Biomedical subjects

Brian L Davis

Publications and source records attributed to Brian L Davis.

6 recordsLinked to original sources

PubMed2006

Laser-induced auto-fluorescence (LIAF) as a method for assessing skin stiffness preceding diabetic ulcer formation.

Recurrent foot ulceration is a major cause of morbidity in diabetic patients. Discrepancy between the stiffness of the plantar skin and underlying soft tissues may influence the likelihood of ulceration. Tissue properties change with diabetes primarily due to high blood glucose which promotes intermolecular cross-linking of structural proteins thus leading to altered structure and function of these structural fibers. This study utilizes a non-invasive method for indirectly assessing skin tissue in the context of plantar ulcer formation in diabetic patients' feet. Control (C, n=13), and diabetic subjects with a history of ulceration (n=16) were matched based on gender, age (42-81years old) and BMI. Six subjects re-ulcerated (U) during their 1-year follow-up. At every visit, each subject's plantar skin was excited with a weak laser light (337nm) to induce tissue fluorescence at three locations on each foot. The spectral area under the curve (AUC) was calculated after background subtraction and normalization. The mean AUC was significantly higher for diabetics compared to control subjects, (mean AUC: 145.6+/-7.2, C=112.6+/-8.3, respectively, p=0.006). For those who re-ulcerated (U, n=6), skin site was not a significant factor, but AUC was diminished at the time of re-ulceration (p<0.05). The alteration of intermolecular bonds in diabetic subjects and thinning of skin prior to ulceration could account for these observations. The decrease in AUC prior to an ulcer formation suggests its potential as a marker of tissue changes, which precede ulceration in the diabetic foot.

Adult↗

PubMed2005

Simultaneous shear and pressure sensor array for assessing pressure and shear at foot/ground interface.

Foot ulceration is a diabetic complication estimated to result in over $1 billion worth of medical expenses per year in the United States alone. This multifaceted problem involves the response of plantar soft tissue to both external forces applied to the epidermis and internal changes such as vascular supply and neuropathy. Increasing evidence indicates that a combination of elevated external forces (pressure and shear) and altered tissue properties is key to the etiology of foot ulcers. The overall goal of this research is to develop a platform-type hardware system that will allow a clinician to measure three-dimensional stress tensors (i.e. pressure and shear patterns) on the plantar surface and identify areas of concern. Experimental results have demonstrated that an optical approach can provide clear indication of both shear and pressure from 50 to 400 kPa with a frequency response of 100 Hz, a stress measurement accuracy of 100 Pa and a spatial resolution of 8.0mm. Initial evaluation of the system shows strong correlation between (i) applied shear and normal stress loads and (ii) the optical phase retardance computed for each stress axis of the polymer-based stress-sensing elements. These special sensing elements are designed to minimize the need for repeated calibration procedures-an issue that has plagued other attempts to develop multisensor shear and pressure systems.

Equipment Design↗

PubMed2005

Jumping in simulated and true microgravity: response to maximal efforts with three landing types.

BACKGROUND: Exercise is a promising countermeasure to the physiological deconditioning experienced in microgravity, but has not proven effective in eliminating the ongoing loss of bone mineral, most likely due to the lack of high-impact forces and loading rates during in-flight activity. We wanted to determine lower-extremity response to high-impact jumping exercises in true and simulated microgravity and establish if 1-G force magnitudes can be achieved in a weightless environment. METHODS: Jumping experiments were performed in a ground-based zero-gravity simulator (ZGS) in 1 G, and during parabolic flight with a gravity-replacement system. There were 12 subjects who participated in the study, with 4 subjects common to both conditions. Force, loading rates, jump height, and kinematics were analyzed during jumps with three distinct landings: two-footed toe-heel, one-footed toe-heel, and flat-footed. Gravity replacement loads of 45%, 60%, 75%, and 100% bodyweight were used in the ZGS; because of time constraints, these loads were limited to 60% and 75% bodyweight in parabolic flight. RESULTS: Average peak ground-reaction forces during landing ranged between 1902+/-607 and 2631+/-663 N in the ZGS and between 1683+/-807 and 2683+/-1174 N in the KC-135. No significant differences were found between the simulated and true microgravity conditions, but neither condition achieved the magnitudes found in 1 G. CONCLUSION: Data support the hypothesis that jumping exercises can impart high-impact forces during weightlessness and that the custom-designed ZGS will replicate what is experienced in true microgravity.

