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Biomedical subjects

M L Hull

Publications and source records attributed to M L Hull.

At least 73 records · Page 4Linked to original sources
PubMed1998

A pedal dynamometer for off-road bicycling.

This paper describes the design and accuracy evaluation of a dynamometric pedal, which measures the two pedal force components in the plane of the bicycle. To realize a design that could be used during actual off-road cycling, a popular clipless pedal available commercially was modified so that both the form and the function of the original design were maintained. To measure the load components of interest, the pedal spindle was replaced with a spindle fixed to the pedal body and instrumented with eight strain gages connected into two Wheatstone bridge circuits. The new spindle is supported by bearings in the crank arm. Static calibration and a subsequent accuracy check revealed root mean square errors of less than 1 percent full scale (FS) when only the force components of interest were applied. Application of unmeasured load components created an error less than 2 percent FS. The natural frequency with half the weight of a 75 kgf person standing on the pedal was greater than 135 Hz. These performance capabilities make the dynamometer suitable for measuring either pedaling loads due to the rider's muscular action or inertial loads due to surface-induced acceleration. To demonstrate this suitability, sample pedal load data are presented both for steady-state ergometer cycling and coasting over a rough surface while standing.

Acceleration↗
PubMed1997

Are more complex implantable cardioverter defibrillators associated with an increased mortality? Lessons learned from clinical trials.

We compared 1-year survival in patients receiving implantable cardioverter defibrillators (ICDs) that provide only shock therapy with more advanced ICDs that provide antitachycardia pacing, bradycardia pacing, low-energy cardioversion, and advanced detection algorithms. Outcome in patients with advanced-generation ICD systems was similar or improved compared with outcome in patients receiving ICDs with only monophasic shock.

Clinical Trials as Topic↗
PubMed1997

Contact pressure and tension in anterior cruciate ligament grafts subjected to roof impingement during passive extension.

Contact between an anterior cruciate ligament graft and the intercondylar roof has been termed roof impingement. Grafts with impingement sustain permanent damage, and if the injury is extensive enough, then the graft may fail, causing recurrent instability. This study evaluated two mechanical factors that could be responsible for the graft injury associated with roof impingement: an increase in graft tension or elevated pressures between the graft and the roof, or both. An anterior cruciate ligament reconstruction was performed using an Achilles tendon graft in five fresh-frozen cadaveric knees. Using a six-degree-of-freedom load application system, the anterior displacement of the knee with the native anterior cruciate ligament was restored in the reconstructed knee at a flexion angle of 30 degrees and with an anterior force of 200 N applied. Pressure between the graft and intercondylar roof, graft tension, and flexion angle were measured during passive knee extension for three tibial tunnel placements (anterior, center, and posterior). Intercondylar roof impingement increased the contact pressure between the graft and the roof but had no significant effect on graft tension. Therefore, during passive knee extension, the contact pressure between the anterior cruciate ligament graft and the intercondylar roof is a more likely cause of graft damage than increased graft tension.

Achilles Tendon↗
PubMed1997

In vivo tensile behavior of a four-bundle hamstring graft as a replacement for the anterior cruciate ligament.

The purpose of this study was to measure the in vivo tensile behavior of a double-looped semitendinosus and gracilis graft used to reconstruct a torn anterior cruciate ligament in the human knee. In 14 subjects, intraoperative tension was measured for each of the four graft bundles during passive motion from 0 to 90 degrees of flexion. Two hypotheses were tested: (a) the peak tension carried by each of the four bundles was equal during passive motion, and (b) the mechanics of the bundles mimicked the functional bands of the native anterior cruciate ligament. The total tension was also calculated and used to determine strength requirements for fixation devices. The peak tensions of the four bundles during passive motion were not equal; however, enough tension was present in each bundle that load-sharing occurred between bundles. The pattern of tension between the anterior and posterior bundles mimicked the reciprocating load-sharing behavior of the functional bands of the native anterior cruciate ligament. Reciprocal tensile behavior was consistently achieved with the use of a single femoral tunnel centered on the most isometric line without the need for two separate femoral sockets. The maximum total tension was 296 N; this was nearly equal to the strength of one commonly used fixation device.

