Cardiovascular autonomic neuropathy in diabetes: Pathophysiology, clinical assessment and implications

Table 2 Heart rate variability time and frequency domain measures[89,90]

	Linear indices - time domain
Parameters	Abbreviation meaning	Interpretation
MNN (ms)	Mean of NN intervals	Long RR intervals are related to a lower heart rate, while short RR intervals denote a high heart rate. It reflects SANS and PANS modulations
SDNN (ms)	Standard deviation of all NN intervals	Reflects the activity of both SANS and PANS
rMSSD (ms)	The square root of the mean squared differences of successive NN intervals	Reflects the PANS activity
NN50 (count)	Number of interval differences of successive NN intervals greater than 50 ms	Reflects the PANS activity
pNN50 (%)	Percentage of successive RR intervals that differ by more than 50 ms	The proportion of NN50 divided by total number of NN, which also represents the PANS activity
	Linear indices - frequency domain
ULF (ms², Hz, %)	Ultra low frequency	Frequency range: 0-0.003 Hz. Commonly, it is not present in HRV results
VLF (ms², Hz, %)	Very low frequency	Frequency range: 0.003-0.04 Hz. It is related to renin-angiotensin-aldosterone system, thermoregulation, peripheral vasomotor tonus and PANS activity
LF (ms², Hz, nu, %)	Low frequency	Frequency range: 0.04-0.15 Hz. It represents the SANS and PANS activity, with a predominance of SANS influence
HF (ms², Hz, nu, %)	High frequency	Frequency range: 0.15-0.4 Hz. It represents the PANS activity
LF/HF	Ratio of LF-to-HF power	So-called sympathovagal index. It represents the sympathovagal balance, the autonomic state resulting from the SANS and PANS influences
Total power (ms²)	Total power	It reflects both SANS and PANS influences, representing the components with frequency range ≤ 0.4 Hz

SANS: Sympathetic autonomic nervous system; PANS: Parasympathetic autonomic nervous system; LF: Low frequency; HF: High frequency; ULF: Ultra low frequency; VLF: Very low frequency; MNN: Mean of NN; SDNN: Standard deviation of all NN.