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

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

doi:10.3389/fmed.2021.672257

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

Front Med (Lausanne). 2021 May 11:8:672257. doi: 10.3389/fmed.2021.672257. eCollection 2021.

Authors

Elisa Damiani¹, Erika Casarotta¹, Fiorenza Orlando², Andrea Carsetti^{1

3}, Claudia Scorcella³, Roberta Domizi³, Erica Adrario^{1

3}, Silvia Ciucani¹, Mauro Provinciali², Abele Donati^{1

3}

Affiliations

¹ Anesthesia and Intensive Care Unit, Department of Biomedical Sciences and Public Health, Università Politecnica delle Marche, Ancona, Italy.
² Experimental Animal Models for Aging Units, Scientific Technological Area, Istituto di Ricovero e Cura a Carattere Scientifico - Istituto Nazionale Ricovero e Cura Anziani, Ancona, Italy.
³ Anesthesia and Intensive Care Unit, Azienda Ospedaliera Universitaria "Ospedali Riuniti Umberto I - Lancisi - Salesi" of Ancona, Ancona, Italy.

Abstract

Objectives: Excessive oxygen (O₂) 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 (FiO₂) on macro-hemodynamics and microvascular perfusion in a rat model. Methods: 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 (FiO₂ 21%, n = 6), hyperoxia (FiO₂ 100%, n = 6) and mild hypoxia (FiO₂ 15%, n = 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). Results: MAP and systemic vascular resistance index increased with hyperoxia and decreased with mild hypoxia (p < 0.001 in both cases, two-way analysis of variance). Hyperoxia induced a reduction in SVI, while this was increased in mild hypoxia (p = 0.002). The HR increased under hyperoxia (p < 0.05 vs. normoxia at 3 h). Cardiax index, as well as systemic O₂ delivery, did not significantly vary in the three groups (p = 0.546 and p = 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 (p < 0.001). Total vessel density and perfused vessel density showed similar tendencies (p = 0.003 and p = 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. Conclusions: Hyperoxia induces vasoconstriction and reduction in skeletal muscle microvascular density, while mild hypoxia has an opposite effect.

Keywords: hemodymamics; hyperoxia; hypoxia; microcirculation; oxygen.