Is fatigue a muscular phenomenon in Parkinson's disease? Implications for rehabilitation.

BACKGROUND: Fatigue in Parkinson's disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. Therefore, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue. AIM: The aim of this study was to assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects. DESIGN: The design was observational controlled study. POPULATION: Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: mini mental state examination ≤24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatigue-related conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched. METHODS: All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fiber conduction velocity, increase of average rectified value. RESULTS: No statistical differences were observed between groups for sEMG variables and muscular electric behavior in all contraction conditions (all P>0.05). CONCLUSIONS: Our results show that parkinsonian muscles do not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility. CLINICAL REHABILITATION IMPACT: In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.

A hybrid approach for continuous detection of sleep-wakefulness fluctuations: validation in patients with Cheyne-Stokes respiration.

Fluctuations in sleep/wake state have been proposed as an important mechanism contributing to the development of oscillatory breathing patterns, including Cheyne-Stokes respiration in patients with heart failure. In order to properly assess the interactions between changes in state and changes in ventilatory parameters, a methodology capable of continuously and reliably detecting state transitions is needed. Traditional fixed-epoch analysis of polysomnographic recordings is not suitable for this purpose. Moreover, visual identification of changes in the dominant electroencephalogram activity at the transition from wakefulness to sleep and vice versa is often very subjective. We have therefore developed a hybrid approach--including both visual scoring and computer-based procedures--for continuous analysis of state transitions from polysomnographic recordings, specifically tailored for fluctuations between wakefulness and non-rapid eye movement-1 and -2 sleep. The overall analysis process comprises three major phases: (1) manual identification of relevant electroencephalogram/electrooculogram features and events, including a sample of unequivocal alpha and theta-delta activity; (2) automatic statistical discrimination of dominant electroencephalogram activity; and (3) state classification (wakefulness, non-rapid eye movement-1 and -2). The latter is carried out by merging information from visual scoring with the output of the discriminator. Validation has been carried out in 16 patients with heart failure during daytime Cheyne-Stokes respiration, using a training and testing set of electroencephalogram polysomnograms. The statistical discriminator correctly classified 99.1 ± 1.4% and 99.2 ± 1.1% of unequivocal alpha and theta-delta activity. This approach has therefore the potential to be used to reliably measure the incidence and location of sleep-wake transitions during abnormal breathing patterns, as well as their temporal relationship with major ventilatory events.

Accounting for respiration is necessary to reliably infer Granger causality from cardiovascular variability series.

This study was designed to demonstrate the need of accounting for respiration (R) when causality between heart period (HP) and systolic arterial pressure (SAP) is under scrutiny. Simulations generated according to a bivariate autoregressive closed-loop model were utilized to assess how causality changes as a function of the model parameters. An exogenous (X) signal was added to the bivariate autoregressive closed-loop model to evaluate the bias on causality induced when the X source was disregarded. Causality was assessed in the time domain according to a predictability improvement approach (i.e., Granger causality). HP and SAP variability series were recorded with R in 19 healthy subjects during spontaneous and controlled breathing at 10, 15, and 20 breaths/min. Simulations proved the importance of accounting for X signals. During spontaneous breathing, assessing causality without taking into consideration R leads to a significantly larger percentage of closed-loop interactions and a smaller fraction of unidirectional causality from HP to SAP. This finding was confirmed during paced breathing and it was independent of the breathing rate. These results suggest that the role of baroreflex cannot be correctly assessed without accounting for R.

Comparison of the prognostic values of invasive and noninvasive assessments of baroreflex sensitivity in heart failure.

