Fig. 1

Dyspnea model in COVID-19. The increase in dyspnea correlates with the increase in ventilation. In the early stages of COVID-19 the alterations are mainly due to alterations of gas exchange and do not cause major changes in respiratory mechanics and mechanical constraints (normal elastance), with a good relationship between respiratory drive and mechanical coupling, and dyspnea will be described as increased work/effort, in the advanced stages there are alterations of respiratory mechanics with mechanical constraint (high elastance) and neuromechanical dissociation and dyspnea will be described as air hunger or difficult inspiration. If hypoxemia is not accompanied by increased ventilation, it will not cause dyspnea and it could be defined “happy or silent hypoxia”. NMD neuromechanical dissociation, V/Q ventilation/perfusion, IND inspiratory drive