Influence of small mechanical loads of variability of breathing pattern.

The effect of low-level mechanical loading on the variability of the human breathing pattern was examined using a small elastic (E) load (approximately 10 cmH2O/1) and a small flow-resistive (R) load (approximately 3 cmH2O.1(-1).s) to approximately halve and double the normal respiratory mechanical time constant. The pooled responses from six subjects showed 1) E loading increased the mean estimated work rate (W); 2) R loading increased the mean tidal volume (VT), inspiratory duration (TI), and estimated W, and decreased mean breathing frequency (f) and mean inspiratory flow (VT/TI), while reducing the variabilities of f and VT/TI; 3) E loading significantly reduced the frequency of occurrence of large breaths from the control state, whereas the effect of R loading on this phenomenon was smaller and not significant; and 4) R loading tended to increase an E loading to decrease the significant VT:TI rank correlation seen in the nonloaded state. The influence of loading on the distributions of VT and f became apparent in the tendency of breath-by-breath values to cluster closer to the minimum of the W-VA-pattern parameter surface.