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Using a 2-factor 6×3 factorial experimental design and the MultistageEvaluation Scale（MES）to estimate the respiratory sensation

we systematicallystudied in 17 healthy young men the physiological and psychological effects of sixlevels of suprathreshold added resistive loads

appliedeparately to eitherinspiration or expiration

or throughout the breathing cycle.We observed that（1）no matter what phase of the breathing cycle was impeded

mask cavity pressureswingas well as total external respiratory workrate（r）was a curvilinearfunction of the total resistive load added（R

T

）

which exhibited an upwardconvexity;（2）the perceived magnitude（PM）of the respiratory sensation estimatedby using MES(S

MES

)was directly related to intensity of the physiologicalstimulus and indirectly related to the intensity of the resistance added;and（3）under different loading conditions

S

MES

was a curvilinear function of theintensity of the physiological stimulus

which exhibited an upward concavity.These results suggest that when we derive the standards of allowable resistancefor respiratory protective equipment

in addition to the total load intensity

theimportance of the ratio between inspiratory and expiratory resistance should alsobe considered.