Risberg J, Skei S, Tyssebotn I
Norwegian Underwater Technology Centre, Ytre Laksevåg, Norway.
Aviat Space Environ Med. 1995 Dec;66(12):1159-68.
Cardiac contractility and myocardial blood flow have been shown to increase when anesthetized and awake rats were exposed to normoxic 0.5 MPa ambient pressure, independent of inert gas composition. Similar changes have been demonstrated in anesthetized rats breathing a dense (relative density (RD) 5) SF6-O2 gas mixture at normobaric pressure.
The purpose of the present study was to further explore whether cardiac contractility increases during hyperbaric exposure as a response to the elevated atmospheric pressure per se or rather as a response to increased breathing gas density.
Arterial pressure, left ventricular pressure (LVP), central venous pressure and intra-esophageal pressure were monitored in anesthetized rats during simulated dives. The rats were exposed to various gas mixtures (air, SF6-N2-O2, He-N2-O2), partial pressures of O2 (PIO2 0.02 and 0.03 MPa) ambient pressure (PTot 0.1-0.3 MPa) and gas density (RD 1-10.1).
Cardiac contractility increased briefly by 5-10% (p < 0.05) during mild hyperoxia (PIO2 0.03 MPa). A concomitant stepwise increase in RD (1-10.1) and PTot (0.1-0.3 MPa) by adding SF6 to air, increased maximal rate of LVP rise (+dP/dt) and fall (-dP/dt) by 30% (p < 0.01). Two groups of rats exposed to either a high density SF6-N2-O2 (RD 5.5) or a normal density He-N2-O2 (RD 1.2) breathing gas of identical PTot 0.2 MPa demonstrated similar rise in dP/dt (peak 72%, p < 0.05).
At moderately increased ambient pressure, pressure per se increases cardiac contractility independently of the breathing gas density.
已表明，当麻醉和清醒的大鼠暴露于常压0.5 MPa的常氧环境压力下时，心脏收缩力和心肌血流量会增加，这与惰性气体成分无关。在常压下呼吸高密度（相对密度（RD）5）的六氟化硫-氧气混合气体的麻醉大鼠中也证实了类似变化。
本研究的目的是进一步探讨在高压暴露期间心脏收缩力增加是对升高的大气压力本身的反应，还是对呼吸气体密度增加的反应。
在麻醉大鼠模拟潜水期间监测动脉压、左心室压力（LVP）、中心静脉压和食管内压。大鼠暴露于各种气体混合物（空气、六氟化硫-氮气-氧气、氦气-氮气-氧气）、氧气分压（吸入氧分压0.02和0.03 MPa）、环境压力（总压0.1 - 0.3 MPa）和气体密度（RD 1 - 10.1）。
在轻度高氧（吸入氧分压0.03 MPa）期间，心脏收缩力短暂增加5% - 10%（p < 0.05）。通过向空气中添加六氟化硫使RD（1 - 10.1）和总压（0.1 - 0.3 MPa）同时逐步增加，左心室压力上升（+dP/dt）和下降（-dP/dt）的最大速率增加了30%（p < 0.01）。两组暴露于相同总压0.2 MPa的高密度六氟化硫-氮气-氧气（RD 5.5）或正常密度氦气-氮气-氧气（RD 1.2）呼吸气体的大鼠，其dP/dt的升高相似（峰值72%，p < 0.05）。
在环境压力适度增加时，压力本身会增加心脏收缩力，与呼吸气体密度无关。
