The effect of positioning on the biomechanical performance of soft shell hip protectors.

Wearable hip protectors represent a promising strategy for reducing risk for hip fracture from a sideways fall. However, small changes in pad positioning may influence their protective benefit. Using a mechanical hip impact simulator, we investigated how three marketed soft shell hip protectors attenuate and redistribute the impact force applied to the hip, and how this depends on displacement from their intended position by 2.5 or 5 cm superiorly, posteriorly, inferiorly or anteriorly. For centrally-placed protectors, peak pressure was reduced 93% below the unpadded value by a 16 mm horseshoe-shaped protector, 93% by a 14 mm horseshoe protector, and 94% by a 16 mm continuous protector. In unpadded trials, 83% of the total force was applied to the skin overlying the proximal femur (danger zone). This was lowered to 19% by the centrally placed 16 mm horseshoe protector, to 34% by the 14 mm horseshoe, and to 40% by the 16 mm continuous protector. Corresponding reductions in peak force delivered to the femoral neck (relative to unpadded) were 45%, 38%, and 20%, respectively. The protective benefit of all three protectors decreased with pad displacement. For example, displacement of protectors by 5 cm anteriorly caused peak femoral neck force to increase 60% above centrally-placed values, and approach unpadded values. These results indicate that soft shell hip protectors provide substantial protective benefits, but decline in performance with small displacements from their intended position. Our findings confirm the need for correct and stable positioning of hip protectors in garment design.

Effect of hip protectors, falling angle and body mass index on pressure distribution over the hip during simulated falls.

BACKGROUND: We examined how a soft shell hip protector affects the magnitude and distribution of force to the hip during simulated falls, and how the protective effect depends on the fall direction and the amount of soft tissue padding over the hip. METHODS: Fourteen young women with either high or low body mass index participated in a "pelvis release experiment" that simulated falls resulting in either lateral, anterolateral or posterolateral impact to the pelvis with/without a soft shell hip protector. Outcome variables were the magnitude and location of peak pressure (d, theta) with respect to the greater trochanter, total impact force, and percent force applied to four defined hip regions. FINDINGS: The soft shell hip protector reduced peak pressure by 70%. The effect was two times greater in low than high body mass index individuals. The protector shunted the peak pressure distally along the shaft of the femur (d=52 mm (SD 22), theta=-21 degrees (SD 49) in the unpadded trials versus d=81 mm (SD 23), theta=-10 degrees (SD 35) in the padded trials). Peak force averaged 12% greater in posterolateral and 17% lower in anterolateral than lateral falls. INTERPRETATION: Our results indicate that the hip protector we tested had a much stronger protective benefit for low than high body mass index individuals. Next generation protectors might be developed for improved shunting of pressure away from the femur, improved protection during posterolateral falls, and greater force attenuation for low body mass index individuals.

Biomechanical energy harvesting: generating electricity during walking with minimal user effort.

We have developed a biomechanical energy harvester that generates electricity during human walking with little extra effort. Unlike conventional human-powered generators that use positive muscle work, our technology assists muscles in performing negative work, analogous to regenerative braking in hybrid cars, where energy normally dissipated during braking drives a generator instead. The energy harvester mounts at the knee and selectively engages power generation at the end of the swing phase, thus assisting deceleration of the joint. Test subjects walking with one device on each leg produced an average of 5 watts of electricity, which is about 10 times that of shoe-mounted devices. The cost of harvesting-the additional metabolic power required to produce 1 watt of electricity-is less than one-eighth of that for conventional human power generation. Producing substantial electricity with little extra effort makes this method well-suited for charging powered prosthetic limbs and other portable medical devices.

Protective effects of glial cell line-derived neurotrophic factor in ischemic brain injury.

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to have trophic activity on dopaminergic neurons. Recent studies indicate that GDNF can protect the cerebral hemispheres from damage induced by middle cerebral arterial ligation. We found that such neuroprotective effects are mediated through specific GDNF receptor alpha-1 (GFRalpha1). Animals with a deficiency in GFRalpha-1 have less GDNF-induced neuroprotection. Ischemia also enhances nitric oxide synthase (NOS) activity, which can be attenuated by GDNF. These.data suggest that GDNF can protect against ischemic injury through a GFRalpha-1/NOS mechanism. We also found that the receptor for GDNF, GFRalpha1, and its signaling moiety c-Ret were upregulated, starting immediately after ischemia. This upregulation suggests that activation of an endogenous neuroprotective mechanism occurs so that responsiveness of GDNF can be enhanced at very early stages during ischemia.

