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Biomedical subjects

L Pruitt

Publications and source records attributed to L Pruitt.

26 records · Page 2Linked to original sources
PubMed1997

Biomechanical effects of e-PTFE implant structure on soft tissue implantation stability: a study in the porcine model.

Successful implantation of biocompatible materials depends on physical aspects of its structure. Meshed implants are stable but cannot be easily removed. Nonporous materials are easily removed, but subject to extrusion. We hypothesized that the microporous structure of expanded polytetrafluoroethylene (e-PTFE) would permit limited fibrous ingrowth into the substance of the material, and that tubular implant shape would increase tissue integration while preserving ease of removal. A two-tailed in vivo study was done comparing implant retention, strength of fixation, and removability between tubular and solid-strip e-PTFE implants. Differences in implant retention within tissues were assessed by implanting 396 implants subcutaneously in five swine for observation periods ranging from 3 weeks to 12 months. Strength of implant attachment to host soft tissues was measured at 52 sites by extraction with a tensiometer with forces both parallel and perpendicular to the implant used. Implant porosity was assessed with scanning electron micrography of tubular and solid-strip e-PTFE implants. Measurements of the force and stress tolerances of the implant-tissue interface demonstrated significantly stronger attachment in tubular than strip-shaped implants (P < 0.005). The 11 N (2.75 lb) force sustained by the tubular implant exceeded the 3.4 N (<1 lb) force for the e-PTFE strip by a statistically significant margin on two-tailed Student's t-test (P < 0.005). Even greater forces were tolerated when applied at right angles to the axis of the tubular implant, emulating tissue suspension (21 N, 5.25 lb). The forces and stresses tolerated by both e-PTFE implants far exceeded the fracture stress measured for the implants. Implant extrusion rates were significantly smaller in tubular (0.85%) than in strip-shaped (4.4%) e-PTFE implants (P < 0.05). Standard error of the mean (SEM) demonstrated lesser porosity in tubular than strip implants, suggesting lesser direct tissue attachment. Tubular e-PTFE implant structure facilitates ingrowth of soft tissue through the tube's lumen. This increases the attachment to surrounding soft tissues, increasing fixation strength, decreasing extrusion rate, but still allowing easy removal. These properties may improve clinical applications in facial implantation.

Animals↗
PubMed1996

Comparative effects of high- and low-intensity resistance training on thigh muscle strength, fiber area, and tissue composition in elderly women.

The effects of 52 weeks resistance training at one of two exercise intensities on thigh muscle strength, fiber cross-sectional area (CSA), and tissue composition were studied in healthy 65-79-year-old women. Subjects were assigned to either a control (CO), high-intensity (HI) or low-intensity (LO) training group. Exercise regimens consisted of three sets of leg press, knee extension, and knee flexion exercises, 3 days/week, at either 80% of one-repetition maximum (1-RM) for seven repetitions (HI) or 40% of 1-RM for 14 repetitions (LO). Dynamic muscle strength was evaluated by 1-RM, thigh lean tissue mass (LTM), fat mass, and bone mineral density (BMD, g/cm2) by dual energy X-ray absorptiometry, and fiber CSA of vastus lateralis m. by histomorphometry. Muscle strength increased, on average (+/- SEM), by 59.4 +/- 7.9% and 41.5 +/- 7.9% for HI and LO, respectively, compared to 1.3 +/- 4.8% in CO (P = 0.0001). Type I fiber CSA increased over time (P < 0.05) in both exercise groups, with a trend for increased type II area (HI, P = 0.06; LO, P = 0.11). There was no significant effect of either exercise program on thigh tissue composition, except for BMD at the 1/3 site (middle third of the femur), where LO and CO groups experienced a decline (P < 0.05) of -2.2 +/- 0.5% and -1.8 +/- 0.6%, respectively, while HI maintained BMD (+1.0 +/- 1.0%). Both training programs produced significant gains in thigh muscle strength, which were associated with fiber hypertrophy, although these did not translate into appreciable alterations in thigh tissue composition.

Absorptiometry, Photon↗
PubMed1995

Cyclic compressive loading results in fatigue cracks in ultra high molecular weight polyethylene.

Wear damage to the articulating surfaces of total joint components made of ultra high molecular weight polyethylene is associated with a fatigue fracture mechanism, despite the fact that these surfaces are subjected to primarily compressive and compressive-tensile cyclic stresses. The question arises as to whether fatigue cracks will form under such loading conditions. In this study, we experimentally demonstrated that fatigue cracks could be initiated and propagated in notched ultra high molecular weight polyethylene specimens subjected to fully compressive and compressive-tensile cyclic loading. Under these loading conditions, growth of fatigue cracks was limited: the cracks arrested without catastrophic failure of the test specimens. The final length of the crack was dependent on the load ratio of the fatigue cycle; fatigue cracks propagated to greater lengths as the load ratio was increased.

Knee Prosthesis↗
PubMed1995

Effect of sustained resistance training on basal metabolic rate in older women.

