Cardiovascular effects of hyperbaric oxygen with and without addition of carbon dioxide

Abstract

It is commonly believed that during hyperbaric oxygen (HBO) treatment, in spite of the vasoconstriction induced by the increased O2 content in the breathing gas, the elevated carrying capacity of O2 in the arterial blood results in augmented O2 delivery to tissues. The experiments described here tested the hypothesis that HBO treatment would be more efficient in delivering O2 to poorly perfused tissues if the vasoconstriction induced by elevated O2 could be abolished or attenuated by adding CO2 to the breathing gas. Organ blood flow (QOBF), systemic hemodynamics, and arterial blood gases were measured before, during and after exposure to either 300 kPa O2 (group 1) or 300 kPa O2 with 2 kPa CO2 (group 2), in awake, instrumented rats. During the HBO exposure the respiratory frequency (fb) fell (4 breaths x min(-1) x 100 kPa O2(-1)), with no changes in arterial CO2 tension (PaCO2), but when CO2 was added, fb and PaCO2 increased. The left ventricular pressure (LVP) and the systolic arterial pressure (SBP) increased. The maximum velocity of LVP (+dP/dt) rose linearly with LVP whether CO2 was added or not (r2 = 0.72 and 0.75 respectively). Similarly, the cardiac output (Qc) and heart rate (fc) fell, while the stroke volume (SV) was unaltered, independent of PaCO2. There was a general vasoconstriction in most organs in both groups, with the exception of the central nervous system (CNS), eyes, and respiratory muscles. HBO reduced the blood flow to the CNS by 30%, but this vasoconstriction was diminished or eliminated when CO2 was added. In group 2, the blood flow to the CNS rose linearly with increased PaCO2 and decreased pH. After decompression fc and SBP stayed high, while Qc returned to control values by reducing the SV; CNS blood flow remained markedly elevated in group 2, while in group 1, it returned to control levels. We conclude that the changes in fc, Qc, LVP, dP/dt, SBP and most QOBF values induced by HBO were not changed by hypercapnia. Blood flow to the CNS decreased during HBO treatment at a constant PaCO2. Hypercapnia prevented this decline. Elevated PaCO2 augmented O2 delivery to the CNS and eyes, but increased the susceptibility to O2 poisoning. A prolonged suppression of O2 supply to the CNS occurred during the HBO exposure and in air following the decompression in the absence of CO2. This suppression was offset by the addition of CO2 to the breathing gas.

Ozone Therapy for Tumor Oxygenation: a Pilot Study

“…Usually, however, this is less effective in modifying hypoxic areas and, as well, the effect is of a very short duration; of the order of 10–15 minutes (33). Furthermore, if applied for more than 15–30 min, these therapies can lead to vaso-constriction resulting in a potential blood-flow decrease, secondary to hyperoxia, in most organs (34) as well as in tumors (33). Our results show that, in the most hypoxic tumors, ozone therapy leads to an improvement in tissue pO 2 for at least 48 h after the second session of therapy.…”

Ozone Therapy on Cerebral Blood Flow: A Preliminary Report

“…Techniques such as carbogen breathing or hyperbaric chambers are used to increase the amount of O 2 dissolved in arterial blood. However, when prolonged for >15–30 min, these therapies can lead to an increase in peripheral vascular resistance along with a generalized vasoconstriction in most organs (15). Decreased cerebral blood flow secondary to hyperoxia has indeed been documented in humans by transcranial Doppler (16) and magnetic resonance (17) studies.…”

Oxygen or carbogen breathing before simulated submarine escape

“…1B, Table 1). The reason that carbon dioxide was added to the prebreathe mixture was to overcome the vasoconstrictive effects of the high PO 2 (1,4) and thus allow a faster washout of nitrogen. The fact that the only two convulsive incidents that occurred in the present study were both in the CPB group suggests that the CNS of the animals in this group were exposed to higher PO 2 levels due to the vasodilation effect of the added carbon dioxide.…”