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Biomedical subjects

N A Hoenich

Publications and source records attributed to N A Hoenich.

At least 19 recordsLinked to original sources
PubMed1992

Cellulose-based haemodialysis membranes: biocompatibility and functional performance compared.

Regenerated cellulose membranes are widely used in the treatment of renal failure. The presence of hydroxyl (OH) groups on the membrane surface plays an important role in initiating complement activation and also influences thrombogenicity. The OH groups may be masked or reduced by alteration of the manufacturing process of the membrane. We have undertaken a clinical study of four cellulose-based membranes (Cuprophan, Hemophan, cellulose acetate, and cellulose triacetate) in which the hydroxyl groups of the membrane have been replaced and the magnitude of replacement has varied from less than 1% to greater than 80%, to assess the role that these modifications play in functional performance, biocompatibility (neutropenia, leukocyte activation, anaphylatoxin generation, and hypoxaemia). Our findings indicate that there does not appear to be a straightforward correlation between the numbers of hydroxyl groups replaced and modification of biocompatibility, suggesting that not all hydroxyl groups behave in a similar way.

Cellulose↗
PubMed1992

Characterisation and evaluation of a new double lumen central venous catheter.

The performance of a new double lumen central venous haemodialysis catheter was tested in two laboratory models. In a bench model the patient's venous system was simulated by a reservoir from which water or glycerol was drawn through a fixed tube. A double lumen silastic catheter was then inserted into the tube, as it would in a major vein, with the tip directed away from the direction of flow. The catheter was linked to a dialysis circuit incorporating pressure sensors and dye was infused at constant rate so that recirculation at the tip could be measured and found to be less than 5%. The same catheters were inserted operatively into the superior vena cava via the external jugular vein of three pigs (weight 27-31 kg). The catheters remained patent for four weeks and when connected to an extracorporeal circuit had recirculation and pressure flow characteristics comparable to the bench model in the range 50-400 ml/min. The new double lumen catheter is worthy of clinical evaluation.

Animals↗
PubMed1990

Particle release from haemodialysers.

Release of particles from eight makes of hollow-fibre and one make of flatplate dialyser have been studied, and the relationship between rinsing volume and particles recovered established. In a supplementary study the effect on the number of particles released was assessed when striking the dialyser header during priming. Particle size distribution indicated that the majority of the particles recovered were less than 5 microns in diameter. A separate analysis of the particles in the 5-30 micron size range showed two different patterns of particle release. In the dialysers containing ethylene vinyl acetate (EVAL) or Cellulate the number of particles recovered were within the 95% range of the particles in the rinsing fluid and did not alter with increasing rinsing volume. In the dialysers containing Cuprophan and Hemophan the initial particle numbers were higher but fell rapidly up to a 450 ml rinse volume; increasing the rinse volume to 1050 ml did not alter particle recovery. Analysis of variance failed to differentiate between individual dialysers. Striking the header during priming resulted in a transient statistically nonsignificant increase in the number of particles recovered.

Biocompatible Materials↗
PubMed1990

Particle spallation and plasticiser (DEHP) release from extracorporeal circuit tubing materials.

Particle spallation and plasticiser (DEHP) release from medical grade polyvinylchloride (PVC), co-extruded PVC-polyurethane (PIVIPOL)R and an experimentally produced co-extruded PVC-ethylene vinyl acetate (EVA) has been studied when used with manually occluded and self-occluding peristaltic pumps over a six hour pumping period. The shore hardness of the tubings studied were similar but the luminal coating thickness differed (0.2 mm polyurethane, 0.99 mm EVA). The pattern of particle release was similar for all materials on the pump type used with the majority of particles released being less than 5 microns in diameter. The number of particles greater than 5 microns released was independent of the tubing material but depended on the pump type. Particle release with self-occluding pumps was significantly higher (p less than 0.001) than for the manually occluded pump. Scanning electron microscopy indicated that the particles released originate from the repeated compression and flexing of the insert during pumping which leads to material structural failure. The higher release observed in the case of self-occluding pumps is suggestive of over-occlusion by the springs utilised in the pump. DEHP release (ppm) over a six hour period while perfused at 300 ml/min was significantly reduced for co-extruded tubing (0.56 +/- 0.05 mg (PVC-polyurethane) and 0.12 +/- 0.04 mg (PVC-EVA) compared with PVC (0.74 +/- 0.05 mg).

