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The effects of added airflow resistance（0.3-3 kPa·L.（-1）·s）on therespiratory flow rate and mask cavity pressure as well as the subject’s perceptionwere investigated in 114 pilots under light physical activities(250kg·m·min

-

).A correlation and stepwise regression analysis was made to reveal the objectivephysiological indexes which could reflect the effects of the added resistance

and aprobit analysis was made to confirm the permissible levels for added resistance.The results suggest that both mask cavity pressure swing（P） and extra respiratorywork per unit ventilation(W.L

-1

)could be used as the objective physiological

indexes for respiratory discomfort

and the former may be more applicable.If Pdoes not exceed 0.60kPa or if W L

-1

does not exceed 0.047 kg·m L

-1

90％ ofthe subjects will feel no respiratory discomfort;if P does not exceed 0.77kPa orW·L

-1

not exceed 0.061 kg·m·L

-1

90％ may only feel less than mediumrespiratory discomfort.The problem concerning the revision of the currentstandards of respiratory resistance of aircraft oxygen equipment is discussed inthis paper.