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1. Quantitative data on the pattern of breathing in normal men and women (Gardner, 1977) have been used to derive expressions that are based on known physiological mechanisms.

2. The relations between the applied chemical drive to breathing (expressed as P_{A, CO2} in high O₂) and the several components of the volume—time patterns described in the companion paper were examined. Neither mean tidal volume (_T), nor mean inspiratory nor mean expiratory times (_I, _E) were uniquely related to the chemical drive across the breakpoint, which could be demonstrated in two and suspected in the third of these plots.

3. Mean inspiratory flow (_T/_I) was linearly related to P_{A, CO2} over the whole range and, like minute ventilation (
), showed no breakpoint. The mean relation was _T/_I = 0·11 (P_{A, CO2} — 35·2). _T/_I was highly correlated with
; in individuals with healthy lungs and under relatively stable conditions of compliance and resistance it may be accepted as a wholly inspiratory alternative to
as an index, on the efferent side, of the total prevailing chemical drive.

4. The description of the relation between _I and _T was essentially the same as that of Clark & Euler (1972): in range 1, _I = either 1·29 - 0·07 _T or the constant 1·24 sec, and in range 2, _I = 0·65/(_T — 0·88) + 0·59.

5. Expiration was described by an equation based on the inverse linkage between _E and chemical drive and the direct link between both mean and breath-by-breath values of T_I and T_E: _E = p_I + q/(drive — r) in which p was 0·64 ± 0·09, q was 11·1 ± 2·64 sec. (torr CO₂)^-1 and r was -2·73 ± 1·09 torr CO₂. All three parameters were necessary for an adequate description.

6. It is argued that the first term of the T_E equation represents influences related to lung volume exerted through the vagus, and that the second represents the effects of over-all chemical stimulation exerted through other pathways.

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				A. JUBRAN, B. J. B. GRANT, and M. J. TOBIN Effect of Hyperoxic Hypercapnia on Variational Activity of Breathing Am. J. Respir. Crit. Care Med., October 1, 1997; 156(4): 1129 - 1139. [Abstract] [Full Text] [PDF]