Influence of small mechanical loads of variability of breathing pattern

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Abstract
The effect of low-level mechanical loading on the variability of the human breathing pattern was examined using a small elastic (E) load (.apprx. 10 cmH2O/l) and a small flow-resistive (R) load (.apprx. 3 cmH2O .cntdot. l-1 .cntdot. s) to approximately halve and double the normal respiratory mechanical time constant. The pooled responses from 6 subjects showed the following: E loading increased the mean estimated work rate (.ovrhdot.W); R loading increased the mean tidal volume (VT), inspiratory duration (TI) and estimated .ovrhdot.W, and decreased mean breathing frequency (f) and mean inspiratory flow (VT/TI), while reducing the variabilities of f and VT/TI; 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 R loading tended to increase and 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 .ovrhdot.W-.ovrhdot.VA[alveolar ventilation]-pattern parameter surface.