Authors' Reply: An Evaluation of Rebreathing Methods for Measuring Mixed Venous Pco2 during Exercise

1972 ◽  
Vol 43 (2) ◽  
pp. 306-307
Author(s):  
S. Godfrey ◽  
Eliana Wolf
Keyword(s):  
Venous Pco2 ◽  
Rebreathing Methods ◽  
Mixed Venous

Effect of analyzer on determination of mixed venous PCO2 and cardiac output during exercise

1995 ◽  
Vol 79 (3) ◽  
pp. 1032-1038 ◽  
Author(s):  
L. Hornby ◽  
A. L. Coates ◽  
L. C. Lands
Keyword(s):  
Cardiac Output ◽  
Gas Mixture ◽  
Arterial Pco2 ◽  
Venous Pco2 ◽  
The Face ◽  
High O2 ◽  
Collision Broadening ◽  
Rebreathing Methods ◽  
Mixed Venous

Cardiac output (CO) during exercise can be determined noninvasively by using the indirect Fick CO2-rebreathing technique. CO2 measurements for this technique are usually performed with an infrared analyzer (IA) or mass spectrometer (MS). However, IA CO2 measurements are susceptible to underreading in the face of high O2 concentrations because of collision broadening. We compared an IA (Ametek model CD-3A) with a MS (Marquette model MGA-1100) to see the effect this would have on mixed venous PCO2 (PVCO2) and CO measurements. After calibration with room air and a gas mixture of 5% CO2–12% O2–83% N2, both devices were tested with three different gas mixtures of CO2 in O2. For each gas mixture, IA gave lower CO2 values than did the MS (4.1% CO2: IA, 3.85 +/- 0.01% and MS, 4.13 +/- 0.01%; 9.2% CO2: IA, 8.44 +/- 0.07% and MS, 9.19 +/- 0.01%; 13.8% CO2: IA, 12.57 +/- 0.15% and MS, 13.82 +/- 0.01%). Warming and humidifying the gases did not alter the results. The IA gave lower values than did the MS for eight other medical gases in lower concentrations of O2 (40–50%). Equilibrium and exponential rebreathing procedures were performed. Values determined by the IA were > 10% higher than those determined by the MS for both rebreathing methods. We conclude that all IAs must be checked for collision broadening if they are to be used in environments where the concentration of O2 is > 21%. If collision broadening is present, then either a special high O2-CO2 calibration curve must be constructed, or the IA should not be used for both arterial PCO2 and PVCO2 estimates because it may produce erroneously low PVCO2 values, with resultant overestimation of CO.

An Evaluation of Rebreathing Methods for Measuring Mixed Venous Pco2 During Exercise

1972 ◽  
Vol 42 (3) ◽  
pp. 345-353 ◽  
Author(s):  
S. Godfrey ◽  
Eliana Wolf
Keyword(s):  
Cardiac Output ◽  
Steady State ◽  
Direct Methods ◽  
Extrapolation Method ◽  
Venous Pco2 ◽  
Technical Factors ◽  
End Tidal ◽  
Male Subjects ◽  
Rebreathing Methods ◽  
Mixed Venous

1. Measurements have been made of mixed venous Pco2 (PV̄co2) by two methods during exercise at 50 and 100 W in five adult male subjects. 2. The equilibration (plateau) method and the extrapolation (Defares) method were performed alternately, five times each, during the steady-state exercise. 3. The coefficient of variation of PV̄,co2 by the extrapolation method was much higher than that of the plateau method. The PV̄,co2 can be estimated to within ± 1 mmHg by the plateau method, and the derived cardiac output to within ± 0·5 1/min in most cases. The cardiac output calculated by this method agrees closely with that found by direct methods in other studies, whereas the extrapolation method usually overestimates the cardiac output in adults. 4. It is suggested that the degree of variation in the extrapolation method is due to technical factors in construction of the line and to the difficulty of deciding what constitutes the end-tidal Pco2.

Comparison of Two Rebreathing Methods for the Determination of Mixed Venous Partial Pressure of Carbon Dioxide during Exercise

1979 ◽  
Vol 56 (5) ◽  
pp. 433-437 ◽  
Author(s):  
G. J. F. Heigenhauser ◽  
N. L. Jones
Keyword(s):  
Co2 Concentration ◽  
Arterial Pco2 ◽  
Equilibrium Method ◽  
Venous Pco2 ◽  
Pulmonary Capillary Blood ◽  
Exponential Method ◽  
Power Outputs ◽  
End Tidal ◽  
Rebreathing Methods ◽  
Mixed Venous

1. Duplicate measurements were made of mixed venous Pco2 (Pv̄, co2) by two rebreathing methods during steady-state exercise at three power outputs in seven subjects. One method employed a high initial bag CO2 concentration to obtain equilibrium of CO2 in the lung—bag system before recirculation (equilibrium method); in the other, a low initial bag CO2 concentration was used and a statistical method was applied to alveolar Pco2 measurements before recirculation, to obtain the asymptote from the exponential rise in end-tidal Pco2 during rebreathing (exponential method). 2. The reproducibility was similar; sd of duplicate determinations of Pv̄, co2 was 0·15 kPa (1·1 mmHg) for the equilibrium method and 0·20 kPa (1·5 mmHg) for the exponential method. Measurements of Pv̄, co2 by the exponential method were systematically lower than the equilibrium method. When the equilibrium Pv̄, co2 was corrected for the alveolar—arterial (‘downstream’) Pco2 difference, using published values, Pv̄, co2 was similar for both methods. 3. As an alveolar to arterial Pco2 difference did not appear to exist with the exponential method, it is concluded that the previously described disequilibrium between alveolar and arterial Pco2 during rebreathing in exercise is mainly related to prevention of net CO2 movement from the pulmonary capillary blood in the equilibrium method, and is not present when continuous CO2 evolution occurs in the exponential method.

