Ponemah versions 5.00 - 5.20 do not have a function to directly derive Time Domain Heart Rate Variability (HRV), only Frequency Domain.  Time Domain parameters must be manually calculated using Excel, as described below.

Calculating Time Domain HRV in Excel

1. Calculate the NN interval
1. Filter the RR interval for ectopic beats (NN interval
1. This can be using various methods, you can calculate 1 overall average of all the RR interval or calculate a running average
2. Delete cycles that are a given standard deviation or percentage from the average
2. Average the remaining cycles (the ones that were not delete from the previous step), this is the NN interval
2. Calculate the SDNN
1. Take the square root of the of the NN interval (calculated in step 1)
3. Calculate the RMSSD
   
   
   
   
1. Copy the NN interval column to a blank column
2. Copy the NN interval to a column next to the column created in step 3a but with a shift down one row
3. In the next column, calculate the difference to the columns created in 3a and 3b.
4. In the next column, square the value calculated in 3c
5. In the next column, calculate the total sum of all the values calculated from step 3d
6. In the next column, count the number of elements in the NN interval (can use values from step 3a)
7. In the next column, take the sum of difference squared (step 3e)/ count of NN intervals (step 3f)
8. Take the square routs of the value created in step 3g and this is the RMSSD value
4. pNNx
1. Count the number of value in the NN interval column that is greater than x. Humans are typically done at 50 msec, pNN