Compact Data Logger Carried on a Crow to Measure RR Intervals During Flight

Birds control respiration through air sacs, and the skeletal muscles that control them are always tense. Electrocardiograms (ECGs) with electrodes placed on the chest wall contain high-amplitude electromyograms. To measure the PR and RP intervals of an ECG accurately in such a physiological noise environment, which cannot be seen in mammals, it is necessary to lower the signal-to-noise ratio physically and reduce fluctuations in the peak R and P waves on the time axis. Therefore, we developed a catheter that can capture an ECG from the esophagus near the center of the thoracic cavity. As a field experiment, we attached the catheter to several carrion crows and obtained data before, during, and after flight. The changes in the PR and RP intervals before and after flight revealed that the sympathetic nerves were dominant during flight. To substantiate this, we also measured temporal fluctuations in the RR interval in chickens that had been administered drugs that act on the autonomic nervous system intravenously. Furthermore, we compared three correlations in regard to autonomic nerve control in chickens: RR interval variation, systolic arterial pressure variation, and cardiac output variation associated with respiration. Regarding the variation in the RR interval in birds, we were able to confirm three types of control with different cycles. In particular, the amplitude was small, and short-period fluctuations are not seen in humans. Therefore, future analysis is needed.