Search results for "reflex"
showing 10 items of 622 documents
Causal linear parametric model for baroreflex gain assessment in patients with recent myocardial infarction
2001
Spectral and cross-spectral analysis of R-R interval and systolic arterial pressure (SAP) spontaneous fluctuations have been proposed for noninvasive evaluation of baroreflex sensitivity (BRS). However, results are not in good agreement with clinical measurements. In this study, a bivariate parametric autoregressive model with exogenous input (ARXAR model), able to divide the R-R variability into SAP-related and -unrelated parts, was used to quantify the gain (αARXAR) of the baroreflex regulatory mechanism. For performance assessing, two traditional noninvasive methods based on frequency domain analysis [spectral, baroreflex gain by autogressive model (αAR); cross-spectral, baroreflex gain…
Substance P Saliva Reduction Predicts Pharyngeal Dysphagia in Parkinson's Disease
2019
Introduction: Although patients with Parkinson's disease (PD) often suffer from oropharyngeal dysphagia, knowledge about the underlying pathophysiological mechanisms is limited. Substance P (SP) is a localization-independent neurotransmitter of the entire nervous system. Reduced levels of SP were found in saliva of patients with impaired cough reflex and in advanced stages of PD. The aim of the study was to investigate SP in PD patients in order to gain further insights into the underlying pathophysiology of PD-related dysphagia and to evaluate the potential of SP as a biomarker for early dysphagia. Methods: Flexible endoscopic evaluation of swallowing (FEES) was used to objectively assess …
Causal analysis of short-term cardiovascular variability: state-dependent contribution of feedback and feedforward mechanisms.
2016
Baroreflex function is usually assessed from spontaneous oscillations of blood pressure (BP) and cardiac RR interval assuming a unidirectional influence from BP to RR. However, the interaction of BP and RR is bidirectionalâRR also influences BP. Novel methods based on the concept of Granger causality were recently developed for separate analysis of feedback (baroreflex) and feedforward (mechanical) interactions between RR and BP. We aimed at assessing the proportion of the two causal directions of the interactions between RR and systolic BP (SBP) oscillations during various conditions, and at comparing causality measures from SBP to RR with baroreflex gain indexes. Arterial BP and ECG sig…
Role of causality in the evaluation of coherence and transfer function between heart period and systolic pressure in humans
2004
To elicit the effects of considering causality in the study of the interactions between RR interval and systolic pressure (SP) variability, the traditional noncausal cross-spectral analysis was compared with a causal method able to separate the two arms of the RR-SP regulatory loop. Estimates of coherence (K) and causal coherences from SP to RR (Ksr) and from RR to SP (Krs), and of noncausal (G) and causal (Gsr) baroreflex gain were evaluated at 0.1 Hz in 10 healthy young subjects in the supine position and after head-up tilt. While K was high in both conditions, at rest Ksr was significantly lower than Krs. After tilt, Ksr increased and Krs decreased significantly. With respect to G, Gsr w…
Information domain approach to the investigation of cardio-vascular, cardio-pulmonary, and vasculo-pulmonary causal couplings
2011
The physiological mechanisms related to cardio-vascular (CV), cardio-pulmonary (CP), and vasculo-pulmonary (VP) regulation may be probed through multivariate time series analysis tools. This study applied an information domain approach for the evaluation of non-linear causality to the beat-to-beat variability series of heart period (t), systolic arterial pressure (s), and respiration (r) measured during tilt testing and paced breathing (PB) protocols. The approach quantifies the causal coupling from the series i to the series j (C(ij)) as the amount of information flowing from i to j. A measure of directionality is also obtained as the difference between two reciprocal causal couplings (D(i…
European Society of Hypertension Working Group on Obesity: background, aims and perspectives.
2007
Clinica Medica, University ofMilano-Bicocca, Ospedale San Gerardo, Monza, Milan, ItalyCorrespondence and requests for reprints to Professor Jens Jordan, ChairmanWorking Group on Obesity, Franz Volhard Clinical Research Center, HELIOSKlinikum Berlin and Medical Faculty of the Charite´, Wiltbergstrase 50, 13125Berlin, GermanyTel: +49 30 9417 2220; fax: +49 30 9417 2265; e-mail: jens.jordan@charite.de
Multiscale Information Decomposition Dissects Control Mechanisms of Heart Rate Variability at Rest and During Physiological Stress.
2019
Heart rate variability (HRV
Pathway CH-1 Study: Sphenopalatine Ganglion (SPG) Stimulation for Acute Treatment of Chronic Cluster Headache (CCH) - Initial Experience (S36.002)
2012
Objective: We aimed to investigate the safety and efficacy of SPG stimulation for the acute treatment of CCH. Background The pain and autonomic symptoms of cluster headache result from activation of the trigeminal parasympathetic reflex, mediated through the SPG. Design/Methods: A multi-center, dose range finding, multiple headache attack (HA), acute treatment study with random insertion of placebo has been initiated. All subjects meet the ICHD-II criteria for CCH with a minimum of 4 HAs/week. Subjects are implanted with a miniaturized neurostimulator which, along with a controller, provides SPG stimulation. Prior to the randomized period, stimulation parameters are adjusted in a titration …
The Stretch-Shortening Cycle
2006
Neuromuscular fatigue has traditionally been examined using isolated forms of either isometric, concentric or eccentric actions. However, none of these actions are naturally occurring in human (or animal) ground locomotion. The basic muscle function is defined as the stretch-shortening cycle (SSC), where the preactivated muscle is first stretched (eccentric action) and then followed by the shortening (concentric) action. As the SSC taxes the skeletal muscles very strongly mechanically, its influence on the reflex activation becomes apparent and very different from the isolated forms of muscle actions mentioned above. The ground contact phases of running, jumping and hopping etc. are example…
Spectral decomposition of RR-variability obtained by an open loop parametric model for the diagnosis of neuromediate syncope
2002
The role of the cardiovascular regulatory mechanism in patients with neuromediate syncope (NS) is poorly understood. The aim of this study was to accomplish continuous non-invasive analysis of the baroreflex mechanism in patients during a head-tip tilt-table test (HTT) using an open-loop autoregressive model with exogenous input. The model describes the causal dependence of the RR interval on the systolic arterial pressure (SAP) variability. Thus, RR variability results as the linear composition of SAP-dependent (Pdep) and SAP-independent parts of the RR power (P). Further, the model allows the estimation of the baroreflex gain using the modulus of the transfer function (G) from SAP to RR i…