.03-2.13, p = 0.036) were significantly more likely to have ALP levels in the third tertile (ALP ≥ 195 IU/L) than the first tertile (ALP ≤ 155 IU/L), after adjusting for cardiovascular risk factors. The mean serum ALP level was significantly higher in patients with SLI or MS-cWMH compared to patients without those findings. After adjustment for confounding factors, the multivariate model found that the statistical significance of serum ALP remained when the presence of SLI (OR: 1.05 per 10 IU/L increase in ALP; 95% CI: 1.02-1.08; p = 0.003) or MS-cWMH (OR: 1.03 per 10 IU/L increase in ALP; 95% CI: 1.00-1.06; p = 0.025) were added to the model. There were no differences in the proportions of patients with LCAS, ICAS, and ECAS across the serum ALP tertiles.

CONCLUSIONS

Our study of neurologically healthy participants found a positive association between serum ALP level and indicators of cSVD, but no association between serum ALP level and the indicators of LCAS.

Changes in skeletal muscle microcirculation after a hemodialysis session correlates with adequacy of dialysis

Background

Monitoring of the microcirculation may add additional information in terms of improving the adequacy of hemodialysis (HD) for patients. Withdrawal of liquid and complement activation during a HD session reduces the external pressure on the microcirculation and leads to an increased dilatation of the peripheral capillaries. The purposes of this study were to assess the effect of a single HD or hemodiafiltration session on the thenar microcirculation in patients with end-stage renal disease (ESRD) with or without diabetes, investigate the possible relationship between changes in the microcirculation and adequacy of dialysis (including Kt/V and parameters indicating secondary hyperparathyroidism), and compare microcirculation measurements obtained from patients with ESRD and those from healthy controls.

Methods

This pilot prospective observational study including eleven patients with ESRD on maintenance HD (nine men of mean age 73±10.5 years, ten [91%] with hypertension), nine patients with ESRD on maintenance hemodiafiltration (six men of mean age 65.5±13.2 years, five [55.5%] with diabetes and four [44.5%] with hypertension), and eight healthy volunteers. Two paired microcirculation assessments were recorded for each HD patient before and after a dialysis session. Near infrared spectroscopy and the vascular occlusion test were used to assess the microcirculation, and blood work samples were collected before and after dialysis when the pump slowed down.

Results

Patients with ESRD showed an increase in thenar cell metabolism at rest after a 4-hour HD session, and changes in cell metabolism correlated with the Kt/V of the session. Pre-dialysis tissue oxygen saturation over the 4-hour HD session correlated with pre-dialysis serum calcium and parathyroid hormones. Vascular reactivity was lower in ESRD patients receiving HD or hemodiafiltration than in healthy controls.

Conclusion

Improvement in skeletal muscle microcirculation noted after a HD session was related to adequacy of dialysis. Evaluation of the microcirculation may provide additional information for management of patients on HD and identify novel targets for treatment. These preliminary findings need to be tested using a larger data set.

Ischemic brain injury in hemodialysis patients: which is more dangerous, hypertension or intradialytic hypotension?

Abnormalities of cognitive function and high levels of depression incidence are characteristic of hemodialysis patients. Although previously attributed to the humoral effects of uremia, it is becoming increasingly appreciated that many elements of the overall disease state in CKD patients contribute to functional disturbances and physical brain injury. These factors range from those associated with the underlying primary diseases (cardiovascular, diabetes etc.) to those specifically associated with the requirement for dialysis (including consequences of the hemodialysis process itself). They are, however, predominantly ischemic threats to the integrity of brain tissue. These evolving insights are starting to allow nephrologists to appreciate the potential biological basis of dependency and depression in our patients, as well as develop and test new therapeutic approaches to this increasingly prevalent and important issue. This review aims to summarize the current understanding of brain injury in this setting, as well as examine recent advances being made in the modification of dialysis-associated brain injury.

Defining uremic arterial functional abnormalities in patients recently started on haemodialysis: combined in vivo and ex vivo assessment