Adolescent↗
PubMed1997

Direct measurement of strain in the posterolateral bundle of the anterior cruciate ligament.

The general objectives of the work reported in this article were to describe and validate a method for directly measuring strain in the posterolateral bundle (PLB) of the anterior cruciate ligament (ACL). The method is a procedure for gaining surgical access to the posterior fibers of the PLB through a portal incised in the joint capsule and then suturing a liquid metal strain gage (LMSG) on to these fibres. Because the incision possibly alters the load-displacement mechanics of the joint, validation included performing experiments to test the hypothesis that the incision did not significantly affect load-displacement relations. To illustrate the utility of the method, strains in both the anteromedial bundle (AMB) and PLB were measured and compared over the full range of flexion. Validation experiments revealed that the capsular incision as well as other incisions had no measurable effect on the load-displacement mechanics of the joint. Also, the PLB strain was significantly different from the AMB strain during passive flexion with a reciprocating function in load sharing evident between the two bundles.

Adult↗
PubMed1997

Pedal and knee loads using a multi-degree-of-freedom pedal platform in cycling.

To provide a scientific basis for the design of bicycle pedals which possibly alleviate over-use knee injuries, two hypotheses were tested in the present study. The two hypotheses were: (1) that the three-dimensional pedal constraint loads; and (2) that the three-dimensional intersegmental knee loads would be reduced more significantly by a foot/pedal platform allowing both adduction/abduction and inversion/eversion rotations simultaneously than by a platform which allowed either rotation individually. To test these hypotheses, pedal load and lower limb kinematic data were collected from 10 subjects who pedaled with four pedal platforms which allowed zero, one, and two degrees of freedom. A number of quantities describing both pedal loads and intersegmental knee loads was computed for each of the four pedal platforms using a previously reported biomechanical model. The quantities included the positive and negative extremes, averages, and areas, as well as the total absolute area and RMS. Quantities were compared using analysis of variance techniques. The key results were that there were significant reductions in the coupled nondriving moments at the pedal for the dual-rotation platform compared to each of the single-rotation cases. The significant reductions in the coupled moments at the pedal were not manifest at the knee. However, a general nonsignificant reduction in both coupled knee moments was evident. Also, the valgus knee moment was significantly reduced by the dual-rotation platform compared to the inversion/eversion only design. Although the axial knee moment was not significantly reduced by the dual-rotation platform over the adduction/abduction design, there was a general nonsignificant reduction. The lack of significance in knee load results occurred because of high intersubject variability. Accordingly, load reduction benefits made by introducing the second degree of freedom need to be considered individually.

Adult↗
PubMed1997

The effect of pedaling rate on coordination in cycling.

To further understand lower extremity neuromuscular coordination in cycling, the objectives of this study were to examine the effect of pedaling rate on coordination strategies and interpret any apparent changes. These objectives were achieved by collecting electromyography (EMG) data of eight lower extremity muscles and crank angle data from ten subjects at 250 W across pedaling rates ranging from 45 to 120 RPM. To examine the effect of pedaling rate on coordination, EMG burst onset and offset and integrated EMG (iEMG) were computed. In addition, a phase-controlled functional group (PCFG) analysis was performed to interpret observed changes in the EMG patterns in the context of muscle function. Results showed that the EMG onset and offset systematically advanced as pedaling rate increased except for the soleus which shifted later in the crank cycle. The iEMG results revealed that muscles responded differently to increased pedaling rate. The gastrocnemius, hamstring muscles and vastus medialis systematically increased muscle activity as pedaling rate increased. The gluteus maximus and soleus had significant quadratic trends with minimum values at 90 RPM, while the tibialis anterior and rectus femoris showed no significant association with pedaling rate. The PCFG analysis showed that the primary function of each lower extremity muscle remained the same at all pedaling rates. The PCFG analysis, which accounts for muscle activation dynamics, revealed that the earlier onset of muscle excitation produced muscle activity in the same region of the crank cycle. Also, while most of the muscles were excited for a single functional phase, the soleus and rectus femoris were excited during two functional phases. The soleus was classified as an extensor-bottom transition muscle, while the rectus femoris was classified as a top transition-extensor muscle. Further, the relative emphasis of each function appeared to shift as pedaling rate was increased, although each muscle remained bifunctional.

