Effects Of Hypocapnia On Pulmonary Circulation Of Rabbits In Simulated High Altitude Environment

Objecyive: To investigate the effect of hypocapnia on pulmonary circulation ofPulmonary artery pressure and serum Angiotensin II level of rabbits in simulated highaltitude environment.Methods:13male rabbits were choosed as a subject of the study, which wereassessed by endotracheal intubation, pulmonary artery catheterization and mechanicalventilation. The rabbits were divided into five stages: blank control（A）; no hypocapniastage（B）,（PaCO₂=35⁴5mmHg, PH=7.35-7.45）; mild hypocapnia stage（C）,（PaCO₂=25～35mmHg，PH>7.45）; moderate hypocapnia stage（D）,（PaCO₂=15～25mmHg， PH>7.50）; severe hypocapnia stage（E）,（PaCO₂<15mmHg，PH>7.55）.Estimated mean Pulmonary arterial Pressure（MPAP） and serum Angiotensin II（AngII）of each stage, and analyze them by statistics. To learn the influence of hypocapnia torabbits Pulmonary artery Pressure and serum Angiotensin II level.Results:1. To compare blank control with no hypocapnia stage, PaCO₂changedfrom （39±4）mmHg to（39±5）mmHg; PaO₂changed from（79±4） mmHg to（80±3） mmHg, there were no significant differences between these groups（P>0.05）. From mild hypocapnia stage to severe hypocapnia stage, PaCO₂dropeddown from（30±4） mmHg to（12±3）mmHg，PaO₂rose from（85±6）mmHgto（92±6）mmHg, in which there were significant differences between thesegroups （P<0.05, respectively）.2. To compare blank control with no hypocapnia stage and mild hypocapnia stage,MPAP changed from（15.86±1.34）mmHg to（15.15±0.78）mmHg, there were nosignificant differences between these groups （P>0.05）. From mild hypocapnia stage to severe hypocapnia stage and mild hypocapnia stage, MPAP dropped down from（15.15±0.78）mmHg to（13.16±0.42）mmHg，in which there were significantdifferences between these groups （P<0.05, respectively）.3. To compare blank control with no hypocapnia stage, AngII changed from（83.36±7.16）pg/l to（80.21±7.91）pg/l，there were no significant differencesbetween these groups （P>0.05）. From mild hypocapnia stage to severe hypocapniastage, AngII dropped down from （80.21±7.91）mmHg to（65.84±6.19）mmHg，in which there were significant differences between these groups （P<0.05,respectively）.4.In each stage，the MPAP was positively correlated with PaCO₂（r=0.744,P<0.05）, AngⅡwas positively correlated with PaCO₂（r=0.670,P<0.05）;and theMPAP was positively correlated with MPAP（r=0.639，P<0.05）.Conclusion: The hypocapnia result from simulative high altitude environmentcan reduce pulmonary arterial pressure. The MPAP was Positively correlated withserum Angiotensin II, and changes in relation to serum Angiotensin Ⅱ...