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Biomedical subjects

M J Mueller

Publications and source records attributed to M J Mueller.

At least 19 recordsLinked to original sources
PubMed2004

Tendon Achilles lengthening for the treatment of neuropathic ulcers causes a temporary reduction in forefoot pressure associated with changes in plantar flexor power rather than ankle motion during gait.

The purposes of this study were to determine the effects of tendon Achilles lengthening (TAL) on ambulatory plantar pressures and ankle range of motion, moment, and power, and to determine whether changes in forefoot pressure after treatment of a neuropathic ulcer are related to changes in ankle dorsiflexion range of motion (DFROM) or plantar flexor (PF) power during gait. Pressure and gait tests were performed before treatment, and at 3 weeks and 8 months after treatment in two randomly assigned groups of subjects with diabetes, equinus deformity, and a neuropathic forefoot ulcer treated with TAL and total contact casting (TAL group, n=14), or total contact casting alone (TCC group, n=14). The TAL group had an initial decrease in forefoot peak pressure (PP) (27%), forefoot pressure-time integral (PTI) (42%), PF moment (53%), and PF power (65%), along with an initial increase in rear foot PP (34%), rear foot PTI (48%), and DFROM (74%). Post-surgical changes in rear foot pressure and DFROM were maintained up to 8 months after treatment with TAL, whereas forefoot pressure and PF moment and power increased significantly. Changes in forefoot pressure after treatment in either group were correlated with changes in PF power (r=0.45-0.60), but not with changes in DFROM during gait (r=-0.02-0.08). Results suggest TAL causes a temporary reduction in forefoot pressure primarily by reducing PF power during gait. The initial decrease in forefoot pressure, followed by progressive reloading of forefoot tissues as PF muscles regain strength after TAL, may help reduce the risk of ulcer recurrence in patients with diabetes.

Achilles Tendon↗
PubMed2003

Novel Award 2002. Comparison of physical activity and cumulative plantar tissue stress among subjects with and without diabetes mellitus and a history of recurrent plantar ulcers.

OBJECTIVES: To compare the amount of weight-bearing activity and estimates of cumulative plantar tissue stress between subjects with and without diabetes mellitus and a history of recurrent plantar ulcers. DESIGN: Cross-sectional study with matched groups. BACKGROUND: Weight-bearing activity among individuals with diabetes is likely to influence the amount of mechanical trauma accumulated by plantar tissues, yet activity levels have not been accounted for in previous measurements of plantar tissue stress or predictions of plantar tissue injury. METHODS: Study groups included subjects with diabetes mellitus and peripheral neuropathy, either with or without a history of recurrent plantar ulcers, and non-diabetic control subjects (n=10 per group). Pressure on the plantar foot was assessed as subjects walked at their preferred speed in the shoes they reported wearing most often each day. Physical activity was monitored over seven consecutive days using an accelerometer. The product of mean daily strides and forefoot pressure-time integral was used to estimate daily cumulative stress on the plantar forefoot. RESULTS: Subjects with diabetes and a history of recurrent plantar ulcers were 46% less active than subjects without diabetes (mean (SD)=2727 (1345) versus 5037 (2624) strides/day, P=0.04), and accumulated 41% less daily stress on the forefoot than non-diabetic and diabetic control subjects without a history of plantar ulcers (mean (SD)= 210 (134) versus 354 (118) and 354 (148) MPas/day respectively, P=0.03). CONCLUSIONS: Subjects with diabetes and a history a previous ulcers may be susceptible to plantar tissue injury even at relatively low levels of cumulative tissue stress. RELEVANCE: Changes in weight-bearing activity following plantar tissue injury in patients with diabetes may influence plantar tissue adaptation and the risk of ulcer recurrence.

Adaptation, Physiological↗
PubMed2001

Precision and accuracy of computed tomography foot measurements.

