Measurements and Modelling in the Cardio-Respiratory System
The heart and lungs, central components of the cardiovascular and respiratory systems respectively, exhibit intricate patterns of coordination that contribute to the body’s ability to adapt to different physiological demands. This synchronization involves the rhythmic interplay between heart rate (the number of times the heart beats per minute) and breathing rate (the number of breaths taken per minute).
This dynamic interaction between the cardiovascular and respiratory systems is orchestrated by the autonomic nervous system, a complex network of nerves that controls involuntary bodily functions. The sympathetic and parasympathetic branches of the autonomic nervous system play crucial roles in regulating heart rate, respiratory rate, and their synchronisation.
The concept of cardiorespiratory synchronization holds significance not only in the realm of basic physiological understanding but also in clinical contexts. Imbalances or disruptions in this synchronization can be indicative of underlying health conditions, such as cardiovascular disorders, respiratory diseases, or even stress-related issues. Moreover, studying the coordination between these systems can yield insights into how the body adapts to stress, exercise, and various environmental factors.
This work had 2 aspects - modelling and measuring.
Modelling
I built a custom model in Matlab to simulate the interactions in the system. This model used a Van der Pol coupled ocsillator to modell the interactions, where respiration would act as the driving oscillator and heart rate would follow. The would was simulated over a number of cylces at varying rates. The Van der Pol ocsillator has relevance to the cardiorespiratory system for several reasons.
First, the cardiorespiratory system exibhits rhythmic and perdioic behaviours, similar to limit cylce oscillations. While the underlying dynamics of the cardiorespiratory system are much more complex than the Van der Pol oscillator, the concept of limit cycles can help describe the sustained rhythmic behavior observed in the heart and lungs.
Secondly, the nonlinear interactions in the cardio respiratory system can be compared to those of the Van der Pol oscillator. Both systems interact and influence eachother in comlex ways, where their dynamics are nonlinear.
Thirdly, the ability fo the Van der Pol oscillator to exhibit chaotic behaviour under specific circumstances makes it able to capture some of the variability involved in the cardioac system through heart rate variability (HRV). This can provide insights into the health and adaptability of the system.
Measurments
I designed an experiment to measure this phenomena on human participants. To do this I had to apply to the university research ethics board to gain ethical approval to conduct experiments on human participants.
The experiment involved 12 volunteers selected from a range of people, and in 3 parts, during which the volunteers electrocardiogram (ECG) and respoiration rate were monitored. Respiration was used as the driving factor. After recording the basline resiting heart rate, the volunteer was required to breath at a rate equal to 90%, 100%, and 120% of the resting heart rate, allowing the heart rate to recover between experiments. This was repeated with the volunteer in the laying down and standing position.
The physiological data was post processed using custom software in Matlab to detect synchronisation. This showed that when participants were breathing at the same rate as their resting heart rate, the ECG peaks synchronised to the resporatory peaks, showing strong interaction between the two signals and a possible resonance in the system. In addition, the effect was more pronounced for i) Volunteers that did more excersise; ii) when laying down.