Endothelial dysfunction is a key initiating event in vascular disease in chronic kidney disease (CKD) patients and haemodialysis (HD) patients exhibit significant vascular abnormalities. To understand this further, we examined how ex vivo intrinsic function in isolated arteries correlates with in vivo assessments of cardiovascular status in HD patients. Abdominal fat biopsies were obtained from 11 HD patients and 26 non-uremic controls. Subcutaneous arteries were dissected and mounted on a wire myograph, and cumulative concentration-response curves to noradrenalin, endothelin-1, a thromboxane A₂ agonist (U46619), angiotensin II, vasopressin, bradykinin (BK), acetylcholine (ACh) and sodium nitroprusside (SNP) were constructed. Pulse wave velocity and blood pressure were measured in HD patients. Enhanced (P<0.05−0.0001) maximal contractile responses (R_max) to all spasmogens (particularly vasopressin) were observed in arteries from HD patients compared to controls, and this effect was more pronounced in arteries with an internal diameter>600 µm. The potency (pEC₅₀) of U46619 (P<0.01) and vasopressin (P<0.001) was also increased in arteries>600 µm of HD patients. The maximal relaxant response to the endothelium-dependent dilators ACh and BK were lower in HD patients (P<0.01-P<0.0001) (worse for ACh than BK); however the endothelium-independent dilator SNP was similar in both groups. PWV was significantly correlated with the vasoconstrictor response to vasopressin (P = 0.042) in HD patients. HD patients are primed for hypertension and end organ demand ischaemia by a highly sensitised pressor response. The failure of arterial relaxation is mediated by endothelial dysfunction. Intrinsic vascular abnormalities may be important in sensitising HD patients to recurrent cumulative ischaemic end organ injury.

Exploring haemodynamics of haemodialysis using extrema points analysis model

Background

Haemodialysis is a form of renal replacement therapy used to treat patients with end stage renal failure. It is becoming more appreciated that haemodialysis patients exhibit higher rates of multiple end organ damage compared to the general population. There is also a strong emerging evidence that haemodialysis itself causes circulatory stress. We aimed at examining haemodynamic patterns during haemodialysis using a new model and test that model against a normal control.

Methods

We hypothesised that blood pressures generated by each heart beat constantly vary between local peaks and troughs (local extrema), the frequency and amplitude of which is regulated to maintain optimal organ perfusion. We also hypothesised that such model could reveal multiple haemodynamic aberrations during HD. Using a non-invasive cardiac output monitoring device (Finometer®) we compared various haemodynamic parameters using the above model between a haemodialysis patient during a dialysis session and an exercised normal control after comparison at rest.

Results

Measurements yielded 29,751 data points for each haemodynamic parameter. Extrema points frequency of mean arterial blood pressure was higher in the HD subject compared to the normal control (0.761Hz IQR 0.5-0.818 vs 0.468Hz IQR 0.223-0.872, P < 0.0001). Similarly, extrema points frequency of systolic blood pressure was significantly higher in haemodialysis compared to normal. In contrary, the frequency of extrema points for TPR was higher in the normal control compared to HD (0.947 IQR 0.520-1.512 vs 0.845 IQR 0.730-1.569, P < 0.0001) with significantly higher amplitudes.

Conclusion

Haemodialysis patients potentially exhibit an aberrant haemodynamic behaviour characterised by higher extrema frequencies of mean arterial blood pressure and lower extrema frequencies of total peripheral resistance. This, in theory, could lead to higher variation in organ perfusion and may be detrimental to vulnerable vascular beds.

Premature aging of the microcirculation in patients with advanced chronic kidney disease

Background

Increasing age and advanced chronic kidney disease (CKD) are both associated with an attenuated vasodilator response of the skin microcirculation. In the present study, we investigated the effect of aging on microvascular reactivity in patients with advanced CKD.

Methods

Acetylcholine (ACh)-mediated endothelium-dependent vasodilation and sodium nitroprusside (SNP)-mediated endothelium-independent vasodilation were assessed by iontophoresis combined with laser Doppler flowmetry. Microvascular function was compared between 52 patients with advanced CKD (stage 4–5: n = 16; end-stage renal disease: n = 36) and 33 healthy control subjects. As aging has an important effect on microvascular function, both control subjects and CKD patients were divided in subgroups younger and older than 45 years. Linear regression analysis was applied to assess potential associations between microvascular function and various demographic and clinical parameters.

Results

There were three main findings. (1) In young patients with advanced CKD, both ACh- and SNP-mediated vasodilations were impaired if compared to young healthy controls (p = 0.04 and p = 0.056, respectively). (2) In young patients with advanced CKD, microvascular function was similar to old healthy controls and elderly patients with advanced CKD. (3) Whereas age was inversely associated with microvascular function in healthy controls (log ACh-mediated vasodilation R = −0.41; p = 0.02 and log SNP-mediated vasodilation R = −0.38; p = 0.03), no such relation was found in patients with advanced CKD.

Conclusions

Our results are consistent with premature aging of the microvascular vasodilatory capacity in patients with advanced CKD.

