A number of physiologic functions and parameters have circadian variations. Pulmonary flow and resistance are not an exception. Our study investigates the day-time variations of the major PFT variables by comparing the mean values of those in nine time intervals- from 8 am to 4 pm.
The study population consisted of all PFT’s done in the study period (3/1997 to 5/2002, N=4835), which were divided into nine subgroups according to the time of the day the test was performed (TableTable.
Demographic characteristics of the studied populationSubgroup (time of PFT)Number of studies- nMale/female ratioAge- mean (SD)BMI-mean (SD)8 (8 am-8:59 am)4260.5257.0 (16.5)28.0 (6.3)9 (9 am-9:59 am)7140.4558.7 (16.4)28.1 (6.5)10 (10 am-10:59 am)6690.4659.3 (16.7)28.2 (6.9)11 (11 am-11:59 am)5200.4958.8 (18.1)27.5 (6.1)12 (12 pm-12:59 pm)4130.4961.3 (15.9)27.3 (6.2)13 (13 pm-13:59 pm)8120.4859.7 (17.4)27.5 (6.5)14 (14 pm-14:59 pm)7320.4559.3 (17.2)28.3 (6.9)15 (15 pm-15:59 pm)4410.4155.5 (18.6)28.1 (6.8)16 (16 pm-16:59 pm)1080.4755.7 (16.7)27.8 (6.2)
PFT- pulmonary function test SD- standard deviation). One-way analysis of variance with Bonferroni pairwise comparisons was applied to evaluate the differences in FEV1, FVC and TLC. Kruskal-Wallis ANOVA was used for the FEV1/FVC ratio with subsequent Dunn’s pairwise multiple comparison procedures. A p-value of 0.05 or less was considered statistically significant. Only one test of a particular individual was allowed into the same subgroup, so the independence of the data in each group was ensured.
The lowest median FEV1/FVC ratio was found in the 12 pm group (72.8%), the highest- in the 3 pm group (78.6%) [Figure]. Therefore, an absolute difference of 5.8% was detected between them(P<0.05). Similarly, the lowest FEV1 (1.81 l) was found in the 12 pm group and the highest- in the 3pm and 4 pm groups (2.12 and 2.17 l). Those differences were again highly statistically significant (p-values <0.001 and 0.035). The PEF (peak expiratory flow) variability was similar and also statistically significant. FVC showed a similar trend with the lowest value in the 12 pm group and the highest at 4pm. However, no statistically significant variation was detected in the pairwise comparison analysis.
During working hours, the airway resistance appears to be the most prominent at noon and reaches its minimum around 4-5 pm.
Along with its pure academic value, this clinically significant variation of the air flow characteristics may have some practical implications, e.g. timing the administration of long-acting bronchodilators, electively extubating patients in the later afternoon hours.
B.I. Medarov, None.