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Biomedical subjects

C F Runge

Publications and source records attributed to C F Runge.

6 recordsLinked to original sources
PubMed1998

Role of vestibular information in initiation of rapid postural responses.

Patients with bilateral vestibular loss have difficulty maintaining balance without stepping when standing in tandem, on compliant surfaces, across narrow beams, or on one foot, especially with eyes closed. Normal individuals (with no sensory impairment) maintain balance in these tasks by employing quick, active hip rotation (a "hip strategy"). The absence of a hip strategy in vestibular patients responding to translations of a short support surface has previously been taken as evidence that the use of hip strategy requires an intact vestibular system. However, many tasks requiring hip strategy alter one or a combination of important system characteristics, such as initial state of the body (tandem stance), dynamics (compliant surfaces), or biomechanical limits of stability (narrow beams). Therefore, the balance deficit in these tasks may result from a failure to account for these support surface alterations when planning and executing sensorimotor responses. In this study, we tested the hypothesis that vestibular information is critical to trigger a hip strategy even on an unaltered support surface, which imposes no changes on the system characteristics. We recorded the postural responses of vestibular patients and control subjects with eyes closed to rearward support surface translations of varying velocity, in erect stance on a firm, flat surface. Subjects were instructed to maintain balance without stepping, if possible. Faster translation velocities (25 cm/s or more) produced a consistent pattern of early hip torque (first 400 ms) in control subjects (i.e., a hip strategy). Most of the patients with bilateral vestibular loss responded to the same translation velocities with similar torques. Contrary to our hypothesis, we conclude that vestibular function is not necessary to trigger a hip strategy. We postulate, therefore, that the balance deficit previously observed in vestibular patients during postural tasks that elicit a hip strategy may have been due to the sensorimotor consequences of the system alterations imposed by the postural tasks used in those studies. Preliminary results from two younger patients who lost vestibular function as infants indicate that age, duration of vestibular loss, and/or the timing of the loss may also be factors that can influence the use of hip strategy as a rapid postural response.

Adult↗
PubMed1997

The use of inverse dynamics solutions in direct dynamics simulations.

Previous attempts to use inverse dynamics solutions in direct dynamics simulations have failed to replicate the input data of the inverse dynamics problem. Measurement and derivative estimation error, different inverse dynamics and direct dynamics models, and numerical integration error have all been suggested as possible causes of inverse dynamics simulation failure. However, using a biomechanical model of the type typically used in gait analysis applications for inverse dynamics calculations of joint moments, we produce a direct dynamics simulation that exactly matches the measured movement pattern used as input to the inverse dynamic problem. This example of successful inverse dynamics simulation demonstrates that although different inverse dynamics and direct dynamics models may lead to inverse dynamics simulation failure, measurement and derivative estimation error do not. In addition, inverse dynamics simulation failure due to numerical integration errors can be avoided. Further, we demonstrate that insufficient control signal dimensionality (i.e., freedom of the control signals to take on different "shapes"), a previously unrecognized cause of inverse dynamics simulation failure, will cause inverse dynamics simulation failure even with a perfect model and perfect data, regardless of sampling frequency.

Biomechanical Phenomena↗
PubMed1995

Estimating net joint torques from kinesiological data using optimal linear system theory.

Net joint torques (NJT) are frequently computed to provide insights into the motor control of dynamic biomechanical systems. An inverse dynamics approach is almost always used, whereby the NJT are computed from 1) kinematic measurements (e.g., position of the segments), 2) kinetic measurements (e.g., ground reaction forces) that are, in effect, constraints defining unmeasured kinematic quantities based on a dynamic segmental model, and 3) numerical differentiation of the measured kinematics to estimate velocities and accelerations that are, in effect, additional constraints. Due to errors in the measurements, the segmental model, and the differentiation process, estimated NJT rarely produce the observed movement in a forward simulation when the dynamics of the segmental system are inherently unstable (e.g., human walking). Forward dynamic simulations are, however, essential to studies of muscle coordination. We have developed an alternative approach, using the linear quadratic follower (LQF) algorithm, which computes the NJT such that a stable simulation of the observed movement is produced and the measurements are replicated as well as possible. The LQF algorithm does not employ constraints depending on explicit differentiation of the kinematic data, but rather employs those depending on specification of a cost function, based on quantitative assumptions about data confidence. We illustrate the usefulness of the LQF approach by using it to estimate NJT exerted by standing humans perturbed by support-surface movements. We show that unless the number of kinematic and force variables recorded is sufficiently high, the confidence that can be placed in the estimates of the NJT, obtained by any method (e.g., LQF, or the inverse dynamics approach), may be unsatisfactorily low.