OBJECTIVE: To test the accuracy and precision of computed tomography (CT) imaging for describing the 3-dimensional structure of the foot in patients with diabetes mellitus and peripheral neuropathy. DESIGN: Experimental, test-retest. SETTING: Clinical CT scanner at a local hospital. SPECIMENS: Two tissue-equivalent phantoms and 6 cadaver feet. MAIN OUTCOME MEASURES: Measurements taken from CT data of phantoms and cadaver feet were compared with physical (caliper) measurements. The feasibility of creating a computer-aided design/rapid prototyping 3-dimensional model from CT data was assessed by using 1 cadaver foot. RESULTS: No bias was found for phantom or cadaver CT measurements compared with caliper measurements. The mean difference between repeat scans of cadaver feet (1 observer) was 0.1 +/- 0.8 mm and between observers, 0.4 +/- 0.8 mm. Comparing caliper measurements of the rapid prototype model and actual foot measurements revealed an error of 0.3 +/- 0.4 mm. CONCLUSION: CT-based 3-dimensional imaging produced accurate and precise foot measurements, enabling description of internal and external structures. This capability will be coupled with plantar pressure measurements to improve our understanding and treatment of foot ulcers in people with diabetes.

Cadaver↗
PubMed2001

Monitoring in-shoe plantar pressures, temperature, and humidity: reliability and validity of measures from a portable device.

OBJECTIVE: To investigate the reliability and validity of measures obtained from a portable electronic device used to monitor changes in plantar pressure, temperature, and humidity that occur within the shoe during prolonged activity. DESIGN: Descriptive study comparing electronic sensor output with criterion values. SETTINGS: Indoor level walkway for pressure data; uncontrolled, outdoor environment for step count data; enclosed environmental control chamber for humidity and temperature data. PARTICIPANTS: Convenience sample of 4 healthy, sensate subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Correlations between sensor output and criterion measures were determined for pressure and temperature data. The absolute differences between sensor output and criterion values of temperature, humidity, and step count were also determined. RESULTS: Pressure measurements from electronic sensors correlated highly with criterion values (r > or =.82), both before and after prolonged use. Relative humidity sensor output were within 5% of hygrometer values. In-shoe temperature data correlated highly with criterion values (r > or =.99), and differed from known temperatures by.50 degrees +/-.84 degrees C and.96 degrees +/- 1.56 degrees C at the forefoot and heel, respectively. Electronic step counts recorded at the central forefoot were within 1 step of visual step counts. Pressure tracings obtained from the device during different weight-bearing activities revealed qualitatively distinct pressure patterns. CONCLUSION: The device provides valid and reliable measures of in-shoe plantar pressures, temperature, and humidity during prolonged activity.

Diabetic Foot↗
PubMed2001

In-shoe multisensory data acquisition system.

Patients with diabetes and peripheral neuropathy are susceptible to unnoticed trauma on the foot that can cause skin breakdown. We have designed an electronic system in a shoe that monitors temperature, pressure, and humidity, storing the data in a battery-powered device for later uploading to a host computer for data analysis. The pressure sensors are located at the heel, and under three metatarsal heads. Temperature sensors are located under the medial metatarsal head and under the heel. The humidity sensor is located in the toe of the shoe. Correlations of data from pressure sensors with known values were high (r > 0.85), even after extended use. Although data currently are being collected for descriptive purposes, the design potentially can be used to provide feedback to patients.

Data Display↗
PubMed2001

Accuracy and reliability testing of a portable soft tissue indentor.