OBJECTIVE: To determine if basal metabolic rate (BMR) could be elevated in older women undertaking a program of progressive resistance exercise of up to 52-weeks duration. DESIGN: Randomized controlled trial with subjects assigned to either a control (CO), high-intensity (HI), or low-intensity (LO) training group for 15 weeks. BMR, body composition, energy intake and expenditure, and muscle strength were assessed at baseline and after 15 weeks. Subjects were encouraged to continue in their assigned exercise group for an additional 37 weeks, after which time they were reevaluated. SETTING: An exercise facility at a medical center. SUBJECTS: Thirty-six community-dwelling healthy women aged 65 to 79 years. INTERVENTION: Exercise groups performed three sets of 10 exercises, 3 days/week, at either 80% of one-repetition maximum (1-RM) for seven repetitions (HI) or 40% of 1-RM for 14 repetitions (LO). MEASURES: BMR by indirect calorimetry, body composition by dual energy X-ray absorptiometry, energy intake and expenditure from 4-day dietary and activity records, and dynamic muscle strength by 1-RM. RESULTS: Muscle strength increased, on average (+/- SEM), by 40 +/- 6% and 36 +/- 7% in the HI and LO groups after 15 weeks, respectively, compared with 4 +/- 1% in the nonexercising subjects (P = .0001). Fat mass decreased after 15 weeks in LO exercisers by 1.0 kg (P < .05), whereas there was a trend for fat-free mass (FFM) to increase in the HI group by 0.7 kg (P = .08). No change occurred in any group for BMR. From weeks 15 to 52, muscle strength increased a further 9 +/- 2% and 11 +/- 2% in HI and LO groups, respectively, compared with 3 +/- 1% in nonexercisers (P < .005). There was no change in BMR or any body composition parameter during this time period. CONCLUSIONS: Neither training program significantly altered BMR and both produced only minimal changes in body composition. However, both the HI and LO exercise regimens resulted in similar and substantial gains in upper and lower body muscle strength that persisted over the course of the year. This suggests that either exercise regimen may prove an effective strategy for preventing frailty and maintaining functional independence in older adults.

Aged↗
PubMed1995

Dynamic muscle strength as a predictor of bone mineral density in elderly women.

Although muscle strength has been shown to predict bone mineral density (BMD) in older adults, the variance explained by isometric and isokinetic testing has been generally low (< 20%) and limited to only a few exercises and muscle groups. To elucidate the relationship of muscle strength to BMD at multiple sites, and to ascertain the most robust predictor of BMD using isotonic strength testing apparatus, we examined dynamic muscle strength and BMD in 40 healthy elderly women aged 65-82 years. BMD of the spine (L2-4), proximal femur (neck, trochanter, Ward's triangle), forearm (midradius), and whole body were measured by dual-energy X-ray absorptiometry. Dynamic strength (1-RM), utilizing isotonic weight-lifting equipment, was assessed for 10 standard upper and lower body exercises. In stepwise multiple regressions, leg press was the only independent predictor of spine (R2 = 0.11), neck and trochanter (R2 = 0.21 and 0.18), forearm (R2 = 0.21), and whole body BMD (R2 = 0.19), while bench press was an independent predictor of Ward's BMD (R2 = 0.12). The most robust predictor of regional and whole body BMD using isotonic equipment was the leg press, which may reflect overall skeletal health in this population. The portion of variance explained by dynamic muscle strength (11-21%) is similar to that reported when strength is assessed by isometric and isokinetic testing. The relationship of dynamic strength to BMD was not generally site-specific.

Absorptiometry, Photon↗
PubMed1994

Effect of recombinant human growth hormone on the muscle strength response to resistance exercise in elderly men.

Normal aging is characterized by detrimental changes in body composition, muscle strength, and somatotropic function. Reduction in muscle strength contributes to frailty and risk for fracture in the elderly. Although older adults increase muscle strength as a result of resistance exercise training, the strength gains quickly level off, with only modest increases thereafter despite continued training. To investigate whether age-related deficits in the somatotropic axis limit the degree to which muscle strength can improve with resistance training in older individuals, we conducted a double blind, placebo-controlled exercise trial. Eighteen healthy elderly men (65-82 yr) initially underwent progressive weight training for 14 weeks to invoke a trained state. Subjects were then randomized to receive either 0.02 mg/kg BW.day recombinant human GH (rhGH) or placebo, given sc, while undertaking a further 10 weeks of strength training. Sequential measurements were made of muscle strength (one repetition maximum), body composition (dual energy x-ray absorptiometry), and circulating levels of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3. For each exercise, strength increased for both groups (P = 0.0001) through 14 weeks of training, with little improvement thereafter. Increases in muscle strength ranged from 24-62% depending on the muscle group. Baseline plasma IGF-I concentrations were similar in both groups (mean +/- SEM, 106 +/- 9 micrograms/L), approximately half that observed in healthy young adults. In the rhGH group, IGF-I levels increased to 255 +/- 32 micrograms/L at week 15 and 218 +/- 21 micrograms/L at week 24 (P < 0.001). In the placebo group, IGF-I increased slightly to 119 +/- 6 micrograms/L at 24 weeks. IGF-binding protein-3 also increased in the rhGH group (P < 0.05). rhGH had no effect on muscle strength at any time, and no systematic difference in muscle strength was observed between groups throughout the study. Body weight did not change in either group, but lean body mass increased, and fat mass decreased (P < 0.05) in the rhGH group. Supplementation with rhGH does not augment the response to strength training in elderly men. These results suggest that deficits in GH secretion do not underlie the time-dependent leveling off of muscle strength seen with training in the elderly and provide no support for the popular view of GH as an ergogenic aid.

Aged↗
PubMedDate not supplied

Rewarming cardiac surgery patients: radiant heat versus forced warm air.

This study compared time required to rewarm, incidence of shivering, and nurses' preferences in hypothermic postoperative cardiac surgery patients treated with a forced air warmer (Bair Hugger) or a noninfrared radiant heater (Thermal Ceiling). Data were collected on 38 subjects and 6 nonsubjects treated with warm blankets. Average minutes to rewarm were: forced air, 100.3; radiant heat, 99.3; and warm blankets, 188.2. The warm air subjects had significantly higher skin temperatures, lower incidence of shivering, and less severe afterdrop, suggesting that rewarming in these patients resulted from heat gained from the environment. Nurses preferred the forced air warmer to the noninfrared radiant heater.

Adult↗