Cardiopulmonary Exercise Testing

Esther de Boer; Irina Petrache; Michael P. Mohning

doi:10.1001/jama.2022.2037

JAMA Diagnostic Test Interpretation

March 10, 2022

Cardiopulmonary Exercise Testing

Esther de Boer, MD, PhD¹; Irina Petrache, MD^1,2; Michael P. Mohning, MD^1,2

Author Affiliations Article Information

¹Division of Pulmonary Sciences and Critical Care Medicine, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora
²Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, National Jewish Health, Denver, Colorado

JAMA. 2022;327(13):1284-1285. doi:10.1001/jama.2022.2037

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A 33-year-old man with a history of intermittent asthma presented with 3 months of dyspnea on exertion, which developed approximately 2 weeks after infection with SARS-CoV-2. His acute COVID-19 symptoms resolved after 5 days and did not require hospitalization. At presentation, his physical examination findings were normal and peripheral oxygen saturation was 97% at rest. Laboratory testing, chest radiographic imaging, chest computed tomographic scan, echocardiography, and pulmonary function testing results were normal. To further evaluate his dyspnea on exertion, the patient underwent cardiopulmonary exercise testing (CPET) on a cycle ergometer with arterial blood gas samples obtained from an indwelling radial artery catheter. Continuous 12-lead electrocardiogram (ECG) findings showed no evidence of arrythmia or ischemia, and the patient stopped exercise due to leg fatigue after 15 minutes. Select exercise data are presented in the Table and Figure.

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2 Comments for this article

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September 6, 2023

Missing Information

Gerald Zavorsky, PhD | University of California, Davis

In this case report:

1) There is no information regarding height, weight, ethnicity, or the altitude of testing. Thus, it's impossible to establish the patient's BMI, and I am uncertain if the patient is overweight or obese. Additionally, calculating VO2 peak (in mL/kg/min) is not possible and yet it provides a better reflection of fitness than L/min.

VO2 rest = 300 mL/min (Figure) and VO2 peak = 2100 mL/min (Figure). However, the predicted VO2 at the patient's peak wattage of 220 W should be = 2500-2720 mL/min (10-11 mL/min/W*220 W+rest), suggesting that the reported VO2 peak is underestimated by 15%. Possible causes for this underestimation could include a mask leak, incorrect calibration of the metabolic cart, or an incorrect cadence (i.e., not self-selected). [Note: If the patient exercised at an altitude of 1609 meters, the VO2 at 220 W should be even higher than the predicted 2500 mL/min].

2) How was peak exercise determined? Guidelines specify that VO2peak should be determined as an average of the three highest consecutive 20-s intervals (or two highest consecutive 30-s intervals), not the highest 10-second average or the highest 15-s average (1). It is unclear whether a 1-minute average at peak exercise was reported.

3) There is no confirmation of the patient's maximal effort. To establish this, a report of the rating of perceived exertion (RPE) reported by the patient at peak exercise is required. This information is crucial to determine whether the patient gave a true effort. To satisfy this requirement, at least 3 criteria should be met: an RER (respiratory exchange ratio) > 1.10 or 1.15, RPE of > 17 (out of 20), and other factors such as a post-exercise blood lactate level of > 8.0 mol/L (measured 3-min post-exercise) and/or a peak HR > 90% of predicted.

Predicted maximal HR for a 33-year-old is calculated as 208 - 0.7 * 33, resulting in 185. The patient's peak HR was 164, approximately 88% of the predicted value. The ATS/ACCP standards recommend achieving > 90% of the predicted maximal HR, which this patient did not reach. Furthermore, given that the heart rate reserve (HRR) at peak exercise was not less than 15 beats/min (calculated as 185 - 164 = 21), these results suggest that the test may have been submaximal.

4) Was the test protocol too lengthy? A cardiopulmonary exercise test (CPET) should ideally lead to volitional exhaustion within 8-12 minutes. Conducting a CPET lasting 15 minutes may have prevented the patient from reaching peak VO2 due to cardiac drift and overheating. Were there measures in place to mitigate this, such as a fan blowing onto the patient's body?

5) Blood gases were not corrected for arterial blood temperature, resulting in an underestimation of the reported PO2. Assuming a 1°C increase in core temperature, the correct values at peak exercise should be as follows: 90 for PO2 (normal), 30 for PaCO2 (normal, indicating adequate ventilation). However, the alveolar-arterial oxygen difference was not reported, though it should have been. Assuming an RER of 1.20 (figure), the AaDO2peak (at sea level) would be 33 mm Hg, not 41 mm Hg mentioned (which is not presented in the Table). An AaDO2 > 35 mmHg suggests the presence of severe gas exchange inefficiencies (J Appl Physiol, 87(6), 1997-2006, 1999).

Consequently, without additional data, it's challenging to conclude that there is a cardiovascular limitation. More likely, the VO2 peak is underestimated for the achieved wattage, and there may not have been a true maximal effort exerted by the patient.

Reference

1. American Thoracic Society; American College of Chest Physicians. ATS/ACCP Statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med. 2003 Jan 15;167(2):211-77. doi: 10.1164/rccm.167.2.211. Erratum in: Am J Respir Crit Care Med. 2003 May 15;1451-2. PMID: 12524257.

CONFLICT OF INTEREST: None Reported

October 11, 2023

Author Reply

Michael Mohning, MD | University of Colorado Anschutz Medical Campus, Aurora

We appreciate the questions brought up by Dr. Zavorsky, which we believe highlight some important technical aspects of exercise testing. Any omissions were related to space constraints, as this paper has a restricted format and was not meant to be a full technical review. We would recommend reviewing the previously cited articles for more detailed information.

1) The patient was exercised at 5280 feet elevation. As per current recommendations, we reported our VO2 as absolute L/min. Normalizing for body weight with this patient who had a weight of 102 kg and BMI of 31 gives an even lower-than-predicted VO2 of 20.6 ml/Kg/min. We would argue that estimating the peak VO2 as suggested can be misleading as the VO2/work slope is not a set relationship and when it is low (eg, in heart failure) it can suggest an abnormality. The low VO2/work relationship that our patient shows is consistent with early reliance on anaerobic metabolism that we describe.

2) We use breath-by-breath data collection for VO2 measurements, using a running average of 5 of 7 breaths with averages reported at 30 second intervals consistent with current recommendations.

3) The patient had an RER of 1.30 at peak, and we place arterial lines to measure lactate throughout testing. The patient had a peak lactate level of 10.6 mol/L. Again, not all data was able to be shown, but these numbers are consistent with a maximal test.

4) The protocol we used performs measurements resting for the first 3 minutes, followed by 3 minutes of unloaded cycling, followed by the ramp. Therefore, total exercise time including the unloaded cycling for this patient was 12 minutes. We apologize that this was not clarified.

5) Measured alveolar-arterial oxygen difference at peak exercise was 10 mmHg.

CONFLICT OF INTEREST: Consulting fees from Diffusion Pharmaceuticals outside the published article

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