Table 1.

CAN prevalence in obesity, pre-DM and the metabolic syndrome

Study and year (reference)	Study design and setting	Population	Number (n)	Test(s) used	Prevalence (%)
Akhter et al. 2011 [51]	Physiology department of medical university, Bangladesh	Obesity BMI ≥ 25 (NGT)	40	1 abnormal result for early CAN from HR response to DB, Valsalva, standing, BP response to handgrip and standing. 2 abnormal results for definite CAN	22.5 early CAN, 0 definite CAN
		BMI 18.5–22.9 control group (NGT)	40		0 early and definite CAN
Putz et al. 2013 [26]	Hospital diabetes clinic, Hungary	IGT	75	1 abnormal result for early CAN from HR response to DB, Valsalva ratio, orthostatic hypotension, handgrip test and triangle index	57.5
Ge et al. 2014 [50]	Population-based sample, China	MetS	833	≥ 2 abnormal cardiovascular autonomic reflex test results obtained from spectral analysis of HRV	24.5
		k-DM (type unspecified)	446		31.2
Ziegler et al. 2015 [19]	Population-based cross-sectional study (the KORA S4 survey), Germany	NGT	565	≥ 2 abnormal for CAN: HRV indices calculated from supine 5-min ECGs as Renyi4 (time domain), TP spectrum (frequency domain), SD of short axis (Poincaré plot) and SD of the word sequence (symbolic dynamics)	4.5
		Pre-DM
		IFG	336		8.1
		IGT	72		5.9
		IFG and IGT	151		11.4
		n-DM	78		11.7
		k-DM (type unspecified)	130		17.5
Dimova et al. 2017 [40]	Hospital diabetes clinic, Bulgaria	NGT	130	≥ 2 abnormal for CAN: HRV indices calculated at rest, during DB, Valsalva challenge, standing challenge	12.3
		Pre-DM
		IFG	125		13.2
		IGT	102		20.6
		IFG and IGT	227		19.8
		T2DM	121		32.2

BMI body mass index, BP blood pressure, CAN cardiac autonomic neuropathy, DB deep breathing, ECG electrocardiogram, HR heart rate, HRV heart rate variability, IFG impaired fasting glucose, IGT impaired glucose tolerance, k-DM known diabetes mellitus, MetS metabolic syndrome, NGT normal glucose tolerance, n-DM newly detected diabetes mellitus, T2DM type 2 diabetes mellitus, TP total power