Time-Domain HRV

• Heart rate variability, or HRV, provides a non-invasive method of approximating the Autonomic Nervous System (ANS)  and can offer valuable insights into an individual’s physical and mental health.   
• HRV is calculated by looking at the fluctuations between individual heartbeats. The time between each consecutive heartbeat is called the R-R interval or BBI- beat to beat interval -and when using specialized platforms like Labfront, researchers are able to collect that granular BBI data from Garmin devices directly. 
• In this video, we’re going to show you what that BBI data looks like, and introduce how researchers can derive HRV from BBI.   
• There are various methods and calculations that can be used to calculate HRV such as time-domain, frequency-domain, and non-linear metrics.
• In this example, we calculate the time-domain (RMSSD) to derive the HRV of a participant over a 5 minute period. 
• First, we would head to our Labfront account to download the data. In the Garmin RR interval file, we would have access to a participant’s BBI data. The data is offered in milliseconds and provided in unix time. In the first blue column, we converted the unix time to the local timezone (broken down by milliseconds). 
• Then, in the next column, we plugged in a simple formula to get a sample range of 5 minutes exactly.  
• Now for the calculations:
• We know we need to derive the following information to calculate time-domain HRV: we need SDRR, RMSSD, RR50, and pRR50. 
• To get the SDRR, we need to calculate the standard deviation of the raw BBI data. 
• To calculate the RR50 and pRR50, we need to first add a “BBI difference” column showing the difference between each BBI value. 
• Once that column has been created, we can calculate the sum of all of the absolute values greater than 50, and that result is our RR50 value. 
• And to get the RMSSD, we need to add a column representing the values SQUARED of the values in the “BBI difference” column. From there, we can calculate the square value, as well as the root of the mean of square values, to derive RMSSD
• So as you can see here, In the final two blue columns, we have our BBI difference column, calculated by subtracting one cell value from the previous cell above it, and we have our squared column, where each value was squared from the previous column. 
• Lastly, to derive the pRR50, which represents the percentage of RR50, simply take the RR50 value and divide it by the total # of data points found in that 5 minute range. 

And that’s how you derive time-domain HRV from raw BBI data. To learn more about deriving HRV from BBI, please feel free to explore our resources shared below!