An Evaluation of Rebreathing Methods for Measuring Mixed Venous <i>P</i>
                  <scp>co</scp>2 During Exercise

Godfrey, Simon; Wolf, E

doi:10.1042/cs0420345

Cited by 29 publications

(20 citation statements)

References 8 publications

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“…37 End tidal tension of CO 2 (P ET CO 2 ) was used to estimate arterial CO 2 tension (P A CO 2 ), and Godfrey's recommendations were used to estimate CO 2 content. 38 This combination has been found to give highly reproducible results (coecient of variation 5.7%) during submaximal exercise in healthy individuals. 20 The results are also in agreement with the results obtained by the direct Fick method 39 and the dye dilution method.…”

Section: Discussionmentioning

confidence: 87%

Improved work capacity but unchanged peak oxygen uptake during primary rehabilitation in tetraplegic patients

Hjeltnes

Wallberg-Henriksson

1998

Spinal Cord

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Individuals with cervical spinal cord lesions are characterised by markedly decreased aerobic capacity, accompanied by increased risk of developing cardiovascular disease. The aim of this study was to evaluate the eects of a primary rehabilitation programme that included three sessions of arm cycling per week on the endurance capacity in 10 male tetraplegic subjects (injury level C6-C8; eight ASIA-A and two ASIA-B). Peak oxygen uptake (peak VO 2 ) was measured three times (at T1 & 99+10 days after injury, T2 & 2 months after T1, and at T3 & 2 months after T2). Ten paraplegic patients admitted to the hospital for primary rehabilitation served as controls. In the tetraplegic patients, mean peak load increased (22+2, 32+5, and 32+7 watt, at T1, T2 and T3 respectively) (P50.01), while mean peak VO 2 did not change during the study (0.78+0.07, 0.86+0.08, and 0.81+0.06 16min 71 , at T1, T2 and T3, respectively) (ns). In contrast peak VO 2 was signi®cantly higher in the paraplegic control group (1.37+0.08, 1.64+0.10 and 1.75+0.08 16min 71 , respectively) (P50.001), and increased signi®cantly during the study period (P50.001). Mean heart rate (HR) and mean stroke volume (SV), measured at corresponding submaximal work loads during the study did not change signi®cantly in the tetraplegic patients. Mean systolic blood pressure (SBP), recorded immediately after peak arm exercise was low at all three tests (93+8, 89+6 and 84+6 mmHg) in the tetraplegic group. However, both muscle strength and`activities of daily life' index improved signi®cantly during the study period. Our results suggest that functional improvement in tetraplegic patients is not necessarily followed by aerobic metabolic improvement. We conclude that more time should be spent on arm endurance training, or training methods which activate larger muscle groups and/or increases blood pressure.

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Section: Discussionmentioning

confidence: 87%

Improved work capacity but unchanged peak oxygen uptake during primary rehabilitation in tetraplegic patients

Hjeltnes

Wallberg-Henriksson

1998

Spinal Cord

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“…MUIESAN et al (1968) reported that good agreement was observed between both ox-PVCO2 values. However, GoDFREY and WOLF (1972) reported that the plateau method gave several Torr higher ox-PVco2 values than the extrapolation method. Actually, it is fairly difficult to obtain consistent values for tr-and ox-PVco2.…”

Section: Discussionmentioning

confidence: 98%

A new indirect method for measuring arteriovenous O2 content difference and cardiac output from O2 and CO2 concentrations by rebreathing air.

et al. 1984

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A new indirect method for measuring the arteriovenous 02 content difference (avDo 2) was developed. The avDo 2 was calculated by dividing the gradient of the C02 dissociation curve by that of a gas exchange ratio against Pco2. The latter slope was obtained from 02 and C02 concentrations in rebreathing air. The validity of the method was tested preliminarily in human subjects by comparing the cardiac output calculated from avDo 2 and 02 uptake (o2) with that measured hitherto by other authors, and then in dogs by comparing the calculated avDo, with the measured value. In the dog experiments, the rebreathing was performed 7 times in each of 7 dogs. Immediately after the rebreathing arterial and mixed venous blood were sampled and analyzed for avDo2. For each rebreathing period the avDo, was calculated by using the C02 dissociation curve obtained in the individual dogs. The correlation coefficient between the measured and calculated avDo2 was 0.87, demonstrating reasonable validity of the method. The Vo2 was further measured from the time interval during which a known amount of pure 02 was consumed. Then, the cardiac output was calculated by dividing the Vo2 by the measured and calculated avDo2. The correlation coefficient between the respective cardiac output values was 0.88, indicating the reliability of using the calculated avDo 2.

