Apparatus for relieving dyspnoea in an ambulatory exercising subject comprises a housing to be worn on the subject, and within which a variable speed air blower motor is located for delivering an air supply to the subject through a mouthpiece at a pressure similar to average intrinsic positive end-expiratory pressure of the subject. A pressure transducer in the mouthpiece monitors the pressure during breathing cycles of the subject, and a control circuit determines the average intrinsic positive end-expiratory pressure of the subject over five breathing cycles. The control circuit operates the air blower motor for delivering the air supply to the subject at a pressure similar to the determined average intrinsic positive end-expiratory pressure.