We have designed, built, and tested a portable indentor device that allows us to determine force/displacement (F/D) measurements on soft tissue in a clinical or research setting. The indentor system consists of a load cell mounted on a three-dimensional measurement device (Metrecom). The output of the load cell and the Metrecom are recorded and analyzed by software running on a notebook computer. The displacement calibration of the Metrecom gave an average error = 0.005 mm [standard deviation (SD) = 0.062)]. The force calibration of the load cell resulted in an average error = 0.022 N (SD = 0.049) and a linearity of 1.0062 (R2 = 0.9998). The indentor device was tested on six different human soft tissues by two different investigators. The interreliabilities and intrareliabilities were 0.99 [interclass correlation (ICC)] indicating that the results were repeatable by more than one investigator. F/D measurements from indentor testing on two materials were comparable to values measured using an Instron device (5.34 versus. 5.52 N/mm, and 0.98 versus 1.04 N/mm). The device was used to measure the soft tissue characteristics on the plantar surface of the foot of one subject. These data were used to calculate the effective Young's modulus for the tissue using equations derived by Zheng et al. [1] and indicated a wide range of values dependent upon the portion of the F/D curve used. All results indicate data from this portable indentor device are reliable, accurate, and sensitive enough to identify mechanical properties of human tissues.

Adult↗
PubMed2000

Formation of isoprostane F(2)-like compounds (phytoprostanes F(1)) from alpha-linolenic acid in plants.

Isoprostanes F(2) are biologically active prostaglandin F(2)-like compounds formed by free radical-catalyzed oxidation of arachidonic acid (C20:4). Here, we show that a series of dinor isoprostanes F(1), which we term phytoprostanes F(1) (PPF(1)s), are formed by nonenzymatic oxidation of linolenate (C18:3) in plants. Identification and quantification of PPF(1)s were achieved by a negative ion chemical ionization gas chromatography-mass spectrometry method using oxygen 18-labeled PPF(1)s as internal standards. PPF(1)s were found in leaves, flowers, and roots of taxonomically distinct plant species at concentrations ranging from 43 to 1380 ng/g of dry weight. In addition, esterified PPF(1)s were found at 10- to 150-fold higher concentrations. During the drying and storage of various plant organs, endogenous PPF(1) levels increased dramatically by 15- to 263-fold. Because the structurally related prostaglandin F(2alpha) and isoprostanes F(2) exert potent biological activities (i.e., broncho- and vasoconstriction) in the nanomolar range, PPF(1)s could potentially exert similar biological activities. Notably, fresh birch pollen, which can easily be inhaled, contains exceedingly high concentrations (32,440 ng/g) of free PPF(1)s.

Animals↗
PubMed2000

Effect of plantar flexor muscle stiffness on selected gait characteristics.

Although plantar flexor muscle strength is known to affect gait characteristics, the effect of plantar flexor (PF) muscle stiffness on gait is unknown. The purpose of this study was to determine the effect of PF muscle stiffness, in addition to PF strength, on the gait characteristics of subjects with diabetes and peripheral neuropathy (DM & PN) and age-matched controls. Thirty-four subjects were tested (17 DM & PN, 17 controls), 10 males and seven females in each group. PF muscle strength (concentric peak torque) explained a significant amount of variance in all gait variables (20-37%). Passive stiffness added a unique contribution to plantar flexor peak moment and walking speed (10-11%). Plantar flexor stiffness, in addition to strength, may be an important factor contributing to gait characteristics. Treatment techniques designed to preserve or increase stiffness may be indicated for patients with limited PF strength.

Ankle Joint↗
PubMed2000

Passive ankle stiffness in subjects with diabetes and peripheral neuropathy versus an age-matched comparison group.

