Heart rate variability to differentiate essential tremor from early-stage tremor-dominant Parkinson's disease

Distinguishing essential tremor from Parkinson's disease: clinical and experimental tools

INTRODUCTION

Essential tremor (ET) and Parkinson's disease (PD) are the most common causes of tremor and the most prevalent movement disorders, with overlapping clinical features that can lead to diagnostic challenges, especially in the early stages.

AREAS COVERED

In the present paper, the authors review the clinical and experimental studies and emphasized the major aspects to differentiate between ET and PD, with particular attention to cardinal phenomenological features of these two conditions. Ancillary and experimental techniques, including neurophysiology, neuroimaging, fluid biomarker evaluation, and innovative methods, are also discussed for their role in differential diagnosis between ET and PD. Special attention is given to investigations and tools applicable in the early stages of the diseases, when the differential diagnosis between the two conditions is more challenging. Furthermore, the authors discuss knowledge gaps and unsolved issues in the field.

EXPERT OPINION

Distinguishing ET and PD is crucial for prognostic purposes and appropriate treatment. Additionally, accurate diagnosis is critical for optimizing clinical and experimental research on pathophysiology and innovative therapies. In a few years, integrated technologies could enable accurate, reliable diagnosis from early disease stages or prodromal stages in at-risk populations, but further research combining different techniques is needed.

Evaluation of Cardiovascular Autonomic Nervous System in Essential Tremor and Tremor Dominant Parkinson's Disease

(1) Background: The differential diagnosis of essential tremor (ET) and tremor-dominant Parkinson's disease (TDPD) can be challenging. Only a few studies have investigated the autonomic nervous system (ANS) in ET. However, some of these suggested that heart rate variability (HRV) might be useful in the differential diagnosis. (2) Methods: Demographic and clinical data, including medications and comorbidities, were collected from 15 TDPD patients, 19 ET patients, and 20 healthy controls. Assessment with the SCOPA-AUT questionnaire, 5 min HRV analysis in time and frequency domains, and evaluation of orthostatic hypotension (OH) with tilt test were performed. (3) Results: There were no significant differences between all groups on the SCOPA-AUT questionnaire. PD patients had OH more frequently and a larger drop in systolic blood pressure (SBP) during the tilt test than ET patients and controls. HRV was affected in PD, but not in ET and controls. Power in the low frequency band, the standard deviation of all normal RR intervals and SBP drop were potentially useful in differential diagnosis with AUCs of 0.83, 0.78, and 0.83, respectively. (4) Conclusions: Cardiovascular ANS dysfunction was present in TDPD, but not in ET and controls. HRV analysis and assessment of SBP drop may be potentially useful in the differential diagnosis of ET and TDPD.

Repetitive bout of controlled soccer heading does not alter heart rate variability metrics: A preliminary investigation

Objectives

There is elevated unease regarding how repetitive head impacts, such as those associated with soccer heading, contribute to alterations in brain function. This study examined the extent heart rate variability (HRV) and cardiac baroreceptor sensitivity (BRS) metrics are altered immediately following an acute bout of soccer heading.

Methods

Seven male elite soccer players (24.1 ± 1.5 years) completed 40 successful soccer headers in 20-min. The headers were performed under controlled circumstances using a soccer ball launcher located 25 meters away and using an initial ball velocity of 77.5 ± 3.7 km/h (heading condition). An accelerometer (xPatch) on the right mastoid process quantified linear/rotational head accelerations. Participants also completed sham (body contact) and control (non-contact) sessions. A three-lead ECG and finger photoplethysmography characterized short-term spontaneous HRV/cardiac BRS, before and after each condition. The SCAT3 indexed symptom scores pre-post exposures to all three conditions.

Results

During the heading condition, cumulative linear and rotational accelerations experienced were 1,574 ± 97.9 g and 313,761 ± 23,966 rad/s², respectively. Heart rate trended toward an increase from pre- to post-heading (p = 0.063), however HRV metrics in the time-domain (ps > 0.260) and frequency-domain (ps > 0.327) as well as cardiac BRS (ps > 0.144) were not significantly changed following all three conditions. Following the heading condition, SCAT3 symptom severity increased (p = 0.030) with a trend for symptom score augmentation (p = 0.078) compared to control and sham.

Conclusion

Whereas, symptoms as measured by the SCAT3 were induced following an acute bout of controlled soccer heading, these preliminary findings indicate they were not accompanied by alterations to autonomic function. Ultimately, this demonstrates further research is needed to understand the physiological underpinnings of alterations in brain function occurring immediately after a bout of soccer heading and how these may, over time, contribute to long-term neurological impairments.

