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This trial aims to perform an exploratory, mechanistic, randomized double-blind sham-control trial in healthy participants to assess the physiologic effects of a single 60 minutes session of bilateral taVNS, on neural networks and autonomic function.
Low level transcutaneous vagus nerve stimulation (LLTS) involves delivery of electrical impulses transcutaneously at the auricular branch of vagus nerve and it has been shown to have anti-inflammatory and anti-arrhythmic effects. In previous studies from our laboratory, we found that LLTS significantly suppressed atrial fibrillation (AF) inducibility and decreased AF duration. The anti-arrhythmic effects of LLTS were similar to those delivered to the cervical VN trunk. LLTS for just one hour significantly shortened the AF duration and decreased inflammatory cytokines. We have also shown that LLTS leads to favorable heart rate variability (HRV) changes and cardiac mechanics in patients with diastolic dysfunction. These results support the use of LLTS as a novel non-pharmacological, non-ablative treatment modality for AF and possibly other inflammatory conditions. However, the optimal stimulation parameters of LLTS remain to be determined. In this study, we aim to examine the effect of 2 different frequencies (5Hz and 20Hz) and 2 different amplitudes (50% below the pain threshold and 1mA below the pain threshold) of LLTS on heart rate variability with deep breathing (HRVdb), mental arithmetic stress test (MAST), frequency domain measures of heart rate variability (HRV) and brain stem evoked potentials (BSEVP) in healthy volunteers and patients with AF or heart failure with preserved ejection fraction (HFpEF). HRV is a marker of vagus nerve activity and can be easily measured by software calculating the distance between consecutive R waves on the ECG. BSEVP are a surrogate for the central projections of the vagus nerve. Patients will be randomized into 4 groups in a 2x2 factorial design. LLTS will be delivered through a transcutaneous electrical nerve stimulation (TENS) device for 15 minutes. HRVdb, HRV and BSEVP will be measured before and after LLTS and compared.
The purpose of this study is to learn more about the effects of abdominal compression and the medication midodrine, two interventions used for the treatment of orthostatic hypotension (low blood pressure on standing), on hemodynamic markers of cardiovascular risk. The study will be conducted at the Vanderbilt University Medical Center and consists of a screening and 2 testing days, one with abdominal compression and one with midodrine. The total length of the study will be about 5 days.
Alpha-synucleinopathies refer to age-related neurodegenerative and dementing disorders, characterized by the accumulation of alpha-synuclein in neurons and/or glia. The anatomical location of alpha-synuclein inclusions (Lewy Bodies) and the pattern of progressive neuronal death (e.g. caudal to rostral brainstem) give rise to distinct neurological phenotypes, including Parkinson's disease (PD), Multiple System Atrophy (MSA), Dementia with Lewy Bodies (DLB). Common to these disorders are the involvement of the central and peripheral autonomic nervous system, where Pure Autonomic Failure (PAF) is thought (a) to be restricted to the peripheral autonomic system, and (b) a clinical risk factor for the development of a central synucleinopathy, and (c) an ideal model to assess biomarkers that predict phenoconversion to PD, MSA, or DLB. Such biomarkers would aid in clinical trial inclusion criteria to ensure assessments of disease- modifying strategies to, delay, or halt, the neurodegenerative process. One of these biomarkers may be related to the neurotransmitter dopamine (DA) and related changes in the substantia nigra (SN) and brainstem. \[18F\]F-DOPA is a radiolabeled substrate for aromatic amino acid decarboxylase (AAADC), an enzyme involved in the production of dopamine. Use of this radiolabeled substrate in positron emission tomography (PET) may provide insight to changes in monoamine production and how they relate to specific phenoconversions in PAF patients. Overall, this study aims to identify changes in dopamine production in key regions including the SN, locus coeruleus, and brainstem to distinguish between patients with PD, MSA, and DLB, which may provide vital information to predict conversion from peripheral to central nervous system disease.
Supine hypertension is a common problem that affects at least 50% of patients with primary autonomic failure. Supine hypertension can be severe and complicates the treatment of orthostatic hypotension. The purpose of this study is to assess whether continuous positive airway pressure (CPAP) decreases blood pressure in autonomic failure patients with supine hypertension.
Patients with autonomic failure are characterized by disabling orthostatic hypotension (low blood pressure on standing), and at least half of them also have high blood pressure while lying down (supine hypertension). Exposure to heat, such as in hot environments, often worsens their orthostatic hypotension. The causes of this are not fully understood. The purpose of this study is to evaluate whether applying local heat over the abdomen of patients with autonomic failure and supine hypertension during the night would decrease their nocturnal high blood pressure while lying down. This will help us better understand the mechanisms underlying this phenomenon, and may be of use in the treatment of supine hypertension.
The purpose of this study is to learn more about the effects of midodrine and droxidopa, two medications used for the treatment of orthostatic hypotension (low blood pressure on standing), on the veins of the abdomen of patients with autonomic failure. The study will be conducted at Vanderbilt University Medical Center, and consists of 2 parts: a screening and 2 testing days. The total length of the study will be about 5 days. About 34 participants will be screened for the study.
Compression garments have been shown to be effective in the treatment of orthostatic hypotension in autonomic failure patients. The purpose of this study is to determine the hemodynamic mechanisms by which abdominal compression (up to 40 mm Hg) improve the standing blood pressure and orthostatic tolerance in these patients, and to compare them with those of the standard of care midodrine. The investigators will test the hypothesis that abdominal compression will blunt the exaggerated fall in stroke volume and the increase in abdominal vascular volume during head up tilt.
This research aims to understand the effect of the Neuro20 Functional Electrical Stimulation Suit on autonomic nervous system function, muscle performance, and gait after amputation or neurologic injury.
This study looks to characterize gradients of dysfunction in the autonomic nervous system in patients with clinically diagnosed multiple sclerosis. The autonomic nervous system plays key roles in regulation of blood pressure, skin blood flow, and bladder health- all issues that individuals with multiple sclerosis typically suffer. Focusing on blood pressure regulation, the most precise metric with broad clinical applicability, the investigators will perform laboratory-based tests to probe the body's ability to generate autonomic responses. For both individuals with multiple sclerosis and uninjured controls, laboratory-based experiments will utilize multiple parallel recordings to identify how the autonomic nervous system is able to inhibit and activate signals. The investigators anticipate that those with autonomic dysfunction with multiple sclerosis will exhibit abnormalities in these precise metrics. The investigators will look to see if any substantial connections exist between different degrees of preserved autonomic function and secondary autonomic complications from multiple sclerosis. In accomplishing this, the investigators hope to give scientists important insights to how the autonomic nervous system works after multiple sclerosis and give physicians better tools to manage these secondary autonomic complications.