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“…The alternative, equilibrium method, has been thought to be more reliable than the exponential method [9], but recently the application of computer analysis to the exponential method has im proved its precision [13]. A number of methods have been proposed for the derivation of the asymptote of the exponential rise in PCO2 in the rebreathing system.…”

Section: Methodsmentioning

confidence: 99%

“…Rebreathing is used to obtain PvC02 and PaCC>2 is estimated from rapid CO2 analysis of end-tidal gas during air breathing. Of the two methods available for estimation of PvCC>2, the equilibrium method, in which a high initial concentration of CO2 is rebreathed [4,20], has been thought to be more reliable [9] than the exponential method, in which a low concen tration of CO2 is rebreathed [6,16,23], Recently, com puter-assisted analysis of CO2 during rebreathing has Rebreathing may be used to measure mixed venous PCO2 during exercise and derive cardiac output (0) using the Fick principle applied to CO2. In the form of the Fick equation used for this purpose: 0 = VCO2/CVCO2 -CaC02, carbon dioxide output (VCO2) is measured by expired gas collection, and the contents of CO2 in venous (CŸCO2) and arterial blood (CaCCh) are derived from by angina or cardiac arrhythmias.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Cardiac Output by C0(2) Rebreathing during Incremental Exercise in Patients with Coronary Artery Disease

Campbell¹,

Mckelvie²,

Heigenhauser³

et al. 1989

Am J Noninvas Cardiol

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In 9 patients with stable coronary artery disease, measurements were made during a progressive incremental maximum exercise test of O(2) intake (VO(2)), CO(2) output (VCO(2)), mixed venous PCO(2) by an exponential rebreathing method, and end-tidal PCO(2) (PETCO(2)) to estimate arterial PCO(2) (PaCO(2)). By applying the Fick principle to CO2, these measurements were used to derive cardiac output at several incremental work loads. Each subject underwent two incremental exercise studies to establish the reproducibility of the technique, and also a steady state exercise study to compare steady state responses with unsteady state incremental exercise. The results were also compared to those previously obtained in healthy subjects. PvCO(2) showed a curvilinear increase with increasing VCO(2) with only a small intersubject variation. Cardiac output-oxygen uptake relationships (Q/VO(2)) were similar in the two incremental studies (intercepts 6.27 and 6.641/min; slopes 4.82 and 4.58 1/min), and also similar to that obtained previously in healthy subjects (intercept 6.441/min; slope 4.71 1/min). Low calculated values for cardiac output were obtained at high exercise levels during the incremental test in those subjects in whom PETCO(2) fell at the highest work loads. This effect could be corrected for by using a PETCO(2) obtained 1 min prior to rebreathing, suggesting that the low values of Q were an artifact due to a transient decrease in PaCO(2) secondary to hyperventilation. At any given VO(2) or VCO2, PvCO(2) and Q were the same in both steady state and unsteady state incremental exercise. The exponential CO(2) rebreathing method may be reliably applied to incremental exercise testing to evaluate the cardiac output responses to exercise in patients with cardiac disease.

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An Evaluation of Rebreathing Methods for Measuring Mixed Venous P co2 During Exercise

Cited by 29 publications

References 8 publications

Improved work capacity but unchanged peak oxygen uptake during primary rehabilitation in tetraplegic patients

Improved work capacity but unchanged peak oxygen uptake during primary rehabilitation in tetraplegic patients

A new indirect method for measuring arteriovenous O2 content difference and cardiac output from O2 and CO2 concentrations by rebreathing air.

Estimation of Cardiac Output by C0(2) Rebreathing during Incremental Exercise in Patients with Coronary Artery Disease

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