Fig. 3.

Peak inspiratory flow was robustly decreased across several doses of heroin and fentanyl. I.v. doses of heroin (300, 600, or 1200 µg/kg; n = 10 female, 11 male) or fentanyl (12, 25, or 50 µg/kg; n = 10 female, 10 male) decreased peak inspiratory flow. Each dose of heroin elicited decreases in peak inspiratory flow, with higher doses producing prolonged effects for up to 60 minutes and no difference between males and females over time (A). Peak inspiratory flow was maximally decreased to ∼45% of baseline following heroin administration, which was significantly different from vehicle for all doses; overall, females had significantly lower values than males (B). Fentanyl administration elicited shorter-lasting decreases in minute ventilation, with higher doses producing prolonged effects for up to 30 minutes and no difference between the sexes (C). There were also robust decreases in peak inspiratory flow following fentanyl independent of sex, with drops to ∼50% of baseline that were significantly different from vehicle for all doses (D). Data are expressed as mean ± S.D. in percentage of baseline in 5-minute bins over −20 to 60 minutes postadministration (A and C) or lowest 5-minute bin value within 25 minutes postadministration (B and D). Dashed line indicates average baseline measure. Filled-in symbols indicate significant difference, P < 0.05, from vehicle group, with gray color indicating overshoot/recovery (i.e., not respiratory depression). *P < 0.05; **P < 0.001, compared with vehicle. ♀, female; ♂, male.