Mixed venous PO2, PCO2, pH, and cardiac output during exercise in trained subjects

The Q˙-V˙O2 diagram: an analytical interpretation of oxygen transport in arterial blood during exercise in humans

A new analysis of the relationship between cardiac output (Q˙) and oxygen consumption V˙O2 is presented (Q˙-V˙O2 diagram). Data from different sources in the literature have been used for validation in three conditions: exercise and rest in normoxia, and exercise in hypoxia. The effects of changes in arterial oxygen concentration CaO2 on Q˙ are discussed, as well as the effects of predominant sympathetic or vagal stimulation. Differences appear depending on whether CaO2 is varied by means of changes in blood haemoglobin concentration or changes in arterial oxygen saturation. The present Q˙-V˙O2 diagram allows comprehensive description of oxygen transport in exercising humans; it expands applicability of the historical Q˙-V˙O2 relationship to include CaO2 variations; it opens new pathways for understanding underlying mechanisms; it allows computation of Q˙ from CaO2 and V˙O2 measurements, when Q˙ cannot be measured.

Revised one-step method for determination of cardiac output

Cardiac output (Q) is a determinant of blood pressure and O(2) delivery and is critical in the maintenance of homeostasis, particularly during environmental stress and exercise. Cardiac output can be determined invasively in patients; however, indirect methods are required for other situations. Soluble gas techniques are widely used to determine (Q). Historically, measurements during a breathhold, prolonged expiration and rebreathing to CO(2) equilibrium have been used; however, with limitations, especially during stress. Farhi and co-workers developed a single-step CO(2) rebreathing method, which was subsequently revised by his group, and has been shown to be reliable and compared closely to direct, invasive measures. V(CO2), P(ACO2), and P(VCO2) are determined during a 12-25s rebreathing, using the appropriate tidal volume, and (Q) is calculated. This method can provide accurate data in laboratory and field experiments during exercise, increased or decreased gravity, water immersion, lower body pressure, head-down tilt, altered ambient pressure or changes in inspired gas composition.

CO2 dissociation curves of oxygenated whole blood obtained at rest and in exercise

In vitro CO2 dissociation curves for oxygenated whole blood were determined in 19 healthy male subjects at rest and during submaximal and maximal bicycle work. Hemoglobin concentration and blood lactate increased with increasing work load and accordingly buffer value of the whole blood increased while bicarbonate and Base Excess (BE) decreased, resulting in a downward shift of the CO2 dissociation curve during exercise. Despite the marked increase in buffer values of the blood, the slopes of the CO2 dissociation curves during exercise were found to be about the same as those obtained at rest. It was inferred that the increasing effect of increased buffer value, on the dissociation slope, was essentially compensated by the decreasing effect of diminished bicarbonate content. The advantages of this relatively constant CO2 dissociation slope for the indirect measurement of cardiac output by the Fick principle are discussed.

Oxygen analyses of chicken embryo blood

According to data obtained previously on the blood gas tensions and the oxygen dissociation curve of chicken embryos, the arteriovenous oxygen saturation difference in the allantoic circulation has been conjectured fairly large. In order to confirm this conjecture as well as to check the validity of the in vitro dissociation curve, both the blood oxygen capacity and content in allantoic artery and vein were measured. The in vivo O2 saturation measured here resulted in a similar value to that estimated from the dissociation curve. The O2 content in allantoic vein ranges from about 7 to 11.5 vol% during the 10th to the 18th days of incubation and that in artery is pronouncedly low in a range of 1 to 2.5 vol%, suggesting that the blood flow rate through the body tissues is fairly larger than that through the gas exchange capillary plexus. Then, the distribution of blood flow was estimated from the analyzed data based on a model of blood circulation and some assumptions. In connection with this estimation, the diffusing capacity for deoxygenation in the tissues was speculated to be much larger than that for oxygenation in the chorioallantoic capillaries.

Cardiac output determination by simple one-step rebreathing technique

We have developed a rebreathing technique for measuring cardiac output in resting or exercising subjects. The data needed are the subject's CO2 dissociation curve, the initial volume and CO2 fraction of the rebreathing bag, and a record of CO2 at the mouth during the maneuver. From these one can obtain all the values required to solve the Fick equation. The combined error due to inaccuracy in reading the tracings and to the simplifying assumptions was found to be small (mean = 0.5%, SD ;.5%). Cardiac output values determined with this technique in normal subjects were on the average 2% higher than those obtained simultaneously with an acetylene rebreathing method (n = 49, SD = 11%). Among the advantages of the technique are that it requires analysis of a single gas, takes less than thirty seconds per determination, allows one to obtain repeated measurements at rapid intervals, is not affected by the ability of lung tissue to store CO2, and eliminates many of the assumptions usually made in non-invasive measurements of cardiac output.

[Pulmonary gas exchange after myocardial infarction in the late period of recovery. II. Investigations during exercise (author's transl)]

After myocardial infarction in the late period of recovery (13-25 months p. infarctum) pulmonary gas exchange in 23 patients was measured besides as hemodynamic parameters during exercise. The parameters take a course similar to that of subjects without lung and heart diseases. Arterial blood gas tensions (Pa02, Paco2) remain unchanged compared to resting values. Alveolar ventilation did show no difference in any of the patients. Minute ventilation VE, the various dead spaces, alveolar-arterial gas differences (AaDo2, aADco2) and ventilation-perfusion ratios of the whole lung VA/Q suggest however that these parameters show different courses according to the physical capacity of the patients. As the physical capacity of each patient is due to different cardiac functions taken by cardiac output and mixed venous blood gas tensions alterations of pulmonary gas exchange seemed to be dependent on the respective left ventricular function of the heart. Of the twenty-three patients, twelve with cardiac failure under exercise showed the most pronounced alterations in pulmonary gas exchange. Therefore, the different physical work capacity of the patients are determined only by cardiac function. No limitation of the productivity due to impeded lung function could be proved.