Interlimb conditioning of lumbosacral spinally evoked motor responses after spinal cord injury.

OBJECTIVE: The importance of subcortical pathways to functional motor recovery after spinal cord injury (SCI) has been demonstrated in multiple animal models. The current study evaluated descending interlimb influence on lumbosacral motor excitability after chronic SCI in humans. METHODS: Ulnar nerve stimulation and transcutaneous electrical spinal stimulation were used in a condition-test paradigm to evaluate the presence of interlimb connections linking the cervical and lumbosacral spinal segments in non-injured (n=15) and spinal cord injured (SCI) (n=18) participants. RESULTS: Potentiation of spinally evoked motor responses (sEMRs) by ulnar nerve conditioning was observed in 7/7 SCI participants with volitional leg muscle activation, and in 6/11 SCI participants with no volitional activation. Of these six, conditioning of sEMRs was present only when the neurological level of injury was rostral to the ulnar innervation entry zones. CONCLUSIONS: Descending modulation of lumbosacral motor pools via interlimb projections may exist in SCI participants despite the absence of volitional leg muscle activation. SIGNIFICANCE: Evaluation of sub-clinical, spared pathways within the spinal cord after SCI may provide an improved understanding of both the contributions of different pathways to residual function, and the mechanisms of plasticity and functional motor recovery following rehabilitation..

Unlike voluntary contractions, stimulated contractions of a hand muscle do not reduce voluntary activation or motoneuronal excitability.

Voluntary force declines during sustained, maximal voluntary contractions (MVC) due to changes in muscle and central nervous system properties. Central fatigue, an exercise-induced reduction in voluntary activation, is influenced by multiple processes. Some may occur independently of descending voluntary drive. To differentiate the effects associated with voluntary drive from other central and peripheral influences, we measured voluntary activation and motoneuron excitability following fatiguing contractions produced voluntarily or by electrical stimulation. On two separate days, participants performed either a 2-min MVC of adductor pollicis muscle or received 2-min continuous supramaximal electrical stimulation of the ulnar nerve. In study 1 (n = 14), the superimposed twitch elicited by ulnar nerve stimulation during brief MVCs was increased, and, hence, voluntary activation was reduced, up to 240 s after the 2-min MVC [-20 ± 12% (SD), P = 0.002] but not the 2-min stimulated contraction (-4 ± 7%), despite large reductions in MVC force (voluntary, -54 ± 18%; stimulated, -46 ± 16%). In study 2 (n = 12), F-waves recorded from the adductor pollicis were reduced in area for 150 s following the 2-min MVC (-21 ± 16%, P = 0.007) but not after the stimulated contraction (5 ± 27%). Therefore, voluntary activation and motoneuron excitability decreased only when descending voluntary drive was present during the fatiguing task. The findings do not exclude a cortical or brain stem contribution to the reduced voluntary activation but suggest that neither sensory feedback from the fatigued muscle nor repetitive activation of motoneurons underlie the changes, whereas they are consistent with motoneuronal inhibition by released factors linked to voluntary drive.NEW & NOTEWORTHY We demonstrate that reductions in voluntary activation and motoneuron excitability following 2-min isometric maximal contractions in humans occur only when fatigue is produced through voluntary contractions and not through electrically stimulated contractions. This is contrary to studies that suggest that changes in the superimposed twitch and therefore voluntary activation are explained by changes in peripheral factors alone. Thus, the interpolated twitch technique remains a viable tool to assess voluntary activation and central fatigue.

Jaw tremor as a physiological biomarker of bruxism.

OBJECTIVE: To determine if sleep bruxism is associated with abnormal physiological tremor of the jaw during a visually-guided bite force control task. METHODS: Healthy participants and patients with sleep bruxism were given visual feedback of their bite force and asked to trace triangular target trajectories (duration=20s, peak force <35% maximum voluntary force). Bite force control was quantified in terms of the power spectra of force fluctuations, masseter EMG activity, and force-to-EMG coherence. RESULTS: Patients had greater jaw force tremor at ∼8 Hz relative to controls, along with increased masseter EMG activity and force-to-EMG coherence in the same frequency range. Patients also showed lower force-to-EMG coherence at low frequencies (<3 Hz), but greater coherence at high frequencies (20-40 Hz). Finally, patients had greater 6-10 Hz force tremor during periods of descending vs. ascending force, while controls showed no difference in tremor with respect to force dynamics. CONCLUSION: Patients with bruxism have abnormal jaw tremor when engaged in a visually-guided bite force task. SIGNIFICANCE: Measurement of jaw tremor may aid in the detection/evaluation of bruxism. In light of previous literature, our results also suggest that bruxism is marked by abnormal or mishandled peripheral feedback from the teeth.

