This study was made to determine the effects of stride length variations on ratings of perceived exertion in experienced recreational runners. Results are presented. (Author/MT)
The study compared the effects on muscular strength and maximal oxygen uptake of a Nautilus circuit weight training program, a free weight strength training program, and a running program. Nautilus ...circuit weight training appears to be equally effective for a training period of short duration. (MT)
Female fast pitch softball batters served in an examination of the dynamic characteristics of the bat during the swing through the use of three-dimensional cinematographic analysis techniques. These ...results were compared with those from previous studies of baseball batting. Findings are listed. (Author/DF)
We provide additional statistical background for the methodology developed in the clinical analysis of knee osteoarthritis in "A Precision Medicine Approach to Develop and Internally Validate Optimal ...Exercise and Weight Loss Treatments for Overweight and Obese Adults with Knee Osteoarthritis" (Jiang et al. 2020). Jiang et al. 2020 proposed a pipeline to learn optimal treatment rules with precision medicine models and compared them with zero-order models with a Z-test. The model performance was based on value functions, a scalar that predicts the future reward of each decision rule. The jackknife (i.e., leave-one-out cross validation) method was applied to estimate the value function and its variance of several outcomes in IDEA. IDEA is a randomized clinical trial studying three interventions (exercise (E), dietary weight loss (D), and D+E) on overweight and obese participants with knee osteoarthritis. In this report, we expand the discussion and justification with additional statistical background. We elaborate more on the background of precision medicine, the derivation of the jackknife estimator of value function and its estimated variance, the consistency property of jackknife estimator, as well as additional simulation results that reflect more of the performance of jackknife estimators. We recommend reading Jiang et al. 2020 for clinical application and interpretation of the optimal ITR of knee osteoarthritis as well as the overall understanding of the pipeline and recommend using this article to understand the underlying statistical derivation and methodology.
Twenty-five human cryopreserved valves with harvest-related warm ischemic times (WITs) ranging from 0 to 20 hours were studied using transmission electron microscopy to characterize the effects of ...harvesting and preservation on leaflet matrix cells. The valves were divided into seven groups on the basis of WIT and processed using standard transmission electron microscopic methods. Each cell (528 micrographs) was graded for reversible and irreversible cellular injury and subjected to a Cochran-Mantel-Haenszel trend analysis. Our results demonstrated a progression in cellular injury with increasing WIT. During the first 12 hours of warm ischemia, reversible cellular injury predominated (0.0%, 30.0%, 51.2%, 31.3%, 35.1%, 45.1%, and 40.0% at WITs of 0, 1, 2, 8, 12, 16, and 20 hours, respectively). A positive correlation (
p < 0.0001) between increasing WIT and reversible cellular injury through the first 12 hours was observed. Minimal morphologic evidence of irreversible injury was noted in valves harvested with less than 12 hours of warm ischemia; however, after 12 hours there was a marked increase (0.0%, 0.0%, 4.7%, 2.4%, 2.7%, 31.4%, and 40.0% at WITs of 0, 1, 2, 8, 12, 16, and 20 hours, respectively) in irreversible cellular injury (
p < 0.001 between 12 and 20 hours WIT). These data demonstrate a progression in cellular injury with increasing WIT. There was virtually no morphologic injury in valves with harvest-related WITs less than 2 hours and minimal irreversible cellular injury observed in valves exposed to 12 hours or less of warm ischemia. If cellular viability is critical to homograft durability then harvest-related warm ischemia may need to be restricted to 12 hours.
