The relation between tidal volume and inspiratory and expiratory times during steady‐state carbon dioxide inhalation in man

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Abstract
Steady-state hyperpnea during rest was induced in normal subjects of both sexes by CO2 inhalation usually in high O2, but sometimes in low PaO2 [arterial O2 partial pressure] .apprx. 200 and 55 torr, respectively). The relations between mean tidal volume .hivin.VT and mean times for inspiration .hivin.TI and expiration .hivin.TE were satisfactorily divided into lower and upper parts (ranges 1 and 2) in 19 of 33 experiments using an objective least-squares method, and polynomials were fitted separately to each of the following pairs of variables .hivin.VT,lower, .hivin.TI; .hivin.VT,lower, .hivin.TE; .hivin.VT,upper, .hivin.TI; .hivin.VT,upper, .hivin.TE. The breakpoints occurred when .hivin.VT was about 1/3 of vital capacity, but there was much variation between subjects. In range 2, .hivin.VT was inversely related to .hivin.TI and .hivin.TE, and there appeared to be linkage between .hivin.TI and .hivin.TE, all as described by Clark and Euler. The relation suggested by Hey, Lloyd, Cunningham, Jukes and Bolton over range 2 was not confirmed. The main part of the relation described by Hey is concerned with range 1. Here the relation between .hivin.VT and .hivin.TI was variable; slight, but significant negative coorrelation predominated. .hivin.VT was strongly and inversely related to .hivin.TE, and plots of (.hivin.TE - .hivin.TI) against .hivin.VT over both ranges showed even less scatter. .hivin.TE is probably related to .hivin.VT through 2 mechanisms, one involving a link with TI and another prominent one being quite independent of TI. Most changes of respiratory frequency in normal man are brought about by change of TE rather than TI. There is no region of constant frequency as implied by Clark and Euler.