Abstract
Ventilatory chaos is strongly linked to the activity of central pattern generators, alone or influenced by respiratory or cardiovascular afferents. We hypothesized that carotid atherosclerosis should alter ventilatory chaos through baroreflex and autonomic nervous system dysfunctions. Chaotic dynamics of inspiratory flow was prospectively evaluated in 75 subjects undergoing carotid ultrasonography: 27 with severe carotid stenosis (>70%), 23 with moderate stenosis (<70%), and 25 controls. Chaos was characterized by the noise titration method, the correlation dimension and the largest Lyapunov exponent. Baroreflex sensitivity was estimated in the frequency domain. In the control group, 92% of the time series exhibit nonlinear deterministic chaos with positive noise limit, whereas only 68% had a positive noise limit value in the stenoses groups. Ventilatory chaos was impaired in the groups with carotid stenoses, with significant parallel decrease in the noise limit value, correlation dimension and largest Lyapunov exponent, as compared to controls. In multiple regression models, the percentage of carotid stenosis was the best in predicting the correlation dimension (p<0.001, adjusted R2: 0.35) and largest Lyapunov exponent (p<0.001, adjusted R2: 0.6). Baroreflex sensitivity also predicted the correlation dimension values (p = 0.05), and the LLE (p = 0.08). Plaque removal after carotid surgery reversed the loss of ventilatory complexity. To conclude, ventilatory chaos is impaired in carotid atherosclerosis. These findings depend on the severity of the stenosis, its localization, plaque surface and morphology features, and is independently associated with baroreflex sensitivity reduction. These findings should help to understand the determinants of ventilatory complexity and breathing control in pathological conditions.
Highlights
Human ventilatory rhythmogenesis arises from the brainstem and the medulla [1]
Nonlinear dynamics in the ventilatory flow output arises as a result of the complex interplay between central processing of the respiratory centers, peripheral afferents [2] and stochastic noise inputs
The aims of the study were: (i) to characterize linear and nonlinear features of inspiratory flow dynamics according to the severity of the carotid stenosis, its localization and characteristics of the plaque, (ii) to determine whether these changes correlate with baroreflex sensitivity, (iii) to study the effects of plaque removal on inspiratory flow chaos abnormalities
Summary
Human ventilatory rhythmogenesis arises from the brainstem and the medulla [1]. It depends on phasic neuronal activities taking place within central respiratory generators located in the brain stem and on their transformation into rib cage movements by the respiratory muscles. In unsedated humans receiving mechanical ventilation, ventilatory flow has been shown to exhibit chaotic properties arising from the intrinsic properties of the respiratory central pattern generator in response to vagal afferent feedbacks [2,6]. Taken together these findings point out that ventilatory chaos is strongly linked to the activity of central pattern generators, alone or influenced by respiratory or cardiovascular afferents [6], via autonomic nervous system. It provides a sensitive means of assessing breathing control
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