Daily variations of spirometric indexes and maximum expiratory pressure in young healthy adults

In order to document possible variations in the main spirometric indexes in young healthy adults due to the time of the day, we performed standard and complete spirometric measurements at three different hours of the same day (8 am, 4 pm and 12 am) in 33 healthy, non-smoking young volunteers of both sexes. An index of airway resistance was also calculated. We confirm a general worsening of spirometric indexes at night-time compared to daily hours. This result also includes the main effort-independent indexes which were not previously measured. Maximum expiratory pressure does not show daily variations, while an index of respiratory system resistance exhibits a progressive increase from morning to night.