Restoration of use of paralyzed limb muscles using sensory nerve signals for state control of FES-assisted walking.

A real-time functional electrical stimulation (FES) state controller was designed that utilized sensory nerve cuff signals from the cat forelimb to control the timing of stimulation of the Palmaris Longus (PalL) muscle during walking on the treadmill. Sensory nerve signals from the median and superficial radial nerves provided accurate, reliable feedback related to foot contact and lift-off which, when analyzed with single threshold Schmitt triggers, produced valuable state information about the step cycle. The study involved three experiments: prediction of the timing of muscle activity in an open-loop configuration with no stimulation, prediction of the timing of muscle activity in a closed-loop configuration that included stimulation of the muscle over natural PaIL electromyogram (EMG), and temporary paralysis of selected forelimb muscles coupled with the use of the state controller to stimulate the PalL in order to return partial support function to the anesthetized limb. The FES state controller was tested in a variety of walking conditions, including different treadmill speeds and slopes. The results obtained in these experiments demonstrate that nerve cuff signals can provide a useful source of feedback to FES systems for control of limb function.

Gait phase information provided by sensory nerve activity during walking: applicability as state controller feedback for FES.

In this study, we extracted gait-phase information from natural sensory nerve signals of primarily cutaneous origin recorded in the forelimbs of cats during walking on a motorized treadmill. Nerve signals were recorded in seven cats using nerve cuff or patch electrodes chronically implanted on the median, ulnar, and/or radial nerves. Features in the electroneurograms that were related to paw contact and lift-off were extracted by threshold detection. For four cats, a state controller model used information from two nerves (either median and radial, or ulnar and radial) to predict the timing of palmaris longus activity during walking. When fixed thresholds were used across a variety of walking conditions, the model predicted the timing of EMG activity with a high degree of accuracy (average error = 7.8%, standard deviation = 3.0%, n = 14). When thresholds were optimized for each condition, predictions were further improved (average error = 5.5%, standard deviation = 2.3%, n = 14). The overall accuracy with which EMG timing information could be predicted using signals from two cutaneous nerves for two constant walking speeds and three treadmill inclinations for four cats suggests that natural sensory signals may be implemented as a reliable source of feedback for closed-loop control of functional electrical stimulation (FES).

Precipitation of serum proteins by polyethylene glycol (PEG) in pretransfusion testing.

Polyethylene glycol (PEG) is used as a potentiator of blood group antigen-antibody interactions. Although PEG is known to precipitate immunoglobulins, we could find no reports of this reagent entrapping red blood cells (RBCs) in irreversible clumps. The patient we describe here had hyperglobulinemia with a reversed albumin:globulin ratio and a diffuse immunoglobulin peak on serum protein electrophoresis. During preparation of serologic tests, a precipitate formed that entrapped the RBCs when PEG was added. Rapid recognition of this phenomenon could prevent delay in the selection of blood for transfusion by substituting PEG-indirect antiglobulin test (IAT) with another technique such as low-ionic-strength solution (LISS)-IAT, and by increasing the number of washes prior to addition of the antiglobulin reagent.

Regional variability of stretch reflex amplitude in the cat medial gastrocnemius muscle during a postural task.

