- A mother brings her 9-year-old boy to your clinic because he has been complaining of being
tired in physical education class at school for the past few months. When you ask him about his
symptoms, he reports having trouble catching his breath after he runs. Past medical history is
negative, and a review of systems reveals only a cough that occurs primarily at night several
times a month. He has grown well, and findings on physical examination are normal. - Of the following, the MOST likely reason for his exercise intolerance is
A. cystic fibrosis
B. exercise-induced asthma
C. iron deficiency anemia
D. vocal cord dysfunction
E. Wolff-Parkinson-White syndrome - Exercise intolerance is the failure to tolerate physical exercise at a level that would be
expected for a person’s age and condition, such as described for the boy in the vignette. For the
child, it is important to determine whether exercise intolerance is due to a primary pulmonary or
extrapulmonary cause. Pulmonary causes include asthma, cystic fibrosis, and acute and chronic
infections of the lung. Among the extrapulmonary causes of exercise intolerance are cardiac
disorders such as congestive heart failure, neuromuscular disorders such as muscular
dystrophy, anemia, and deconditioning. - Exercise intolerance is measured primarily by the maximal oxygen consumption test, and
examining the components of maximal oxygen consumption can be useful in understanding the
reasons for exercise intolerance associated with various disease states. The Fick equation for
maximal oxygen consumption is:
VO2max = SVmax x HRmax x (CaO2 — CvO2)max
where VO2 = oxygen consumption, SV=stroke volume, HR=heart rate, CaO2=oxygen
content of arterial blood, and CvO2=oxygen content of mixed venous blood. - A sedentary lifestyle and certain cardiac diseases such as congestive heart failure and cyanotic heart
disease can cause a decrease in stroke volume. Diseases such as asthma, cystic fibrosis,
anemia, and vocal cord dysfunction lower the oxygen content of arterial blood. States causing
muscle weakness, such as muscular dystrophy or general deconditioning, can result in
decreased oxygen use by the tissues. Alterations in any of these components can lead to
decreased maximal oxygen consumption and exercise intolerance. - The shortness of breath after running and a nighttime cough described for the boy in the
vignette make exercise-induced bronchoconstriction (EIB), also called exercise-induced asthma,
the most likely diagnosis. Children who have EIB generally experience shortness of breath,
chest tightness, and cough approximately 10 to 15 minutes after beginning exercise.
Administration of a short-acting beta2 agonist or inhaled cromolyn sodium prior to exercising can
help to prevent the symptoms. For patients who have poorly controlled asthma and experience
EIB, the most appropriate management is the use of inhaled corticosteroids and possibly other
maintenance medications to control overall asthma symptoms. If a child who has presumed EIB
fails to respond to pretreatment with beta2 agonists or inhaled cromolyn sodium, other
diagnoses such as vocal cord dysfunction should be considered. - Vocal cord dysfunction is the paradoxic adduction of the vocal cords during inspiration,
causing airway obstruction during exercise. Inspiratory wheezing and throat tightness are
common symptoms, but cough at night is not. Cystic fibrosis is unlikely in any child who is
growing well and has no extrapulmonary symptoms. Iron deficiency anemia can cause exerciseinduced
dyspnea, but the boy’s history is not suggestive of this condition. Wolff-Parkinson-White
syndrome causes re-entrant tachycardia; syncope rather than exercise intolerance is the usual
clinical manifestation
Dr. Jayaprakash
Superintendent, ICH.
Institute of Child Health.
Gov. Medical College Kottayam.
Kerala, India.