Adult↗
PubMed1997

Determinants of nonthoracotomy biphasic defibrillation.

The clinical variables affecting DFT for ICD systems are not completely determined, especially with regard to biphasic shocking devices. To distinguish which factors correlate with DFT, we examined data from patients who were enrolled in the Ventak P2/Endotak protocol. A total of 284 patients were enrolled in the study. Two patients had a DFT > 25 J and did not receive the device; 154 did not undergo stepdown to failure DFT testing. The remaining 128 patients had formal DFT testing and were suitable for analysis. Variables available for analysis included age, body surface area (BSA), LVEF, gender, lead configuration, primary arrhythmia, primary cardiac disease, and use of cardioactive medication. Data were evaluated using regression analysis, fitting DFT (range, 1-25 J, mean 11 +/- 5 J) as a function of each variable. As a univariate predictor. BSA was found to be significant in predicting DFT, but accounted for only 9% of the total variation on the DFT (P < 0.01, r = 0.3). This study suggests that DFT using a biphasic shocking waveform is modestly in fluenced by the BSA of the patient. Other specific factors, including LVEF, do not predict DFT.

Age Factors↗
PubMed1997

A dynamic system model of an off-road cyclist.

To optimize the performance of off-road bicycle suspension systems, a dynamic model of the bicycle/rider system would be useful. This paper takes a major step toward this goal by developing a dynamic system model of the cyclist. To develop the cyclist model, a series of four vibrational tests utilizing random inputs was conducted on seven experienced off-road cyclists. This allowed the transfer functions for the arms and legs to be determined. To reproduce the essential features (i.e., resonance peaks) of the experimental transfer functions, the system model included elements representing the visceral mass along with the arms and legs. Through simulations, the frequency responses of the system model of the rider in each of the four tests were computed. Optimal stiffness and damping parameter values for each subject were determined by minimizing the difference between the experimental and simulation results. Good agreement between experimental and simulation results indicates that modeling the rider as a lumped parameter system with linear springs and dampers is possible.

Bicycling↗
PubMed1997

An in vitro osteotomy method to expose the medial compartment of the human knee.

This study was conducted to validate a new in vitro method to expose the medial compartment of the knee to be used in subsequent studies aimed at examining the load bearing capabilities of medial meniscal allografts. The new method involves an osteotomy and reattachment of the medial femoral condyle. The primary hypothesis was that the new method does not alter tibio-femoral contact pressure and area. To validate this method, the baseline contact pressure of the intact medial compartment was measured using a new nondestructive procedure for inserting pressure measurement film into the intact medial hemijoint. A secondary and related hypothesis was that incising the coronary ligament, a destructive method used by previous investigators to position pressure measurement film, alters the normal tibio-femoral contact pressure. To test these hypotheses, Fuji Prescale pressure-sensitive film was used to measure both tibio-femoral contact pressure and area within the medial compartment of the (1) intact knee, (2) the knee after osteotomizing and reattaching the medial femoral condyle, and (3) the osteotomized knee with an incised coronary ligament, using seven cadaver specimens. Measurements were taken at a compressive load of approximately two times body weight with the knee in 0, 15, 30, 45 deg of flexion. No significant differences between the intact and osteotomized knee were detected. Likewise, no significant differences were observed between the osteotomized knee and the osteotomized knee with an incised coronary ligament. These results confirm the utility of the new method in exposing the medial compartment for manipulation and placement of medial meniscal allografts in future studies examining the load-bearing characteristics of meniscal allografts.

Cadaver↗
PubMed1996

Strain in the medial collateral ligament of the human knee under single and combined loads.

