title: Relationship between transmural pressure and aortic diameter during free drop-induced microgravity in anesthetized rats.
abstract: To test the hypothesis that the aortic wall is stretched without increasing aortic pressure (AP) during microgravity (microG), the AP, intrathoracic pressure (ITP), and aortic diameter (AD) were measured in anesthetized Sprague-Dawley rats during 4.5 s of microG produced by freefall. A smooth and immediate reduction in gravity (G) occurred during freefall, microG being achieved 100 ms after the start of the drop. Acute microG elicited an immediate increase in AD, which was not accompanied by an increase in AP. However, the ITP decreased during microG resulted in an increase in the calculated transmural pressure (TP = AP-ITP) of the aortic wall. A simple linear regression analysis showed that the slopes of the plot of AP vs. AD differed at 1 G and microG, whereas those for the plot of TP vs. AD did not. Thus, the increase in AD during microG was accounted for by the increase in TP. These results suggest that a decrease in ITP, resulting in an increase in TP of the aorta, is a key issue in understanding cardiovascular responses to microG.
authors.affiliation: Department of Physiology, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan. morita@cc.gifu-u.ac.jp
authors.forename: Hironobu
authors.initials: H
authors.lastname: Morita
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Fujiki
authors.forename: Taro
authors.initials: T
authors.lastname: Gotoh
authors.forename: Tomoko
authors.initials: T
authors.lastname: Matsuda
authors.forename: Gao
authors.initials: G
authors.lastname: Shuang
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000758:Anesthesia; D000818:Animals; D001011:Aorta / Q000033:anatomy & histology* / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001330:Electronic Data Processing; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D016014:Linear Models; D008297:Male; D011312:Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013686:Telemetry / Q000379:methods; D013909:Thorax / Q000502:physiology*; D018474:Weightlessness Simulation