Effects of deep brain stimulation target on the activation and suppression of action impulses.

OBJECTIVE: Deep brain stimulation (DBS) is an effective treatment to improve motor symptoms in Parkinson's disease (PD). The Globus Pallidus (GPi) and the Subthalamic Nucleus (STN) are the most targeted brain regions for stimulation and produce similar improvements in PD motor symptoms. However, our understanding of stimulation effects across targets on inhibitory action control processes is limited. We compared the effects of STN (n = 20) and GPi (n = 13) DBS on inhibitory control in PD patients. METHODS: We recruited PD patients undergoing DBS at the Vanderbilt Movement Disorders Clinic and measured their performance on an inhibitory action control task (Simon task) before surgery (optimally treated medication state) and after surgery in their optimally treated state (medication plus their DBS device turned on). RESULTS: DBS to both STN and GPi targets induced an increase in fast impulsive errors while simultaneously producing more proficient reactive suppression of interference from action impulses. CONCLUSIONS: Stimulation in GPi produced similar effects as STN DBS, indicating that stimulation to either target increases the initial susceptibility to act on strong action impulses while concomitantly improving the ability to suppress ongoing interference from activated impulses. SIGNIFICANCE: Action impulse control processes are similarly impacted by stimulating dissociable nodes in frontal-basal ganglia circuitry.

Essential tremor impairs the ability to suppress involuntary action impulses.

Essential tremor (ET) is a movement disorder characterized primarily by action tremor which affects the regulation of movements. Disruptions in cerebello-thalamocortical networks could interfere with cognitive control over actions in ET, for example, the ability to suppress a strong automatic impulse over a more appropriate action (conflict control). The current study investigated whether ET impacts conflict control proficiency. Forty-one ET patients and 29 age-matched healthy controls (HCs) performed a conflict control task (Simon task). Participants were instructed to give a left or right response to a spatially lateralized arrow (direction of the arrow). When the action signaled by the spatial location and direction of the arrow were non-corresponding (induced conflict), the inappropriate action impulse required suppression. Overall, ET patients responded slower and less accurately compared to HCs. ET patients were especially less accurate on non-corresponding conflict (Nc) versus corresponding (Cs) trials. A focused analysis on fast impulsive response rates (based on the accuracy rate at the fastest reaction times on Nc trials) showed that ET patients made more fast errors compared to HCs. Results suggest impaired conflict control in ET compared to HCs. The increased impulsive errors seen in the ET population may be a symptom of deficiencies in the cerebello-thalamocortical networks, or, be caused by indirect effects on the cortico-striatal pathways. Future studies into the functional networks impacted by ET (cortico-striatal and cerebello-thalamocortical pathways) could advance our understanding of inhibitory control in general and the cognitive deficits in ET.

Skipping has lower knee joint contact forces and higher metabolic cost compared to running.

BACKGROUND: The health benefits of running based exercise programs are plentiful however the high rate of injury in these programs often reduces or eliminates exercise participation. Skipping has shorter steps, reduced vertical ground reaction forces (GRFs), and lower knee extensor torques, compared to running forming the basis of the present hypothesis that skipping would have lower tibio-femoral and patello-femoral joint contact forces. RESEARCH QUESTION: The purpose of this study was to compare knee contact forces between skipping and running at the same speed. We also compared metabolic cost of these two gaits to examine the idea that the larger vertical displacement in skipping is a primary factor in its previously reported high metabolic cost. METHODS: The study evaluated joint contact forces through musculoskeletal modeling with GRF and 3D kinematic data and metabolic cost using oxygen consumption data from 20 young, healthy, trained participants as they skipped and ran on an instrumented treadmill at 2.68 m/s. RESULTS: Skipping, compared to running, had substantially lower tibio-femoral and patello-femoral joint contact forces and linear impulses on both per-step and per-kilometer (i.e. lower cumulative loads) bases and also 30% higher metabolic cost. The lower joint loads in skipping were directly associated with its shorter steps and the higher metabolic cost was directly associated to its larger vertical displacement through the stride. SIGNIFICANCE: As joint loads may predispose individuals to running related injuries, skipping presents an attractive alternative exercise modality with additional increased aerobic benefits.

Gait biomechanics of skipping are substantially different than those of running.

The inherit injury risk associated with high-impact exercises calls for alternative ways to achieve the benefits of aerobic exercise while minimizing excessive stresses to body tissues. Skipping presents such an alternative, incorporating double support, flight, and single support phases. We used ground reaction forces (GRFs), lower extremity joint torques and powers to compare skipping and running in 20 healthy adults. The two consecutive skipping steps on each limb differed significantly from each other, and from running. Running had the longest step length, the highest peak vertical GRF, peak knee extensor torque, and peak knee negative and positive power and negative and positive work. Skipping had the greater cadence, peak horizontal GRF, peak hip and ankle extensor torques, peak ankle negative power and work, and peak ankle positive power. The second vs first skipping step had the shorter step length, higher cadence, peak horizontal GRF, peak ankle extensor torque, and peak ankle negative power, negative work, and positive power and positive work. The first skipping step utilized predominately net negative joint work (eccentric muscle action) while the second utilized predominately net positive joint work (concentric muscle action). The skipping data further highlight the persistence of net negative work performed at the knee and net positive work performed at the ankle across locomotion gaits. Evidence of step segregation was seen in distribution of the braking and propelling impulses and net work produced across the hip, knee, and ankle joints. CONCLUSIONS: Skipping was substantially different than running and was temporally and spatially asymmetrical with successive foot falls partitioned into a dominant function, either braking or propelling whereas running had a single, repeated step in which both braking and propelling actions were performed equally.

Implementation and enforcement of ventilator-associated pneumonia prevention strategies in trauma patients.

BACKGROUND: We hypothesized that strict enforcement of ventilator-associated pneumonia (VAP) prevention (VAPP) strategies would decrease the incidence of VAP and improve patient outcomes. METHODS: This retrospective study examined 696 consecutive ventilated patients in a Level One trauma center. Three study groups were compared: Pre-VAPP, VAPP implementation, and VAPP enforcement. Ventilator days were compared with occurrences of VAP, defined by the U.S. Centers for Disease Control and Prevention National Nosocomial Infection Surveillance criteria. Patients with and without VAP were compared to evaluate the effect of VAP on patient outcome. Fisher exact, Kruskal-Wallis, and chi-square analyses were used, and p < 0.05 was considered significant. RESULTS: During the pre-VAPP protocol period, 5.2 cases of VAP occurred per 1,000 days of ventilator support. The number of cases of VAP decreased to 2.4/1,000 days (p = 0.172) and 1.2/1,000 days (p = 0.085) in the implementation and enforcement periods, respectively. However, when including all trauma patients, regardless of head Abbreviated Injury Score (AIS) score, the difference in the rate of VAP was statistically significant in the enforcement period, but not in the implementation period, compared with the pre-VAPP period (p = 0.014 and 0.062, respectively). A significant decrease was seen in the mortality rate (p = 0.024), total hospital days (p = 0.007), intensive care unit days (p = 0.002), ventilator days (p = 0.002), and hospital charges (p = 0.03) in patients without VAP compared with patients having VAP. CONCLUSIONS: There was a statistically significant decrease in the occurrence of VAP with strict enforcement of a VAPP protocol, regardless of head AIS score. Although the difference in patients with a head AIS score <3 was not statistically significant, it was clinically meaningful, decreasing the already-low rate of VAP by half. Strict enforcement of VAPP protocols may be cost efficient for hospitals and prevent decreased reimbursement under the Medicare pay-for-performance strategies.