Adrenergic receptors modulate motoneuron excitability, sensory synaptic transmission and muscle spasms after chronic spinal cord injury.

The brain stem provides most of the noradrenaline (NA) present in the spinal cord, which functions to both increase spinal motoneuron excitability and inhibit sensory afferent transmission to motoneurons (excitatory postsynaptic potentials; EPSPs). NA increases motoneuron excitability by facilitating calcium-mediated persistent inward currents (Ca PICs) that are crucial for sustained motoneuron firing. Spinal cord transection eliminates most NA and accordingly causes an immediate loss of PICs and emergence of exaggerated EPSPs. However, with time PICs recover, and thus the exaggerated EPSPs can then readily trigger these PICs, which in turn produce muscle spasms. Here we examined the contribution of adrenergic receptors to spasms in chronic spinal rats. Selective activation of the α(1A) adrenergic receptor with the agonists methoxamine or A61603 facilitated Ca PIC and spasm activity, recorded both in vivo and in vitro. In contrast, the α(2) receptor agonists clonidine and UK14303 did not facilitate Ca PICs, but did decrease the EPSPs that trigger spasms. Moreover, in the absence of agonists, spasms recorded in vivo were inhibited by the α(1) receptor antagonists WB4010, prazosin, and REC15/2739, and increased by the α(2) receptor antagonist RX821001, suggesting that both adrenergic receptors were endogenously active. In contrast, spasm activity recorded in the isolated in vitro cord was inhibited only by the α(1) antagonists that block constitutive receptor activity (activity in the absence of NA; inverse agonists, WB4010 and prazosin) and not by the neutral antagonist REC15/2739, which only blocks conventional NA-mediated receptor activity. RX821001 had no effect in vitro even though it is an α(2) receptor inverse agonist. Our results suggest that after chronic spinal cord injury Ca PICs and spasms are facilitated, in part, by constitutive activity in α(1) adrenergic receptors. Additionally, peripherally derived NA (or similar ligand) activates both α(1) and α(2) adrenergic receptors, controlling PICs and EPSPs, respectively.

Initial experience with a modification of the follicle aspiration, sperm injection, and assisted rupture technique.

OBJECTIVE: To establish cycle fecundity with a modification of the follicle aspiration, sperm injection, and assisted rupture (FASIAR) technique. DESIGN: Prospective, observational study. SETTING: University and health maintenance organization-based infertility centers. PATIENT(S): Infertile couples were enrolled from our professional practices. All patients were 16-18 mm in diameter by transvaginal ultrasonography. A modified FASIAR procedure was performed 22 to 28 hours after hCG injection. MAIN OUTCOME MEASURE(S): Clinical pregnancy rate. RESULT(S): No clinical pregnancies were observed with the modified FASIAR technique. CONCLUSION(S): The FASIAR technique is still an attractive and economical technique. Our modification of the FASIAR technique, however, resulted in a suboptimal cycle fecundity.

The F-Scan system with EDG module for gait analysis in the pediatric patient.

The Electrodynogram (EDG) system of foot-fall measurement has been in clinical use for more than 15 years. Recently the EDG was acquired by Tekscan, which manufactures the F-Scan system of foot-pressure analysis. The new F-Scan system with EDG module retains all of the benefits of the F-Scan system while incorporating the valuable temporal and pressure data comparisons offered by the EDG. This merging of technologies has resulted in a system that is more suitable for application in the pediatric patient than either system alone.

The effect of posture on the induction of epidural anesthesia for peripheral vascular surgery.

BACKGROUND AND OBJECTIVES: A study was done to determine whether a difference existed in the quality and time to maximum anesthesia between the induction of lumbar epidural anesthesia in the sitting and supine position in patients undergoing infrainguinal arterial reconstruction. METHODS: An epidural catheter was inserted at L3-L4 in 40 patients who were randomly assigned to two groups. In group 1, with the patient sitting, 3 mL lidocaine 1.5% with 5 micrograms/mL epinephrine was given as a test dose, followed 3 minutes later by 12 mL bupivacaine 0.75% injected over 2 minutes through the catheter. After remaining in the sitting position for 5 minutes, the patient was placed supine and the quality of anesthesia assessed at 3-minute intervals for 30 minutes. Anesthesia was assessed by loss of sensation to pinprick and the Bromage scale for loss of motor function. In group 2, after placement of the catheter, the patient was immediately placed supine, the same doses of local anesthesia were given at the same time intervals as in group 1, and the onset of anesthesia was similarly assessed. In addition to a comparison between groups in the quality and time to maximum anesthesia, a correlation was sought between these variables and the age, weight, height, and body surface area (BSA) of the patients in each group. RESULTS: The demographically similar groups showed no difference in maximum cephalad spread of anesthesia (median, interquartile range; group 1: T4, T2.5-T6; group 2: T4, T2.5-T7), motor block (group 1: 3, 2-4; group 2: 4, 4-6), or time to maximum motor block (mean +/- SD; group 1, 17.4 +/- 8.7 minutes; group 2, 17.9 +/- 6.8 minutes). The time to maximum cephalad spread of anesthesia was shorter in group 1 (13.8 +/- 6.9 minutes; group 2, 18.6 +/- 6.6 minutes; P = .03). Neither the age nor weight of the patients in either group had any influence on the quality and time to maximum anesthesia. There was, however, a significant correlation between the height (r = 0.48, P = .0303) and BSA (r = 0.48, P = .0318) of the patients in group 1 and the time to maximum cephalad spread of anesthesia. CONCLUSIONS: When lumbar epidural anesthesia was induced in the sitting rather than supine position, the time to maximum cephalad spread was shorter and correlated directly with the height and BSA of the patient. The position of the patient during induction had no effect on the final level of cephalad spread and degree of motor block.

