R-wave Amplitude Changes and Atypical Heart Rate Changes Accompanying Breath Hold During Low Breathing Rates

This paper reports an interesting phenomenon that the amplitude of the QRS complex reduces during inhalation and increases during exhalation and the variation can exceed even 100% during very slow breathing rates (BR). The phenomenon has been consistent in all the nine normal male subjects we have studied with age ranging from 23 to 61 years. Further, at very low respiration rates which included breath holds both after inhalation and exhalation, there are highly significant second and third harmonics of the respiration frequency in the heart rate variability spectrum. On the other hand, the R-wave amplitude changes do not have any noticeable higher harmonics of the BR. Thus, the observed changes in the R-wave amplitude are neither connected to the movement of the heart nor changes in its relative position with respect to the recording electrodes nor the fluctuations in the stroke volume.