Sequence-based polymorphisms in the mitochondrial D-loop and potential SNP predictors for chronic dialysis

Background

The mitochondrial (mt) displacement loop (D-loop) is known to accumulate structural alterations and mutations. The aim of this study was to investigate the prevalence of single nucleotide polymorphisms (SNPs) within the D-loop among chronic dialysis patients and healthy controls.

Methodology and Principal Findings

We enrolled 193 chronic dialysis patients and 704 healthy controls. SNPs were identified by large scale D-loop sequencing and bioinformatic analysis. Chronic dialysis patients had lower body mass index, blood thiols, and cholesterol levels than controls. A total of 77 SNPs matched with the positions in reference of the Revised Cambridge Reference Sequence (CRS) were found in the study population. Chronic dialysis patients had a significantly higher incidence of 9 SNPs compared to controls. These include SNP5 (16108Y), SNP17 (16172Y), SNP21 (16223Y), SNP34 (16274R), SNP35 (16278Y), SNP55 (16463R), SNP56 (16519Y), SNP64 (185R), and SNP65 (189R) in D-loop of CRS. Among these SNPs with genotypes, SNP55-G, SNP56-C, and SNP64-A were 4.78, 1.47, and 5.15 times more frequent in dialysis patients compared to controls (P<0.05), respectively. When adjusting the covariates of demographics and comorbidities, SNP64-A was 5.13 times more frequent in dialysis patients compared to controls (P<0.01). Furthermore, SNP64-A was found to be 35.80, 3.48, 4.69, 5,55, and 4.67 times higher in female patients and in patients without diabetes, coronary artery disease, smoking, and hypertension in an independent significance manner (P<0.05), respectively. In patients older than 50 years or with hypertension, SNP34-A and SNP17-C were found to be 7.97 and 3.71 times more frequent (P<0.05) compared to patients younger than 50 years or those without hypertension, respectively.

Conclusions and Significance

The results of large-scale sequencing suggest that specific SNPs in the mtDNA D-loop are significantly associated with chronic dialysis. These SNPs can be considered as potential predictors for chronic dialysis.

Are there neurological consequences of recurrent intradialytic hypotension?

Structural abnormalities of the brain are common in hemodialysis (HD) patients, as are a wide range of severe functional deficiencies of cerebral function. Both depression and increasing dependency are highly prevalent in HD patients and worsen severely within the first 12 months of dialysis initiation. HD, as it is commonly practiced, is associated with significant recurrent episodes of circulatory stress. This results in acute injury to the heart, skin, kidney and gut, and drives longer term end-organ chronic injury. This article aims to explore the hypothesis that the cerebral microcirculation is also sensitive to dialysis-based circulatory stress (and other multiorgan consequences of recurrent dialysis-induced ischemia), and that this may drive specific patterns of brain injury with resultant psychiatric and functional consequences.

Uraemic vasculopathy in children with chronic kidney disease: prevention or damage limitation?

Since the inception of pediatric dialysis programmes nearly 50 years ago, there have been vast improvements in both the technology and expertise in the care of children with chronic kidney disease (CKD). Nevertheless, children on dialysis continue to have a significantly higher mortality than their healthy peers and cardiovascular disease (CVD) is the most common cause of death in this group. Chronic kidney disease is described as the "perfect storm" of risk factors for CVD development, and vascular calcification is a highly regulated cell-mediated process with several promoters and inhibitors of calcification. CVD begins early in the course of CKD and there is an independent and graded association between cardiovascular morbidity and renal decline. Also, it is shown that once vascular damage and calcification begin, they progress inexorably in the uraemic milieu and may only be partially reversed after successful transplantation. Thus, preventing the development of CVD is key, and early identification and management of specific CVD-related risk factors should begin from the early stages of CKD. While the vasculopathy of childhood CKD is clearly multifactorial, clinical, epidemiological and cell biology studies provide converging evidence pointing to the role of dysregulated mineral metabolism as an important modifiable risk factor in the development of vascular calcification. In this review we focus on the role of calcium, phosphate, parathyroid hormone and vitamin D in ectopic vascular calcification, and discuss the role of screening, early intervention and management of established vascular calcification.

Capillary rarefaction in advanced chronic kidney disease is associated with high phosphorus and bicarbonate levels

BACKGROUND

In patients with chronic kidney disease (CKD), disorders of mineral metabolism are associated with vascular calcifications and mortality. Microvascular dysfunction, by affecting flow resistance and tissue perfusion, may explain the cardiovascular sequelae of CKD-associated disorders of mineral metabolism. We investigated whether advanced CKD is associated with a decrease in the functional and structural number of capillaries in skin and subsequently whether capillary rarefaction is related to mineral metabolism.

