Table 2.

Changes in baseline parameters during various stages of the experimental protocols

Parameter	Group	Pre	Initial max	Pre H-H	H-H max	Post-H-H max
Frequency (breaths/min)	Vehicle	95 ± 4	99 ± 5	93 ± 3	176 ± 8†	81 ± 4*
	Morphine	88 ± 6	94 ± 7	108 ±5*	138 ± 9†‡	127 ± 9*,‡
Tidal Volume (mls)	Vehicle	2.65 ± 0.02	2.85 ± 0.17	2.91 ± 0.23	5.22 ±0.44†	3.21 ± 0.24
	Morphine	2.51 ± 0.17	1.82 ± 0.11*,‡	2.43 ± 0.31	5.20 ± 0.37†	2.85 ± 0.21
Minute Volume (mls/min)	Vehicle	245 ± 9	254 ± 10	262 ± 10	918 ± 64†	253 ± 14
	Morphine	229 ± 13	164 ± 6*,‡	272 ± 22	726 ± 22†‡	342 ± 29†‡
Inspiratory Time (sec)	Vehicle	0.21 ± 0.02	0.22 ± 0.01	0.21 ± 0.01	0.15 ± 0.01†	0.23 ± 0.01
	Morphine	0.22 ± 0.02	0.34 ± 0.03*,‡	0.28 ± 0.03*	0.20 ± 0.02†‡	0.21 ± 0.02
Expiratory Time (sec)	Vehicle	0.43 ± 0.03	0.40 ± 0.03	0.45 ± 0.04	0.19 ± 0.02†	0.53 ± 0.05*
	Morphine	0.45 ± 0.04	0.32 ± 0.03	0.27 ± 0.02*,‡	0.24 ± 0.02	0.34 ± 0.03*,‡
End Inspiratory Pause (msec)	Vehicle	6.6 ± 0.4	6.7 ± 0.4	6.6 ± 0.5	6.2 ± 0.4	6.4 ± 0.4
	Morphine	6.4 ± 0.5	15.7 ± 1.7*,‡	16.5 ± 2.2*,‡	6.5 ± 0.5†	8.8 ± 0.7*,‡
Peak Inspiratory Flow (mls/sec)	Vehicle	20 ± 2	19 ± 2	21 ± 1	47 ± 3†	20.9 ± 1.2
	Morphine	18 ± 1	10 ± 1*,‡	14 ± 2*,‡	38 ± 4†	23.2 ± 1.9
Peak Expiratory Flow (mls/sec)	Vehicle	17 ± 2	17 ± 2	18 ± 1	58 ± 5†	18.6 ± 1.7
	Morphine	17 ± 1	11 ± 1*,‡	14 ± 1*,‡	39 ± 3†‡	19.9 ± 0.9

Data are shown as mean ± SEM. H-H, hypoxic-hypercapnic challenge. There were six rats in each group.

^*P < 0.05, significant change from Pre values.

^†P < 0.05, H-H max versus Pre-H-H

^‡P < 0.05, morphine versus vehicle.