Relationship between treadmill exercise test parameters and heart rate variability in patients with nonischemic diabetic autonomic neuropathy

Objectives: We investigated the relationship between heart rate variability (HRV) and treadmill variables in nonischemic neuropathic patients. Study design: The study included 38 patients (20 men, 18 women; mean age 50 +/- 11 years). All the patients underwent standard tests for cardiovascular autonomic neuropathy (CAN), maximal exercise treadmill testing according to the Bruce protocol, 24-hour Holter ECG monitoring, and time-and frequency-domain analysis of HRV. Time-dependent parameters included SDNN, SDANN, SD, RMSSD, and PNN50, with cut-off values being 100 ms, 25 ms, 92 ms, 35 ms, and 7500, respectively. Results: MET scores and exercise time reached in exercise test showed varying correlations with the lowest and mean heart rates recorded by Holter ECG monitoring and HRV parameters, in particular with SD and SDNN, whereas they were not correlated with CAN scores. Moderate correlations were found between chronotropic parameters of exercise test (maximal heart rate and percent maximal heart rate) and pressure-rate product associated with CAN severity. Patients with an insufficient treadmill test had significantly higher minimal rates on Holter monitoring (p= 0.05) and significantly lower values for SDNN, SD, RMSSD, and PNN50 (p<0.05). Patients with an effort capacity of 5 METs or lower had significantly decreased SDANN values, while those reaching 10 METs or more had above-normal SDANN values (p<0.05). Conclusion: Autonomic neuropathy is closely related with HRV parameters in patients with nonischemic type II diabetes and is associated with a disturbed exercise response.