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.
Previous: CPET Test Interpretation, Part 3: Circulation
Cheat sheet:
CPET Interpretation Cheat Sheet
Previous
discussions of CPET issues:
How
does a CPET show a Cardiac limitation?
Exercise
and the IC, EELV and Vt/IC ratio
When
hypoventilation is the primary CPET limitation
What
does an inverse I:E ratio during exercise mean?
The
effects of anemia on exercise
Diagnosing
Mitochondrial Myopathies
The
CPET’s not over until it’s over
There’s
more than one way to determine AT
What’s
a normal post-pneumonectomy CPET?
What
does it mean when Ve exceeds its predicted during a CPET?
Is
it dynamic hyperinflation or something else?
When
a Pulmonary Mechanical Limitation to exercise isn’t the real
limitation
Ve-VCO2
slope: Just to AT or all the way to the peak?
Exercise
oscillatory ventilation
PETCO2
during exercise, a quick diagnostic indicator
Chronotropic
Index and O2 pulse
Recommended
reading:
ATS/ACCP
Statement on cardiopulmonary exercise testing. Am J Resp Crit Care
2003; 167: 211-277.
Balady
GJ; et al. Clinician’s guide to cardiopulmonary exercise testing in
adults: A scientific statement from the American Heart Association.
Circulation 2010; 122: 191-225.
Palange
P, et al. ERS Task Force: Recommendations on the use of exercise
testing in clinical practice. Eur Respir J 2007; 29: 185-209.
Wasserman
K, Hansen JE, Sue DY, Stringer WW, Whipp BJ. Principles of exercise
testing and interpretation. Lippincott, Williams and Wilkins,
publisher.
PFT
Blog by Richard
Johnston
is
licensed under a Creative
Commons Attribution-NonCommercial 4.0 International License.
