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

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.

Altered blood gas tensions of oxygen and carbon dioxide confound coronary reactivity to apnea

“…Additionally, an animal study showed that in swine who were mildly hypoxemic at rest, myocardial oxygenation was still maintained during a 60-s period of apnea, despite a significantly greater blood desaturation than observed during apnea conducted at normoxemia [41]. Other studies have looked at the protective effect of hypercapnia or mild hypoxemia on the skeletal microvascular function [42] and the brain. For example, in a rat model assessing cerebral ischemia, hypercapnia was found to be therapeutic under mild-to-moderate hypoxemia, although detrimental when combined with severe hypoxemia (PaO 2 < 50 mmHg) [43].…”

Resuscitating the macro- vs. microcirculation in septic shock

“…The use of direct visualization techniques to guide resuscitation in sepsis faces several barriers despite the improvement of quality imaging devices and automated analysis tools [26,27]. The patients tongue needs to remain immobile for at least 5 s to acquire adequate quality video sequences.…”

Effect of an ionic antineoplastic agent Cytoreg on blood chemistry in a Wistar rat model

“…Our data are comparable with those from other studies on the same species and strain of rat ( Table 1 ). 12 13 14 15 16 The average pH values determined at T0’ (pre-treatment), T30’, and T60’ are 7.45 ± 0.046, 7.25 ± 0.11, and 7.22 ± 0.09, respectively ( Figure 1A ). Values which differ significantly from the initial pH (T0’) ( P < 0.05) are still within the tolerated range for the organism, since they can be compensated by physiological buffers.…”