Again if there is an anaerobic threshold, the PETCO2 at that time also tends not to be the maximum PETCO2. For COPD patients PETCO2 tends to rise throughout testing. Patients with pulmonary hypertension however, show a distinctly different pattern where PETCO2 declines throughout testing and if anaerobic threshold is attained, the PETCO2 at that time is not the maximum PETCO2.ĬOPD patients also tend to have distinct pattern, that is pretty much the opposite of pulmonary hypertension. Patients with cardiac disease show a similar pattern to normal patients with the exception that the maximum PETCO2 is reduced below 35 and the degree of reduction correlates well with the NYHA stage of cardiac disease. Mixed-expired and end-tidal CO2 distinguishes between ventilation and perfusion defects during exercise testing in patients with lung and heart diseases. The PETCO2 then increases to its maximum value (usually at AT) and then decreases to peak exercise.įrom: Hansen JE, Ulubay G, Chow BF, Sun X-G, Wasserman K. The PETCO2 pattern that normal patients show during a CPET is to start off with a relatively low PETCO2. The overall pattern of the patient’s PETCO2 during exercise was also wrong for COPD. Most COPD patients we see for CPETs have a PETCO2 of 30 or less and Ve-VCO2 slopes greater than 40. When the Ve-VCO2 slope was calculated however, it was 28, which is well within normal limits. We do not routinely do diffusion capacity testing as part of a cardiopulmonary exercise test so that part will have to remain speculative. This by itself is what told me that despite the reduced FEV1 and the diagnosis of COPD, with a PETCO2 of 40 at anaerobic threshold the patient probably had normal gas exchange. The maximum PETCO2 is reduced below 35 in both cardiac and pulmonary disease and the amount of reduction tends to correlate well with the severity of the disease. The maximum PETCO2 usually occurs at or near anaerobic threshold and the lower limit of normal is around 35 mm Hg. PETCO2 should be evaluated in terms of its maximum observed value and in its overall pattern during and following exercise. When ventilation is increased relative to CO2 production during exercise this fact shows up in the Ve-VCO2 slope, the mixed-expired CO2 (PECO2) and the PETCO2. Ventilation-perfusion mismatching and an exaggerated ventilatory response to exercise is a common features in diseases as different as COPD, pulmonary hypertension and ventricular failure. When there is a mismatch between ventilation and perfusion, ventilation has to increase in order to maintain the same level of gas exchange. Numerous investigators have developed algorithms that correlate PETCO2 with arterial CO2 but during exercise PETCO2 can be well below PaCO2 because of ventilatory inefficiency or it increase well above PaCO2 because it can become dominated by mixed-venous PCO2. Alveolar CO2 fluctuates cyclically with ventilation and since Vd/Vt is never zero PETCO2 is always higher than the average PACO2. There is a correlation between PETCO2 and both alveolar CO2 (PACO2) and arterial CO2 (PaCO2) however the correspondance is far from exact or predictable. Although End-tidal CO2 (ETCO2) is not a quantitative measurement in the same sense that minute ventilation or oxygen consumption is, it is still able to provide a lot of useful information about ventilatory efficiency and disease states.ĮTCO2 is related in various degrees to tidal volume, respiratory rate, the deadspace to tidal volume ratio (Vd/Vt) and CO2 production. There are a number of CO2-related values that are useful when assessing exercise test results. That test value was the PETCO2 at anaerobic threshold, which happened to be 40. I then saw just one exercise test value and knew immediately that this wasn’t going to be an ordinary test. I had looked at the spirometry results first (we always do spirometry pre- and post-exercise) and seeing that the patient had severe airway obstruction (FEV1 < 50% of predicted) assumed the review would be relatively straightforward. The test was part of a pre-op workup for a patient with lung cancer who also had a diagnosis of COPD. I was reviewing a cardiopulmonary exercise test (CPET) recently.
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