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Frequency domain heart rate variability and plasma norepinephrine level in the coronary sinus during handgrip
1Division of Biomedical Engineering, National Defense Medical College, Saitama, Japan.
Insights
Heart rate variability indices reflect autonomic nerve activity in healthy individuals but not in those with coronary artery disease during handgrip exercise. This suggests reduced adaptability to physical stress in CAD patients.
Area of Science:
- Cardiology
- Autonomic Nervous System
- Exercise Physiology
Background:
- Heart rate (HR) variability is a key noninvasive indicator of autonomic nervous system activity.
- The link between HR variability and cardiac norepinephrine (NE) during coronary ischemia is not well understood.
Purpose of the Study:
- To investigate if HR variability indices can accurately reflect cardiac NE levels during handgrip exercise.
- To compare these responses in individuals with and without coronary artery disease (CAD).
Main Methods:
- Simultaneous measurement of HR variability and cardiac NE overflow rate during isometric handgrip exercise.
- Study included 32 participants: 20 with CAD and 12 healthy controls.
Main Results:
- In healthy subjects, high-frequency (HF) spectra of HR variability increased significantly, correlating negatively with cardiac NE overflow.
- In CAD subjects, low-frequency (LF) and LF/HF ratios increased, with no significant correlation to cardiac NE.
- Vagal modulation of HR variability was more pronounced in healthy individuals than in those with CAD.
Conclusions:
- HR variability indices are reliable indicators of autonomic nerve activity in individuals with normal coronary arteries.
- These indices are less reliable in CAD patients, likely due to diminished adaptation to physical stress.
Background:
Heart rate (HR) variability has been recognized as an important noninvasive index of autonomic nervous activities. However, the relationship between HR variability and cardiac circulating norepinephrine (NE), especially with respect to coronary ischemia, remains unclear.
Hypothesis:
This study was undertaken to determine whether HR variability indices can reflect cardiac NE levels during handgrip exercise.
Methods:
We simultaneously measured HR variability and cardiac NE overflow rate in 32 patients (30 men, 2 women) during a 6-min isometric handgrip exercise. Among the 32 subjects, 20 (19 men, 1 woman) had coronary artery disease (CAD) and 12 (control group; 11 men, 1 woman) did not.
Results:
Hemodynamics and cardiac NE overflow rates among subjects at rest were not significantly different between the two groups. In the normal subjects, low-frequency (LF) spectra and LF/HF (high-frequency) ratios were not significantly changed during handgrip exercise, but HF spectra significantly increased from 10.1 +/- 4.5 to 12.2 +/- 7.0 ms (p < 0.05). In the subjects with CAD, LF and LF/HF spectra were significantly (p < 0.05 and 0.01, respectively) increased by handgrip exercise. High-frequency spectra were not significantly changed by handgrip exercise. In the normal subjects, a significant negative relation (r = -0.76, p < 0.01) was obtained between HF change and cardiac NE overflow rate, whereas this relationship was not significant in the subjects with CAD. The correlation between changes of LF/HF and cardiac NE overflow rate was significant in the normal (r = 0.56, p < 0.05) but not in subjects with CAD.
Conclusion:
These results suggest that vagal modulation of HR variability is more prominent in normal coronary artery subjects than in CAD subjects during handgrip exercise. Heart rate variability indices may thus serve as adequate indicators of autonomic nerve activity in subjects with normal coronary arteries but not in those with CAD, probably due to decreased adaptation to physical stress during handgrip exercise.
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