Strain within the medial collateral ligament (MCL) was measured in 13 human knee specimens to determine both the single and combined external loads most likely to cause injury. Using a load application system which allowed six degrees of freedom with flexion angle being fixed, both single loads of anterior/posterior force, medial/lateral force, varus/valgus torque, and internal/external axial torque and all pairs of these loads were applied at flexion angles of 0 degrees and 30 degrees. Liquid mercury strain gages were used to measure strain at four sites in the MCL. Two of the sites were the anterior fibers superior and inferior to the joint line and the other two were posterior of the two anterior sites. A factorial analysis revealed a significant interaction between the site experiencing the greatest strain and flexion angle. The posterior superior site experienced significantly greater strain at 0 degree flexion whereas strains was significantly greater at the anterior superior site at 30 degree flexion. Of the single moments, external axial was more damaging than valgus in that the strain developed at equivalent load was significantly greater. None of the moment-moment combinations was identified as being significantly more damaging. A similar result held for the force-moment combinations.

Adult↗
PubMed1996

An improved accuracy six-load component pedal dynamometer for cycling.

This paper describes a new six-load component pedal dynamometer designed for study of knee overuse injury in cycling. A unique capability of the dynamometer is the ability to interface with multiple pedal platforms of varying height while maintaining a desired elevation of the foot above the pedal spindle axis. The dynamometer was designed using a concept described in an earlier article by Quinn and Mote (1991, Exp. Mech. 30, 40-48) which measures shear strain across multiple, thin cross-sections. An optimal design technique was used for choosing dimensions of the load measuring cross-sections. A dynamometer was designed and built using the optimal results. Calibration, accuracy results, and sample data are presented. A comparison of accuracy reveals that the new dynamometer is more accurate than previously reported instruments.

Bicycling↗
PubMed1996

Serial defibrillation lead impedance in patients with epicardial and nonthoracotomy lead systems.

INTRODUCTION: The stability of implantable cardiac defibrillation lead impedance subsequent to implantation has not been reported and may have important clinical implications. The objective was to characterize the incidence and degree of impedance changes occurring after implantation of defibrillation lead systems. METHODS AND RESULTS: The study cohort consisted of patients who received epicardial or nonthoracotomy lead systems. Defibrillation impedance was recorded at implantation, prior to hospital discharge (predischarge), and during follow-up. For each individual the magnitude of the impedance change relative to implantation was characterized. Among patients with an epicardial system, a significant decrease in impedance was observed at predischarge (mean 9.3 omega). The magnitude of the decrease was large in 39% and moderate in 31% of individuals. Subsequently, a gradual rise in mean impedance was apparent. At 18-21 months postimplantation, impedance was significantly increased relative to implantation (mean 6.8 omega). At this time, the magnitude of the increase was large in 46% and moderate in 23% of patients. Among patients with a nonthoracotomy lead system including a subcutaneous patch, a significant decrease in mean impedance was observed at predischarge (mean 3.5 omega). The magnitude of the decrease was large in 8% and moderate in 50% of individuals. Subsequently, a gradual rise in impedance was apparent. At 5-6 months, it was significantly increased relative to implantation (mean 2.3 omega). The magnitude of the increase was large in 10% and moderate in 33% of patients. Among the group of patients whose nonthoracotomy lead system did not include a subcutaneous patch, there was no significant change in mean impedance at predischarge relative to implantation. In subsequent intervals, a gradual rise was apparent. At 5-6 months, impedance was significantly increased relative to implantation (mean 4.3 omega). The magnitude of the increase was large in 16% and moderate in 47% of individuals. CONCLUSION: Significant changes in defibrillation lead impedance occur after implantation of epicardial and nonthoracotomy defibrillation lead systems. These data may serve as a standard for identifying the anticipated maximum change in lead impedance and thus may be useful as a tool for recognizing problems with defibrillation lead integrity.

Defibrillators, Implantable↗
PubMed1995

Accuracy assessment of methods for determining hip movement in seated cycling.

