Chronobiological aspects of bronchial tone.

The aim of the investigation was to demonstrate the existence of cyclic variations of bronchial tone, correlated with the increase of vagal tone during nocturnal hours and with the increase of adrenergic tone in the late morning and afternoon. Twenty-five healthy subjects were tested, utilizing forced expiration curve (V/V loop), Raw and SGaw. We did not detect a statistically significant rhythm for FVC, FEV1, PEF, because they are effort-dependent parameters. On the contrary, we demonstrated significant fluctuations for V max50, FEF25.75 (acrophase in the later morning and early afternoon), for Raw (acrophase in late evening) and for SGaw (Acrophase in antiphase with Raw); these parameters are effort-independent as well as direct and sensitive indexes of the tone of peripheral and central airways.