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Biomedical subjects

L M Jennings

Publications and source records attributed to L M Jennings.

12 recordsLinked to original sources
PubMed2004

Effects of a peracetic acid disinfection protocol on the biocompatibility and biomechanical properties of human patellar tendon allografts.

Patellar tendon allografts, retrieved from cadaveric human donors, are widely used for replacement of damaged cruciate ligaments. In common with other tissue allografts originating from cadaveric donors, there are concerns regarding the potential for disease transmission from the donor to the recipient. Additionally, retrieval and subsequent processing protocols expose the graft to the risk of environmental contamination. For these reasons, disinfection or sterilisation protocols are necessary for these grafts before they are used clinically. A high-level disinfection protocol, utilising peracetic acid (PAA), has been developed and investigated for its effects on the biocompatibility and biomechanics of the patellar tendon allografts. PAA disinfection did not render the grafts either cytotoxic or liable to provoke an inflammatory response as assessed in vitro . However, the protocol was shown to increase the size of gaps between the tendon fibres in the matrix and render the grafts more susceptible to digestion with collagenase. Biomechanical studies of the tendons showed that PAA treatment had no effect on the ultimate tensile stress or Young's modulus of the tendons, and that ultimate strain was significantly higher in PAA treated tendons.

Adult↗
PubMed2001

The influence of ventricular input impedance on the hydrodynamic performance of bioprosthetic aortic roots in vitro.

BACKGROUND AND AIM OF THE STUDY: Hydrodynamic function testing using pulsatile flow simulators provides a valuable means of comparative assessment of heart valves in vitro. The majority of pulsatile flow simulators consist of modular rigid chambers and a positive displacement pump with an infinite input impedance, in which the inertia of the test fluid results in pressure oscillations when the valves under test are opening and closing. For mechanical and stented bioprosthetic valves these pressure oscillations decay quickly. However, due to the highly compliant nature of tissue roots, the resulting pressure and flow oscillations are extreme and extend throughout systole. With increasing interest in the use of free-sewn roots and valves it is most desirable to improve this hydrodynamic model. The aim of this study was to investigate the influence in changes in ventricular input impedance on the hydrodynamic characteristics of free-sewn aortic roots and stented valves. METHODS: The Leeds pulsatile flow simulator was modified to incorporate additional compliance chambers in the form of a viscoelastic impedance adaptor (VIA) at the pump/ventricular interface. Six 23 mm bioprosthetic aortic roots fixed with 0.5% buffered glutaraldehyde at zero pressure, and a size 23 mm stented porcine aortic bioprosthesis were tested in this modified simulator, at the conditions of maximum and minimum input compliance. RESULTS: The pressure and flow waveforms for the fixed aortic roots showed considerable differences at the conditions of maximum and minimum input compliance. Indeed, the extreme pressure oscillations observed at minimum compliance (infinite input impedance) were not present at maximum compliance, and the forward flow waveform was much smoother. In contrast, for the stented valve, the differences in the pressure and flow waveforms between maximum and minimum input compliance were minimal, but this was expected due to the lack of compliance in the stented valve itself. In addition, the flow and pressure waveforms at maximum compliance in the VIA were comparable for the fixed aortic roots and the stented bioprosthesis, thus allowing direct comparison of the characteristics of these two different devices. Using test conditions of maximum input compliance, effective orifice area for the roots was 1.69 cm2 compared with 1.47 cm2 for the stented valve. CONCLUSION: An appropriate physiological model for the hydrodynamic testing of compliant tissue roots has been established.

Aortic Valve↗
PubMed1992

Clinical comparison of tolerance to elemental or polymeric enteral feedings in the postoperative patient.

Thirty consecutive patients (19-71 years of age) undergoing abdominal operations and having feeding catheter jejunostomy tubes placed, were prospectively randomized and studied for tolerance to elemental (amino acid) or polymeric (intact protein isolates) dietary formulas. The groups were matched for sex, age, height, weight, operations, and caloric goal. Nutritional profiles of the patients were similar preoperatively. The number of stools/day and stool consistency were direct indicators of tolerance; nutrient intake was an indirect indicator. Diarrhea is defined as greater than or equal to five stools/day. We found no significant difference between the groups. There were no patients with diarrhea on days 1 or 2. Formula intake as an indirect measure of tolerance was not significantly different for the two groups from days 1-4. On day 5, intake of the elemental group exceeded that of the polymeric group (p less than 0.02). Enteral caloric intake as percent of caloric goal did not differ. Nitrogen intake, urinary nitrogen, serum prealbumin, body weight, serum sodium, and serum potassium did not differ significantly between the two groups throughout the study. Serum chloride decreased significantly (105 to 99.8 mEq/L) in the elemental group (p less than 0.03). Our study shows that patients undergoing routine gastrointestinal operations will tolerate early enteral feedings (day 1) and that there is no significant difference in tolerance to elemental or polymeric dietary formulas.

Adult↗
PubMed1989

Gamma-globulin enhances survival in pneumococcal-challenged asplenic infant rats.