The goal of this research was to examine the accuracy of three methods used to indicate the hip joint center (HJC) in seated steady-state cycling. Two of the methods have been used in previous studies of cycling biomechanics and included tracking a marker placed over the superior aspect of the greater trochanter, a location that estimates the center of rotation of the hip joint, and assuming that the hip is fixed. The third method was new and utilized an anthropometric relationship to determine the hip joint location from a marker placed over the anterior-superior iliac spine. To perform a comparative analysis of errors inherent in the three methods, a standard method which located the true hip joint center was developed. The standard method involved establishing a pelvis-fixed coordinate system using a triad of video markers attached to an intracortical pin. Three-dimensional motion analysis quantified the true hip joint center position coordinates. To provide data for the comparative analysis, the intracortical pin was anchored to a single subject who pedaled at nine cadence-workrate combinations while data for all four methods were simultaneously recorded. At all cadence-workrate combinations the new method was more accurate than the trochanter method with movement errors lower by a factor of 2 in the vertical direction and a factor of 3 in the horizontal direction. Relative to the errors introduced by the fixed hip assumption, the new method was also generally more accurate by at least a factor of 2 in the horizontal direction and had comparable accuracy in the vertical direction. For computed kinetic quantities, the new method most accurately indicated hip joint force power but the fixed hip method most accurately indicated the work produced by the hip joint force over the crank cycle.

Bicycling↗
PubMed1995

The effect of rider weight on rider-induced loads during common cycling situations.

Motivated by the desire to provide information useful in the design analysis of bicycle frames, the hypothesis tested was that a simple linear model would relate the maximum magnitudes of rider-induced loads to rider weight. Rider-induced loads are loads developed as a result of weight and muscular actions during pedalling. To test this hypothesis, five riders spanning a wide weight range rode a bicycle unrestrained on a treadmill. Dynamometers measured six components of pedal loads and five components of both seat and handlebar loads while riders rode three common cycling situations--seated cruising, seated climbing, and standing climbing. Average, average maximum, and average minimum values were computed for all load components and each was analyzed statistically. For all three test cases, the regression slope was significant for the force component normal to the pedal surface. Because the normal pedal force component has been shown previously to dominate frame stress at the point most likely to fatigue (Hull and Bolourchi, 1988, J. Strain. Anal. 23, 105-114), the results of this study should be useful in designing frames optimized for minimum weight and acceptable structural reliability.

Adult↗
PubMed1995

Dynamic optimization analysis for equipment setup problems in endurance cycling.

The goals of the work reported by this article are two-fold. The first is to develop a dynamic optimization framework for analysis of equipment setup problems in endurance cycling. The second is to illustrate the application of the approach by determining an optimal chainring shape. To achieve these goals, a mathematical model of the pedaling motion for given trajectories of the net joint moments and the rate of change of the chainring radius was derived, and chainring optimization was posed as an optimal control problem. The cost functional produced a chainring shape that reduced the cost of endurance cycling at 250 W and 90 rpm, apparently by taking advantage of mechanical interactions that arise as a natural consequence of the movement. However, the predicted joint moments required larger peak values during phases of significantly increased joint velocity. Thus, the 'optimal' performance predicted by the cost functional appears opposed to expectations based on muscle mechanics and illustrates the need for further analysis of endurance cycling with a physiologically based cost functional.

Algorithms↗
PubMed1995

Pre-ovulatory oxytocin administration promotes the onset of the luteinizing hormone surge in human females.

Luteinizing hormone (LH) secretion during the ovulatory cycle is believed to be predominantly regulated by gonadotrophin-releasing hormone. Investigations in animals have strongly suggested that oxytocin also participates in LH control and the physiological events controlling LH surge initiation. In the human female, however, there has been no evidence supporting oxytocin's involvement in the processes leading to ovulation. In this study the effect of a preovulatory infusion of oxytocin on the onset of the LH surge was investigated in women aged 20-35 years who had natural ovulatory menstrual cycles of lengths between 25-35 days. Vaginal ultrasound scanning monitored follicular growth during the late follicular phase. When a follicle > 14 mm in diameter was observed each woman was randomized into one of two groups. One group (n = 8) received an oxytocin infusion of 256 mIU/min for 2 h, the other group (n = 8) received normal saline. The women who were administered oxytocin at this late follicular stage had an earlier onset of the LH surge than those who had received saline (P < 0.01). The results indicate that oxytocin promotes the onset of the LH surge in humans.

Adult↗