OBJECTIVES: No studies have compared the prognostic values of invasive (phenylephrine, Phe) and noninvasive (transfer function) assessments of baroreflex sensitivity (BRS). METHODS: Three hundred and one heart failure patients [age: 53 ±â€Š8 years, New York Heart Association class II-III: 88%, left-ventricular ejection fraction (LVEF): 28 ±â€Š8%] underwent an 8 min ECG and arterial pressure recording, followed by Phe administration. RESULTS: Phe-BRS and transfer function BRS (TF-BRS) could be measured in 89 and 72% of cases, respectively. The correlation and the 5-95th percentiles of the difference between the two methods were 0.61 (P < 0.0001), and -7.6, +7.5 ms/mmHg, respectively. During a median of 36 months, 23% of the patients experienced a cardiac event. In the common dataset of 202 patients, both BRS measurements (<3 ms/mmHg) were significantly associated with the outcome (both P < 0.001), but Phe-BRS had a better discriminatory power (area under the curve (AUC): 0.74 vs. 0.66, P  = 0.03). Patients with a missing BRS (due to high grade ectopic activity) had a higher event rate (Phe-BRS: 38 vs. 24%, P  = 0.23; TF-BRS: 37 vs. 19%, P  = 0.002). Using this information, a prognostic index was derived for each BRS method, increasing measurability to 94 and 98%, respectively. Both indexes significantly predicted the outcome after adjustment for clinical covariates [hazard ratio (95% CI): 1.9 (1.1-3.3), P  = 0.03 for Phe index and 2.0 (1.1-3.7), P  = 0.02 for transfer function index]. CONCLUSION: Although the measurability of TF-BRS in heart failure patients is impaired, prognostic information can be extended to almost all patients, with a predictive power similar to that of Phe-BRS. The two measurements, however, convey a certain amount of independent prognostic information. Hence, TF-BRS can be integrated with but not replace Phe-BRS.

Rehabilitation: Periodic somatosensory stimulation increases arterial baroreflex sensitivity in chronic heart failure patients.

BACKGROUND: One of the beneficial effects of exercise training in chronic heart failure (CHF) is an improvement in baroreflex sensitivity (BRS), a prognostic index in CHF. In our hypothesis-generating study we propose that at least part of this effect is mediated by neural afferent information, and more specifically, by exercise-induced somatosensory nerve traffic. OBJECTIVE: To compare the effects of periodic electrical somatosensory stimulation on BRS in patients with CHF with the effects of exercise training and with usual care. METHODS: We compared in stable CHF patients the effect of transcutaneous electrical nerve stimulation (TENS, N = 23, LVEF 30 ± 9%) with the effects of bicycle exercise training (EXTR, N = 20, LVEF 32 ± 7%). To mimic exercise-associated somatosensory ergoreceptor stimulation, we applied periodic (2/s, marching pace) burst TENS to both feet. TENS and EXTR sessions were held during two successive days. RESULTS: BRS, measured prior to the first intervention session and one day after the second intervention session, increased by 28% from 3.07 ± 2.06 to 4.24 ± 2.61 ms/mmHg in the TENS group, but did not change in the EXTR group (baseline: 3.37 ± 2.53 ms/mmHg; effect: 3.26 ± 2.54 ms/mmHg) (P(TENS vs EXTR) = 0.02). Heart rate and systolic blood pressure did not change in either group. CONCLUSIONS: We demonstrated that periodic somatosensory input alone is sufficient and efficient in increasing BRS in CHF patients. This concept constitutes a basis for studies towards more effective exercise training regimens in the diseased/impaired, in whom training aimed at BRS improvement should possibly focus more on the somatosensory aspect.

Circadian variations of short-term heart period irreversibility in healthy and chronic heart failure patients.

We exploited time irreversibility analysis to characterize short heart period sequences (256 samples) derived from 24h Holter recordings in normal healthy (NO) subjects and chronic heart failure (CHF) patients. We found a significant presence of irreversible dynamics over short time scales, whereas over dominant, longer time scales irreversibility was marginal. Over short time scales in NO subjects the percentage of irreversible dynamics was larger during daytime than during nighttime, thus indicating a larger presence of non linear dynamics during daytime. Same circadian variation was detected in CHF patients but the percentage of irreversible series was higher. In NO subjects during daytime the non linear behavior was mostly the result of bradycardic runs shorter than tachycardic ones. In CHF population this pattern was as present as the reverse pattern (i.e. tachycardic runs shorter than bradycardic ones). Time irreversibility analysis provides useful and reliable indexes even in uncontrolled experimental conditions and during daily activities.