Validation in the sheep of an ultrasound velocity dilution technique for haemodialysis graft flow

BACKGROUND: A simple, rapid, inexpensive method for measuring the flow in a patient's vascular access would permit routine monitoring during haemodialysis, and hence provide information of access graft deterioration sufficiently early to increase the success of minimally invasive remedial procedures. This paper reports the validation of such a method in animals. METHODS: A PTFE graft was implanted in sheep between the carotid artery and the jugular vein. While the sheep was under general anaesthesia and on an haemodialysis circuit, ultrasound velocity in its blood was perturbed by the injection of a 5-10 ml bolus of isotonic NaCl. The pump tubing flow was measured by a transit-time blood flow meter. This flow was combined with the areas of perturbation generated by the injection before and after mixing in the access flow to estimate graft flow. The calculated graft flow was compared to flow measured directly by a transit-time probe on the same carotid artery. RESULTS: Over a 10-fold range, 120-1260 ml/min, graft flow measured by ultrasound velocity dilution agreed well with graft flow measured directly with a scatter of 76 ml/min about the regression line. CONCLUSION: Ultrasound velocity dilution provides a method for measuring flow in the graft accurate enough for clinical evaluation of patients on dialysis.      

The development of acid-base reaction cements as formulations for the controlled release of trace elements

Novel acid-base reaction cements have been developed for use as controlled release formulations. Many new ones have been discovered and assessed; these include those which are capable of releasing copper, cobalt or selenium singly or in combination. A selection was made of the most suitable formulations for this purpose and these were subjected to field trials.     

Positive and negative staircase effect during single twitch and train-of-four stimulation: a laboratory study in dogs

A positive staircase effect is well documented during neuromuscular monitoring. However, the increase in twitch amplitude may not remain stable over time. We compared the staircase phenomenon and twitch stability during single twitch (ST) or train-of-four (TOF) stimulation in anesthetized dogs. Force of contraction was measured in ten dogs. Each thoracic limb was stimulated with ST 0.1 Hz or TOF q 12 s for 25 min (random order). No neuromuscular blockers were administered. Every 5 min, ST and T1 amplitudes were compared within and between groups. Stability of twitch amplitude (<5 % change in 5 min) was also evaluated. ST and T1 amplitude increased over time without significant differences between groups. After 10 min of ST stimulation, the average ST amplitude had increased significantly to 107 %, and remained unchanged thereafter. T1 amplitude was significantly greater than baseline only at 5 (111 %) and 10 min (109 %); a decline towards baseline occurred thereafter. Stability was reached after 15 min for all dogs in the ST group, however, three dogs continued to have changes >5 % with TOF. An initial increase in ST amplitude remained stable over the observation period, but the increase in T1 amplitude during TOF was frequently followed by a decay. A stable twitch amplitude (variation <5 % in 5 min) was observed in all dogs with ST after 15 min of stimulation, which was not the case during TOF stimulation. Therefore, it appears at least in dogs, that ST might offer some advantages over T1 for measuring twitch amplitude.     

Effect of Direction and Rate of Change of Calcium on Parathyroid Hormone Secretion in Uraemia

We have studied the control of amino-terminal parathyroid hormone(PTH) secretion in haemodialysis patients in response to slowor fast calcium infusion and during acute hypocalcaemia. Innine patients, fast calcium infusion (0.4 mmol/kg bodyweightper hour) for 15 min increased ionised calcium and reduced PTH,with an initial t of 12.8 min. After the infusion had ceased,calcium decreased steadily, and PTH increased, mean PTH reachingbaseline values when calcium was still significantly greaterthan pre-infusion values. During slow calcium infusion for 2.5h (0.1 mmol/kg bodyweight per hour), parathyroid suppressionwas evident at 15 min, when the calcium increment was only 0.03mM. After 60 min, PTH did not decrease further despite progressivehypercalcaemia. Hypocalcaemic haemodialysis led to rapid increasesin PTH. After 15 min, the mean calcium decrement was 0.09 mM(P<0.01) and the mean PTH increment was 283 pg/ml (P<0.01).The parathyroid response was maximal at 30 min, and did notincrease subsequently, despite progressive hypocalcaemia fora further 90 min. During recovery from hypocalcaemia, PTH reducedand, despite comparable hypocalcaemia, PTH during periods ofincreasing calcium was always lower at a given calcium concentrationthan while calcium was decreasing. This influence of the directionof change of calcium was not seen during hypocalcaemia. Theresults showed that even in advanced renal disease, the parathyroidglands are highly responsive to small initial increments (0.03mM) and decrements (0.09 mM) in blood calcium, though less soto further perturbation of blood calcium. During hypocalcaemia,the parathyroid glands respond to both the absolute value ofblood calcium and also to the direction of change of calcium.     

