Respiratory system mechanics in guinea pigs after acute hemorrhage

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Abstract
We evaluated the effects of acute blood loss on the respiratory mechanics of guines pigs. We measured respiratory system elastance (Ers) and resistance (Rrsmax) using the end-inflation occlusion method. Rrsmax was partitioned into its homogeneous component (Rrsmin) and that due to the uneveness within the respiratory system (Rrsu). Respiratory mechanics were studied both before and immediately after bleeding in eight animals. Another eight guinea pigs had received propranolol previously and were also submitted to hemorrhage. Propranolol-treated animals showed higher control values of Rrsmax (p < 0.02) and Rrsmin p < .0001). Animals not treated with propranolol exhibited a decrease (p < 0.001) in Rrsmax after hemorrhagic hypovolemia (from 0.375 .+-. 0.051 to 0.323 .+-. 0.042 cm H2O/ml .cntdot. sec), due to a decrease (p < 0.005) in Rrsmin (from 0.140 .+-. 0.031 to 0.094 .+-. 0.032 cm H2O/ml .cntdot. sec), whereas Ers and Rrsu did not change. Propranolol-treated animals showed an increase (p < .001) in Rrsmax (from 0.512 .+-. 0.133 to 0.664 .+-. 0.144 cm H2O/ml .cntdot. sec), Rrsu (p < 0.01) from 0.252 .+-. 0.09 to 0.345 .+-. 0.139 cm H2O/ml .cntdot. sec, and Ers (p < 0.001) (from 4.565 .+-. 0.933 to 5.402 .+-. 1.23 cm H2O/ml) after bleeding. The results indicate that the immediate effects of acute bleeding on respiratory mechanics are significantly influenced by catecholamines.