A SciTechnol Journal Review Article
Baba, Int J Cardiovasc Res 2020, 9:4
DOI: 10.37532/icrj.2020.9(4).405
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International Journal of
Cardiovascular Research
International Publisher of Science,
Technology and Medicine
Cardiopulmonary Exercise
Testing in Children and
Adolescents: Focusing on the
Oxygen Uptake Efficiency
Slope
Reizo Baba*, Koji Kitatsuji, Yukiko Okamura, Norio Hotta and
Hisayoshi Ogata
Abstract
Cardiopulmonary Exercise Testing (CPET) is a clinical testing that
allows for the analysis of gas exchange during exercise. Maximal
oxygen uptake (VO
2
max), comprehensive index of cardiac,
respiratory, and skeletal muscle functions, is one of the most
important measurements obtained in CPET. Anaerobic threshold,
the exercise intensity at which lactate starts to accumulate in the
blood, is widely used, as it represents an exercise level that is not
too strenuous, but not too mild. The Minute Ventilation/Carbon
Dioxide Output relationship (VE/VCO
2
slope) is often used as a
prognostic marker of cardiac failure. The Oxygen Uptake Efficiency
Slope (OUES), a submaximal index of cardiorespiratory functional
reserve, correlates strongly with VO2max and is utilized as a
prognostic tool for various heart diseases including congenital heart
defects.
Keywords
Cardiopulmonary exercise testing; Oxygen uptake; Oxygen uptake
efficiency slope
*Corresponding author: Dr. Reizo Baba, Department of Lifelong Sports and
Health Sciences, Chubu University College of Life and Health Sciences, 1200
Matsumoto-cho, Kasugai, Aichi 487-8501, Japan, Mobile: 81568519212; E-mail:
reizobaba@gmail.com
Received: June 06, 2020 Accepted: June 22, 2020 Published: June 29, 2020
Introduction
In our everyday clinical practices of pediatric cardiology,
various clinical tests at rest, e.g., chest x-ray, electrocardiogram,
echocardiogram, blood gas analysis, serum biochemical tests, etc.
are essential and indispensable for their evaluation. However, these
clinical tests at rest can only observe, in a sense, extraordinary
sedentary unloaded physiological functions of the patients, not at
all their status during everyday activities like playing, exercising,
standing, or sleeping. erefore, appropriate evaluations of their
physiological and cardiopulmonary responses to various stresses are
essential in our clinical practices.
CPET is a test indispensable for the evaluation of functional
reserve in subjects with cardiorespiratory diseases, predicting their
prognosis, and effectiveness of treatment [1]. erefore, this review
overviews the basics of various measurements obtained from CPET
sessions, e.g., VO
2
max, Anaerobic reshold (AT), the VE, VCO
2
regression slope (VE/VCO
2
slope), and the OUES, in mainly pediatric
population.
What does the VO2max mean?
e VO
2
max, one of the most important and accurate prognostic
indices of patients with heart failure, shows the “maximal power
output” of a subject, which is determined comprehensively by the
reserve functions of the circulatory, respiratory, and the skeletal
muscles [2].
When one mole of glucose is aerobically metabolized, a total of
6 moles of oxygen is used and 36 moles of Adenosine Triphosphate
(ATP) is produced, namely:
C
6
H
12
O
6
+6O
2
+36ADP+36Pi→6CO
2
+42H
2
O+36ATP
ATP is called “currency of energy” which produces certain
amount of energy (30.5 kJ/mol) when it is hydrolyzed to ADP. e
proportional relationship addressed in this chemical formula tells
us that measuring the amount of oxygen utilized in (or taken into)
the body in a certain period (usually in a minute) is proportional to
the amount of energy produced in the body during the period, i.e.,
measuring the work rate (power output) of the subject. Although we
cannot measure the power produced by the body directly, we can
measure it indirectly by measuring the amount of oxygen taken into
the body in a certain period, i.e., the oxygen uptake (VO
2
). erefore,
measuring the maximal amount of oxygen one can take into the body
in a certain period is nothing other than measuring the maximal
energy output a person can produce.
With the Fick’s LAW, VO2 is described as:
VO
2
= C.O.×(CaO2-CVO2) = C.O.×(C
PV
-C
PA
),
where C.O. is minute cardiac output, CaO
2
, C
V
O
2
, C
PV
and C
PA
,
are oxygen content of the arterial, mixed venous, pulmonary venous,
and pulmonary arterial blood. As C.O., CaO
2
- C
V
O
2
, and CaO
2
- C
V
O
2
indicate the functions of the heart, efficiency of skeletal muscular
oxygen utility, and oxygen intake function of the lungs, respectively,
VO
2
max can be considered as an index of comprehensive reserves of
cardiac, skeletal muscular, and respiratory functions. A normal value
of VO
2
max for a normal, non-regularly exercising man is about 30-
40ml/min/kg, with slightly lower value in a woman.
Limitation of the VO
2
max
e VO
2
max is, however, only a “conceptual gold standard”.
Maximal exercise is oſten difficult and sometimes dangerous
because it may lead to myocardial ischemia [3,4]. We therefore
have to compromise by using submaximal measurements. e most
frequently used measurement is the peak VO
2
, the value at the end of
incremental exercise testing. Other indices that do not need maximal
exercise are anaerobic threshold (AT), the slope of the Minute
Ventilation (VE)/ Carbon Dioxide Production (VCO
2
) regression,
and the OUES.
AT and ventilatory threshold
Since the 1920s, the phenomenon of the rise in serum lactate
concentration during strenuous exercise has been known, which is