Control of expired CO2 level and minute-ventilation during a hyperventilation challenge for asthmatics.

Hyperventilation of cold dry air initiates bronchospasm in most if not all asthmatics. The hyperventilation challenge is a useful means of studying asthma and the evaluation of anti-asthma drugs and treatments; two key elements of such a challenge are the means of achieving a target minute-ventilation and the maintainance of constant arterial CO2 levels during hyperventilation. The author describes a simple cold air eucapnic hyperventilation challenge which allows a subject to hyperventilate to a predetermined target minute-ventilation whilst maintaining a constant expired level of CO2.