Use of a catheter-based system to measure blood flow in hemodialysis grafts during angioplasty procedures

PURPOSE: The goals of this investigation were to evaluate the accuracy and reliability of the Angioflow meter system with use of in vitro and in vivo methods and to compare it to the standard Transonics HD01 system in a clinical setting. MATERIALS AND METHODS: The Angioflow meter system consists of a 6-F endovascular catheter and a laptop computer containing proprietary software for this application. Bench-top testing with use of a flow model was performed to determine the accuracy of the Angioflow meter system. Initial in vivo studies were performed with use of an animal model to assess the endovascular performance of the Angioflow meter system. Subsequently, a human clinical trial was performed to compare the Angioflow meter to the standard Transonics HD01 system. Twenty-five patients with dysfunctional (<600 mL/min) hemodialysis grafts were referred for fistulography and angioplasty. Intragraft blood flow measurements were obtained before and after angioplasty with use of both the Angioflow meter system and the Transonics HD01 system. A comparison of the two systems was performed. RESULTS: Bench-top testing and animal studies demonstrated an excellent (r =.98) correlation between the measurements of the Angioflow meter and volumetric flow measurements. In the clinical trial, there was reasonable correlation (r =.72) between the blood flow measurements obtained with use of the Angioflow meter and Transonics HD01 system. The reproducibility of consecutive measurements with the Angioflow meter was excellent (r =.98). The mean increase in intragraft blood flow after angioplasty was 320 mL/min. CONCLUSION: The Angioflow meter is an accurate and reliable endovascular device for measuring intragraft blood flow during interventional procedures. Use of this catheter-based system should prove beneficial for quantifying the success of endovascular interventions, the assessment of arterial inflow, and identification of inconspicuous lesions.     

Modification of maternal and fetal oxygenation with the use of tracheal gas infusion

A new technique is described for producing changes in fetal blood gases in the chronically instrumented pregnant sheep. Gas mixtures were infused directly into the maternal trachea. Maternal and fetal carotid arterial blood gases and pH were measured. Air infusion at 16 L X min-1 produced no change. Oxygen infusion caused significant increases in maternal PaO2 at 2 L X min-1 and in fetal PaO2 at 4 L X min-1. Nitrogen infusion significantly decreased maternal anf fetal PaO2 at 4 L X min-1. During 4 L X min-1 oxygen infusion, maternal PaO2 rose rapidly to plateau at 314 +/- 47 mm Hg at 4 minutes and fetal PaO2 rose to plateau at 28.7 +/- 2.8 mm Hg after 7 to 8 minutes. Maternal PaO2 fell to 56.4 +/- 4.3 mm Hg during nitrogen infusion (4 L X min-1) while fetal PaO2 fell to 15.9 +/- 1.8 mm Hg. Continuous infusion for 5- to 6-hour periods produced a consistent rise in maternal PaO2 during oxygen infusion and a consistent decrease during nitrogen infusion. Tracheal infusion of gases can be used to change maternal and fetal PaO2 rapidly and predictably.     

Regulation of preproparathyroid hormone messenger RNA and hormone synthesis in human parathyroid adenomata

Preproparathyroid hormone (preproPTH) mRNA and PTH secretion were measured in human parathyroid adenomata (n = 8) cultured in 1.0 or 3.0 mmol calcium/l and compared with changes in bovine parathyroid glands (n = 3) as a control. Incubation of bovine glands in 3.0 mmol calcium/l for 24 h resulted in a fall in mRNA levels to 47.3 +/- 21.7% (mean +/- S.D.) compared with cells incubated in 1.0 mmol calcium/l, with a concomitant decrease in secretion to 62.6 +/- 10.8%. These values fell further to 30.1 +/- 15.5% and 42.1 +/- 18.7% respectively after 48-h incubation. One human adenoma responded to high levels of calcium in a similar manner with mRNA levels falling to 44.6 +/- 11.9% and secretion to 30.3 +/- 17.3% within 24 h. However, in the majority of adenomata (seven out of eight), after 24-h incubation in 3.0 mmol calcium/l, mRNA levels fell to 54.1 +/- 14.6% but there was no change in secretion. In two of these adenomata which were cultured for 48 h, there was no suppression of secretion despite mRNA levels having fallen to approximately 60% of control. Incorporation of [35S]methionine into PTH secreted from human adenomatous cells was quantified by densitometry. There was no difference in the amount of radiolabelled PTH secreted from cells incubated in high levels of calcium compared with those in normal levels of calcium. In similar experiments, the effects of high calcium on the synthesis of PTH in bovine cells was assessed by determination of radiolabelled intracellular PTH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary carbohydrate restriction in type 2 diabetes mellitus and metabolic syndrome: time for a critical appraisal

