Modelling the dynamic ventilatory response to hypoxia in normal subjects.
We have developed a mathematical model to describe the dynamic ventilatory response to hypoxia. The ventilatory response to both transient (two to three breaths nitrogen) and 3 min step change hypoxic stimuli were measured in ten normal subjects during moderate exercise (oxygen consumption 0.96 +/- 0.08 1 min-1). The simplest model relating ventilation to ear oxygen saturation which adequately described the responses in all subjects consisted of two linear differential equations in parallel; both using the fall in oxygen saturation as input, and with the outputs summed to give the rise in ventilation. One equation had a fast time constant (< 3 sec), and the other a slow time constant. Non-linear terms included were (i) a "saturating" effect, similar to that described by the Michaelis-Menten equation, reducing the gain of the equation with the slow time constant as oxygen saturation falls, and (ii) "inhibition" or "potentiation" of the gain of the equation with a slow time constant as the output of the fast time constant equation increased. Repeated measurements in four subjects showed intra- and inter-subject variability for all parameters, with significant between-subject variability for the gain of the fast time constant equation. The final model structure is similar to that describing the peripheral chemoreceptor-mediated hypoxic ventilatory response in anaesthetized cats.
Kirby
T P
TP
Rayne Laboratory, Unit of Respiratory Medicine, University of Edinburgh, Scotland, U.K.
Wraith
P K
PK
De Cort
S C
SC
Airlie
M A
MA
Hill
J E
JE
Carson
E R
ER
Flenley
D C
DC
Warren
P M
PM
D000328:Adult; D003198:Computer Simulation; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008954:Models, Biological