Browsing by Subject "Fatigue"

Chronic and acute back injuries are widespread, affecting people in environments where they are exposed to vibration and repeated shock. These issues have been widely reported among personnel on aircraft and small watercraft; operators of heavy industrial or construction equipment may also experience morbidity associated with cyclic loading. To prevent these types of injuries, an improved understanding is needed of the spine’s tolerance to fatigue injury and of the factors that affect fatigue tolerance.

These types of vibration and shock exposures are addressed by international standards that propose limitations on the length and severity of the accelerations to which an individual is subjected. However, the current standard, ISO 2631-5:2004, provides an imprecise health hazard assessment. In this dissertation, a detailed technical critique is presented to examine the assumptions on which ISO 2631-5:2004 is based. An original analysis of existing data yields an age-based regression of the ultimate strength of lumbar spinal units and demonstrates sources of error in the strength regression in the standard. This dissertation also demonstrates that, contradicting earlier assumptions, the ultimate strength of the spine does not lie on a power-law S-N curve, and fatigue tolerance cannot be extrapolated from ultimate strength tests.

An alternative approach is presented for estimating the injury risk due to repeated loading. Drawing from existing data in the literature, a large dataset of in vitro fatigue tests of lumbar spinal segments was assembled. Using this fatigue data, a survival analysis approach was used to estimate the risk of failure based on several factors. Number of cycles, load amplitude, sex, and age all were significant predictors of bony failure in the spinal column. The parameter described by ISO 2631-5:2004 to quantify repeated loading exposure was modified, and an injury risk model was developed based on this modified parameter which relates risk of vertebral failure to repeated compressive loading. Notably, the effect of sex on fatigue tolerance persisted after normalizing by area, emphasizing the need for men and women to be addressed separately in the creation of injury risk predictions and occupational guidelines.

Posture has also been implicated in altering the injury mechanisms and tolerance to fatigue loading. However, few previous investigations in cyclic loading have addressed non-neutral postures. To assess the influence of dynamic flexion on the fatigue tolerance of the lumbar spine, a series of tests were conducted which combined a cyclic compressive force with a dynamic flexing motion. A study of 17 spinal segments from six young male cadavers was conducted, with tests ranging from 1000 to 500 000 cycles. Of the 17 specimens, 7 failed during testing. These failures were analyzed using a Cox Proportional Hazards model. As in compressive fatigue behavior, significant factors were the magnitude of the applied load and the age of the specimen. However, when the dynamically flexed specimens in these tests were compared to the specimens in the axial fatigue dataset, the flexion condition did not have a detectable effect on fatigue tolerance.

The Hybrid III dummy is a critical tool the assessment of such loading. Although the Hybrid III was originally designed for automotive frontal impact testing, these dummies have since been used to measure exposures and estimate injury risks of a wide variety of scenarios. These scenarios often involve using the dummy under non-standard temperatures or with little recovery interval between tests. Series of tests were conducted on the Hybrid III neck and lumbar components to assess the effects of rest duration intervals and a range of temperatures. Variations in rest duration intervals had little effect on the response of either component. However, both components were extremely sensitive to changes in temperature. For the 50th percentile male HIII neck, the stiffness fell by 18% between 25°C and 37.5°C; at 0°C, the stiffness more than doubled, increasing by 115%. Temperature variation had an even more pronounced effect on the HIII lumbar. Compared to room temperature, the lumbar stiffness at 37.5°C fell by 40%, and at 12.5°C, the stiffness more than doubled, increasing by 115%.

This dissertation has advanced the state of knowledge about the fatigue characteristics of the spine. An injury risk function has been developed that can serve as a tool for health hazard assessment in occupational standards. It has also contributed a fatigue dataset with dynamic flexion. This work will improve the scientific community’s ability to prevent repeated loading injuries. This dissertation has also demonstrated the immense sensitivity to temperature of the Hybrid III spinal components. This finding has major implications for the interpretation of previously published work using the Hybrid III, for the conduct of future research, and for future dummy design.

Background

Objectives

Methods

Results

Conclusions

Background: Patients with gastrointestinal (GI) cancers experience 10 to 15 co-occurring symptoms during chemotherapy that decrease their functional status, quality of life (QOL), and overall survival. The purposes of this dissertation were to describe symptom experiences and self-management strategies for multiple co-occurring symptoms in patients with gastric cancer; identify the subgroups of patients with GI cancers based on their distinct symptom experience profiles; and determine differences among these subgroups in demographic and clinical characteristics, as well as co-occurring symptoms and QOL outcomes.

Methods: An integrative review, a qualitative study, and three quantitative studies (i.e., one was cross-sectional, two were longitudinal) were used in this dissertation. Twenty-five studies were included and systematically evaluated in the review. Ten participants were interviewed for their symptom experiences and self-management strategies. Patients (n=405) completed questionnaires (e.g., the Memorial Symptom Assessment Scale, the Lee fatigue Scale, the General Sleep Disturbance Scale) six times over two cycles of chemotherapy. Content analysis was used to analyze the qualitative data. Latent class/profile analysis was used to identify the subgroups of patients with distinct symptom profiles. Differences in demographic and clinical characteristics as well as co-occurring symptoms and QOL outcomes among the subgroups were evaluated using parametric and non-parametric analyses.

