Fraction of air coming from conductive airways has the negative balance in heat dissipation after maximal effort exercise—a physiological basis for exercise-induced bronchoconstriction

Abstract

Exhaled breath temperature (EBT) has recently been used as a tool to assess the level of inflammation in airways. The newest technology can also assess EBT coming from different fractions of exhaled air (fEBT). We aimed to assess the changes in fEBT after a maximal cardio-pulmonary exercise test in healthy athletes. Forty-four healthy professional athletes (two females) were included. Their mean (±SD) age was 22.9 ± 4.8 years. An innovative device (FractAir®) was used for fEBT measurement, dividing the exhaled air into three fractions (V1, V2 and V3) coming from different parts of the lungs; the large airways (anatomic dead space), conductive airways (functional dead space) and the peripheral part. For V3 an EBT point measured at 1200 ml of exhaled volume was used to obtain the information about the distant parts of the lungs while eliminating the difference in the volume of total exhaled air before and after the exercise. The difference (temperature gain) between the starting and peak EBT for each fraction was also calculated. The peak fEBT values before and after exercise did not differ significantly (p > 0.05 for all three fractions). Temperature gain analysis for each fEBT showed a significant fall after exercise for V2 (1.71 °C ± 0.43 versus 1.38 °C ± 0.50, p < 0.001), but not for the other two fractions (p > 0.05 for both). The lower heat emission from this part of the airway (conductive airway) after exercise could mean that during hyperventilation heat emission is increased in this specific fraction. We can conclude that the changes of fEBT after physical exercise are not linear. They affect different fractions of the lungs in different ways, and the relationship between flow and volume on one side and the temperature of exhaled air on the other can vary significantly.