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Novak, Peter

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Novak

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Peter

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Novak, Peter
Author's Publications: search.filters.isAuthorOfPublication.67c0dc11-7b3c-45ac-877f-f782f7bb28ca

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    Cerebral Blood Flow, Heart Rate, and Blood Pressure Patterns during the Tilt Test in Common Orthostatic Syndromes
    (Hindawi Publishing Corporation, 2016) Novak, Peter
    Objective:. The head-up tilt test is widely used for evaluation of orthostatic intolerance. Although orthostatic symptoms usually reflect cerebral hypoperfusion, the cerebral blood flow velocity (CBFv) profile in orthostatic syndromes is not well described. This study evaluated CBFv and cardiovascular patterns associated with the tilt test in common orthostatic syndromes. Methods. This retrospective study analyzed the tilt test of patients with history of orthostatic intolerance. The following signals were recorded: ECG, blood pressure, CBFv using transcranial Doppler, respiratory signals, and end tidal CO2. Results. Data from 744 patients were analyzed. Characteristic pattern associated with a particular orthostatic syndrome can be grouped into abnormalities predominantly affecting blood pressure (orthostatic hypotension, orthostatic hypertension syndrome, vasomotor oscillations, and neurally mediated syncope—cardioinhibitory, vasodepressor, and mixed), cerebral blood flow (orthostatic hypoperfusion syndrome, primary cerebral autoregulatory failure), and heart rate (tachycardia syndromes: postural tachycardia syndrome, paroxysmal sinus tachycardia, and inappropriate sinus tachycardia). Psychogenic pseudosyncope is associated with stable CBFv. Conclusions. The tilt test is useful add-on in diagnosis of several orthostatic syndromes. However diagnostic criteria for several syndromes had to be modified to allow unambiguous pattern classification. CBFv monitoring in addition to blood pressure and heart rate may increase diagnostic yield of the tilt test.
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    Electrochemical Skin Conductance Correlates with Skin Nerve Fiber Density
    (Frontiers Media S.A., 2016) Novak, Peter
    Purpose: Electrochemical skin conductance (ESC) using reverse iontophoresis and chronoamperometry has been used to evaluate abnormal function of small fibers. How ESC correlates with loss of small fibers in skin is unclear. Methods: This was a prospective, blinded study. The primary outcome measure was the correlation between ESC at the feet and results of skin biopsies including epidermal nerve fiber density (ENFD) and sweat gland nerve fiber density (SGNFD) at the distal leg. ESC, ENFD, and SGNFD data were normalized by adjusting for weight. The secondary outcome measures were the correlation between ESC and the following variables: quantitative sudomotor axon reflex test (QSART) and symptom scales (neuropathy, pain and autonomic). Results: Eighty-one patients (mean ± sd): age = 53.3 ± 17.3, men/women = 25/56 were enrolled in the study. ESC was reduced in subjects with abnormally low ENFD (ENFD normal/abnormal, ESC = 1.17 ± 0.27/0.87 ± 0.34 μSiemens/kg, p < 0.0008) and abnormally low SGNFD (SGNFD normal/abnormal ESC = 1.09 ± 0.34/0.78 ± 0.3 μSiemens/kg, p < 0.0003). ESC correlated with ENFD (ρ = 0.73, p = 0.0001) and SGNFD (ρ = 0.64, p = 0.0001). ESC did not correlate with symptom scales. Conclusion: ESC is diminished in subjects who have a reduced number of small fibers in the skin and the ESC reduction is proportional to ENFD and SGNFD. ESC can be useful in detecting loss of small nerve fibers.
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    Association of Blood Pressure Elevation and Nocturnal Dipping With Brain Atrophy, Perfusion and Functional Measures in Stroke and Nonstroke Individuals
    (Oxford University Press (OUP), 2010-01) Hajjar, Ihab; Zhao, Peng; Alsop, David; Abduljalil, Amir; Selim, Magdy; Novak, Peter; Novak, Vera
    Background Although blood pressure elevation and lower nocturnal dipping both increase vascular risk, it is not known if either or both are also associated with brain atrophy, cerebral perfusion, and functional status. Methods We investigated the association of elevated blood pressure and nocturnal dipping based on 24-hour ambulatory recordings with brain atrophy and perfusion and functional status in 80 older adults with and without stroke (age 66.4±0.8 years, 51% women, 16% non-white, 46% prior ischemic stroke, 55% hypertension). Anatomical and 3-D continuous arterial spin labeling brain MRI measuring volumes and perfusion and 24-h ambulatory blood pressure readings were completed. Results Nocturnal dipping of lesser magnitude in systolic (non-stroke: p=0.03; stroke: p=0.005) and pulse pressure (non-stroke: p=0.002; stroke: p=0.01) was associated with greater brain atrophy, affecting preferentially the fronto-parietal regions. Dipping of lesser magnitude in systolic blood pressure (non-stroke: p=0.01; stroke: p=0.03) and greater brain atrophy (non-stroke: p=0.04; stroke: p= 0.05) were also associated with slower gait speed and worse functional outcome post stroke. Higher 24-hour blood pressure averages were associated with lower cerebral perfusion but not atrophy in those with and without stroke. Conclusions In those with and without stroke, dipping of lesser magnitude in systolic and pulse pressure is associated with brain atrophy and worse functional status. Nocturnal dipping, in addition to elevated blood pressure, should be considered as an additional important target in the clinical evaluation of those at risk for cerebrovascular disease or functional loss.