Coupling of dyspnea perception and tachypneic breathing during hypercapnia

► We measured thresholds for air hunger and respiratory frequency during hypercapnia. ► The thresholds were taken as the end-tidal CO2 fraction. ► Air hunger and respiratory frequency started to increase rapidly at the threshold. ► The threshold for respiratory frequency was correlated with that for air hunger. ► The thresholds for air hunger and respiratory frequency showed good agreement.