After having gone through the descriptive checklists for ventilatory, gas exchange and circulatory limitations the reason(s) for a patient’s exercise limitation, if any, should be reasonably clear. However, one of the first questions that should be asked when reading an exercise test is what was the purpose of the test?
- Maximum safe exercise capacity for Pulmonary Rehab?
- Rule in/rule out exercise-induced bronchospasm?
- Pre-operative assessment?
- Dyspnea of uncertain etiology?
- What is the primary limitation to exercise (pulmonary or cardiac)?
- Is deconditioning suspected?
The interpretation and summary should address these concerns.
The descriptions checklist is the main groundwork for the actual interpretation and any abnormal findings there may signal the need for specific comments. The interpretation should start by indicating whether or not the patient’s exercise capacity was normal and then should indicate the presence or absence of any limitations.
What was the patient’s maximum exercise capacity (maximum VO2)?
- >120% = Elevated
- 80% to 120% = Normal
- 60% to 79% = Mildly reduced
- 40% to 59% = Moderately reduced
- <40% = Severely reduced
Example: There was a {elevated | normal | mildly reduced | moderately reduced | severely reduced} exercise capacity as indicated by the maximum oxygen consumption of XX%.
Why was the test terminated?
Does the reason the test was terminated have any clinical significance?
Example: Testing was terminated due to xxxxxxx.
Was the test adequate or submaximal?
Testing was adequate if:
- The maximum VO2 was ≧80% of predicted
- The maximum Minute Ventilation was ≧85% of predicted
- SaO2 decreased >3% during exercise
- RER was greater than 1.10 (bicycle ergometer) or 1.05 (treadmill)
- The maximum Heart rate was ≧85% of predicted
- There was a VO2 plateau
- FEV1 decreased by ≧15% following exercise-induced
- Testing was terminated due to safety concerns (ECG abnormalities, systolic or diastolic hypertension, chest pain, patient dizziness or fainting)
If the test was not adequate then it was submaximal.
Example: {There was an adequate exercise test effort as indicated by xxxxxx. | Test was submaximal.}
Was there a ventilatory limitation to exercise?
The gold standard for a ventilatory limitation is whether the maximum minute ventilation was ≧85% of predicted. In patients with COPD a ventilatory limit can also be shown when the Vt/IC ratio is ≧85% and there has been an increase in EELV of ≧0.25 L.
Example: {There was no ventilatory limitation to exercise. | There was a ventilatory limit to exercise as indicated by {the maximum minute ventilation of XX% of predicted | the Vt/IC of X.XX and increase in EELV of X.XX L.}}
Was there an abnormal ventilatory response to exercise?
An abnormal ventilatory response to exercise can include a respiratory rate >55, an blunted increase in tidal volume of less than 2 times baseline, a Vt/IC ratio ≧85% or an increase in EELV of ≧0.25 L. In an adequate test and in the absence of an true ventilatory limitation these factors will likely contribute to the patient’s sensation of dyspnea.
Example: {The elevated respiratory rate | blunted increase in tidal volume | elevated Vt/IC ratio | elevated increase in EELV} likely contributes to the patient’s sensation of dyspnea.
Was there post-exercise bronchoconstriction or bronchodilation?
A significant change in post-exercise FEV1 is a decrease or increase of ≧15%.
Example: {There was a significant decrease in FEV1 following exercise which suggests Exercise-Induced Bronchoconstriction. | There was no significant changed in FEV1 following exercise. | There was a significant increase in FEV1 following exercise which although normal suggests the presence of labile airways.}
Was there evidence of a gas exchange limitation?
The gold standard for a gas exchange limitation is whether the SaO2 decreased by ≧3%. Pulmonary vascular disease is likely when this is accompanied by a low DLCO and/or an elevated Ve/VCO2.
Example: {There was no significant gas exchange limitation. | There was a gas exchange limitation to exercise as indicated by the decrease in SaO2 of X%.} {{The reduced DLCO of XX% of predicted | The elevated Ve/VCO2 of XX} suggests pulmonary vascular disease.}
Was there evidence of inefficient ventilation?
Inefficient ventilation is indicated by an elevated Ve/VCO2 or Ve-VCO2 slope, or by a reduced maximum PetCO2. In an adequate test and in the absence of a true gas exchange limitation these factors likely contribute to the patient’s sensation of dyspnea.
Example: The {elevated Ve/VCO2 | reduced maximum PetCO2}indicates an inefficient ventilatory response to exercise which likely contributes to the patient’s sensation of dyspnea.
Was there evidence of a circulatory limitation to exercise?
The gold standard for a circulatory limitation is a reduced VO2 at Anaerobic threshold. In an adequate test a reduced maximum O2 pulse of <80% of predicted suggests a low stroke volume while a reduced chronotropic index of less than 0.80 suggests chronotropic incompetence.
Example: {There was no significant evidence of a circulatory limitation to exercise. | There was a circulatory limitation to exercise as indicated by the VO2 at Anaerobic Threshold of XX%.} {The reduced maximum O2 pulse suggests a stroke volume limitation. | The reduced Chronotropic Index suggests chronotropic incompetence {possibly secondary to the patient’s beta blocker medication xxxxxx.}}
Was there evidence of an abnormal circulatory response to exercise?
A reduced maximum O2 pulse (<80% of predicted) and a reduced (<0.80) or elevated Chronotropic Index (>1.30) in an adequate test and in the absence of true circulatory limitation to exercise will likely contribute to the patient’s sensation of dyspnea.
Example: The {reduced maximum O2pulse | {reduced | elevated} Chronotropic Index} indicates an abnormal circulatory response to exercise which likely contributes to the patient’s sensation of dyspnea.
Was there evidence of hypertension or hypotension?
If the systolic blood pressure was >160 mm Hg or the diastolic blood pressure was >100 mm Hg at rest or during exercise then there was a hypertensive response to exercise. If the systolic pressure did increase at least 10 mm Hg or decreased during exercise then there was a hypotensive response to exercise.
Example: {There was a normal blood pressure response to exercise. | There was a {systolic | diastolic} hypertensive response to exercise as indicated by the blood pressure of XXX/XXX. | There was a hypotensive response to exercise as indicated by {the increase in systolic pressure of <10 mm Hg | the decrease in systolic pressure to XXX.}
Was there clinical or ECG evidence of cardiac ischemia?
Any significant ECG changes or patient complaint of chest pain should be documented.
Example: {There were significant ECG changes in the {presence | absence} of chest pain. | There was chest pain in the absence of significant ECG changes.}
Summary:
The summary should include only the primary findings from the interpretation. Determining the primary cause of any exercise limitation is easiest when there is only one significant limitation. When there are multiple significant limitations then a judgment call needs to made about which limitation seems to be primary and which seem to be secondary.
Example: Testing showed a {elevated | normal | mildly reduced | moderately reduced | severely reduced} exercise capacity in an {adequate | submaximal} exercise test. The primary exercise limitation was {ventilatory | gas exchange | circulatory}. {There was a secondary {ventilatory | gas exchange | circulatory }limitation to exercise.} {An {abnormal ventilatory | inefficient gas exchange | abnormal circulatory} response to exercise likely contributes to the patient’s sensation of dyspnea.}
Interpreting a CPET requires a good understanding of cardiopulmonary physiology but it really isn’t that much more difficult than interpreting regular PFTs. Although at first glance the multitude of parameters may look confusing each parameter has something distinct to say about any limitations to the flow of oxygen and carbon dioxide during exercise and once they are organized the results become much clearer. Hopefully the approach I’ve detailed here will help make the interpretive process more straightforward.