Algorithms↗
PubMed1992

Hearing loss prevalence and management in nursing home residents.

OBJECTIVES: To determine the prevalence and management of hearing loss and hearing handicap among non-demented nursing home residents. DESIGN: Descriptive study of total population of two nursing homes. PARTICIPANTS: All 121 eligible residents. SETTINGS: Two nursing homes. MINI OUTCOME MEASURES: Audiometry, questionnaires of nurses and subjects regarding perceived hearing handicap, and documentation in medical records of hearing loss. RESULTS: 77% had at least a mild (greater than or equal to 26 dB Hearing Level) hearing loss in the better ear, and 51% had a moderate to severe loss (greater than or equal to 41 dB HL). Self-assessments of hearing handicap by residents, together with audiometric findings and expressed interest in a hearing aid, were more useful guides for aural rehabilitation needs than were nurses' assessments of residents' handicaps. Medical records failed to identify 48% of residents with moderate to severe hearing losses. Fifty-eight percent of residents with severe hearing loss currently had hearing aids, and 38% more would like to have an aid. CONCLUSIONS: Residents should have hearing evaluations with documentation of results on admission and periodically under the direction of a nurse trained as a hearing specialist. Environmental modifications of the NH plus use of hearing aids can improve hearing.

Aged↗
PubMed1982

The use of magnesium-containing phosphate binders in patients with end-stage renal disease on maintenance hemodialysis.

We investigated the safety and efficacy of magnesium hydroxide as a phosphate binder in patients with end-stage renal disease on maintenance hemodialysis, 9 volunteers participated in a four-phase study during which each ingested (1) no phosphate binders, (2) magnesium hydroxide (Mg(OH)2) alone, (3) Mg(OH)2 and aluminum hydroxide (A1(OH)3) together and (4) A1(OH)3 alone. Serum magnesium (SMg) concentrations were maintained at less than 4.5 mEq/1 (2.3 mmol/l) in all subjects while they were ingesting 0.75-3 g Mg(OH)2/day and no magnesium toxicity was noted. In individuals taking a constant daily dose, SMg remained stable over 8-12 weeks. Serum phosphorus (SP) decreased from 9.0 mg/dl (2.9 mmol/l)d during the control period to 8.1 mg/dl (2.6 mmol/l) during the Mg(OH)2 period (p less than 0.05) and increased from 6.1 mg/dl (2.0 mmol/l) during the Mg(OH)2 and A1(OH)3 period to 7.0 mg/dl (2.3 mmol/l) during the Al(OH)3 period (p less than 0.05) indicating that Mg(OH)2 could significantly lower SP. However, SP was best controlled (6.1 mg/dl; 2.0 mmol/l) when Al(OH)3 and Mg(OH)2 were used together and all participants preferred the combination therapy to either of the agents alone. These results indicate that Mg(OH)2 is a potentially useful adjunct to A1(OH)3 for managing hyperphosphatemia in patients on maintenance hemodialysis. In this short-term study Mg(OH)3 for managing hyperphosphatemia in patients on maintenance hemodialysis. In this short-term study Mg(OH)2 was well tolerated and with appropriate monitoring did not cause uncontrolled hypermagnesemia. Further studies are clearly required to determine whether long-term therapy with Mg-containing agents is safe in dialysis patients.

Aluminum Hydroxide↗