A New Open-Circuit Method for Estimating Carbon Dioxide Tension in Mixed Venous Blood

1977 ◽  
Vol 52 (4) ◽  
pp. 377-382 ◽  
Author(s):  
Reiah Al-Dulymi ◽  
R. Hainsworth
Keyword(s):  
Carbon Dioxide ◽  
Venous Blood ◽  
Carbon Dioxide Tension ◽  
Open Circuit ◽  
Mixed Venous Blood ◽  
Arterial Blood ◽  
Venous Pco2 ◽  
Rebreathing Methods ◽  
Mixed Venous ◽  
Good Agreement

1. A new open-circuit respiratory method was developed to estimate mixed venous Pco2 more rapidly and accurately than is possible with rebreathing techniques. 2. The subject breathes a mixture of CO2 in air from an open circuit. Carbon dioxide is added to the air flowing through the circuit at a rate such that the Pco2 in the inspired and expired gases (recorded continuously with a CO2 analyser) are almost identical. 3. Results from respiratory and cardiac patients showed that equilibrium occurred in less than 10 s. There was good agreement between the tensions of CO2 in the respiratory plateaux and in mixed venous and arterial blood withdrawn during equilibrium. 4. During exercise, the tensions of CO2 of the plateaux and arterial blood at equilibrium also showed good agreement. 5. It is suggested that the new method represents an improvement over rebreathing methods as equilibrium is achieved rapidly before the mixed venous tension rises from recirculation.

Estimation of mixed venous Pco2 by rebreathing for one minute

1967 ◽  
Vol 61 (3) ◽  
pp. 131-135
Author(s):  
L.H. Capel ◽  
H. Zeitlin ◽  
E.C. Fletcher
Keyword(s):  
Venous Pco2 ◽  
Mixed Venous

Gas-blood CO2 equilibration in parabronchial lungs of birds

1976 ◽  
Vol 41 (3) ◽  
pp. 302-309 ◽  
Author(s):  
M. Meyer ◽  
H. Worth ◽  
P. Scheid
Keyword(s):  
Steady State ◽  
Venous Blood ◽  
Blood Perfusion ◽  
Co2 Exchange ◽  
Mixed Venous Blood ◽  
O2 Uptake ◽  
Venous Pco2 ◽  
Avian Lung ◽  
Mixed Venous ◽  
Haldane Effect

We have conducted two experimental series in the chicken in order to study CO2 exchange in the parabronchial lungs of birds.In the first series, the animals were artifically ventilated and end-expired PCO2, PE'CO2,was measured and compared with mixed venous PCO2, PVCO2. On the average, PECO2 exceeded PVCO2 by 2.8 Torr. In the second series, rebreathing was used to investigate the mechanism of this positive (PE'-PV)CO2 difference.Lung gas PCO2 was found to equilibrate with PVCO2 if both CO2 and O2 exchange in the lung was abolished during rebreathing. Only if O2 uptake continued, we observed a positive gas-to-mixed venous blood PCO2 difference. The results suggest that positive gas-blood PCO2 differences both during rebreathing and steady-state ventilation are brought about by the Haldane effect.Model calculations show that in the homogeneous avian lung, unlike in the alveolar lung, the Haldane effect can produce positive (PE'-PV)CO2 differences during steady-state breathing due to the peculiarities of the crosscurrent arrangement and parabronchial ventilation and blood perfusion.

Gas-blood PCO2 gradients during avian gas exchange

1975 ◽  
Vol 39 (3) ◽  
pp. 405-410 ◽  
Author(s):  
D. G. Davies ◽  
R. E. Dutton
Keyword(s):  
Gas Exchange ◽  
Exchange System ◽  
Arterial Pco2 ◽  
Charged Membrane ◽  
Venous Pco2 ◽  
Avian Lung ◽  
Gas Exchange System ◽  
Spontaneously Breathing ◽  
Membrane Mechanism ◽  
Mixed Venous

The avian respiratory system is a crosscurrent gas exchange system. One of the aspects of this type of gas exchange system is that end-expired PCO2 is greater than arterial PCO2, the highest possible value being equal to mixed venous PCO2. We made steady-state measurements of arterial, mixed venous, and end-expired PCO2 in anesthetized, spontaneously breathing chickens during inhalation of room air or 4–8% CO2. We found end-expired PCO2 to be higher than both arterial and mixed venous PCO2, the sign of the differences being such as to oppose passive diffusion. The observation that end-expired PCO2 was higher than arterial PCO2 can be explained on the basis of crosscurrent gas exchange. However, the observation that end-expired PCO2 exceeded mixed venous PCO2 must be accounted for by some other mechanism. The positive end-expired to mixed venous PCO2 gradients can be explained if it is postulated that the charged membrane mechanism suggested by Gurtner et al. (Respiration Physiol. 7: 173–187, 1969) is present in the avian lung.

scholarly journals Correlation Between the Physical Signs of Hypercapnia and the Mixed Venous Pco2

BMJ ◽  
1963 ◽  
Vol 2 (5365) ◽  
pp. 1096-1097 ◽  
Author(s):  
N. J. Gross ◽  
J. D. Hamilton
Keyword(s):  
Venous Pco2 ◽  
Mixed Venous
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