Vinoth K. Ranganathan

Effects of aging on hand function

OBJECTIVES: The purpose of this study was to quantify age‐induced changes in handgrip and finger‐pinch strength, ability to maintain a steady submaximal finger pinch force and pinch posture, speed in relocating small objects with finger grip, and ability to discriminate two identical mechanical stimuli applied to the finger tip.

United States Registered Nurse Workforce Report Card and Shortage Forecast

Registered nurses (RNs) play a critical role in health care delivery. With an aging US population, health care demand is growing at an unprecedented pace. Using projected changes in population size and age, the authors developed demand and supply models to forecast the RN job shortage in each of the 50 states. Letter grades were assigned based on projected RN job shortage ratios. The number of states receiving a grade of “D” or “F” for their RN shortage ratio will increase from 5 in 2009 to 30 by 2030, for a total national deficit of 918 232 (725 619 - 1 112 112) RN jobs. There will be significant RN workforce shortages throughout the country in 2030; the western region will have the largest shortage ratio of 389 RN jobs per 100 000. Increased efforts to understand shortage dynamics are warranted.

Relationship between motor activity-related cortical potential and voluntary muscle activation.

Abstract. The purpose of this study was to investigate the relationship between EEG-derived motor activity-related cortical potential (MRCP) and voluntary muscle activation. Eight healthy volunteers participated in two experimental sessions. In one session, subjects performed isometric elbow-flexion contractions at four intensity levels [10%, 35%, 60%, and 85% maximal voluntary contraction (MVC)]. In another session, a given elbow-flexion force (35% MVC) was generated at three different rates (slow, intermediate, and fast). Thirty to 40 contractions were performed at each force level or rate. EEG signals were recorded from the scalp overlying the supplementary motor area (SMA) and contralateral sensorimotor cortex, and EMG signals were recorded from the skin surface overlying the belly of the biceps brachii and brachioradialis muscles during all contractions. In each trial, the force was used as the triggering signal for MRCP averaging. MRCP amplitude was measured from the beginning to the peak of the negative slope. The magnitude of MRCP from both EEG recording locations (sensorimotor cortex and SMA) was highly correlated with elbow-flexion force, rate of rising of force, and muscle EMG signals. These results suggest that MRCP represents cortical motor commands that scale the level of muscle activation.

Brain activation during human finger extension and flexion movements

Corticospinal projections to the motor neuron pool of upper-limb extensor muscles have been reported to differ from those of the flexor muscles in humans and other primates. The influence of this difference on the central nervous system control for extension and flexion movements is unknown. Cortical activation during thumb extension and flexion movements of eight human volunteers was measured using functional magnetic resonance imaging (fMRI), which detects signal changes caused by an alteration in the local blood oxygenation level. Although the relative activity of the extensor and flexor muscles of the thumb was similar, the brain volume activated during extension was substantially larger than that during flexion. These fMRI results were confirmed by measurements of EEG-derived movement-related cortical potential. Higher brain activity during thumb extension movement may be a result of differential corticospinal, and possibly other pathway projections to the motoneuron pools of extensor and flexor muscles of upper the extremities.

Evidence of inability to fully activate human limb muscle

The purpose of this study was to determine whether muscle activation level estimated by twitch interpolation technique was different when an electrical stimulus was applied during a dynamic force (DF; force rising) task from that when the stimulus was applied during a static force (SF; constant force) task. Fourteen subjects performed voluntary SF and DF contractions involving isometric elbow flexion at seven voluntary force levels. At each level, the electrical stimulation was applied to the surface of the biceps brachii muscle when the force was steady (SF task) and when the force was rising (DF task). The voluntary activation level of the biceps brachii muscle during the SF maximal voluntary contraction (MVC) was 98.5% and that during the DF MVC task was significantly lower (94.5%; P < 0.05). The motoneurons and/or muscle fibers may become more excitable during the DF task so that the same stimulus can recruit those that are otherwise less excitable during the SF task.

Cancer-related fatigue: central or peripheral?

To evaluate cancer-related fatigue (CRF) by objective measurements to determine if CRF is a more centrally or peripherally mediated disorder, cancer patients and matched noncancer controls completed a Brief Fatigue Inventory (BFI) and underwent neuromuscular testing. Cancer patients had fatigue measured by the BFI, were off chemotherapy and radiation (for more than four weeks), had a hemoglobin level higher than 10 g/dL, and were neither receiving antidepressants nor were depressed on a screening question. The controls were screened for depression and matched by age, gender, and body mass index. Neuromuscular testing involved a sustained submaximal elbow flexion contraction (SC) at 30% maximal level (30% maximum elbow flexion force). Endurance time (ET) was measured from the beginning of the SC to the time when participants could not maintain the SC. Evoked twitch force (TF), a measure of muscle fatigue, and compound action potential (M-wave), an assessment of neuromuscular-junction transmission were performed during the SC. Compared with controls, the CRF group had a higher BFI score (P<0.001), a shorter ET (P<0.001), and a greater TF with the SC (CRF>controls, P<0.05). This indicated less muscle fatigue. There was a greater TF (P<0.05) at the end of the SC, indicating greater central fatigue, in the CRF group, which failed to recruit muscle (to continue the SC), as well as the controls. M-Wave amplitude was lower in the CRF group than in the controls (P<0.01), indicating impaired neuromuscular junction conduction with CRF unrelated to central fatigue (M-wave amplitude did not change with SC). These data demonstrate that CRF patients exhibited greater central fatigue, indicated by shorter ET and less voluntary muscle recruitment during an SC relative to controls.

