RESUMO
This study was undertaken to clarify the relationship between respiratory period and respiratory arrhythmia. Five healthy male university students voluntarily changed the respiratory period over a range of 3-30 seconds while maintaining tidal volume constant (; 21) . Maximum and minimum cardiac cycles (RRmax and RRmin) and amplitude of cardiac cycle variability (ΔRR), the difference between RRmax and RRmin, were measured from electrocardiogram and respiratory curve.<BR>1. Amplitude of cardiac cycle variability was small for shorter respiratory periods and increased with respiratory period, attaining maximum at respiratory periods of 8-14 seconds followed by decrease at longer respiratory periods.<BR>2. The time from the onset of inspiration to the minimum cardiac cycle was the same for respiratory periods of 8-14 seconds (about 3.6 seconds) .<BR>3. Phase difference between cardiac cycle variability and respiration was determined at each respiratory period. When the minimum or maximum cardiac cycle coincided with the onset of inspiration, this situation being defined as 0°, RRmin was delayed by 180°, 90°, and 0° at respiratory periods of 2.3, 14.4, and 26.5 seconds, respectively and by 360°, 270°, and 180° at respiratory periods of 2.7, 15.0, and 27.3 seconds, respectively.<BR>Based on these results, respiratory arrhythmia is concluded to be quite stable at respiratory periods of 8-14 seconds. At short respiratory periods, tachycardia was found to occur during inspiration and bradycardia during expiration. During long respiratory periods, bradycardia was noted during inspiration and tachycardia during expiration.