There are a number of special terms for the analysis of the the autonomic nervous system. They are reflecting the underlying analytical method:

• Heart rhythm variability (HRV)
• Cycle length variability (CLV)
• Heart rate variability (HRV)
• RR variability (RRV)

… these are all different names for the measurement and evaluation of the RR intervals (time period between successive heartbeats) either by means of a chest strap (wireless) or by using ECG electrodes (wired).

The measurement is based on a technically flawless electrocardiogram that allows for clean and noise-free recording and processing of the individual R spikes. There are so called short-term measurements lasting 5-10 minutes and long-term measurements recorded over a 24 hour period. The scientific standards for HRV measurements/ANS Analyses were precisely defined by an expert commission in 1996. Based on these standards the ANS Analysis was included as a basic diagnostic procedure in the evidence-based German Disease Management Guidelines. 

The sequence of the intervals can be analyzed by using various mathematical and statistical methods. Here we differentiate between the following:

• Time-domain parameters
• Frequenzy-domain parameters
• Non-linear parameters e.g. DFA - Alpha1

In the following, the main focus will be on the measuring parameters that are relevant for the practice: time-domain parameters and non-linear parameters

The frequenzy-domain parameters are used mainly for scientific studies. They are rarely relevant for the practice though.