Influence of mental stress on breathing pattern parameters in students with different circadian typology

The work objective is to analyze external breathing reactions in students with different chronotypes under mental stress generated by an information load in the morning, in the afternoon and in the evening. Materials and Methods. A total of 160 students were examined (38 «larks», 64 «doves» and 58 «owls»). Circadian rhythms (chronotypes) were determined by the morningness-eveningness questionnaire (MEQ), developed by James A. Horne and Olov Ostberg (A.A. Putilov's version). Spirography test was used to record external respiration just before and after cognitive load (attention tests and mental arithmetic) in the morning (from 7:30 to 9:00), in the afternoon (from 13:00 to 14:30) and in the evening (from 18:00 to 19:30). The changes of volume and frequency parameters of breathing pattern were evaluated. Results. The most significant changes in breathing pattern at cognitive loads were observed in «larks» in the morning and in the afternoon. In the morning their respiratory frequency increased but their respiratory minute volume decreased due to tidal volume reduction. In the afternoon their respiratory minute volume increased due to deviations of spirogram frequency parameters. «Doves» occupied the second place in the variability of respiratory reactions. In this group the authors observed the increase of respiratory frequency and significant decrease of respiratory minute volume caused by tidal volume reduction during daytime cognitive loads. Insignificant variations of respiratory minute volume at cognitive loads were observed among «owls» in the morning and in the evening. Conclusion. The data obtained indicate the specificity of regulatory influence on external breathing and the variability of basal breathing patterns under cognitive loads in students with different chronotypes.