Ischemia-induced reflex sympathoexcitation during the recovery period after maximal treadmill exercise testing

Heart rate variability (HRV) analysis is problematic during maximal treadmill exercise testing (ET) due to rapidly changing heart rate.

The aim of this study was to assess HRV spectral components during treadmill ET in patients with coronary artery disease (CAD) and in healthy controls, and to search for possible differences between the two groups.

Thirty patients with CAD and 30 age-matched healthy controls underwent symptom-limited ET and continuous electrocardiographic monitoring. For adequate assessment of HRV during maximal ET, we calculated the HRV measures [normalized units (NU)]--low-frequency (0.040-0.150 Hz) power (LF), high-frequency (0.150-0.400 Hz) power (HF), and the LF/HF ratio--from all the sequential stages of the ET with limited changes (20 beats/min) in heart rate (stress 80-100, 100-120, 120-140, 140-160, 160-180/recovery 180-160, 160-140, 140-120, 120-100, 100-80).

Both LF and HF were found to decrease gradually during ET and to increase during the recovery period in both patients and controls (p < 0.001). LF values were higher during the recovery period than during the respective stages of exercise time in both patients and controls, and LF/HF ratio was higher during recovery in patients only.

During maximal ET (1) vagal tone withdraws during the exercise time and increases during the recovery period; (2) the sympathetic activity predominates during the recovery period, especially in patients with CAD and exercise-induced myocardial ischemia. This finding raises the possibility of ischemia-induced cardiocardiac sympathetic excitatory reflexes.