QUALITATIVE ASPECTS OF EXERTIONAL BREATHLESSNESS IN CHRONIC AIR-FLOW LIMITATION - PATHOPHYSIOLOGIC MECHANISMS

We compared qualitative aspects of the sensory experience of exertiona l breathlessness in normal subjects and in patients with chronic airfl ow limitation (GAL) and sought a physiologic rationale for these. Twel ve patients (66 +/- 2 yr of age, mean +/- SEM) with severe CAL (FEV(1) = 37 +/- 5% predicted) and 12 age-matched normal subjects (FEV(1) = 1 03 +/- 5% predicted) were studied. Perceived inspiratory difficulty (B org(IN)), inspiratory effort (esophageal pressure expressed as a fract ion of maximal esophageal pressure at isovolume [Pes/PImax]), breathin g pattern, and operational lung volumes (end-expiratory/inspiratory lu ng volumes [EELV/EILV]) were measured during symptom-limited increment al cycle exercise testing and compared at a standard VO2 of 50% predic ted maximum in normal subjects and in patients with GAL. Qualitative d escriptors of breathlessness were selected immediately after exercise. Breathlessness was qualitatively different between normal subjects an d patients with GAL. Both normal subjects and patients with CAL chose descriptors of increased ''work/effort'' and ''heaviness'' of breathin g; however, only patients with CAL consistently chose descriptors deno ting ''increased inspiratory difficulty'' (75%), ''unsatisfied inspira tory effort'' (75%), and ''shallow breathing'' (50%). Stepwise regress ion analysis identified the ratio of Pes/PImax to VT/predicted VC as t he strongest correlate of standardized Borg(IN) (n = 24, r = 0.86, p < 0.001). This latter measurement, which reflects the relationship betw een effort and ventilatory output, correlated strongly with dynamic EE LV/TLC at isotime (r = 0.78, p < 0.001). In conclusion, the qualitativ ely discrete respiratory sensations of exertional inspiratory difficul ty peculiar to patients with CAL may have their origins in thoracic hy perinflation and the resultant disparity between inspiratory effort an d ventilatory output.