The autonomic nervous system (ANS) is one of the effector pathways for circadian variation of many physiological parameters. Autonomic tone and airways caliber have been reported to exhibit circadian variation in separate studies. A simultaneous investigation of heart rate variability (HRV) and airway caliber might ascertain how airway caliber is modulated by autonomic tone. This study was planned to identify the variations in airway caliber and autonomic function tone during a 24-hour span. A total of 56 healthy male subjects with almost similar daily routines were studied. Time domain, frequency domain and nonlinear analysis of R-R interval from 5 min electrocardiogram (ECG) was done seven times during the daytime wake span at 3-hour intervals starting at 05:00 h in the morning until 23:00 h in the night. Simultaneously peak expiratory flow rate (PEFR) was determined using a mini Wright’s peak flow meter. Rhythmometric analysis was done for PEFR and HRV parameters. Significant circadian variation in low frequency (LF) and high frequency (HF) variance was identified in this group of healthy subjects. The circadian rhythm of LF variance was characterized by a gradual increase and corresponding reciprocal change in HF variance from morning until night. The LF/HF ratio and SD2/SD1 ratio reflecting sympatho-vagal balance showed low to high values from morning to evening. The acrophase of the PEFR temporal pattern is similar to that of LF power and almost opposite in phase to that of HF power. PEFR is positively correlated with LF power. The circadian rhythm of airway caliber co-varies with cardiac autonomic tone. It appears that the temporal pattern of cardiac autonomic tone precedes in time that of airways caliber, thereby suggesting the latter operates under the modulatory effect of the 24-hour pattern in sympatho-vagal balance.

自主神经系统（ANS）是许多生理参数的昼夜变化的效应途径之一。据报道，自主音调和气道口径在单独的研究中显示出昼夜节律变化。同时研究心率变异性（HRV）和气道口径可能会确定自主口气如何调节气道口径。计划进行这项研究以发现24小时内气道口径和自主功能音调的变化。总共研究了56名健康男性受试者，他们的日常活动几乎相似。白天起床时间跨度，频域和从5分钟心电图（ECG）开始的RR间隔的非线性分析在白天的醒来时间段内进行了7次，间隔为3小时，时间为早晨05:00至晚上23:00。同时使用微型赖特峰流量计测定呼气峰流速（PEFR）。对PEFR和HRV参数进行了韵律分析。在这组健康受试者中，低频（LF）和高频（HF）方差的昼夜节律变化明显。低频方差的昼夜节律的特征是从早到晚，高频方差的逐渐增加和相应的相互变化。反映交感迷走神经平衡的LF / HF比值和SD2 / SD1比值从早到晚显示从低到高的值。PEFR时间模式的顶相类似于LF功率，并且与HF功率的相位几乎相反。PEFR与LF功率呈正相关。气道口径的昼夜节律与心脏自主神经张力有关。