Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

ABSTRACT Background A joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt). Method: The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison. Results: We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes. Conclusion: Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

Sympathetic Responses in Caloric Stimulation:Role in the Cardiovascular Control of Anesthetized Rats / 航天医学与医学工程

Objective To explore the potential connection between sympathetic response, heart rate and blood pressure modulation after caloric irrigation in order to study the role of vestibular stimuli in cardiovascular control. Method Efferent splanchnic nerve firing rates, ECG and blood pressure were recorded simultaneously during caloric stimuli on intact anesthetized(CON) rats(n=5), sinoaortic denervated (SAD)rats(n=5) and bilateral vestibular destroyed (VD) rats(n=5). Result It was found that after caloric stimulation with ice water mean blood pressure CON rats with intact reflex became lower and the mean heart rates became slower, splanchnic sympathetic nerve activities increased for a moment and then dropped significantly. SAD rats had significant stronger splanchnic sympathetic nerve activities VD rats after caloric stimulation, and their blood pressures changed to apposite directions. The coupled respiratory component on splanhnic sympathetic nerve activities were strongly affected by the caloric stimulation. Conclusion It is suggested that semicircular canal stimulation participate at least in the short-term blood pressure control mechanism and the role of central nervous system on respiratory drive may also be involved. Baro-reflex and vestibular afferent may play different role in the control of blood pressure they may work synergically in some physiological control processed.