Variability of respiratory rhythm and pattern of breathing changes in patients with bronchial asthma and cold airway hyperresponsiveness

The role of control of breathing in modulation of bronchomotor tonus has been studied very little. It is unknown if there is a correlation between cold airway hyperresponsiveness (CAHR) and changes of respiration regulation. The aim of the study was to reveal the changes in respiratory rhythm and pattern of breathing and their correlation with bronchoconstrictor reaction to cold air hyperventilation in bronchial asthma (BA). 35 patients with BA and 6 healthy persons were examined. The group of BA patients was divided according to whether there was CAHR (14 patients) or there was not any (21 patients). CAHR was defined by 10% FEV 1 fall after 3-minute isocapnic cold air (-20°C) hyperventilation. Respiratory rhythm variability was evaluated by the value of mean-square deviation of respiration cycle duration during 15-minute interval. In result, a big variability of respiratory rhythm in BA patients with CAHR was revealed. Mean-square deviation was 0.86±0.13 vs. 0.56±0.06 in patients without CAHR (p<0.05). Significant changes in pattern of breathing in patients with CAHR were registered: inspiration shortening (0.37±0.01 s vs. 0.41±0.01 s in healthy persons, p<0.01), expiration lengthening (0.63±0.01 s vs. 0.59±0.01 s, p<0.01, respectively) at the absence of established differences in FEV 1 between the groups. There was a direct correlation between FEV 1 and tidal volume in healthy subjects and asthmatics without CAHR (r=0.89 and r=0.75, respectively, p<0.05). Patients with CAHR did not have such a correlation. The obtained data suggested a distinct interrelationship between the control of breating and cold airway hyperresponsiveness in BA patients.