To assess the initial metabolic phase of cellular injury from cardiac valve processing, high-energy phosphate concentrations were analyzed in valve leaflets subsequent to critical processing steps. ...Using a porcine model, valves were processed in a manner identical to human homografts, with 58 randomly assigned to five groups representing distinct preparation phases. Group I (controls) sustained 40 minutes of warm ischemia concluded by liquid nitrogen immersion. Remaining groups similarly endured 40 minutes of ischemia, but were subsequently prepared according to stepwise design: II, warm ischemia + 24 hours of 4 °C ischemia; III, warm ischemia + 24 hours of 4 °C antibiotic disinfection; IV, warm ischemia + 24 hours at 4 °C (without antibiotics) + cryopreservation (−1 °C/min cryoprotected freezing); and V, warm ischemia + disinfection + cryopreservation. At each regimen's conclusion leaflet extracts were assayed by high-performance liquid chromatography for high-energy adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate) and catabolites. A 47% and 86% decrease in cellular adenosine triphosphate level was observed in group III and group V leaflets, respectively. The level of total adenine nucleotides was maintained up to cryopreservation; thereafter a 74% decrease was noted. Catabolite analysis confirmed incomplete degradation of adenine nudeotides indicating cellular metabolic resilience throughout standard homograft preparation in valves previously exposed to 40 minutes of warm ischemia.
Preparation protocols for human cardiac valves are intended to minimize cytotoxicity because it has been thought that viable leaflet interstitial cells may enhance homograft durability. ...Preimplantation factors influencing the status of these cells at the time of transplantation include ischemia, disinfection, and cryopreservation freezing programs. In these experiments, adenine nucleotide quantitation was undertaken to assess metabolic consequences of preparation; preharvest ischemia served as an independent variable to examine the relationship between time of procurement (postmortem) and high-energy phosphate status of the cryopreserved leaflets at thaw. Nucleotides were measured using high-performance liquid chromatography performed on extracts of semilunar cusps from 25 cryopreserved human valves with documented ischemic times. Results indicate total adenine nucleotides (TAN; ATP + ADP + AMP, in nmol TAN/mg leaflet protein) are higher (
P < 0.05) after <2 h of harvest ischemia (1.16 ± 0.36) than with ischemic times of 3-6 h (undetected), 7-12 h (0.18 ± 0.07), and 13-20 h (0.06 ± 0.06). Depletion of ATP was similar, with many leaflets devoid of detectable levels. Net utilization of leaflet energy stores demonstrates time dependency when assayed after completed processing. However, relatively elevated catabolites, even with brief ischemia, and infrequently identified ATP, ADP, and AMP, suggest a consumption so accelerated that the following cryopreservation it is virtually independent of procurement-associated ischemia. We conclude resumption of a functional cell population obligates significant
de novo phosphoanhydride boned reformation or a repopulation of dead/dying interstitial cells from a subset surviving the apparently severe rigors of valve preparation.
Cryopreserved allograft valves are increasingly being used as valvular replacements. Leaflet fibroblast viability has been suggested to influence clinical durability. The warm ischemic time is ...thought to be a critical determinant of this cell viability. The purpose of this study was to apply quantitative morphometric methods to characterize, by transmission electron microscopy, valvular cellular injury resulting from progressive warm ischemic time. Porcine aortic valves were harvested with a spectrum of warm ischemic times (40 minutes and 2, 6, 12, 24, and 36 hours; five valves per warm ischemic time; n = 30) and processed by standard electron microscopic methods. To ensure randomized tissue selection within each warm ischemic time interval, we randomly selected one thin section from each leaflet. The first ten cells in each thin section were photographed and cellular injury was assessed (cell disruption, dilation of endoplasmic reticulum, cytoplasmic edema, nuclear and mitochondria! changes). Nine hundred micrographs have been analyzed by Cochran-Mantel-Haenszel statistics to determine if a significant association between warm ischemic time and cellular injury exists. Our findings indicate a significant association between reversible cell injury through 24 hours of warm ischemic injury (p < 0.0001). Furthermore, a significant association between irreversible cell injury and progressive warm ischemia through 36 hours was also found. These findings indicate that the ischemic interval after donor death is associated with progressive leaflet cell injury. Cellular damage begins shortly after donor death and continues incrementally throughout 36 hours. After 2 hours of warm ischemic injury 37 % of the cells had morphologic evidence of injury. After 6 hours of warm ischemic injury the number of injured cells increased to 73%. By 36 hours 22% of the cells appeared normal. Irreversible cell injury increases with prolonged ischemia and becomes quantitatively impressive at 24 hours, by which time 26% of cells are so affected. Conversely, some cells are resistant to irreversible injury for a prolonged ischemic interval. (J Thorac Cardiovasc Surg 1992:103:253—8)
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