Adult↗

PubMed2003

Novel hyaluronic acid coating for potential use in glucose sensor design.

Biocompatibility issues such as protein deposition and fibrous capsule formation significantly reduce the sensitivity of implanted glucose sensors. One of the approaches to improve the sensor biocompatibility is to disguise the sensors with coatings that mimic body conditions. We anticipate that a biomimetic coating based on hyaluronic acid (HA) would minimize the problems related to protein deposition and fibrous tissue formation. Diffusion experiments were conducted to assess the transport properties of HA coating on a polyvinyl alcohol (PVA) membrane using a classic diffusion cell. HA was coated on PVA membranes, as cross-linked HA membranes alone have poor mechanical strength. The effective diffusivities of glucose and oxygen in a HA/PVA membrane (95% confidence interval) are 1 +/- 0.26 x 10(-4) and 1.42 +/- 0.34 x 10(-4) cm(2)/min, respectively. The effective diffusivities of glucose and oxygen in HA/PVA membranes were approximately two-thirds when compared with the diffusivities of glucose and oxygen (7.29 x 10(-5) and 2.34 x 10(-4) cm(2)/min, respectively) in pure PVA membranes. The results indicate that the HA/PVA membranes have transport properties similar to the commonly used pure PVA membranes, and thus may find usefulness as a coating for implantable glucose sensors.

Biocompatible Materials↗

PubMed2002

Simultaneous measurement of plantar pressure and shear forces in diabetic individuals.

Plantar foot ulceration is a diabetic complication whose underlying causative factors are still not fully understood. The goal of the current work was to simultaneously record plantar pressure and shear and examine the interrelationship of these forces; specifically, if peak shear and pressure occurred at the same site/time and whether adjacent shear forces had a greater tendency to be directed towards or away from each other. A custom built 16 transducer array was used to record forefoot shear and pressure during gait initiation in a cohort of 12 neuropathic diabetic individuals. The individuals were barefoot and the transducers were covered with a 5 mm thick layer of Minorplast. The greatest pressure occurred in the medial metatarsal heads (189 kPa) and the greatest shear in the lateral metatarsal heads (33 kPa). The interaction of the shear forces revealed that the plantar tissue was stretched to a greater magnitude than it was bunched (24 kPa vs 12 kPa, averaged over all regions). Normal distributions were determined for stretching and bunching in both the medial-lateral and anterior-posterior directions. When shear and pressure were considered in combination, half of the neuropathic individuals had peak shear and pressure occurring at the same site. These peak stresses did not occur at the same time (average difference of 0.186 s). The results of this study help to further characterize tissue stresses experienced on the plantar surface of the foot during gait initiation in neuropathic diabetic individuals.

Adult↗

PubMedDate not supplied

Lower-extremity amputations in patients with diabetes: pre- and post-surgical decisions related to successful rehabilitation.

BACKGROUND: Peripheral vascular disease and diabetes account for the majority of lower-extremity amputations in the adult population. Whenever a patient presents to a surgeon regarding a diseased limb, the initial basic decision is to determine whether to attempt limb salvage or proceed with an amputation. Unfortunately, limb salvage is not an option for many of these patients. Once amputation is chosen as a treatment option, the optimal level of amputation has to be determined by the surgeon, who is then faced with selecting the optimal level of amputation compatible with wound healing and subsequent prosthetic fitting. METHODS: Methods for objectively determining optimal amputation level include vascular evaluations, assessing the level of cellulites or osteomyelitis, or intra-operatively, by looking at the amount of bleeding in skin flaps. RESULTS: The net outcome is that there is currently no universally accepted method for determining the level of amputation for successful wound healing or for preventing subsequent higher amputations. CONCLUSIONS: What is generally recognized is that there are disparities in the rates of amputation for type 1 versus type 2 diabetic patients, for different ethnic groups and for patients with multiple co-morbidities. However, with advances in surgical techniques and with modern prosthetics, all categories of patients are benefiting from surgeries in which a longer residual limb can be kept (within surgical constraints related to proper wound healing), and where appropriate biomechanical considerations are taken into account.

Amputation, Surgical↗