Methods

This protocol was approved by the Research Ethics Boards of the Toronto General and Humber Regional Hospitals. Consecutive subjects were recruited from patients at these centers undergoing training prior to conversion from CHD to NHD. None had left ventricular systolic dysfunction or any acute illness. Written informed consent was obtained from each patient.

Each subject was studied first while receiving CHD and again 1 and 2 months after conversion to a stable dose of NHD. Experiments were conducted in the Toronto General Hospital Clinical Cardiovascular Physiology Laboratory. Baseline studies were performed the morning after a conventional hemodialysis day (i.e. a minimum of 18 hours after dialysis). To minimize circadian variation, and replicate steady state NHD conditions, subsequent experiments were performed at the same time of day (a minimum of four hours after the regular NHD session). All subjects abstained from tobacco and caffeine on each study day.

Heart rate was measured continuously. Resting blood pressure was determined non-invasively from the arm contra-lateral to the arteriovenous fistula (Dinamap Pro 100, Critikon LLC, Tampa, Florida). An 18–gauge peripheral venous cannula was inserted into an antecubital vein of the arm opposite to the vascular access. After 30 minutes of supine rest, blood was drawn to determine plasma urea and ADMA concentrations to relate these variables to concurrently determined vascular responsiveness.

Vascular responsiveness

EDV and endothelium independent vasodilation (EIV) in the brachial artery of the arm contra-lateral to the dialysis fistula were then determined by quantifying responses to post-ischemic reactive hyperemia and sublingual nitroglycerin (GTN). Briefly, the arterial diameter was imaged with a 7 – 10 MHz linear array transducer (B mode ultrasound: ATL UM9, ATL Ultrasound, Bothell, Washington). The arm and transducer were stabilized, and a longitudinal section of the brachial artery was scanned across a segment 2 to 5 cm above the elbow. To induce post-ischemic reactive hyperemia in the forearm, an occluding blood pressure cuff placed at least 5 cm below the antecubital fossa was inflated to 50 mmHg above systolic pressure for 4.5 minutes. A second 2 minute scan was acquired, commencing 30s before cuff deflation. GTN (400ug) was administered 10 minutes after hyperemia. Diameter and flow images were acquired 3 minutes later. Arterial responses to hyperemia and GTN expressed as the percent increase from baseline diameter were analysed blindly by an investigator unaware of the patient study session or intervention, or whether the image has acquired pre or post intervention1.

Dialysis prescriptions

Initially, each patient received CHD over 4 hours, 3 times per week. Vascular access was achieved through either a long-term internal jugular catheter or an arteriovenous fistula. A dialysate flow rate of 500 – 750 ml per minute and F80 polysufone dialyzers (Fresenius Medical Care, Lexington, Massachusetts) were used. After conversion to NHD, patients received NHD at home for 8 to 10 hours 6 nights a week via similar vascular access. A dialysate flow rate of 300 ml per minute and F80 polysufone dialyzers or Polyflux-17 polyamide dialyzers (Gambro Inc., Lund, Sweden) were used.

Dialysis dose per treatment was estimated by equilibrated Kt/V (eKt/V) as described by Daugirdas and colleagues where eKt/V = spKt/V – 0.6(spKt/V)/t + 0.03 (spKt/V = single pool Kt/V, K = delivered clearance, t = dialysis time and V = urea distribution volume)2. Single pool Kt/V was determined using blood urea reduction ratio3.

Metabolic Analyses

Plasma ADMA concentration was determined by published ELISA method4. Plasma samples were kept at –70°C until analysis. The concentration of ADMA in the plasma of healthy individuals, as measured by this assay, has a mean value of 0.65 mmol/L with a limit of quantification of 0.05 mmol/L.

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References

1. Chan CT, Harvey PJ, Picton P, Pierratos A, Miller JA, Floras JS. Short-term blood pressure, noradrenergic, and vascular effects of nocturnal home hemodialysis. Hypertension. 2003;42:925-31.

2. Daugirdas JT, Greene T, Depner TA, Gotch FA, Star RA. Relationship between apparent (single-pool) and true (double-pool) urea distribution volume. Kidney International. 1999;56:1928-33.

3. Jindal KK, Manuel A, Goldstein MB. Percent reduction in blood urea concentration during hemodialysis (PRU). A simple and accurate method to estimate Kt/V urea. ASAIO Transactions. 1987;33:286-8.

4. Schulze F, Wesemann R, Schwedhelm E, Sydow K, Albsmeier J, Cooke JP, Boger RH. Determination of asymmetric dimethylarginine (ADMA) using a novel ELISA assay. Clin Chem Lab Med. 2004;42:1377-83.