AUTHOR=Damiani Elisa , Casarotta Erika , Orlando Fiorenza , Carsetti Andrea , Scorcella Claudia , Domizi Roberta , Adrario Erica , Ciucani Silvia , Provinciali Mauro , Donati Abele 

TITLE=Effects of Normoxia, Hyperoxia, and Mild Hypoxia on Macro-Hemodynamics and the Skeletal Muscle Microcirculation in Anesthetised Rats

JOURNAL=Frontiers in Medicine

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2021.672257

DOI=10.3389/fmed.2021.672257

ISSN=2296-858X

ABSTRACT=<p><bold>Objectives:</bold> Excessive oxygen (O<sub>2</sub>) administration may have a negative impact on tissue perfusion by inducing vasoconstriction and oxidative stress. We aimed to evaluate the effects of different inhaled oxygen fractions (FiO<sub>2</sub>) on macro-hemodynamics and microvascular perfusion in a rat model.</p><p><bold>Methods:</bold> Isoflurane-anesthetised spontaneously breathing male Wistar rats were equipped with arterial (carotid artery) and venous (jugular vein) catheters and tracheotomy, and randomized into three groups: normoxia (FiO<sub>2</sub> 21%, <italic>n</italic> = 6), hyperoxia (FiO<sub>2</sub> 100%, <italic>n</italic> = 6) and mild hypoxia (FiO<sub>2</sub> 15%, <italic>n</italic> = 6). Euvolemia was maintained by infusing Lactate Ringer solution at 10 ml/kg/h. At hourly intervals for 4 h we collected measurements of: mean arterial pressure (MAP); stroke volume index (SVI), heart rate (HR), respiratory rate (by means of echocardiography); arterial and venous blood gases; microvascular density, and flow quality (by means of sidestream dark field videomicroscopy on the hindlimb skeletal muscle).</p><p><bold>Results:</bold> MAP and systemic vascular resistance index increased with hyperoxia and decreased with mild hypoxia (<italic>p</italic> &lt; 0.001 in both cases, two-way analysis of variance). Hyperoxia induced a reduction in SVI, while this was increased in mild hypoxia (<italic>p</italic> = 0.002). The HR increased under hyperoxia (<italic>p</italic> &lt; 0.05 vs. normoxia at 3 h). Cardiax index, as well as systemic O<sub>2</sub> delivery, did not significantly vary in the three groups (<italic>p</italic> = 0.546 and <italic>p</italic> = 0.691, respectively). At 4 h, microvascular vessel surface (i.e., the percentage of tissue surface occupied by vessels) decreased by 29 ± 4% in the hyperoxia group and increased by 19 ± 7 % in mild hypoxia group (<italic>p</italic> &lt; 0.001). Total vessel density and perfused vessel density showed similar tendencies (<italic>p</italic> = 0.003 and <italic>p</italic> = 0.005, respectively). Parameters of flow quality (microvascular flow index, percentage of perfused vessels, and flow heterogeneity index) remained stable and similar in the three groups.</p><p><bold>Conclusions:</bold> Hyperoxia induces vasoconstriction and reduction in skeletal muscle microvascular density, while mild hypoxia has an opposite effect.</p>