METHODS

Capillary density was measured by nailfold microscopy in 19 predialysis and 35 CKD Stage 5 (CKD5) patients and 19 controls. In CKD patients, calcium, phosphorus, parathyroid hormone, 25-hydroxyvitaminD3 (25vitD3) and 1,25-dihydroxyvitaminD3 (1,25vitD3) were analysed as well.

RESULTS

Capillary density at baseline was 42 ± 15/mm(2) in predialysis patients, 45 ± 17/mm(2) in CKD5 patients and 56 ± 20/mm(2) in controls (patients versus controls, respectively, P < 0.05 and P = 0.05). Absolute capillary recruitment during post-occlusive reactive hyperaemia was 17 ± 7/mm(2), 14 ± 6/mm(2) and 23 ± 8/mm(2), respectively (P < 0.05 for both patients and controls). Capillary density during venous occlusion was 59 ± 20/mm(2), 59 ± 21/mm(2) and 77 ± 21/mm(2), respectively (P < 0.05 for both patients and controls). In multiple regression analysis, both serum phosphorus and bicarbonate values were independently and inversely associated with capillary density at baseline (r(2) of model = 19%) as well as during venous occlusion (r(2) of model = 28%). Furthermore, both serum phosphorus and bicarbonate were inversely and female gender positively correlated with capillary density during recruitment (r(2) of model = 37%).

CONCLUSION

Advanced CKD is characterized by an impaired functional and structural capillary density in skin, which is related to both high phosphorus and bicarbonate values.

Peritoneal dialysis is not associated with myocardial stunning

BACKGROUND

Hemodynamic changes during hemodialysis can precipitate subclinical myocardial ischemia, which over time contributes to the development of cardiac failure and is associated with a poor prognosis. Peritoneal dialysis (PD) is also associated with acute changes in systemic hemodynamics and a similarly high incidence of cardiovascular disease; we therefore sought to examine whether the hemodynamic effects of a PD exchange would be sufficient to induce subclinical myocardial ischemia.

METHODS

10 patients on PD entered a prospective observational study to determine whether left ventricular (LV) regional wall motion abnormalities (RWMAs) developed following a dialysate exchange. Serial echocardiography with quantitative analysis was used to assess ejection fraction and regional systolic LV function (shortening fraction). Blood pressure (BP) and hemodynamic variables were measured using continuous pulse wave analysis.

RESULTS

We observed a very low frequency of RWMA development (5/100 regions). Only 1 patient had more than 1 RWMA and 6 patients were entirely unaffected. Overall mean shortening fraction increased when comparing pre and post values for both 2-chamber (from 3.06% ± 1.5% to 4.26% ± 1.3%, p = 0.001) and 4-chamber (from 3.00% ± 0.7% to 3.67% ± 0.9%, p = 0.021) analyses. Mean arterial pressure fell by a small degree during drainage of dialysate, with a larger rise in BP observed during instillation. These changes were driven by changes in peripheral resistance that fell during drainage and rose during instillation.

CONCLUSIONS

In contrast to hemodialysis, the acute effects of PD do not result in subclinical myocardial ischemia.

Hemodialysis-induced repetitive myocardial injury results in global and segmental reduction in systolic cardiac function

BACKGROUND AND OBJECTIVES

Hemodialysis (HD)-induced regional wall motion abnormalities (RWMAs) are common in HD patients and driven by ischemia. In nondialysis patients, repeated ischemia leads to chronic reduction in left ventricular (LV) function. HD-induced myocardial ischemia may initiate the same process. We examined the effect of HD-induced repetitive myocardial stunning on global and regional LV function.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

We analyzed data from 30 patients, previously identified as developing HD-induced myocardial ischemia. Serial echocardiographic assessments of global and regional LV performance were performed at baseline and repeated after 12 mo.

RESULTS

Several patients developed segments with a fixed reduction in systolic function of >60% after 1 yr. In this patient group, there was a significant reduction in resting LV ejection fraction (EF) from 61.5 +/- 10.1% to 52.9 +/- 8.6% (P < 0.007). Peak LV EF in response to dialysis also decreased from 59.5 +/- 10% versus 49.9 +/- 6.5% (P < 0.003), with a consequent increase in HD-induced hypotension (P < 0.0001).

CONCLUSIONS

HD-induced myocardial stunning may progress over 12 mo to the development of regional fixed systolic dysfunction, consistent with underlying myocardial hibernation and fibrosis. This may be an important and potentially modifiable process in the development of heart failure in HD patients.

