[Dyspnea--disproportion between expense and success].

There is no comprehensive theory for the various reasons for dyspnea. It is proposed to regard the disproportion between "input" and "output" as the common cause of the various forms. This disproportion may be located between psychological drive and neural response or between neural excitation and muscular response or between muscular activity and ventilatory effect. Thus insufficient perfusion of respiratory muscles--as in cardiac failure--may cause dyspnea. Arterial oxygen pressure as the criterion of sufficient ventilation is misleading in anemia and CO-poisoning, so that there is no dyspnea despite of insufficient O2-transport.