INTERRELATIONSHIP OF BREATH COMPONENTS IN NEIGHBORING BREATHS OF NORMAL EUPNEIC SUBJECTS

To determine the fraction of variational activity that is correlated o n a breath-to-breath basis from uncorrelated random fluctuations, we p erformed autocorrelation analysis in 33 normal subjects during resting breathing. A calibrated inductive plethysmograph was used to nonobtru sively record 700 breaths in each subject. The group mean autocorrelat ion coefficients at a lag of 1 breath for each of the three primary br eath components, tidal volume (VT), inspiratory time (TI), and expirat ory time (TE), were significantly different from zero (p < 0.001). The autocorrelation coefficients for VT, 0.295 +/- 0.148 (SD), and TE, 0. 259 +/- 0.121, were greater than that for TI, 0.201 +/- 0.135 (p < 0.0 01 and p < 0.01, respectively). The autocorrelation coefficients for e ach breath component remained significant for similar to 3 consecutive breaths (p < 0.001), indicating the presence of ''short-term memory.' ' Cross-correlation analysis revealed significant interrelationships ( p < 0.001) for all component irrespective of which component was leadi ng or following, with the exception of the pairing of VT in the leadin g breath and TI in the subsequent breath. In conclusion, in resting he althy subjects breath components display considerable breath-to-breath variability that is not completely random in nature, but which, inste ad, has a significant fraction of structured correlated variational ac tivity.