Diethylhexyl Phthalate↗
PubMed1988

Blood-membrane interactions during haemodialysis with cellulose and synthetic membranes.

Haemodialysis is associated with transient leucopenia, hypoxia and activation of the patient's complement system, mediated by blood-membrane contact. Changes in white blood cell counts, blood gases (PaO2 and PaCO2), carbon monoxide diffusing capacity (DLCO) and complement activation (C3d and C3a) were measured pre-treatment and during dialysis. The degree of complement activation, leucopenia and changes in DLCO were influenced by membrane type; these changes were most marked for cellulosic membranes and were much reduced for synthetic membranes. A significant relationship between the degree of leucopenia and the magnitude of change in DLCO during dialysis was demonstrated.

Acrylic Resins↗
PubMed1988

Surgical management of long-term central venous access in uraemic patients.

Over a 5-year period, 1980-1985, 39 patients from a dialysis population of over 400 treated at this centre experienced major difficulties in achieving adequate access for dialysis by conventional techniques (i.e. arteriovenous fistula or CAPD). This study has evaluated the long-term results of a new approach to circulatory access, central venous catheterisation (CVC) for so called "high risk" patients. CVC consists of inserting a single-lumen CAPD-type silastic catheter into the right atrium via an external or internal jugular vein. Forty-seven catheters have been inserted into 39 uraemic patients. All patients had failed on, or were unsuitable for, conventional access to haemodialysis or CAPD. Ten patients (26%) had previous failed renal transplants. The median duration of catheter use was 7 months (range 1-60 months) and a total of 6500 high-performance dialyses have been performed using this technique. No patient has died of catheter-related problems. The catheters were easily managed by nurses and well tolerated by the patients. The incidence of complications among patients was low: displacement (1), catheter thrombosis (2), skin exit-site infections (5), septicaemia (2). Central venous catheterisation is a method of providing safe and reliable long-term vascular access which is immediately usable by high-risk patients who have either failed on or are unsuitable for conventional circulatory access.

Adolescent↗
PubMed1987

Haemodialysis-induced respiratory changes.

Eight patients receiving maintenance haemodialysis were studied under six different dialysis protocols, comprising Cuprophan and polyacrylonitrile (PAN 15) membranes, each used with dialysate containing 40 mmol/l acetate, 30 mmol/l acetate or bicarbonate (35 mmol/l), all other constituents being identical. Blood and expired gas determinations as well as transfer factor (DLCO) measurements, serum acetate concentrations, and WBC counts were performed. Rapid reductions in arterial oxygen (PaO2) were observed with Cuprophan (P less than 0.001), and with both strengths of acetate. Polyacrylonitrile used with acetate also demonstrated reductions in PaO2 but these were less severe than those observed with Cuprophan. Bicarbonate buffer resulted in a reduction in the severity of hypoxaemia, but failed to totally eliminate its occurrence. Hypoventilation was observed with both strengths of acetate dialysates, but not with bicarbonate. The respiratory exchange ratio decreased by 25% as a result of decreases in lung CO2 excretion when using acetate. Transfer factor declined by 40% for Cuprophan compared with 14% with polyacrylonitrile (P less than 0.01). Leucopenia was more severe with Cuprophan than with polyacrylonitrile. We conclude that amelioration of hypoxaemia may be achieved by the use of bicarbonate, but its cause is multifactorial, with contributions from hypoventilation secondary to dialyser CO2 losses and pulmonary dysfunction due to leucostasis. These observations suggest that the treatment of patients who have compromised cardiovascular function is most optimal with the use of biocompatible membranes which induce minimal leucopenia, used in conjunction with dialysate that utilises bicarbonate as the base replacement.

Blood Gas Analysis↗
PubMed1986

Biocompatibility of haemodialysis membranes.

