Diagnostic Tests of Cardiovascular Autonomic Neuropathy
| TEST | METHOD/ PARAMETERS |
|---|---|
| Resting heart rate Beat-to-beat heart rate Variation* | >100 beats/min is abnormal. With the patient at rest and supine (no overnight coffee or hypoglycemic episodes), breathing 6 breaths/min, heart rate monitored by EKG or ANSCORE device, a difference in heart rate of >15 beats/min is normal and <10 beats/min is abnormal, R-R inspiration/R-R expiration >1.17. All indices of HRV are age-dependent**. |
| Heart rate response to Standing* | During continuous EKG monitoring, the R-R interval is measured at beats 15 and 30 after standing. Normally, a tachycardia is followed by reflex bradycardia. The 30:15 ratio is normally >1.03. |
| Heart rate response to Valsalva maneuver* | The subject forcibly exhales into the mouthpiece of a manometer to 40 mmHg for 15 s during EKG monitoring. Healthy subjects develop tachycardia and peripheral vasoconstriction during strain and an overshoot bradycardia and rise in blood pressure with release. The ratio of longest R-R shortest R-R should be >1.2. |
| Spectral analysis of heart rate variation, very low frequency power (VLFP 0.003-0.04) and high frequency power (HFP 0.15-0.40 Hz) | Series of sequential R-R intervals into its various frequent components. It defines two fixed spectral regions for the low-frequency and high-frequency measure. |
| Systolic blood pressure response to standing | Systolic blood pressure is measured in the supine subject. The patient stands and the systolic blood pressure is measured after 2 min. Normal response is a fall of <10 mmHg, borderline is a fall of 10-29 mmHg, and abnormal is a fall of >30 mmHg with symptoms. |
| Diastolic blood pressure response to isometric exercise | The subject squeezes a handgrip dynamometer to establish a maximum. Grip is then squeezed at 30% maximum for 5 min. The normal response for diastolic blood pressure is a rise of >16 mmHg in the other arm. |
| EKG QT/QTc intervals Spectral analysis with respiratory frequency | The QTc (corrected QT interval on EKG) should be <440 ms. VLF peak (sympathetic dysfunction) LF peak (sympathetic dysfunction) HF peak (parasympathetic dysfunction) LH/HF ratio (sympathetic imbalance) |
| Neurovascular flow | Using noninvasive laser Doppler measures of peripheral sympathetic responses to nociception. |
These can now be performed quickly (<15 min) in the practitioners' office, with a central reference laboratory providing quality control and normative values. LF, VLF, HF =low, very low and high frequency peaks on spectral analysis. These are now readily available in most cardiologist's practice.** Lowest normal value of E/I ratio: Age 20-24:1.17, 25-29:1.15, 30-34:1.13, 35-30:1.12, 40-44:1.10, 45-49:1.08, 50-54:1.07, 55-59:1.06, 60-64:1.04, 65-69:1.03, 70-75:1.02 .
From: Diabetic Neuropathies
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