BACKGROUND AND PURPOSE: Patients with diabetes mellitus and peripheral neuropathy (DM and PN) often complain of joint stiffness. Although stiffness may contribute to some of the impairments and functional limitations found in these patients, it has not been quantified in this population. The purpose of this study was to quantify and compare passive ankle stiffness and dorsiflexion (DF) range of motion in subjects with DM and PN versus an age-matched comparison group. SUBJECTS: Thirty-four subjects were tested (17 subjects with DM and PN and 17 subjects in an age-matched comparison group). There were 10 male subjects and 7 female subjects in each group. METHODS: A Kin-Com dynamometer was used to measure passive plantar flexor torque as each subject's ankle was moved from plantar flexion into dorsiflexion at 60(/s. The following variables were compared using a Student t test: initial angle (angle of onset of plantar flexor torque), maximal dorsiflexion angle, plantar flexor muscle excursion (difference between initial angle and maximal dorsiflexion angle), slope of the first half of the plantar flexor torque curve (stiffness 1 measurement), and slope of the second half of the plantar flexor torque curve (stiffness 2 measurement). RESULTS: The subjects with DM and PN had smaller maximal dorsiflexion angles and less plantar flexor muscle excursion than the comparison group. There was no difference in initial angle, stiffness 1 measurement, or stiffness 2 measurement. CONCLUSION AND DISCUSSION: Although the subjects with DM and PN had less dorsiflexion range of motion than did the comparison group, there was no difference in stiffness between the groups. This finding suggests that people with DM and PN have "short" versus "stiff" plantar flexor muscles.

Adult↗
PubMed2000

Analysis of oxidative stress and wound-inducible dinor isoprostanes F(1) (phytoprostanes F(1)) in plants.

Isoprostanes F(2) are arachidonate autoxidation products in mammals that have been shown to be induced during several human disorders associated with enhanced free-radical generation. Isoprostanes F(2) represent not only extremely reliable markers of oxidative stress in vivo, but they also exert potent biological effects. Therefore, it has been postulated that isoprostanoids are mediators of oxidant injury in vivo. Higher plants, however, do not synthesize arachidonic acid or isoprostanes. Here we show that a series of isoprostane F(2) analogs termed phytoprostanes F(1) (previously dinor isoprostanes F(1)) are formed by an analogous pathway from alpha-linolenate in plants. High-performance liquid chromatography and gas chromatography-mass spectrometry methods using [(18)O](3)phytoprostanes F(1) as internal standard have been developed to quantify phytoprostanes F(1). In fresh peppermint (Mentha piperita) leaves, phytoprostanes F(1) were found in free form (76 ng/g of dry weight) and at about 150-fold higher levels esterified in lipids. It is notable that these levels of phytoprostanes F(1) are more than two orders of magnitude higher than the basal levels of isoprostanes F(2) in mammalian tissues. Furthermore, wounding, as well as butyl hydroperoxide or cupric acetate stress triggered a dramatic increase of free and esterified phytoprostanes F(1). Thus phytoprostanes F(1) may represent a sensitive measure of oxidative damage in plants similar to isoprostanes in mammals. However, one of the most exciting issues to be clarified is the possibility that linolenate-derived phytoprostanes F(1) exert biological activities in plants and/or animals.

Adaptation, Physiological↗
PubMed2000

Effects of a tendo-Achilles lengthening procedure on muscle function and gait characteristics in a patient with diabetes mellitus.

STUDY DESIGN: Case report with repeated measures. OBJECTIVES: To describe the effects of a tendo-Achilles lengthening (TAL) and total contact casting (TCC) on wound healing, motion, plantar pressure, and function in a patient with diabetes mellitus, peripheral neuropathy, neuropathic ulcer, and limited dorsiflexion range of motion (DFROM). BACKGROUND: Limited DFROM has been associated with increased forefoot pressures and skin breakdown. A TAL was expected to increase DFROM and reduce forefoot pressures during walking, but the influence on muscle performance and function was unknown. METHODS AND MEASURES: The patient was a 42-year-old man with a 20-year history of type 1 diabetes (NIDDM) and a recurrent neuropathic plantar ulcer. Outcome measures were DFROM, isokinetic plantar flexor muscle peak torque, in-shoe and barefoot peak plantar pressure, physical performance test (PPT) score, and peak ankle and hip moments during walking obtained from an automated gait analysis. All tests were completed pre-TAL, 8 weeks post-TAL (after immobilization in a TCC), and 7 months post-TAL. RESULTS: The wound healed in 40 days. The TAL resulted in a sustained increase in DFROM (0 to 18 degrees). Plantar flexor peak torque was reduced by 21% 8 weeks after the TAL compared with the torque before surgery but recovered fully at 7 months. Seven months following TAL, in-shoe forefoot peak plantar pressure was reduced by 55%, barefoot pressure decreased by 14%, PPT score increased by 24%, peak ankle plantar flexor moment remained decreased by 30%, and the peak hip flexor moment increased by 41% during walking. CONCLUSION: For this patient, a TAL resulted in short-term deficits in peak plantar flexor torque, but a 7-month follow-up showed improvements in ankle DFROM, walking ability, and a decrease in forefoot in-shoe peak plantar pressure.