Haemodialysis is widely used as a method of treatment for renal failure; it relies on diffusion across a semipermeable membrane. The exposure of blood to the membrane is associated with a rapid transient fall in white cells, activation of the complement system and a fall in arterial oxygenation. The interrelationship between these phenomena, their dependence on the type of membrane used and their clinical implications are reviewed and discussed.

Cellulose↗
PubMed1986

Surface alterations in dialysis roller pump inserts: a scanning electron microscopy study.

Scanning electron microscopy has been used in a study of particle spalling from silicone and PVC elastomer inserts of dialysis roller pumps. In an experimental circuit using Isoton II, pump occlusion, pressure, pump revolutions and temperature were monitored. Scanning electron microscopy was performed on inserts exposed to 1-10 h of pumping using Silastic (medical grade) and a Watson-Marlow MHRE pump, with PVC and Pivipol, a polyurethane coated PVC (Bellco) using a Bellco BL705N pump. Changes included longitudinal splits (single and multiple), superficial cracks (random and orientated), deformations of normal surface pattern, holes, craters and detaching particles. There was an increase in these abnormalities with time for all types of pump insert, the changes being most marked for the Silastic/Watson-Marlow pump combination and least prevalent with the PVC/Bellco pump combination.

Humans↗
PubMed1986

Particle spallation induced by blood pumps in hemodialysis tubing sets.

The repeated flexion and compression of pump segments by the rollers of peristaltic pumps results in cracking and abrasion of the inner surfaces of the pump segment, leading to shedding of particles into the extracorporeal circuit. A series of studies to assess the rate of particle release from silicone rubber, polyvinyl chloride (PVC), and Pivipol, a coextruded polyurethane-coated PVC tubing, when these materials were used with blood pumps of the type found in hemodialysis units, was undertaken. The studies show that with all tubing/pump combinations there is an overall increase in the total number of particles released, but an analysis of the particle size distribution indicates that the majority of the particles are less than 16 micron in diameter. The rate of increase may be reduced, however, by decreasing the occlusion pressure.

Analysis of Variance↗
PubMed1986

Haemodialysis-induced activation of complement. Effects of different membranes.

The ability of cellulose-based (Cuprophan, saponified cellulose ester) and synthetic (polyacrylonitrile, polycarbonate, polymethylmethacrylate) haemodialysis membranes to activate complement during treatment was compared, using functional, immunochemical, radioimmunoassays, and fast centrifugal analysis assay techniques. Cellulosic and synthetic membranes show a striking similarity in their complement activation when measured by immunochemical assays. Functional haemolytic assays for alternate pathway and CH50 demonstrate no significant differences from predialysis values. C3d levels were also unable to demonstrate differences between the membranes. C3a levels, on the other hand, demonstrated significant differences between cuprophan, polyacrylonitrile, and polymethylmethacrylate but not between Cuprophan and polycarbonate membranes. Since comparable alternate-pathway activity of both cellulosic and synthetic membranes was demonstrated, but their C3a release differed, it is possible that certain surfaces that activate complement also possess the ability to absorb components of the alternate pathway.

Acrylic Resins↗
PubMed1986

Complement activation in haemodialysis: a comparison of new and re-used dialysers.

The magnitude of leucopenia and complement activation when reusing cellulose based (Cuprophan) and synthetic (polyacrylonitrile AN-69S) haemodialysis membranes as well as their modifications by the priming of the dialysers with fresh frozen plasma and by the introduction of a period of stagnation during haemodialysis were studied using radioimmunoassay (C3a), centrifugal analysis (C3d), immunochemical (C3, Factor B) and functional (CH50 and alternate pathway) assays. Our findings demonstrate that complement activation and leucopenia induced by Cuprophan are linked and are modified when the membrane is reused, or primed with plasma protein. However, chemical exposure during reuse to sodium hypochlorite modifies these observations. Reuse of the AN-69S membrane resulted in no modification of either leucopenia or complement activity, but this membrane consistently demonstrated lower levels of C3a than observed with either first use or reused Cuprophan membranes.

Acrylic Resins↗