Higher arteriovenous fistulae blood flows are associated with a lower level of dialysis-induced cardiac injury

Native arteriovenous fistulae (AVF) remain the vascular access of choice for hemodialysis (HD). Despite being associated with superior long-term outcomes (cf. catheter use), little is known about the systemic hemodynamic consequences of AVFs. Repetitive myocardial injury (myocardial stunning) is an under-recognized common consequence of HD. The aim of this study was to examine the impact of AVF flow (Qa) on dialysis-induced cardiac injury. We studied 50 chronic HD patients. All patients underwent echocardiography (and subsequent quantitative offline analysis) at baseline, during and post dialysis, to assess left ventricular function and the development of regional wall motion abnormalities. Qa was measured using ionic dialysance. Patients were divided into Qa tertiles (<500, mean 291+/-101 mL/min, 500-1000, mean 739+/-130 mL/min and >1000, mean 1265+/-221 mL/min). There were no significant differences between the groups in terms of age, sex, diabetes, or resting ejection fraction. Patients with Qa>1000 mL/min had a lower prevalence of left ventricular hypertrophy (55% vs. 76%, P=0.01). Dialysis-induced myocardial stunning (seen in 65% of the patients studied) was significantly and sequentially reduced in those patients with higher Qas. This was seen in a lower number of segments and ventricular regions developing regional wall motion abnormalities, as well as a significantly reduced mean and cumulative percentage reduction in fractional shortening of those ventricular segments affected (-187+/-37%, -161+/-26%, and -101+/-25%, respectively, P=0.04). Relatively higher AVF flows appear to be associated with a lower level of observed HD-induced cardiac injury.

Upregulation of Matrix Metalloproteinase-2 in the Arterial Vasculature Contributes to Stiffening and Vasomotor Dysfunction in Patients With Chronic Kidney Disease

Background— Cardiovascular disease is the leading cause of mortality in chronic kidney disease patients on maintenance dialysis. Given the importance of matrix metalloproteinase-2 (MMP-2) in matrix integrity, vascular cell function, and structural stability, we hypothesized that MMP-2 was elevated in the macrovasculature in dialyzed chronic kidney disease patients compared with chronic kidney disease patients not on dialysis and kidney donors.

Methods and Results— Arteries from live kidney donors (A donor ; n=30) and recipients (nondialysis [A nondialyzed ], n=17; dialysis [A dialyzed ], n=23 [peritoneal dialysis, n=10; hemodialysis, n=13]) were harvested during the transplantation procedure. Compared with A donor , MMP-2 upregulation was evident in both recipient groups. Protein expression of latent plus active MMP-2 in A dialyzed was 2-fold that in A nondialyzed . MMP-2 activity increased with length of dialysis ( r =0.573, P =0.004). In A dialyzed , medial elastic fiber fragmentation was pronounced, and the ratio of external elastic lamina to media was negatively correlated with MMP-2 activity ( r =−0.638, P =0.001). A dialyzed was 25% stiffer than A nondialyzed ; this increased stiffness correlated with MMP-2 activity ( r =0.728, P <0.0001) and the severity of medial calcium deposition ( r =0.748, P =0.001). The contractile function and endothelium-dependent relaxation were reduced by 35% to 55% in A dialyzed and were negatively associated with MMP-2 activity ( r =−0.608, P =0.002; r =−0.520, P =0.019, respectively). Preincubation with MMP-2 inhibitor significantly improved contractility and relaxation in A dialyzed .

Conclusions— We describe a strong correlation between MMP-2 activation and elastic fiber disorganization, stiffness, calcification, and vasomotor dysfunction in the arterial vasculature in dialyzed chronic kidney disease patients. These findings may contribute to an improved understanding of mechanisms important in vascular health in chronic kidney disease patients.

Advances in the cardiovascular assessment of patients with chronic kidney disease

Cardiovascular mortality is grossly elevated in patients with chronic kidney disease (CKD), and is associated with a wide variety of structural and functional abnormalities. These issues have driven additional attempts to further characterise these abnormalities to elucidate the pathophysiology involved, assess individual risk and/or target and monitor therapies specifically directed at the cardiovascular (CV) system. This review aims to assess the techniques that are currently available for the study of the CV system. This includes conventional assessments of the whole CV system from heart to peripheral microcirculation (although not deal with VC assessment), as well as the key functional consequences relating to stress induced cardiovascular reserve, perfusion and vasoregulation. In addition this review will introduce a variety of techniques aiming to expand the envelope of conventional measurements.