Fig 6.

The effect of fentanyl (FEN) on cardiorespiratory responses to PBG after blocking histamine H₁ and H₂ receptors. A, a representative recording showing that fentanyl still converted the PBG (4.5 μg/kg)-induced RSB into an apnea after the blockage of histamine H₁ and H₂ receptors by diphenhydramine and ranitidine (DPH/RTD). The traces from the top to bottom are arterial blood pressure (BP) and tidal volume (V_T). B, the corresponding group data. N = 7; mean ± SE. Note: all the cardiorespiratory responses to PBG were significant (P < 0.01). * P < 0.05 and ** P < 0.01 compared with before fentanyl. HR, heart rate; MBP, mean arterial blood pressure; T_E, expiratory duration.