Table 1.
Autonomic indices measured in the selected RCTs
| Parameters measured as outcomes | Units | Description of the parameter |
|---|---|---|
| Heart rate | bpm | Normal resting HR ranges from 60-100 bpm [31]; but elevated resting HR of 90-100 bpm could occur in diabetic patients with CAN [32] |
| Frequency-domain measures of HRV | ||
| Total power (TP) | ms2 | Sum of the VLF, LF, and HF bands from short-term ECG recordings [33] |
| Very low frequency power of heart rate variability (VLF) | ms2 | Absolute power of the VLF band (0.0033–0.04 Hz) [33] |
| Low frequency power of heart rate variability (LF) |
ms2 or NU |
Absolute power of the LF band (0.04–0.15 Hz) or Relative power of the LF band in normalised units [33] |
| High frequency power of heart rate variability (HF) |
ms2 or NU |
Absolute power of the HF band (0.15–0.40 Hz) or Relative power of HF band in normalised units [33] |
| Low-to-high frequency ratio (LF/HF) | No units | Ratio of LF to HF power [33] |
| Time-domain measures of HRV | ||
| Standard deviation of RR intervals (SDRR) | ms | Standard deviation of the RR intervals including abnormal and false beats [33] |
| Standard deviation of NN intervals (SDNN) | ms | Standard deviation of the normal RR intervals in a 24 h ECG recording [33] |
| Standard deviation of means of NN intervals (SDANNi) | ms | Mean of the standard deviations of the normal RR intervals in each of the 5-min segments of a 24 h ECG recording [33] |
| Root mean square of successive differences between NN intervals (RMSSD) | ms | Root mean square of time differences between successive normal RR heartbeats [33] |
| Percentage of differences > 50 ms between adjacent NN intervals (pNN50) | % | Percentage of adjacent normal RR intervals with difference > 50 ms [33] |
| Coefficient of variation in heart rate variability (CV) | % | Standard deviation of the RR intervals divided by the mean of RR intervals [33] |
| Cardiovascular autonomic reflex tests (CARTs) | ||
| Expiration-to-inspiration ratio (E/I) | No units | Ratio of the mean of the longest RR intervals during each expiration and the mean of the shortest intervals during each inspiration over 6 cycles of deep breathing [34] |
| Mean circular resultant of vector analysis (MCR) | No units | RR intervals obtained from deep breathing test are plotted on a time axis using vector analysis [35] |
| Valsalva ratio | No units | Ratio of the longest RR interval measured after the Valsalva manoeuvre and the shortest RR interval during the manoeuvre [36] |
| Ratio of RR intervals at 15th and 30th heartbeats after standing (30:15) | No units | Ratio of the shortest RR interval at the 15th beat and the longest RR interval at the 30th beat during a change from supine to standing position [37] |
| Orthostatic hypotension (OH) | mmHg | Decrease in SBP of 30 mmHg after a change from supine to standing position [1] |
| Blood pressure response to sustained handgrip | mmHg | Increase in the blood pressure of a subject that grips at 30% of their maximum strength for up to 5 min [37] |
| Other blood pressure parameters | ||
| Mean arterial pressure (MAP) | mmHg | Average arterial pressure throughout one cardiac cycle comprising of systole and diastole [38] |
| Systolic blood pressure (SBP) | mmHg | Highest blood pressure reading when the ventricles of the heart contract [39] |
| Diastolic blood pressure (DBP) | mmHg | Lowest blood pressure reading right before the next contraction of the ventricles of the heart [39] |
| Time index of DBP | % | Proportion of time that the DBP was above the normal reference range [40] |
| Standard deviation of DBP | mmHg | Degree of variation in the diastolic blood pressure in relation to the mean [41] |
| Diurnal index (DI) | % | Difference in mean daytime and nighttime blood pressure is divided by mean daytime blood pressure, then multiplied by 100 [40] |
HRV heart rate variability, bpm beats per minute, s seconds, ms milliseconds, ms2 milliseconds squared, ECG electrocardiogram, NU normalised units, % Percent, Hz Hertz, mmHg millimetres of mercury