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Phase-dependent heartbeat modulation by muscle contractions during dynamic handgrip in humans
1Laboratory of Biological Informatics, Department of Electrical and Information Engineering, Faculty of Engineering, Yamagata University, Yonezawa 992, Japan. nzq@eie.yz.yamagata-u.ac.jp
Insights
The timing of handgrip contractions during the cardiac cycle influences heart rate response. Muscle contractions timed to the middle of the cardiac cycle showed the strongest effect on heart rate variability.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Human Exercise Physiology
Background:
- Heart rate variability (HRV) reflects autonomic nervous system activity.
- The cardiac pacemaker's response to physiological stimuli can be influenced by the cardiac cycle phase.
- Understanding the interplay between muscle activity and cardiac timing is crucial for cardiovascular health.
Purpose of the Study:
- To investigate how the timing of dynamic hand contraction within the cardiac cycle affects heart rate response.
- To determine if cardiac phase modulates the influence of muscle contraction on cardiac pacemaker activity.
- To identify the specific cardiac phases that elicit distinct heart rate alterations during handgrip.
Main Methods:
- Studied eight healthy young men performing heartbeat-synchronized handgrip contractions.
- Measured changes in R-R interval (RRI) at different cardiac phases.
- Utilized frequency domain analysis to isolate the direct effect of muscle contraction on RRI by removing respiratory and slow variations.
- Employed cross-correlograms to assess the coupling between muscle contraction timing and RRI fluctuations.
Main Results:
- Muscle contraction coupling to RRI was strongest when occurring in the middle phase of the cardiac cycle.
- Contractions during the systolic phase tended to shorten RRI (heart rate advance).
- Contractions during the middle or later cardiac phases tended to prolong RRI (heart rate delay).
Conclusions:
- Cardiac phase significantly influences the heart rate response to dynamic muscle contraction.
- A neuronal circuit modulates cardiac pacemaker activity based on the timing of muscle contraction within the cardiac cycle.
- These findings highlight the importance of considering cardiac timing in understanding exercise-induced autonomic cardiovascular regulation.
Abstract:
The influence of cardiac phase on the response of the cardiac pacemaker to dynamic hand contraction in eight healthy young men was studied to determine whether heart rate response to muscle contraction varied as a function of timing within the cardiac cycle. Changes in R-R interval (RRI) in response to muscle contraction were measured at various cardiac phases during heartbeat-synchronized handgrip at a rate of one contraction per two heartbeats. To extract the direct effect of the muscle contraction on the RRI, spontaneous slow variations and respiratory sinus arrhythmia were removed from the total RRI fluctuations in the frequency domain. Cross-correlograms between the extracted RRI fluctuations and muscle contraction showed that the coupling was strong when the muscle contraction occurred at the middle phase of the cardiac cycle. Muscle contraction at the systolic phase of the cardiac cycle had a tendency to produce a phase advance (shortening of RRI), whereas muscle contraction at the middle phase or later had a tendency to produce a phase delay (prolongation of RRI). The results showed the presence of a neuronal circuit that modulates the cardiac pacemaker activity depending on the timing of muscle contraction in the cardiac cycle.