Achilles Tendon↗
PubMed2000

Relationships between plantar flexor muscle stiffness, strength, and range of motion in subjects with diabetes-peripheral neuropathy compared to age-matched controls.

STUDY DESIGN: Descriptive study to compare relationships between muscle performance measures in 2 subject groups. OBJECTIVES: To determine the relationships between plantar flexor (PF) muscle stiffness, strength (concentric peak torque), and dorsiflexion (DF) range of motion (ROM) in subjects with diabetes who have peripheral neuropathy (n = 17, 10 men, 7 women; age = 58 +/- 11 years) and age-matched controls (n = 17, 10 men, 7 women; age = 62 +/- 6 years). BACKGROUND: The relationships between muscle stiffness, strength, and joint ROM have not been clearly established. Furthermore, the effect of neuromuscular pathology on these relationships is unknown. METHODS AND MEASURES: PF stiffness and strength measurements were obtained with an isokinetic dynamometer. DF ROM was measured with a goniometer. A Pearson correlation matrix was constructed for each subject group using stiffness, strength, and ROM variables. The percent contribution of passive torque to total torque was computed at 2 joint angles. RESULTS: In subjects with diabetes and peripheral neuropathy (DM-PN) peak concentric PF torque was positively correlated with passive torque at 5 degrees DF (r = 0.77), Stiffness #1 (r = 0.58), and Stiffness #2 (r = 0.50). The percentage of passive PF torque at 5 degrees DF was greater in subjects with DM-PN, compared to control subjects (29.3 +/- 9.4% versus 12.6 +/- 5.9%). CONCLUSIONS: The positive correlation between PF stiffness and strength, and the greater percentage of passive PF torque in subjects with DM-PN suggest that patients with decreased strength may use passive torque to maximize total torque. Therefore, treatment methods designed to decrease stiffness should be used cautiously.

Aged↗
PubMed2000

Timing of peak plantar pressure during the stance phase of walking. A study of patients with diabetes mellitus and transmetatarsal amputation.

High plantar pressures contribute to skin breakdown in patients with diabetes mellitus and peripheral neuropathy. The primary purpose of this study was to determine the point during the stance phase of walking that corresponds with forefoot peak plantar pressures. Results indicate that peak plantar pressures occurred at 80% +/- 5% of the stance phase of gait in subjects with diabetes and transmetatarsal amputation, as well as in control subjects. Improved methods of footwear design or walking strategies proposed to patients should focus on the demands of the foot during the late stance phase of walking in order to increase available weightbearing area or to decrease forces, which will minimize plantar pressures and reduce trauma to the neuropathic foot.

Adult↗
PubMed1999

Analyses of prostaglandin D2 metabolites in urine: comparison between enzyme immunoassay and negative ion chemical ionisation gas chromatography-mass spectrometry.