Weakening of functional corticomuscular coupling during muscle fatigue.

OBJECTIVE Recent research has shown dissociation between changes in brain and muscle signals during voluntary muscle fatigue, which may suggest weakening of functional corticomuscular coupling. However, this weakening of brain-muscle coupling has never been directly evaluated. The purpose of this study was to address this issue by quantifying EEG-EMG coherence at times when muscles experienced minimal versus significant fatigue. METHODS Nine healthy subjects sustained an isometric elbow flexion at 30% maximal level until exhaustion while their brain (EEG) and muscle (EMG) activities were recorded. The entire duration of the EEG and EMG recordings was divided into the first half (stage 1 with minimal fatigue) and second half (stage 2 with severer fatigue). The EEG-EMG coherence and power spectrum in each stage was computed. RESULTS The power of both EEG and EMG increased significantly while their coherence decreased significantly in stage 2 compared with stage 1 at beta (15-35 Hz) band. CONCLUSIONS Despite an elevation of the power for both the EEG and EMG activities with muscle fatigue, the fatigue weakens strength of brain-muscle signal coupling at beta frequency band. SIGNIFICANCE Weakening of corticomuscular coupling may be a major neural mechanism contributing to muscle fatigue and associated performance impairment.

Myoelectrical manifestation of fatigue less prominent in patients with cancer related fatigue.

Purpose A lack of fatigue-related muscle contractile property changes at time of perceived physical exhaustion and greater central than peripheral fatigue detected by twitch interpolation technique have recently been reported in cancer survivors with fatigue symptoms. Based on these observations, it was hypothesized that compared to healthy people, myoelectrical manifestation of fatigue in the performing muscles would be less significant in these individuals while sustaining a prolonged motor task to self-perceived exhaustion (SPE) since their central fatigue was more prominent. The purpose of this study was to test this hypothesis by examining electromyographic (EMG) signal changes during fatiguing muscle performance. Methods Twelve individuals who had advanced solid cancer and cancer-related fatigue (CRF), and 12 age- and gender-matched healthy controls performed a sustained elbow flexion at 30% maximal voluntary contraction till SPE. Amplitude and mean power frequency (MPF) of EMG signals of the biceps brachii, brachioradialis, and triceps brachii muscles were evaluated when the individuals experienced minimal, moderate, and severe fatigue. Results CRF patients perceived physical “exhaustion” significantly sooner than the controls. The myoelectrical manifestation of muscular fatigue assessed by EMG amplitude and MPF was less significant in CRF than controls. The lower MPF even at minimal fatigue stage in CRF may indicate pathophysiologic condition of the muscle. Conclusions CRF patients experience less myoelectrical manifestation of muscle fatigue than healthy individuals near the time of SPE. The data suggest that central nervous system fatigue plays a more important role in limiting endurance-type of motor performance in patients with CRF.

The Importance of the Microenvironment of Support Surfaces in the Prevalence of Pressure Ulcers

Soft tissue breakdown is a major cause of disablement in the United States. External pressure has been the most frequently discussed stress factor in the formation of ulcers. Analysis of published data on the prevalence of pressure ulcers and interface pressures at various anatomic sites indicate a nearly non-existent or slightly negative correlation between prevalence and interface pressure for the general and the spinal cord injured populations respectively. This lack of direct relation suggests the major influence of environmental factors in addition to mechanical factors (pressure, shear strain and friction, etc.,) on ulcer formation and indicates the need for control of the support surface microenvironment. However, most of the reported results from studies evaluating support surfaces focus mainly on pressure relief and neglect to address adequately the environmental contributing factors of ulcer formation. Studies directly relating primary stress factors and tissue viability with prevalence and incidence of pressure ulcers are needed to better understand the benefits of pressure relieving support surfaces and to improve the effectiveness of prevention and treatment interventions. The effects of microenvironment on support surface function are reviewed here to aid the healthcare providers in the choosing of the most appropriate support surface to meet the patient’s needs.

Evidence of Significant Central Fatigue in Patients with Cancer-Related Fatigue during Repetitive Elbow Flexions till Perceived Exhaustion

Objective To investigate whether fatigue induced by an intermittent motor task in patients with cancer-related fatigue (CRF) is more central or peripheral. Methods Ten patients with CRF who were off chemo and radiation therapies and 14 age-matched healthy controls were enrolled. Participants completed a Brief Fatigue Inventory (BFI) and performed a fatigue task consisting of intermittent elbow-flexion contractions at submaximal (40% maximal voluntary contraction) intensity till self-perceived exhaustion. Twitch force was elicited by an electrical stimulation applied to the biceps brachii muscle. The relative degree of peripheral (muscle) vs. central contribution to fatigue induced by the intermittent motor task (IMT) was assessed using twitch force ratio (TFratio) defined as post IMT twitch force to pre IMT twitch force. The total number of trials (intermittent contractions) and total duration of all trials performed by each subject were also quantified. Results BFI scores were higher (p<0.001) in CRF than controls, indicating greater feeling of fatigue in CRF patients than controls. A significantly smaller number of trials and shorter total duration of the trials (p<0.05) were observed in CRF than control participants. The TFratio (0.81±0.05) in CRF was higher (p<0.05) compared with that of controls (0.62±0.05), suggesting CRF patients experienced a significantly lower degree of muscle (peripheral) fatigue at the time of perceived exhaustion. Conclusion Consistent with prior findings for fatigue under submaximal sustained contraction, our results indicate that motor fatigue in CRF is more of central than peripheral origin during IMT. Significant central fatigue in CRF patients limits their ability to prolong motor performance.