Cold Airflow for the Semicircular Canals Decreases Heart Rate

Abstract

Background Arterial pressure (AP) and heart rate (HR) near or after the end of cold caloric test or the test of semicircular canal function were not changed, but those were not measured from the beginning of the test continuously. This study was aimed to evaluate the changes in AP and HR continuously during caloric test and 2) relationship between those changes and the semicircular canal function. Methods the Basic Principles of the Declaration of Helsinki and their expansion in the regulations governing research supported by the U.S. Government. This study was approved by the Institutional Review Boards, and written informed consent was obtained from all subjects. Airflow at 15°C was applied to the left ear (Ear15), and the left tragus (Tragus15); another airflow at 37°C was applied to the left ear (Ear37) for one minute each in healthy subjects. AP, HR were recorded and analyzed in time series. Furthermore, the cold airflow was applied to the right and left ear for one minute, and maximum changes in AP, HR and slow phase velocity (SPV) of nystagmus were measured in outpatients. Results AP remained constant or decreased during the Ear15, whereas their HR immediately decreased at the onset of the airflow uniformly. Thus, the decrease in HR was unlikely induced by the baroreflex. Neither AP nor HR changed during the Ear37 and Tragus15 stimulation. Thus, the decreases in HR were not induced by the mechanical stimulation and stimulation for the skin. Degree of nystagmus was significantly correlated with the changes in HR but in AP in outpatients. Conclusions Cold airflow for the ears immediately decreased HR, and the semicircular canals might be related the change.