Stay on the Beat with Interbeat Interval

Interbeat Interval: What is it? 

Our bodies are constantly facing various forms of stress. These stressors can arise from an external source such as cold air temperature or be internal like indigestion. Because of the ever-changing nature of our bodies and environments, a healthy heart needs to be resistant enough to adapt, as needed, when faced with a new challenge. 

Contrary to what most would assume, the heart is not a metronome that constantly follows the same rhythm. Instead, the time between each heartbeat should change from beat to beat. This change is called heart rate variability (HRV) and can be used to analyze the overall health of an individual. An overly inconsistent heartbeat can indicate the presence of abnormal heart rhythms whereas a heart that shows limited variability can be a sign that there are underlying health issues such as cardiac disease or mental illness.  A resilient, adaptable, and healthy body tends to have just the right amount of HRV: not too variable but not too constant either.

Beat-to-beat data needs to be collected in order to properly calculate HRV. This data has many names attributed to it including interbeat interval (IBI), beat-to-beat interval (BBI), heart period, pulse interval, and RR interval. 

When looking at an electrocardiogram (ECG or EKG) there can be three identifiable parts to every electrical stimulation of the heart ventricles. This is called the QRS complex and shows up as three waves on the ECG heart monitor. Each wave is the result of change in the overall direction of the electrical (actually ionic) current passing through the biggest chambers of the heart, the ventricles. The positive deflecting wave is the R wave. The interval between each R wave is calculated in milliseconds and is called the interbeat interval.

How can interbeat interval be measured? 

Traditionally collecting BBI data would involve setting up an EKG device that uses electrodes stuck to the chest to detect all the electrical activations of the heart. Irregular RR on the heart monitor can be used to detect arrhythmias or abnormal electrical conduction patterns. 

Another method for measuring BBI is performing a blood flow or “photoplethysmography” measurement. This is done by using different colored lights to measure blood flow changes in the body: red light is often used to assess transmission of light through the body, while green light is used to measure reflection of light.  Since a watch’s optical sensors are located on the same side as the light source, reflected - not transmitted - light is measured with the use of a green-colored light. An optical sensor will detect the amount of blood passing through the small vessels in the skin. Patterns in blood flow are in direct correlation with heart pulsations, making pulse wave measurements a great solution for calculating interbeat interval. 

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Consumer wearables like Garmin smartwatches present an accessible solution for calculating BBI using blood flow measurements. Both short-term and long-term analyses can be conducted since the wearable can be easily and comfortably worn throughout the day and night. Collected data can also be collected and analyzed remotely using Labfront's platform.

How interbeat interval can be used to improve your research 

Using BBI data in your research presents a great opportunity to better analyze how different conditions affect overall health. Because both short and long-term analyses can be performed, no matter your time or resource availability, calculating BBI can add value to your research. 

Normal changes in BBI throughout the day can be attributed to both fluctuating heart rate and blood pressure. While resting and at night, heart rate and blood pressure should drop which will affect BBI. Monitoring BBI long-term, over a 24-hour period or longer can provide a deeper understanding of an individual’s ability to cope physically and mentally with their environments. Instead of needing to be strapped into an EKG, wearables like smartwatches make conducting long-term BBI analysis easy and accessible. 

Various research applications

BBI is a great indicator of cardiac health but that is not the only way interbeat variation data can be applied. Analyzing HRV and BBI can provide valuable insights into the body’s ability to cope with various non-cardiac related diseases and disorders, particularly in psychological research. Common research applications include the study of mental health disorders like depression, sleep disorders such as sleep apnea/hypopnea, neurodevelopmental disorders like autism, and anxiety disorders.