Short-term autonomic nervous control of the cardiovascular system: a system theoretic approach.

A non-linear model of the human cardiovascular regulation system (CVS) has been developed, with the aim of studying the short-term regulation process by the autonomic nervous system (ANS). This restricts the time interval under study to range from fractions of seconds to about 30 seconds. As a consequence, the only feedback mechanism taken into account is the baroreceptors loop. Our main guideline has been first to try to capture the main features of the system that have been observed and reported in the relevant publications in physiology--main non-linearities in the elementary components of the system, intrinsic periodicities--while keeping to a minimum the number of model parameters, with the question of identifiability from real data in mind. Also, we have tried to retain as much physiological significance to these parameters as possible, for forthcoming diagnosis purposes, while using non invasive measurements only. At the present time, no venous return has been taken into account but should be included later on. The long term objective of this research is to develop tools for helping in medical diagnosis. This may go through the detection of defaults in this closed loop system, within the framework of control systems theory, hereby using all the known concepts from that field, that have been much used for engineering systems (mechanical, electrical etc...): these include signal processing techniques as well as control algorithms or identification and detection methods.

Instant power spectrum analysis of heart rate variability during orthostatic tilt using a time-/frequency-domain method.

BACKGROUND: Spectral analysis of heart rate (HR) variability (HRV) requires, as a rule, some level of stationarity and, as a result, is inadequate to quantify biological transients. A time-/frequency-domain method (TF) was developed to obtain an instant spectral power (SP) of HRV during tilt. METHODS AND RESULTS: HR was recorded by Holter monitoring in volunteers and analyzed with a TF, the smoothed pseudo-Wigner-Ville transformation (SPWVT), with the table inclination randomly set or continuously increased while the table rotated in head-up position. (1) The SPWVT assesses, beat by beat, the instant center frequency (ICF) of the SP. ICF correlates better with instant HR than the ratio of low- (LF) to high-frequency (HF) oscillations. The transient effect of tilt is better characterized as a shift of SP toward lower frequencies than by changes in amplitudes. (2) The method evidences variations of HR from one second to another. During the passage to head-up position, the vagal withdrawal and the sympathetic activation occur nearly simultaneously, as indicated by the instant changes in both LF and HF amplitudes and ICF. (3) The averaged results of the SPWVT give results similar to those previously obtained with autoregressive algorithms. CONCLUSIONS: The SPWVT is a new tool to explore HR transitions such as periods before episodes of arrhythmias on a time scale of one beat and allows quantification of an instant frequency index (ICF) that closely reflects the instantaneous relationship between sympathetic and vagal modulations.

Decreased heart rate variability in transgenic mice overexpressing atrial beta 1-adrenoceptors.

Heart rate variability (HRV) depends on various reflexes, including the baroreflex or respiratory reflex. Experimental studies have suggested that the sinoatrial node density in G protein-linked receptors may be involved. Transgenic mice, with a specific eightfold atrial overexpression of human beta 1-adrenoceptor (beta 1-AR), have been generated to evaluate the role of the atrial beta 1-AR density on HRV. The heart rate was monitored using telemetry, and the signal was analyzed using a quantitative time-frequency domain analysis, the smoothed pseudo-Wigner-Ville method, and phase portrait maps. 1) Heart rate was unchanged, but the two normal components of HRV were decreased in transgenic mice. Transgenic mice have an unshortened life span and no arrhythmias. 2) Challenge of the animals by propranolol showed no modulation of the HRV in transgenic mice compared with controls. 3) In isolated atrial strips from transgenic mice, basal contractility was increased and there was no isoproterenol-induced inotropic effect. 4) The basal level of adenosine 3',5'-cyclic monophosphate production was lowered in transgenic mice, suggesting a shift in adenylate cyclase isoforms.

Linear and non-linear analyses of heart rate variability: a minireview.

To complete traditional time- and frequency-domain analyses, new methods derived from non-linear systems analysis have recently been developed for time series studies. A panel of the most widely used methods of heart rate analysis is given with computations on mouse data, before and after a single atropine injection.