Respiratory-cardiovascular interactions

Much of biology is rhythmical and comprises oscillators that can couple. These have optimized energy efficiency and have been preserved during evolution. The respiratory and cardiovascular systems contain numerous oscillators, and importantly, they couple. This coupling is dynamic but essential for an efficient transmission of neural information critical for the precise linking of breathing and oxygen delivery while permitting adaptive responses to changes in state. The respiratory pattern generator and the neural network responsible for sympathetic and cardiovagal (parasympathetic) tone generation interact at many levels ensuring that cardiac output and regional blood flow match oxygen delivery to the lungs and tissues efficiently. The most classic manifestations of these interactions are respiratory sinus arrhythmia and the respiratory modulation of sympathetic nerve activity. These interactions derive from shared somatic and cardiopulmonary afferent inputs, reciprocal interactions between brainstem networks and inputs from supra-pontine regions. Disrupted respiratory-cardiovascular coupling can result in disease, where it may further the pathophysiological sequelae and be a harbinger of poor outcomes. This has been well documented by diminished respiratory sinus arrhythmia and altered respiratory sympathetic coupling in animal models and/or patients with myocardial infarction, heart failure, diabetes mellitus, and neurological disorders as stroke, brain trauma, Parkinson disease, or epilepsy. Future research needs to assess the therapeutic potential for ameliorating respiratory-cardiovascular coupling in disease.

Heart Rate Variability Analyses in Parkinson's Disease: A Systematic Review and Meta-Analysis

Recent evidence suggests that the vagus nerve and autonomic dysfunction play an important role in the pathogenesis of Parkinson's disease. Using heart rate variability analysis, the autonomic modulation of cardiac activity can be investigated. This meta-analysis aims to assess if analysis of heart rate variability may indicate decreased parasympathetic tone in patients with Parkinson's disease. The MEDLINE, EMBASE and Cochrane Central databases were searched on 31 December 2020. Studies were included if they: (1) were published in English, (2) analyzed idiopathic Parkinson's disease and healthy adult controls, and (3) reported at least one frequency- or time-domain heart rate variability analysis parameter, which represents parasympathetic regulation. We included 47 studies with 2772 subjects. Random-effects meta-analyses revealed significantly decreased effect sizes in Parkinson patients for the high-frequency spectral component (HFms²) and the short-term measurement of the root mean square of successive normal-to-normal interval differences (RMSSD). However, heterogeneity was high, and there was evidence for publication bias regarding HFms². There is some evidence that a more advanced disease leads to an impaired parasympathetic regulation. In conclusion, short-term measurement of RMSSD is a reliable parameter to assess parasympathetically impaired cardiac modulation in Parkinson patients. The measurement should be performed with a predefined respiratory rate.

Patterns of intrinsic brain activity in essential tremor with resting tremor and tremor-dominant Parkinson's disease

The clinical pictures of essential tremor (ET) with resting tremor (rET) and tremor-dominant Parkinson's disease (tPD) are often quite mimic at the early stage, current approaches to the diagnosis and treatment therefore remain challenging. The regional homogeneity (ReHo) method under resting-state functional magnetic resonance imaging (rs-fMRI) would help exhibit the patterns in neural activity, which further contribute to differentiate these disorders and explore the relationship between symptoms and regional functional abnormalities. Sixty-eight Chinese participants were recruited, including 19 rET patients, 24 tPD patients and 25 age- and gender-matched healthy controls (HCs). All participants underwent clinical assessment and rs-fMRI with a ReHo method to investigate the alterations of neural activity, and the correlation between them. Differences were compared by two-sample t-test (corrected with AlphaSim, p < 0.05). Compared with HCs, patients' groups both displayed decreased ReHo in the default mode network (DMN), bilateral putamen and bilateral cerebellum. While tPD patients specifically exihibited decreased ReHo in the bilateral supplementary motor area (SMA) and precentral gyrus (M1). The correlation analysis revealed that ReHo in the bilateral putamen, right SMA and left cerebellum_crus I were negatively correlated with the UPDRS-III score, respectively, in tPD group. Our results indicated the rET patients may share part of the pathophysiological mechanism of tPD patients. In addition, we found disorder-specific involvement of the SMA and M1 in tPD. Such a distinction may lend itself to use as a potential biomarker for differentiating between these two diseases.