Rainbow-enhanced forward glory from fused-silica spheres.

A tertiary rainbow enchances the forward glory scattering from a fused-silica sphere because of its refractive index m ≍ 1.465. The scattered light contains a strong cross-polarized component and varies rapidly in brightness with changes in m. In experiments m is varied by the use of a range of argon and dye laser wavelengths. The forward cross-polarized scattering is found to be in agreement with Mie theory calculations. A reflective coating on small areas around the equator and polar caps of the sphere increases the forward scattering by a factor of ~ 180.

Temporal characteristics of proximally-induced accommodation.

This study sought to determine whether proximally-induced accommodation (PIA) is capable of sustaining an accommodative response over time. Accordingly, the steady-state PIA response was measured during the course of a continuous 5 min stimulus period for targets located at distances of 0.2 or 6 m. The vergence and accommodation loops were opened by subjects (n = 8) monocularly viewing the targets through a 0.5 mm pinhole, while accommodation was assessed using an objective, open-field, infrared optometer. The mean PIA response did not change significantly during the fixation period. This finding suggests that PIA is indeed capable of maintaining a sustained response. This observation is consistent with the constancy of apparent target distance perception during extended fixation of a stationary object of regard under these conditions.

Induction of hypothalamic opioid activity with transdermal estradiol administration in postmenopausal women.

The effects of estradiol (E2) administered by a transdermal system on the induction of hypothalamic opioid activity was examined in 18 postmenopausal women. Women were given 25, 50, 100, or 200 micrograms/d dosages of E2 for 28 days each. Naloxone at a dosage of 2 mg/h was infused intravenously for 4 hours, and serum was obtained every 15 minutes for 6 hours. With increasing doses, rises of serum E2 and estrone were elicited across the range seen in premenopausal women. A stepwise reduction of luteinizing hormone (LH) levels was observed with increasing dosages of E2. The naloxone infusions resulted in significant increases of LH when E2 was being given but not during the pretreatment studies. These data indicate E2, in physiological concentrations, induces hypothalamic opioid activity.

Lower extremity functional dynamics.

An overview of the normal and abnormal functional equilibrium of the lower extremity has been presented. The biomechanical and pathomechanical implications of activity and inactivity on this system have been discussed. Special emphasis has been placed on the effects of musculoskeletal imbalances on foot function. Evaluation and management guidelines for the restoration and rehabilitation of lower extremity functional equilibrium have been outlined. Familiarization with these concepts and techniques will enable the astute practitioner to prevent disruptions of extremity functional equilibrium and allow the individual to lead a more healthy, active lifestyle.

A comparison of the effects of Buserelin versus danazol on plasma lipoproteins during treatment of pelvic endometriosis.

Twelve patients receiving Buserelin and seven patients receiving danazol for treatment of endometriosis were studied to assess the effect of medication on plasma lipoproteins. Danazol significantly lowered plasma HDL-C levels at 6 months of treatment. Total plasma cholesterol was elevated at 6 months of therapy in the Buserelin group. No effect by either drug on plasma triglycerides was seen.

Developmental flatfoot.

An overview of the clinical entity referred to as developmental flatfoot has been discussed. Specific reference has been made to its occurrence, etiology, identification, pathomechanics, clinical significance, and management rationale. This often overlooked, inconspicuous condition is the most common musculoskeletal abnormality affecting the foot of the child under 6 years of age. Recognition of the fact that the developmental flatfoot is the logical precursor of foot dysfunction, deformity, and resultant disability later in life will allow the practitioner to design a management program for today that will meet the foot health needs of tomorrow.