Perception and subjective ratings of multiple breath resistive loads in males and females

Resistive (R) load magnitude estimation (ME) and subsequent subjective ratings were measured over multiple breaths in healthy subjects in two experiments. It was hypothesized that multiple breaths against a small resistive load will result in a decreased perceived load magnitude as the number of inspiratory efforts increase. It was further hypothesized that multiple breaths against large resistive loads will increase the perceived load magnitude as well as subjective ratings with increased breath number.;Subjects were screened by the experimenter, seated in a sound isolated room and respired through a non-rebreathing valve, the inspiratory port connected to the loading manifold. For study 1, the subject inspired to a peak airflow target for each breath. Each R load and no-loads were presented for 10 continuous breaths. The subject estimated the load at breath 1, 5, and 10 using a modified Borg scale. Each load was presented in a randomized block 3 times each in a single experimental session. For study 2, each R load and no-loads were presented for 20 continuous breaths. The subject estimated the load at breath 1, 10, and 20 using a modified Borg scale. Each load was presented in a randomized block 3 times each in a single experimental session.;For study 1, there was no significant sex group difference between the ME for breath 1 and 10 for small R loads, but a significant sex group difference for large R loads. The ME for males did not change between breath 1 and 10 for the small load magnitudes, but decreased with large loads. The ME for the 10 breath of the large R load was greater than the 1st breath for females. Males estimated the large R load on the 1st breath the same as females but the ME on the 10th breath was significantly less for males compared to females. For study 2, there was no significant sex group difference between the ME for breath 1 and 20 for small R loads, but a significant sex group difference for large R loads. The ME for males did not change between breath 1 and 20 for the small load magnitudes, but decreased with large loads. The ME for the 20th breath of the large R load was greater than the 1st breath for females. Males estimated the large R load on the 1st breath the same as females but the ME on the 20th breath was significantly less for males compared to females. Subjective responses of fear, fear of suffocation, happiness, chest pressure, faintness, dizziness, fear of losing control, trembling, tingling and unreality were significantly greater for females.;For study 1, these results demonstrate that magnitude estimation of large resistive loads with a sustained 10-breath trial elicits a significant increase in ME for females, but a significant decrease in males. The increase in ME may represent increased respiratory discomfort. For study 2, these results demonstrate that magnitude estimation of large resistive loads with a sustained 20-breath trial elicits a non-significant increase in ME in females, but a significant decrease in ME for males. The decrease in ME may represent increased adaptation to load. Loads larger than 15 cmH2O/L*s-1 elicited significant negative affect.