The relationship between local fibre stretch velocity (mechanical input) and the corresponding local reflex electromyographic (EMG) amplitude (a measure of the neural output) was assessed to determine the contribution of muscle spindle feedback in postural control. We hypothesized that traditionally measured input variables (e.g., the velocity of an external movement or whole muscle velocity) may not accurately represent the mechanical input to the muscle spindles, especially when the background forces are small. Three cats were trained to stand on pedestals while ankle rotations were applied to the left hindlimb. EMG and fiber movement in both proximal and distal regions of the muscle were recorded in addition to muscle length and tendon force. We found that local muscle velocity was correlated poorly with whole muscle velocity, demonstrating that internal and external muscle movements are often dissimilar, particularly during tasks that involve modest levels of muscle activation. Local EMG reflex amplitudes were correlated well with the corresponding local fiber stretch velocities (R values ranging from 0.5 to 0.8) but not with muscle stretch velocity. The lack of crossed correlations between fiber stretch velocities and reflex EMG amplitudes measured in proximal versus distal regions of the muscle suggests the presence of a local reflex component. It is concluded that changes in local muscle fiber length represent the mechanical input to spindles better than changes in the total muscle length. Additionally, spindles have a specific role in the reflex activation of nearby muscle fibers.

A measure of peripheral nerve stimulation efficacy applicable to H-reflex studies.

BACKGROUND: When H-reflexes are recorded during movement in human subjects, the stimulator current output is not a good indicator of sensory stimulation efficacy because of unavoidable nerve movement relative to the stimulus electrodes. Therefore, the M-wave amplitude has been used by researchers as an indicator of the efficacy of the stimulus. In this study we have examined the general validity of the hypothesis that the M-wave amplitude is directly proportional to the group I sensory afferent volley evoked by the stimulus. METHODS: A nerve recording cuff, stimulating electrodes, and EMG recording electrodes were implanted in cats. Nerve cuff recordings of centrally propagating volleys evoked by electrical stimuli were directly compared to M-waves produced by the same stimuli. Compound action potentials (CAPs) recorded in the sciatic nerve were compared with soleus M-waves during either tibial nerve or soleus muscle nerve stimulation. CAPs in the ulnar nerve were correlated with flexor carpi ulnaris M-waves during ulnar nerve stimulation. RESULTS AND CONCLUSIONS: Our findings indicate that for mixed nerve stimulation (e.g., tibial or ulnar nerve) the M-wave can be a reliable indicator of the centrally propagating sensory volley. Due to the high correlation between CAP and M-wave amplitude in these nerves, a small number of M-waves can give a good estimate of the size of the group I sensory volley. On the other hand, when nerves with only partially overlapping fibre diameter populations are stimulated (e.g., the soleus muscle nerve), the M-wave is not well correlated with the group I sensory volley and thus may not be used as a measure of the size of the input volley for H-reflex studies.

Neural signals for command control and feedback in functional neuromuscular stimulation: a review.

In current functional neuromuscular stimulation systems (FNS), control and feedback signals are usually provided by external sensors and switches, which pose problems such as donning and calibration time, cosmesis, and mechanical vulnerability. Artificial sensors are difficult to build and are insufficiently biocompatible and reliable for implantation. With the advent of methods for electrical interfacing with nerves and muscles, natural sensors are being considered as an alternative source of feedback and command signals for FNS. Decision making methods for higher level control can perform equally well with natural or artificial sensors. Recording nerve cuff electrodes have been developed and tested in animals and demonstrated to be feasible in humans for control of dorsiflexion in foot-drop and grasp in quadriplegia. Electromyographic signals, being one thousand times larger than electroneurograms, are easier to measure but have not been able to provide reliable indicators (e.g., of muscle fatigue) that would be useful in FNS systems. Animal studies have shown that information about the shape and movement of arm trajectories can be extracted from brain cortical activity, suggesting that FNS may ultimately be directly controllable from the central nervous system.

Effect of pronase on high-incidence blood group antigens and the prevalence of antibodies to pronase-treated erythrocytes.

Pronase is a useful and relatively nonspecific protease that cleaves many red blood cell (RBC) membrane proteins that carry blood group antigens. Unexpected findings in tests using pronase-treated RBCs during the investigation of a patient's blood sample led us to test which high-incidence blood group antigens were sensitive and which were resistant to pronase treatment, and to determine the prevalence of antipronase in the serum of blood donors. Our results show that antigens in the Cromer and Lutheran blood group systems and the JMH antigen were sensitive to pronase treatment of RBCs. Antigens in the Dombrock blood group system and Sc1 were either sensitive to or markedly weakened by pronase treatment of RBCs. The following high-incidence antigens were resistant to treatment of RBCs with pronase: AnWj, Ata, Coa, Co3, Dib, EnaFR, Era, Fy3, Jk3, Jra, k, Kpb, Jsb, K14, Lan, Oka, Rh17, U, Vel, and Wrb. Over half of the serum samples from normal blood donors contained antibodies to pronase-treated RBCs. When testing human serum against pronase-treated RBCs, it is essential either to use an autocontrol or to perform the testing with an eluate.

