title: Change in intrathoracic pressure in rats with spontaneous and controlled ventilation during microgravity by parabolic flight.
abstract: We previously reported that the intrathoracic pressure (ITP) decreases and the transmural pressure of the aortic wall (TMP) increases during 4.5 s of microgravity (muG) induced by free drop. To examine the ITP response to a longer period of muG in the absence of the respiratory rate (RR) decrease, i.e., bradypnea, which occurs at the onset of muG, we measured the aortic blood pressure at the diaphragma level (AP) and ITP. We then calculated the TMP at the aortic arch level during 20 s of muG induced by parabolic flight in anesthetized rats (n = 7) with either spontaneous ventilation (SPN-V) or controlled ventilation (CONT-V). In the SPN-V group, the bradypnea was observed in all rats after the onset of the muG (RR change -13.9 +/- 2.9/min). The ITP during muG (-9.3 +/- 0.9 mmHg) was significantly lower than that during 1 G (-7.7 +/- 0.9 mmHg), and the TMP was significantly increased during muG (112 +/- 6 mmHg) compared to 1 G (103 +/- 5 mmHg). Similar changes in ITP and TMP were observed in the CONT-V group: During muG and 1G, respectively, the ITP was -8.4 +/- 0.6 mmHg and -5.9 +/- 0.7 mmHg, and the TMP was 112 +/- 6 mmHg and 101 +/- 6 mmHg, whereas no change in RR was observed because of the controlled ventilation. These results show that the ITP decreases and the TMP increases during muG, and they are not affected by a disturbance of respiratory rhythm.
authors.affiliation: Department of Physiology, Gifu University School of Medicine, Gifu, 501-1194 Japan. a2001072@hotmail.com
authors.forename: Taro Miyahara
authors.initials: TM
authors.lastname: Gotoh
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Fujiki
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tanaka
authors.forename: Hironobu
authors.initials: H
authors.lastname: Morita
mesh_terms: D000758:Anesthesia; D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001826:Body Fluids / Q000502:physiology; D008297:Male; D011312:Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D015656:Respiratory Mechanics / Q000502:physiology*; D013909:Thorax / Q000502:physiology*; D014893:Weightlessness