THE CONTROL OF HUMAN MOTOR UNITS

1. The motor unit, consisting of a single motor neuron and the skeletal muscle fibres that it innervates, is the final output pathway of the motor system. 2. Much is now known about the way that human motor neurons are recruited and controlled during voluntary and reflex movements. This review briefly summarizes some of the recent experimental data that has contributed to our present understanding. The review is largely limited to data obtained in human experiments. While much of what we know about the organization of the nervous system has come from studies of the anatomy and physiology of experimental animals, there are some questions that cannot be addressed in reduced animal preparations. The development of new techniques has made it possible to investigate the human nervous system at a level of detail that has not hitherto been possible.     

Transcanal cochlear implantation under monitored anesthesia care.

OBJECTIVE: Given the associated risk of general anesthesia in elderly patients with cardiovascular disease, the authors set out to determine the feasibility of transcanal cochlear implantation under local anesthesia with monitored anesthesia care. METHODS: A 70-year-old man with a history of coronary artery bypass grafting, diabetes mellitus, and an American Society of Anesthesiologists Class III cardiac status underwent cochlear implantation under local with monitored anesthesia care. RESULT: With the described technique and regimen of intravenous remifentanil and dexmedetomidine, the patient tolerated the 60-minute procedure without tachycardia, hyper- or hypotension, or cardiac ischemia. CONCLUSION: Cochlear implantation using the pericanal electrode technique performed under local anesthesia with monitored anesthesia care is possible in patients at risk for undergoing general anesthesia for cochlear implantation.     

Actin-free Gc globulin: a rapidly assessed biomarker of organ dysfunction in acute liver failure and cirrhosis.

Reductions in serum levels of Gc globulin, a hepatically synthesized component of the extracellular actin scavenger system responsible for complexing circulating actin and attenuating intravascular microthrombus formation, are associated with poor outcome in acute liver failure. Clinically applicable assays of the important actin-free fraction (Af-Gc) have not been available until now. We measured actin-free Gc globulin levels with a novel, rapid assay in 61 cases of acute liver failure (ALF) and in 91 patients with cirrhosis (40 of whom were clinically unstable with extrahepatic organ dysfunction), and studied associations with liver dysfunction, extrahepatic organ dysfunction, indices of disseminated coagulation, and outcome. Reductions in Af-Gc levels mirrored hepatic dysfunction and organ dysfunction in both groups, and discriminated patients with poor prognosis from those with good prognosis in the ALF cohort. Levels were lowest in patients with ALF (10% of control values), but levels were also markedly reduced in both unstable (28%) and stable (44%) patients with cirrhosis. Associations with markers of disseminated intravascular coagulation were seen in both groups, most notably in the cirrhosis cohort, supporting a pathophysiological role for reduced Af-Gc in the evolution of organ dysfunction. In acetaminophen-induced ALF, Af-Gc identified patients with poor prognosis as well as did the Acute Physiology and Chronic Health Evaluation (APACHE II) score (area under the receiver operating characteristic curve, 0.7), and in cirrhosis, Af-Gc was an independent predictor of mortality by multifactorial analysis. In conclusion, the importance of Af-Gc reductions in the development of multiple organ dysfunction in ALF and cirrhosis is highlighted, probably resulting from reduced hepatic production and peripheral exhaustion of this arm of the extracellular actin scavenger system.     

Adult Liver Transplant Candidate Attitudes Toward Graft Sharing Are Not Obstacles to Split Liver Transplantation

Split liver transplantation (SLT) benefits society by increasing the total number of transplants that can be performed, but it is yet unknown if a decreased post-transplant survival (in comparison to whole liver transplantation) would make participation in SLT less appealing to adult liver transplant candidates. A 20-item questionnaire was administered to 50 adult candidates to assess attitudes toward SLT and organ sharing. The overall attitudes of 60% of participants were classified as utilitarian (maximizing benefit to greatest number of candidates), while 26% were classified as self-preserving (maximizing individual benefit) and 14% were undecided. Ninety percent of participants would be willing to share even if expected survival was less than that of whole liver transplantation, and 69% felt that pediatric candidates should have priority over adult candidates. In conclusion, attitudes toward graft sharing and the possibility of compromised survival benefit are not barriers to SLT for most adult liver transplant candidates.     

Limb asymmetries in landing and jumping 2 years following anterior cruciate ligament reconstruction.

OBJECTIVE: Female athletes who are at increased risk for anterior cruciate ligament (ACL) injury demonstrate biomechanical differences between limbs during athletic tasks that may persist following anterior cruciate ligament reconstruction (ACLR). This may limit an athlete's potential for safe return to sports competition. The purpose of this study was to determine if female athletes demonstrate lower limb asymmetries in landing and takeoff force following ACLR and clearance for return to competitive sports participation. We hypothesized that females following ACLR would demonstrate side-to-side differences in landing and jumping kinetics after their return to sport (2+ years) that would not be observed in a group of healthy female controls. DESIGN: Case control study. SETTING: The Sports Medicine Biodynamics Center at Cincinnati Children's Hospital Medical Center. PATIENTS: Fourteen female athletes at a mean of 27 months following ACLR and 18 healthy female athletes participated in the study. ASSESSMENT: All subjects executed a drop vertical jump (DVJ) task onto 2 force plates. Vertical ground reaction force (VGRF) was measured during landing and takeoff and was used to calculate landing phase loading rates. A 2-way analysis of variance was used to determine differences between the involved, uninvolved, and control limbs. RESULTS: Females who had undergone ACLR demonstrated increased VGRF (P = 0.001) and loading rate (P < 0.001) on the uninvolved limb during landing when compared with the involved limb and the control group. During takeoff, the involved limb showed significantly less ability to generate force (P = 0.03) than the uninvolved limb and the control limbs. CONCLUSIONS: Female athletes who have undergone ACLR and returned to sport may continue to demonstrate biomechanical limb asymmetries 2 years or more after reconstruction that can be identified during landing.