Table 1.

Physiologic ratios highly correlated with increasing dyspnea throughout exercise

Physiologic ratio	Response during exercise and significance
VE/MVC [103, 104]	Ventilation increasing to maximum capacity
Pes/Pes,max [6, 105]	Respiratory effort approaches maximum volitional value
VT/IC [88, 89, 106]	Mechanical constraints on tidal volume become critical
EMGdi/EMGdi,max [19, 20]	Tidal IND to the diaphragm approaches maximum volitional value

EMGdi diaphragmatic electromyography, EMGdi/EMGdi,max inspiratory neural drive, IC inspiratory capacity, IND inspiratory neural drive, MVC maximum ventilatory capacity, Pes esophageal pressure, Pes,max maximum esophageal pressure, V_T tidal volume, V_E minute ventilation