A quantitative description of the pattern of breathing during steady‐state CO2 inhalation in man, with special emphasis on expiration

Abstract

Quantitative data on the breathing pattern of normal men and women were used to derive expressions that are based on known physiological mechanisms. The relations between the applied chemical drive to breathing (expressed as .DELTA.PA, CO2 in high O2) and the several components of the volume-time patterns described in the companion paper were examined. Neither mean tidal volume (.hivin.VT) nor mean inspiratory nor mean expiratory times (.hivin.TI, .hivin.TE) were uniquely related to the chemical drive across the breakpoint, which could be demonstrated in 2 and suspected in the 3rd of these plots. Mean inspiratory flow (.hivin.VT/.hivin.TI) was linearly related to PA, CO2 over the whole range and, like minute ventilation .**GRAPHIC**. showed no breakpoint. The mean relation was .hivin.VT/.hivin.TI = 0.11 (PA, CO2-35.2). .hivin.VT/.hivin.TI was highly correlated with .**GRAPHIC**. in individuals with healthy lungs and under relatively stable conditions of compliance and resistance it may be accepted as a wholly inspiratory alternative to .**GRAPHIC**. as an index, on the efferent side, of the total prevailing chemical drive. The description of the relation between .hivin.TI and .hivin.VT was essentially the same as that of Clark and Euler: in range 1, .hivin.TI = either 1.29-0.07 .hivin.VT or the constant 1.24 S; and in range 2, .hivin.TI = 0.65/(.hivin.VT-0.88) + 0.59. Expiration was described by an equation based on the inverse linkage between .hivin.TE and chemical drive and the direct link between both mean and breath-by-breath values of TI and TE: .hivin.TE = p.hivin.TI + q/(drive-r) in which p was 0.64 .+-. 0.09, q was 11.1 .+-. 2.64 s (torr CO2)-1 and r was -2.73 .+-. 1.09 torr CO2. All 3 parameters were necessary for an adequate description. The 1st term of the TE equation may represent influences related to lung volume exerted through the vagus, and the 2nd may represent the effects of over-all chemical stimulation exerted through other pathways.