Prodromal Markers of Parkinson's Disease in Patients With Essential Tremor

Background: Essential tremor (ET) is manifested as an isolated syndrome of bilateral upper limb action tremor. Parkinson's disease (PD) is the second most common neurodegenerative disease, with typical motor symptoms of bradykinesia, rigidity, and resting tremor. ET-PD describes the new-onset of PD in ET patients. Recently, numerous studies on epidemiology, genetics, pathology, clinical features, and neuroimaging studies are challenging the idea that ET is an isolated disease, suggesting that patients with ET have the tendency to develop PD. Methods: In this review article, we collected recent findings that reveal prodromal markers of PD in patients with ET. Results: Substantia nigra hyperechogenicity serves as a prodromal marker for predicting the development of PD in patients with ET and provides a reference for therapeutic strategies. Additional potential markers include other neuroimaging, clinical features, heart rate, and genetics, whereas others lack sufficient evidence. Conclusion: In consideration of the limited research of PD in patients with ET, we are still far from revealing the prodromal markers. However, from the existing follow-up studies on ET patients, Substantia nigra hyperechogenicity may enable further exploration of the relationship between ET and PD and the search for pathogenesis-based therapies.

L. L. Pinheiro D, de la Rosa T, G. de Almeida AC, A. Scorza F, A. Scorza C. Propolis as A Potential Disease-Modifying Strategy in Parkinson's Disease: Cardioprotective and Neuroprotective Effects in the 6-OHDA Rat Model

Patients with Parkinson's disease (PD) manifest nonmotor and motor symptoms. Autonomic cardiovascular dysregulation is a common nonmotor manifestation associated with increased morbimortality. Conventional clinical treatment alleviates motor signs but does not change disease progression and fails in handling nonmotor features. Nutrition is a key modifiable determinant of chronic disease. This study aimed to assess the effects of propolis on cardiological features, heart rate (HR) and heart rate variability (HRV) and on nigrostriatal dopaminergic damage, detected by tyrosine hydroxylase (TH) immunoreactivity, in the 6-hydroxydopamine (6-OHDA) rat model of PD. Male Wistar rats were injected bilaterally with 6-OHDA or saline into the striatum and were treated with propolis or water for 40 days. Autonomic function was assessed by time domain parameters (standard deviation of all normal-to-normal intervals (SDNN) and square root of the mean of the squared differences between adjacent normal RR intervals (RMSSD)) of HRV calculated from electrocardiogram recordings. Reductions in HR (p = 1.47×10-19), SDNN (p = 3.42×10-10) and RMSSD (p = 8.2×10-6) detected in parkinsonian rats were reverted by propolis. Propolis attenuated neuronal loss in the substantia nigra (p = 5.66×10-15) and reduced striatal fiber degeneration (p = 7.4×10-5) in 6-OHDA-injured rats, which also showed significant weight gain (p = 1.07×10-5) in comparison to 6-OHDA-lesioned counterparts. Propolis confers cardioprotection and neuroprotection in the 6-OHDA rat model of PD.

Glutamate and GABA neurotransmission are increased in paraventricular nucleus of hypothalamus in rats induced to 6-OHDA parkinsonism: Involvement of nNOS

AIM

Parkinson's disease (PD) is a progressive neurodegenerative disease that manifests itself clinically after reaching an advanced pathological stage. Besides motor signals, PD patients present cardiovascular and autonomic alterations. Recent data showed that rats induced to Parkinsonism by 6-hydroxydopamine (6-OHDA) administration in the substantia nigra pars compacta (SNpc) showed lower mean arterial pressure (MAP) and heart rate (HR), as reduction in sympathetic modulation. The paraventricular nucleus of the hypothalamus (PVN) is an important site for autonomic and cardiovascular control, and amino acid neurotransmission has a central role. We evaluate PVN amino acid neurotransmission in cardiovascular and autonomic effects of 6-OHDA Parkinsonism.

METHODS

Male Wistar rats were submitted to guide cannulas implantation into the PVN. 6-OHDA or sterile saline (sham) was administered bilaterally in the SNpc. After 7 days, cardiovascular recordings in conscious state was performed.

RESULTS

Bicuculline promoted an increase in MAP and HR in sham group and exacerbated those effects in 6-OHDA group. NBQX (non-NMDA inhibitor) did not promote changes in sham as in 6-OHDA group. On the other hand, PVN microinjection of LY235959 (NMDA inhibitor) in sham group did not induced cardiovascular alterations, but decreased MAP and HR in 6-OHDA group. Compared to Sham group, 6-OHDA lesion increased the number of neuronal nitric oxide synthase (nNOS)-immunoreactive neurons in the PVN and, nNOS inhibition promoted higher increases in MAP and HR.