Results: The most common symptoms were categorized into physical and affective/cognitive domains. Patients reported a large amount of inter-individual variability and dynamic nature in their experiences of multiple co-occurring symptoms. Four symptom self-management strategies were identified: medications for symptoms, information-seeking from the clinician team, lifestyle modifications, and psychosocial and spiritual support. The risk factors for a higher symptom burden included younger age, not being married/partnered, being unemployed, having childcare responsibilities, lack of regular exercise, having a lower functional status, having a higher comorbidity burden, and self-reported diagnosis of depression. Patients with a more severe symptom profile reported higher levels of morning and evening fatigue, sleep disturbance, anxiety, depressive symptoms, and pain, as well as lower levels of attentional function and QOL scores at enrollment.

Conclusions and Implications: This dissertation is the first to identify the subgroups of patients with GI cancers with distinct symptom experience profiles and examine a number of risk factors associated with more severe symptom profiles, as well as describe symptom experiences and self-management strategies for multiple co-occurring symptoms in patients with gastric cancer. Additional research is warranted to explore underlying mechanisms that contribute to the development of multiple co-occurring symptoms during chemotherapy. Clinicians need to assess for common risk factors and associated co-occurring symptoms, as well as initiate personalized symptom management interventions and referrals.

Extending the functional lifetime of acrylic poly(methyl methacrylate) (PMMA) bone cement may reduce the number of revision total joint replacement (TJR) surgeries performed each year. We developed a system utilizing an encapsulated water-reactive, FDA-approved tissue adhesive, 2-octyl cyanoacrylate (OCA), as a healing agent to repair microcracks within a bone cement matrix. The proposed research tested the following hypotheses: (1) reactive OCA can be successfully encapsulated and the resulting capsules thoroughly characterized; (2) the static mechanical properties of the PMMA composite can be improved or maintained through inclusion of an optimal wt% of OCA-containing capsules; (3) PMMA containing encapsulated OCA has a prolonged lifetime when compared with a capsule-free PMMA control as measured by the number of cycles to failure; and (4) the addition of capsules to the PMMA does not significantly alter the biocompatibility of the material. Based on the experiments reported herein, the primary conclusions of this dissertation are as follows: (1) functional OCA can be encapsulated within polyurethane spheres and successfully incorporated into PMMA bone cement; (2) lower wt% of capsules maintained the tensile, compressive, fracture toughness, and bending properties of the PMMA; (3) inclusion of 5 wt% of OCA-containing capsules in the matrix increased the number of cycles to failure when compared to unfilled specimens and those filled with OCA-free capsules; and (4) MG63 human osteosarcoma cell proliferation and viability were unchanged following exposure to OCA-containing PMMA when compared with a capsule-free control.

Synthetic cartilage implants have the potential to deeply transform the treatment of articular cartilage degeneration as well as the progression of osteoarthritis in load-bearing applications of various joints in the human body. To reduce patient morbidity and enhance range of motion, surgeons and material scientists alike are looking to synthetic alternatives re-establish articular cartilage function without introducing higher cost and health burdens. These implants are rigorously tested for their compressive and wear properties over longer timeframes, with the first instance of approved human use coming in the 1st metatarsophalangeal (MTP) joint with poly(vinyl alcohol) (PVA) being the predominant polymer in composition. Despite their promise of dissipating stress and providing smooth joint movement, these synthetic cartilage implants are not well-studied for their tensile fatigue properties which are extremely critical to in vivo performance and implant survival. As a synthetic substitute to match the properties of cartilage in human beings, hydrogels are extensively researched due to their potential biocompatibility. This research describes work dedicated to the advanced mechanical study of synthetic hydrogel systems for cartilage-based applications. The materials of interest are designed to have enhanced monotonic tensile properties for supplementary investigation via tensile fatigue testing. Superior mechanical behavior was achieved through the use of bio-friendly additives, freezing-thawing cyclic processing, and fiber reinforcement. Lastly, the long-term failure mechanisms through flaw development for these synthetic hydrogel systems and biological tissue will be explored.

Fatigue is a common and debilitating symptom for adult patients with end-stage renal disease on hemodialysis and has been associated with decreased survival and quality of life. Patients on hemodialysis must find ways to manage their fatigue and mitigate its effects on their lives. Currently, there is no description of the experience of fatigue for American hemodialysis patients, nor is there any description of the ways in which they manage their fatigue. The purpose of this qualitative descriptive work was to describe the experience and self-management of fatigue as well as how fatigue changes over time from one dialysis session to the next. Several themes were identified which included: the nature of fatigue, cycles of fatigue, management of fatigue, consequences of fatigue, and correlates of fatigue. Further, hemodialysis patients experience two types of fatigue, post-dialysis fatigue, fatigue that occurs acutely after the dialysis session and resolves after sleep or rest, and constant fatigue, a persistent, underlying fatigue that patients experience at all times and worsens after the dialysis session usually requiring a prolonged period of recovery.