Breathing pattern and subjective responses to small inspiratory resistance during submaximal exercise

Breathing patterns and subjective responses to small resistances were investigated in seven subjects during moderate exercise. Inspiratory resistances of 0.15 (R1), 0.25 (R2) and 0.30 (R3) kPa.l-1.s were tested against control of 0.06 kPa.l-1.s with no added resistance. Subjective responses to small inspiratory resistances were evaluated through whole experiments including periods before and after exercise, herein called SNS. Average SNS significantly increased above the R2 condition. Above the R2 condition, significant changes in the breathing components of volume, flow and timing were also observed during exercise. SNS grew as a power function of peak inspiratory pressure (P(imax)) measured during exercise within such small range of stimulation less than the R3 condition and individual differences in the relationship between SNS and P(imax) were observed. All subjects felt at least some discomfort below the resistance of R3 and two subjects felt it below around R1 condition. It was suggested that breathing pattern was selected to limit peak pressure at the R3 condition by further increasing inspiratory work for a breath and this tendency was reinforced in load-sensitive subjects with longer inspiratory time and lower peak flow rate. We concluded that breathing patterns depend mainly on peak work, especially in load-sensitive individuals, which is likely to be one of the primary determinants of a worker's tolerance to respirators.