Background

Lifestyle, genetics and environmental factors are established determinants of bone density. We aimed to describe the bone characteristics of competitive top-ranked Nigerian male athletes using calcaneal ultrasound and to assess whether intensive training promotes higher bone density in an environment with reportedly low calcium intake; to compare the bone characteristics of footballers with runners and other sportsmen; and to assess the correlation of stiffness index (SI) with activity level, since energy expenditure correlates with length of training and by extension, magnitude of skeletal loading.

Methods

We recruited 102 male athletes: these included football (n = 68), running (n = 15), handball (n = 7), taekwando (n = 6), cycling (n = 2), judo (1), badminton (1) and high jump (1). Anthropometric data were first recorded on a structured form and energy expenditure was indirectly estimated with a validated questionnaire. Bone density was assessed using the Lunar Achilles+ calcaneal ultrasonometer.

Results

The mean age of athletes was 25 ± 6 years. The means of BMI and energy expenditure were 21.9 ± 2.0 kg/m² and 35.0 ± 13.7 kcal/kg/day, respectively. Footballers were younger (p < 0.001) and heavier (p < 0.001) than runners. Football was a significant determinant of BUA independent of age, BMI and energy expenditure (p = 0.001). Football was also a significant determinant of SOS independent of age, height, weight and BMI (p < 0.001). The mean SI was 127 ± 16 and the median T-score was 0.82 (-1.88, 3.35). The mean SI of footballers (130 ± 15), runners (130 ± 12) and other sportsmen (115 ± 18) differed significantly (p = 0.001). Multivariate analyses revealed that football (p < 0.001) and running (p < 0.001) were significant determinants of SI independent of age and BMI. Footballers when compared with other sportsmen had a higher mean SI independent of age and BMI (p < 0.001). Age was not correlated with SI. The median T-score of footballers, 0.94 (-1.0, 3.35) was higher than that of other sportsmen.

Conclusion

Repetitive skeletal loading at the heel has the potential to improve bone density in black male athletes. The magnitude of increase may be higher in medium impact sports such as soccer and running compared with low or non-impact sports such as judo or taekwando, and is independent of age and BMI. However, future longitudinal data will be required to support our observations.     

Implantation success and infection in cardiovascular implantable electronic device procedures utilizing an antibacterial envelope

Background: Cardiovascular implantable electronic device (CIED) infection rates are increasing faster than implantation rates. More effective antimicrobial prophylaxis may help reduce CIED infections and improve clinical outcomes. The AIGIS_Rx^® antibacterial envelope is a polymer mesh implanted in the generator pocket with the CIED. After implantation it releases two antibiotics, minocycline and rifampin, that have been shown to reduce infections associated with other medical devices. The purpose of this retrospective cohort study is to determine the rate of CIED implantation success and CIED infection in procedures utilizing the antibacterial envelope. Methods: This study enrolled consecutive CIED procedures utilizing the antibacterial envelope at 10 US academic, community, and Veterans Affairs medical centers. Procedures following an explantation for a prior CIED infection or off‐label use of the antibacterial envelope were excluded. Results: The 624 eligible procedures (age 70 ± 13 years, 68.1% men, 27.2% renal insufficiency, 35.4% oral anticoagulant use, 67.8% replacement/revision procedures) utilized pacemakers (35%), implantable cardioverter‐defibrillators (ICD)(29%), and cardiac resynchronization therapy with defibrillator devices (CRT‐D)(36%). Nearly half of the patients (49%) had at least three predefined risk factors for CIED infection. CIED implantation was successful in 621 procedures (99.5%[95% confidence interval (CI) 98.8–99.9]). There were three major infections (0.48%[95%CI 0.17–1.40]) after 1.9 ± 2.4 months follow‐up. The infections followed one ICD revision and two CRT‐D replacements. There were seven deaths; none was a result of the antibacterial envelope or the CIED procedure. Conclusions: CIED procedures that utilized an antibacterial envelope had a high rate of CIED implantation success (>99%). Although the follow‐up to date is short, there was also a low rate of infection (<0.50%) in this population at high risk for CIED infection. (PACE 2011; 34:133–142)