The second example of Lu:-7 phenotype: serology and immunochemical studies.

We describe the second example of red blood cells (RBCs) with the Lu:-7 phenotype in a 37-year-old Latino female (SA). Her RBCs were nonreactive with anti-Lu7 (Mrs. GA) but were reactive with all other antibodies to high-prevalence antigens tested, including those in the Lutheran blood group system. No Lu:-7 RBCs were available for testing. SA's serum was nonreactive by the indirect antiglobulin test against (1) recessive and dominant Lu(a-b-) RBCs and (2) trypsin-treated or a-chymotrypsin-treated RBCs of common phenotype. By immunoblotting, eluates containing anti-Lu7 from both Mrs. GA and SA reacted with apparently the same bands in RBC membranes of common phenotype as did human anti-Lub, reacted weakly with Lu(a-b-) RBCs of the dominant type, and were nonreactive with SA's RBC membranes. These findings raise the Lu7 antigen from its Lutheran-related (para-Lutheran) status to a bona fide member of the Lutheran blood group system.

New transducers for measuring muscle length in unrestrained animals.

Muscle length in unrestrained, chronically implanted animals is conventionally measured with gauges consisting of a compliant silicone rubber tube filled with either hypertonic saline or mercury, the measurement principle being a continuous change in the electrical resistance of the fluid column inside the tubing with stretch. These gauges have two major disadvantages: (1) changes in resistance that are not related to changes in length, such as those produced by changes in temperature or osmotic dilution of the hypertonic saline, cause the measurements to drift, and (2) there is no direct and accurate way to calibrate the measurements. In this communication two new types of muscle length gauge are described that eliminate both problems. Both types make use of the principle of sonomicrometry, i.e., the measurement of distances with pulsed ultrasound. Both types have been successfully used to measure the length of the medial gastrocnemius muscle in chronically implanted cats during treadmill locomotion.

Velocity of ultrasound in active and passive cat medial gastrocnemius muscle.

The lengths and pinnation angles of muscle fibers in the medial gastrocnemius (MG) muscle have recently been measured in freely moving cats [Hoffer et al., Progr. Brain Res. 80, 75-85 (1989); Muscle Afferents and Spinal Control of Movement (1992)] using an ultrasound transit-time (USTT) technique. This method assumed that the velocity of ultrasound through intact muscles was constant, independent of fiber orientation, muscle activity, load, belly shape, or fiber movement. However, the velocity of ultrasound along and across the fibers has been reported to depend on the state of muscle activation in frog muscle experiments in vitro [Hatta et al., J. Physiol. 403, 193-209 (1988)]. In the present study, the assumption of constant velocity of ultrasound in the cat MG muscle was evaluated. In acute experiments, done in situ with intact blood supply, the USTT was measured along and across cat MG muscle fibers in the passive, reflexly activated and tetanically activated states, with and without changes in muscle fiber length, for situations that reproduced the length and force ranges normally used by cats during locomotion. The velocity of ultrasound was found to be independent of the state of activation or motion of the muscle, and independent of the direction of the measurement with respect to the fiber orientation, within a measurement uncertainty less than or equal to 0.2%. These results validate the use of the USTT technique for the measurement of intramuscular dimensions in freely moving animals.

Ethical decision making for nurse administrators.

The authors' purpose is to offer a theoretical perspective to help the nurse administrator make ethical decisions congruent with social policies in allocating scarce resources. The goal is approached in two ways: by exploring the philosophical principle of morality on which decisions to distribute scarce resources can be made and by clarifying the principles of justice and distributive justice in two classic moral theories. Principles of distributive justice that serve as guidelines for social justice policy are delineated. A case study illustrates the dilemma.