CONCLUSION

Our data suggest that the decreased baseline blood pressure and heart rate in animals with Parkinsonism may be due to an increased GABAergic tone via nNOS in the PVN.

Central modulation of parasympathetic outflow is impaired in de novo Parkinson's disease patients

Task- and stimulus-based neuroimaging studies have begun to unveil the central autonomic network which modulates autonomic nervous system activity. In the present study, we aimed to evaluate the central autonomic network without the bias constituted by the use of a task. Additionally, we assessed whether this circuitry presents signs of dysregulation in the early stages of Parkinson’s disease (PD), a condition which may be associated with dysautonomia. We combined heart-rate-variability based methods for time-varying assessments of the autonomic nervous system outflow with resting-state fMRI in 14 healthy controls and 14 de novo PD patients, evaluating the correlations between fMRI time-series and the instantaneous high-frequency component of the heart-rate-variability power spectrum, a marker of parasympathetic outflow. In control subjects, the high-frequency component of the heart-rate-variability power spectrum was significantly anti-correlated with fMRI time-series in several cortical, subcortical and brainstem regions. This complex central network was not detectable in PD patients. In between-group analysis, we found that in healthy controls the brain activation related to the high-frequency component of the heart-rate-variability power spectrum was significantly less than in PD patients in the mid and anterior cingulum, sensorimotor cortex and supplementary motor area, insula and temporal lobe, prefrontal cortex, hippocampus and in a region encompassing posterior cingulum, precuneus and parieto-occipital cortex. Our results indicate that the complex central network which modulates parasympathetic outflow in the resting state is impaired in the early clinical stages of PD.

Early differentiation of dementia with Lewy bodies and Alzheimer's disease: Heart rate variability at mild cognitive impairment stage

OBJECTIVE

Our study aimed to investigate whether heart rate variability (HRV) could be a useful diagnostic screening tool at MCI (mild cognitive impairment) stage of Dementia with Lewy bodies (DLB) from Alzheimer's disease (AD).

METHODS

This retrospective study used a selected sample from Ajou neurological registry. We identified MCI patients who underwent HRV testing at baseline, and who developed probable DLB (MCI-DLB: n = 23) or AD (MCI-AD: n = 32).

RESULTS

The MCI-DLB group exhibited significantly lower levels of almost all HRV parameters compared with the MCI-AD group. Fronto-executive function and visuospatial abilities were poorer in the MCI-DLB group, whereas the extent of verbal memory impairment was greater in the MCI-AD. Verbal memory score was negatively correlated with overall HRV parameters, and visuospatial function was positively correlated with the frequency domain of HRV. Receiver operating curve area under the curve (AUC) analysis revealed that the low frequency component was the best potential diagnostic marker (AUC = 0.88).

CONCLUSION

MCI-DLB patients exhibited greater cardiac autonomic dysfunction (as measured by HRV) and greater fronto-executive and visuospatial deficit compared with MCI-AD patients.

SIGNIFICANCE

HRV may be useful method to differentiate DLB from AD in patients with MCI; this would facilitate early disease-specific intervention.

Sympathetic skin response and heart rate variability in predicting autonomic disorders in patients with Parkinson disease

The purpose of this study was to evaluate sympathetic skin response (SSR) and heart rate variability (HRV) in determining autonomic nervous system (ANS) involvement in patients with Parkinson disease (PD). Forty-eight idiopathic PD patients and 30 healthy controls participated in this study. SSR, HRV, Unified Parkinson's Disease Rating Scale (UPDRS) III, the Scales for outcomes in Parkinson's Disease-Autonomic (SCOPA-AUT), Hoehn and Yahr (H&Y) scale were evaluated. Absent lower limb SSR was determined unilaterally in 2, bilaterally in 1 of 3 advanced PD patients; there was significant difference between PD and control groups in terms of the SSR (P < 0.01), significant prolonged SSR latencies and decreased SSR amplitudes from bilateral hands and feet. Significant difference was noted in HRV between PD and control groups except for root mean square of successive differences (rMSSD) and high-frequency (HF) power (P < 0.05). There was a significant different correlation between the parameters of SSR and the SCOPA-AUT, and between the parameters (except HF power) of HRV and the SCOPA-AUT. Some parameters of SSR were relevantly associated with HRV. The right hand SSR amplitude correlated positively with the (SD) of all R-R interval, total spectral power, very low frequency. The right foot amplitude correlated positively with total spectral power. Both SSR and HRV parameters are sensitive in determining ANS dysfunction not only in late but also in the early stage of PD, which can be used for early detection of autonomic dysfunction in patients with PD and have the potential to serve as electrophysiological markers of dysautonomia of PD.