The Autonomic (involuntary) Nervous System incorporates two branches which are the Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS). These branches innervate all body organs, including the cardiovascular system.
The SNS and PNS help to control blood pressure and heart rate through baroreflexes/baroreceptor reflex control(1) and is understood to be responsible for controlling heart rate variability(2) in humans.
The baroreflex is a homeostatic physiological mechanism that regulates blood pressure at constant levels. Baroreceptors are located in major arteries and veins, and in the heart. Through their feedback mechanism, these baroreceptors enable the autonomic nervous system to swiftly adjust the heart rate and arterial resistance using a rapid negative feedback loop.
Heart Rate Variability is the variation of time interval between consecutive heartbeats. This interval is known as the interbeat interval (IBI). A healthy heart can make adaptive variations of its inter-beat intervals based upon the physiological requirements of the body. It also depends on subject age and sex.
The variability is controlled by the autonomic nervous system in a similar way to the baroreflex feedback. The balance between the SNS and PNS behind the scenes, automatically regulates our heart rate, blood pressure, breathing, and digestion among other key physiologic processes involuntarily.
Baroreflex sensitivity (BRS) and Heart Rate Variability (HRV) are important homeostatic mechanisms and reliable cardiovascular analytical enpoints that can be used preclinically to detect changes that could involve cardiovascular diseases but also neurological disorders (stress, depression, anxiety etc.), physical disorders (e.g., inflammation, chronic pain, diabetes, asthma, insomnia, fatigue) or cancer.
For instance, reductions in HRV and/or BRS are strongly correlated to heart disease, poor cardiac autonomic tone, reduced autonomic protection against ventricular arrhythmias, high blood pressure and various metabolic syndromes.
Time and frequency domain analysis are effective methods to analyse heart rate dynamics with respect to Heart Rate Variability (HRV).
The HRV Module in ecgAUTO provides the ability to perform both time and frequency domain analysis with little effort and a high degree of flexibility. The time-domain indices in the HRV module quantify the amount of variability in measurements of the interbeat interval (IBI) observed during monitoring periods that are user defined but can be as small as 2 min and up to 24 h. Frequency-domain values calculate the absolute or relative amount of signal energy within frequency bands. These frequency bands are in part defined by The Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996). The Fast Fourier Transform (FFT) is responsible for converting the R-R’ intervals, after being resampled, into the frequency domain.
The FFT imposes several constraints which affect the selection of analysis parameters, that are described in this document: Frequency Domain Analysis of Heart Rate Variability in ecgAUTO.
In ecgAUTO, BRS is computed using what is usually called the “sequence method”.
The software locates “sequences” of #n consecutive beats, where Blood Pressure (BP, i.e systolic, diastolic, or mean) and Beat to Beat Interval (BB, i.e the time between 2 consecutive beats) both increase.
The software plots BB vs BP of every sequence found in a record and performs a linear regression of the BB vs SBP plots.
The slope of the linear regression is the baroreflex sensitivity (BRS). A high value of BRS means that heart rate is significantly affected by a change of pressure.
The variations in blood pressure and heart rate are signals that can be monitored in vivo using implanted telemetry. Standard parameters such as systolic, diastolic and mean blood pressure may be retrieved through an intraarterial catheter. Telemetry methods allow for continuous and stress-free measurement of variations in these parameters.
emkaPACK5 system allows for simultaneous acquisition of ECG and Blood pressure data in large animals to without confounding effects of surgery or anesthesia.
When subjects are particularly fragile and cannot tolerate surgery or anesthesia, as with cardiomyopathy or pulmonary hypertension, emkaPACK5 is a good alternative to implanted telemetry.
ecgTUNNEL benefits of an innovative design allowing for ECG acquisition in small animals without confounding effects of surgery or anesthesia.
When subjects are particularly fragile and cannot tolerate surgery or anesthesia, as in cardiomyopathy disease, ecgTUNNEL is a good alternative to implanted telemetry.
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