Quantifying the Cardiopulmonary Rhythm Locking by the Ratio of Heart Rate to Respiratory Rate in Healthy Subjects during Different Sleep Stages

Based on the ratio of heart rate to respiratory rate, this paper quantifies the cardiopulmonary rhythm locking of healthy subjects during different sleep stages. Totally 10 healthy sleep records (ten healthy subjects, 9 males and 1 female, age: 40 ± 10 years; one record for one subject) were used in this paper from the public database ISRUC-Sleep of AASM standard. The heart rate was obtained from the ECG waveform and the respiratory rate was obtained from the oronasal airflow respiration during each 30-second segment. The relationship between the ratio of heart rate to respiratory rate and the standard ratio m:n was studied. The following results were obtained when N = 4 and Th = 0.07, (1) Totally 656 segments (7.38%) with cardiopulmonary rhythm locking were obtained from all 8889 segments. (2) Among these cardiopulmonary rhythm locking segments, awakening accounted for 7.47%, REM sleep accounted for 3.96%, N1 sleep accounted for 4.57%, N2 sleep accounted for 26.07%, and N3 sleep accounted for 57.93%. (3) The most common m:n is 4:1, followed by 7:2. (4) The percentage of cardiopulmonary rhythm locking segments in the corresponding sleep stage was 2.88% (awakening), 2.10% (REM sleep), 2.67% (N1 sleep), 6.00% (N2 sleep), and 19.23% (N3 sleep). For combinations of N and Th with other values, N3 sleep also accounts for the highest proportion. The cardiopulmonary rhythm locking mainly occurs during N3 sleep in healthy subjects of the whole night sleep.