Author/Authors :
Kazimierska, Agnieszka Department of Biomedical Engineering - Faculty of Fundamental Problems of Technology - Wroclaw University of Science and Technology - Wroclaw, Poland , Placek, Michał M Department of Biomedical Engineering - Faculty of Fundamental Problems of Technology - Wroclaw University of Science and Technology - Wroclaw, Poland , Uryga, Agnieszka Department of Biomedical Engineering - Faculty of Fundamental Problems of Technology - Wroclaw University of Science and Technology - Wroclaw, Poland , Wachel, Paweł Department of Control Systems and Mechatronics - Faculty of Electronics - Wroclaw University of Science and Technology - Wroclaw, Poland , Burzynska, Małgorzata Department of Anesthesiology and Intensive Care - Wroclaw Medical University - Wroclaw, Poland , Kasprowicz, Magdalena Department of Biomedical Engineering - Faculty of Fundamental Problems of Technology - Wroclaw University of Science and Technology - Wroclaw, Poland
Abstract :
Baroreflex is a mechanism of short-term neural control responsible for maintaining stable levels of arterial blood pressure (ABP)
in an ABP-heart rate negative feedback loop. Its function is assessed by baroreflex sensitivity (BRS)—a parameter which quantifies
the relationship between changes in ABP and corresponding changes in heart rate (HR). The effect of postural change as well as the
effect of changes in blood O2 and CO2 have been the focus of multiple previous studies on BRS. However, little is known about the
influence of the combination of these two factors on dynamic baroreflex response. Furthermore, classical methods used for BRS
assessment are based on the assumption of stationarity that may lead to unreliable results in the case of mostly nonstationary
cardiovascular signals. Therefore, we aimed to investigate BRS during repeated transitions between squatting and standing in
normal end-tidal CO2 (EtCO2) conditions (normocapnia) and conditions of progressively increasing EtCO2 with a decreasing
level of O2 (hypercapnia with hypoxia) using joint time and frequency domain (TF) approach to BRS estimation that overcomes
the limitation of classical methods. Noninvasive continuous measurements of ABP and EtCO2 were conducted in a group of 40
healthy young volunteers. The time course of BRS was estimated from TF representations of pulse interval variability and systolic
pressure variability, their coherence, and phase spectra. The relationship between time-variant BRS and indices of ABP and HR
was analyzed during postural change in normocapnia and hypercapnia with hypoxia. In normocapnia, observed trends in all
measures were in accordance with previous studies, supporting the validity of presented TF method. Similar but slightly attenuated response to postural change was observed in hypercapnia with hypoxia. Our results show the merits of the nonstationary
methods as a tool to study the cardiovascular system during short-term hemodynamic changes.
Keywords :
Baroreflex , Hypercapnia , Time-Frequency , EtCO2