Measurements of the prostaglandin (PGD2) metabolite 9 alpha, 11 beta-PGF2 in unextracted urine performed by enzyme immunoassay (EIA) were compared with values obtained by negative chemical ionisation gas chromatography-mass spectrometry (NCI GC-MS). Values determined by NCI GC-MS were in the same range but consistently lower than those obtained by EIA, suggesting that other endogenous compounds could be contributing to the immunoreactivity. Isoprostanes were generated by autoxidation of arachidonic acid and the 9 alpha, 11 beta-PGF2 antibody demonstrated less than 0.7% crossreactivity to the mix, making it unlikely that isoprostanes in urine interfere with quantification of 9 alpha, 11 beta-PGF2 by EIA. This was further supported by the 70% reduction in immunoreactive material measured in urine after three days treatment in a healthy volunteer with the cyclooxygenase inhibitor ibuprofen. Purification of urine samples by reverse phase high-performance liquid chromatography (HPLC) revealed the presence of two immunoreactive compounds in addition to 9 alpha, 11 beta-PGF2. The compounds were identified as dinor compounds by NCI GC-MS. One of the compounds was identical to 9 alpha, 11 beta-2,3-dinor-PGF2 which was generated by beta-oxidation of 9 alpha, 11 beta-PGF2 and identified by electron impact (EI)-GC-MS. In conclusion, urinary 9 alpha, 11 beta-PGF2 concentrations measured by EIA represent the sum of 9 alpha, 11 beta-PGF2 and two isomers of its dinor metabolite. Thus, the direct EIA is fast, sensitive and sufficiently specific to monitor activation of the PGD2 pathway, thereby providing a valuable clinical tool to assess the status of mast cell activation in vivo.

Adult↗
PubMed1999

Application of plantar pressure assessment in footwear and insert design.

This clinical perspective describes the application of plantar pressure assessment in footwear and insert design. First, the rationale and evidence for using pressure assessment to assist in the design of footwear for patients with diabetes is described. I discuss 2 important measures obtained from pressure assessment: peak pressure, because it represents the magnitude of potential mechanical stresses that can contribute to skin breakdown, and contact area, because this identifies the treatment areas. Using measures obtained from pressure assessment, guidelines are presented to maximize contact area of the insert to the foot and reduce highest peak pressures on the skin, with the goal of preventing skin breakdown. Second, a rationale and guidelines are presented for the application of plantar pressure assessment in the evaluation and design of footwear for people without impairments (i.e., the general public). Finally, future applications of pressure assessment to improve the design and fit of shoes are discussed. Benefits and limitations of using pressure assessment to assist in footwear design are addressed throughout.

Biomechanical Phenomena↗
PubMed1999

Use of computed tomography and plantar pressure measurement for management of neuropathic ulcers in patients with diabetes.

BACKGROUND AND PURPOSE: Total contact casting is effective at healing neuropathic ulcers, but patients have a high rate (30%-57%) of ulcer recurrence when they resume walking without the cast. The purposes of this case report are to describe how data from plantar pressure measurement and spiral x-ray computed tomography (SXCT) were used to help manage a patient with recurrent plantar ulcers and to discuss potential future benefits of this technology. CASE DESCRIPTION: The patient was a 62-year-old man with type 1 diabetes mellitus (DM) of 34 years' duration, peripheral neuropathy, and a recurrent plantar ulcer. Although total contact casting or relieving weight bearing with crutches apparently allowed the ulcer to heal, the ulcer recurred 3 times in an 18-month period. Spiral x-ray computed tomography and simultaneous pressure measurement were conducted to better understand the mechanism of his ulceration. OUTCOMES: The patient had a severe bony deformity that coincided with the location of highest plantar pressures (886 kPa). The results of the SXCT and pressure measurement convinced the patient to wear his prescribed footwear always, even when getting up in the middle of the night. The ulcer healed in 6 weeks, and the patient resumed his work, which required standing and walking for 8 to 10 hours a day. DISCUSSION: Following intervention, the patient's recurrent ulcer healed and remained healed for several months. Future benefits of these methods may include the ability to define how structural changes of the foot relate to increased plantar pressures and to help design and fabricate optimal orthoses.

Casts, Surgical↗