BREATH-TO-BREATH RELATIONSHIPS BETWEEN RESPIRATORY CYCLE VARIABLES INHUMANS AT FIXED END-TIDAL PCO2 AND PO2

This study examined the statistical properties of breath-to-breath var iations in the inspiratory and expiratory volumes and times during res t and light exercise. Sixty data sets were analyzed. Initial data and residuals after fitting time-series models were examined for 1) sustai ned periodicities with use of spectral analysis, 2) temporal changes i n signal power with use of evolutionary spectral analysis, and 3) auto - and cross correlations with use of a portmanteau test. The major fin dings were as follows: I) no sustained periodic components were detect ed; 2)temporal changes in signal power were normally present, but thes e did not affect significantly the results from time-series modeling; 3) for all variables, a simple autoregressive moving average (ARMA) AR (1)MA(1) model generally described the autocorrelation; 4) considerabl e cross correlation remained between residuals from the AR(1)MA(1) mod el; 5) relationships between variables could be described by using a m ultivariate time-series model; 6) residual fluctuations in end-tidal P CO2 had little influence; and 7) responses were broadly similar betwee n rest and exercise, although some quantitative differences were found . The multivariate model provides a description of the structure of th e interrelationships between cycle variables in a quantitative and a q ualitative form.