Early augmentation of a patient's immune system can be a valuable adjunct to standard supportive and antibiotic treatment of overwhelming postsplenectomy sepsis (OPSS). Normal humoral immune factors against pneumococcal sepsis are replenished by the parenteral administration of human gamma-globulin (HGG). Monthly prophylactic administration of HGG to asplenic individuals to prevent OPSS has been suggested. The cost of such measures is prohibitive, and the risk of serum-transmitted disease is significant. We administered HGG to splenectomized infant rats with pneumococcal sepsis to determine if mortality rates could be reduced and survival time prolonged. Fifty-six three-day-old rats underwent splenectomy and another 56, laparotomy without splenectomy. Twenty-eight animals from each operative group were administered HGG and the other 28, human serum albumin (HSA), 12 and 24 hours after inoculation with varying dosages of log-phase Streptococcus pneumoniae. The LD50 for asplenic animals was less than 50 colony forming units (cfu) per animal, while for the group with spleens, the LD50 was 250 to 500 cfu. There were no significant intragroup variations in LD50 between HGG and HSA subgroups. Survival times were compared using the BMDP1L-Life Tables and Survival Functions, and the generalized Wilcoxon t-test. These data show that host immunity to pneumococcal challenge in asplenic infant animals might be fully restored by the administration of HGG, even after the onset of symptoms. Survival of an asplenic child with evidence of OPSS might be enhanced by immediate administration of HGG.

Animals↗
PubMed1987

Serum albumin (oncotic pressure) correlates with enteral feeding tolerance in the pediatric surgical patient.

The influence of serum oncotic pressure (Serum Albumin [SA]) on gastrointestinal (GI) tolerance of enteral feedings was prospectively studied in two phases. Phase I consisted of 46 patients, aged 3 months to 12 years, (mean 47 months) selected for enteral tube feeding via the stomach or small bowel. Twenty-eight patients had an SA greater than 3.0 g/dL and received 82% of predicted caloric and protein needs. Administration of the enteral diet was stopped for two or more days in four of the 28 patients because of GI intolerance. Eighteen patients had an SA less than 3.0 g/dL and received 51% of predicted protein needs. Ten of the 18 patients had diet intolerance for two or more days, (P less than .001). Student's t-test was used for data analysis. In phase II, 20 patients, aged 4 months to 14 years (mean 49 months), with an SA less than 3.0 g/dL underwent repletion with salt poor albumin as calculated by the following formula: Albumin Replacement = [3.5 g/dL--Serum Albumin (g/dL)] X [weight (kg) X 3] Mean prereplacement SA was 2.31 g/dL; immediately after replacement it was 3.43 g/dL, and 1 week later it was 3.41 g/dL. These patients received 87% of predicted calories and nitrogen and only two of 20 had diet intolerance for two or more days. These data suggest that correction of SA levels allows for better tolerance of enteral diets and that SA will remain normal after intravenous replacement if adequate nutrients are provided while correcting the SA.

Adolescent↗
PubMed1987

Steroid administration potentiates urinary nitrogen losses in head-injured children.

Exogenous steroid administration has been shown to increase post-traumatic nitrogen excretion in adults. Children sustaining head injuries and treated with steroids have previously been shown to have markedly increased total urinary nitrogen levels; the amount of nitrogen excreted is also directly related to the degree of injury, as evidenced by the Modified Injury Severity Score (MISS). It is unclear whether the increased protein breakdown in these patients is a result of the head injury or a result of the catabolic effects of steroids. Nineteen children aged 4-14 years, suffering head injuries, were prospectively studied. In ten children, management included steroid administration (1-1.5 mg/kg/day dexamethasone X 3-5 days); the remaining nine were similarly managed; however, without steroids. The groups were matched for age, weight, MISS, and Glasgow Coma Scale Score. The steroid-treated group showed a significantly higher urinary nitrogen excretion (mean, 256 +/- 24 mg/kg/day) than the nonsteroid-treated group (mean, 172 +/- 29 mg/kg/day) (p less than 0.02). These data suggest that steroids potentiate an already accelerated post-traumatic catabolic response seen in children with head injuries. Our data suggest that steroid use, which is common, mandates aggressive nutritional support in the management of children with head injuries.

Adolescent↗
PubMed1987

"Spot" urine collections do not accurately represent 24-hour sodium excretion in surgically stressed children.

Deranged metabolism in posttraumatic or surgically stressed children makes fluid and electrolyte management difficult. Clear guidelines for salt and fluid administration have not been established. Recent management trends utilize four-hour and eight-hour "spot" urine collection measurement to imply 24-hour requirements. Six children, having suffered traumatic disease or surgical stress, were studied on an hourly basis for characterization of urinary sodium loss. Measured hourly values were combined to represent four-hour and eight-hour "spot" collections and then extrapolated to represent 24-hour losses. A great variation in sodium excretion was demonstrated on hourly samples; the variations were compounded by extrapolation. The extrapolated values varied from the measured hourly sodium losses by 0.66 to 123%. The four-hour extrapolations varied from measured values 14 to 198% (mean 55.2%). The eight-hour combinations varied 6.59 to 136% (mean 44.1%). On the basis of these data, we discourage the use of extrapolated values to imply 24-hour requirements. We support the use of a standard intravenous fluid (one-half strength normal saline or Ringer's lactate) with frequent urinary sodium determinations to individualize fluid and electrolyte management.

Adolescent↗
PubMed1987

Efficacy of anomalous pancreatic drainage in choledochal cysts correlates with age of presentation and suggests etiology.

The etiology and pathogenesis of choledochal cysts, although frequently debated, are as yet unknown. Findings in three recent patients suggest a possible etiology that may also explain the variability in age at presentation. Each of these patients (ages 12 months, four years, and ten years) was found to have an Alonso-Lej Type I cyst and at operation had an absence of the distal intraduodenal common bile duct, suggesting the lack of a common channel with the main pancreatic duct. Partial decompression of the anatomically obstructed bile duct was afforded by an anomalously high insertion of the accessory pancreatic duct and communication with the duodenum by way of the main pancreatic duct. All patients were managed by excision and retrocolic choledochojejunostomy. The efficacy of decompression correlated with the age of presentation and size of the cyst. These findings suggest agenesis-atresia of the distal common bile duct as one possible etiology of choledochal cysts and may explain the variable age at presentation.

Biliary Tract↗