Item – Thèses Canada

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Numéro d'OCLC
35926078
Auteur
Li, Zhixing,1958-
Titre
Assessment of autonomic nervous control of the cardiovascular system by spectral analysis.
Diplôme
Ph. D. -- École Polytechnique de Montréal, 1994
Éditeur
Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 1994.
Description
2 microfiches.
Notes
Includes bibliographical references.
Résumé
Oscillations in heart rate and arterial blood pressure (BP) reflect autonomic modulation of cardiovascular activity. To assess the autonomic control of the cardiovascular system, spectral analysis of RR intervals, BP and respiratory signals were applied to human and canine subjects. Spectral powers in VLF (.005-.05 Hz), LF (.05-.15 Hz), HF (.15-0.4 Hz) bands were measured for each time series. A study was first performed on 41 normal subjects in resting supine, passive head-up tilt and active standing positions. Principal results may be summarized as follows: (1) in response to tilt, HR and diastolic blood pressure increased and systolic and pulse pressures decreased. For RR intervals, HF power decreased; LF power increased; consequently LF/HF ratio increased. For BP, LF and HF powers increased significantly except for HF power in diastolic pressure. These are due to the activation of sympathetic and decrease of vagal activities. (2) High frequency variations in BP and RR were higher in the passive tilt than those in the active standing (N = 27). (3) Spectra of AV conduction time clearly showed 3 peaks. In response to tilt, HF power increased significantly and in contrast to RR, the LF/HF ratio of AR decreased. Data indicated that the AV node is also influenced by the autonomic nervous system and the AV conduction time is mediated mainly by the vagal system. Secondly, analyses were performed on 14 essential hypertension subjects and 24 syncope-prone subjects to assess abnormality of autonomic function. In supine rest, the hypertensive may be characterized by loss of RR variability, larger variabilities in BP, larger VLF power and lower HF power in all variables. In response to active standing, depressed response of the vagal system in hypertensives was noted. This was characterized by a smaller decrease of HF power of RR and no change of HF power in all BP variables due to a lower vagal activity at baseline. In the syncope group, VLF power of RR was higher, while HF power of RR was lower at resting supine. The data showed a higher VLF variability in RR at both supine and tilt in the syncope group, while the VLF powers in BP were similar to those of the normal group. This instability of the HR control in the VLF band may contribute to the fainting in syncope prone patients. The third stage of the study consisted in the evaluation of the power spectrum of RR in 8 mongrel dogs. With perfusion of epinephrine (EPI), RR decreased and LF power increased, suggesting that EPI activates presynaptic $\beta\sb2$ adrenoceptor leading to an increase in neurotransmitter release. With yohimbine, HF power did not change, while LF power increased significantly due to a facilitation of the NE release. With fenoterol, LF power was significantly higher than that at baseline while the HF power was higher than those in both baseline and after yohimbine. Stimulation of left stellate ganglion resulted in a decrease of mean RR and an increase of LF power. This confirms that the LF power reflects the sympathetic tone. Vagal blockade decreased the mean RR and SD as well as the LF and HF powers. Finally, a conceptual model to explain interactions among the different cardiovascular variables has been proposed. (Abstract shortened by UMI.)
ISBN
0315933895
9780315933897