A Case of a Healthy, Athletic Teenager Who Presents With Isolated Symptoms of Exercise-Induced Dyspnea | Patient Case Quiz

Mar 12, 2015 | Dipankar Gupta, MD; Mutasim Abu-Hasan, MD

A 16-year-old athletic female who has a past medical history of asthma requiring bronchodilators as needed, presents with shortness of breath with exercise. Symptoms usually occur 15 minutes after exercise, are worse with intense physical activity, and cause her to stop running.

There is no history of associated wheezing or stridor. There were no environmental triggers or history of recent infections. There was also no history of palpitations or syncope.

She was diagnosed with exercise-induced asthma two years ago and was prescribed an albuterol inhaler without significant benefit. On examination, she is a relatively thinly built female with a body mass index (BMI) of 22 kg/m². Chest and cardiac auscultation are normal. Electrocardiogram (ECG) reveals first-degree heart block and echocardiogram demonstrates normal biventricular size and function.

Spirometry and lung volume reveal the following data (Table 1).

Table 1

	Actual	% Predicted
FVC	3.07L	92
FEV1	2.89L	97
FEV1/FVC	94
FEF 25/75	4.3L	115
FRC	2.22L	94
RV	1.08L	84
TLC	4.19L	90
RV/TLC	26	93

She undergoes a cardiopulmonary exercise stress test with incremental increase in either speed or incline every minute as tolerated. During the test, breath-by-breath analysis of oxygen consumption (VO₂), CO₂ production (VCO₂), tidal volume (VT) and minute ventilation (VE) are obtained. Also, pre- and post-exercise spirometry are done and showed no significant decreased in FEV1 after exercise. Peak cardiovascular and ventilatory responses are outlined in Table 2.

Table 2

	Predicted	Measured	% Predicted
VO₂ (L/min)	1.94	2.38	123
VCO₂ (L/min)	1.86	2.27	122
Anaerobic Threshold (AT)	>0.777	1.94
Heart Rate (bpm)	188	164	87
O₂ Pulse	10.6	14.5	137
VE Max (L/min)	96.8	81.5	84
VT (L)	1.38	0.99	72
VT/FVC	0.6	0.33	54%
Respiratory Rate (RR)	<50	79
Breathing Reserve (%)	20-40	15

On a follow-up evaluation, pulmonary function tests continue to be normal with persistent symptoms. She undergoes maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) measurements that reveal the following results (Table 3).

Table 3

	Predicted	Measured	% Predicted
PImax/MIP(cmH₂O)	-75.4	-46.13	61
PEmax/MEP(cmH₂O)	100.8	45.34	45

Which of the following statements best explains the cause of this patient's symptoms?

A. Respiratory muscle weakness.
B. Restrictive lung disease due to thoracic cage abnormality.
C. Exercise-induced asthma.
D. Cardiomyopathy.
E. Deconditioned athlete.
F. Exercise-induced vocal cord dysfunction.

Show Answer

The correct answer is: A. Respiratory muscle weakness.

Exercise-induced asthma is a common cause of exercise-induced dyspnea (EID). However, the exercise test showed no evidence of exercise-induced bronchospasm, evident by no decrease in FEV1 after exercise.

Exercise-induced vocal cord dysfunction can be misdiagnosed as asthma. This sub-group of patients presents with paradoxical cord movement (adduction with inspiration) causing increased upper airway resistance, dyspnea, and stridor. In our patient, there was no history of stridor and no evidence of upper airway obstruction on spirometry.

Peak cardiovascular and respiratory variables including maximal VO₂, O₂ pulse and anaerobic threshold suggest that she has good cardiovascular conditioning. Thoracic cage abnormalities like scoliosis can result in restrictive lung disease; however, there were no such abnormalities in this patient.

However, MIP and MEP measurements are significantly low, suggestive of respiratory muscle weakness. Weak respiratory muscles can affect tidal volume and minute ventilation and can result in a patient's feeling of shortness of breath. The patient's breathing pattern is fast and shallow as suggested by the low tidal volume (72% of predicted) and, more importantly, the low tidal volume to vital capacity ratio (VT/FVC) of 54% predicted. Figure 1 shows the patient's VT over VE and demonstrates her shallow and fast breathing pattern.

Figure 1

Normal individuals with no respiratory limitation use less than 80% of their maximal minute ventilation capacity and leave 20% of breathing reserve. Since this patient has only 15% of breathing reserve at peak exercise, this suggests that respiratory muscle weakness is the cause of her symptoms.

Disproportionate weakness of respiratory muscles in athletic individuals is more likely due to poor training of these muscles than intrinsic muscle disease.

The diagnosis is further substantiated by the resolution of symptoms after the patient underwent respiratory muscle training with marked improvement in MIP and MEP in the six-month period as shown in Table 4.

Table 4

	Predicted	Measured	% Predicted
PImax/MIP(cmH₂O) Baseline	-77.05	-90.57	118
PEmax/MEP(cmH₂O) 4 months later	100.8	59.84	59

A Case of a Healthy, Athletic Teenager Who Presents With Isolated Symptoms of Exercise-Induced Dyspnea | Patient Case Quiz

Table 1

Table 2

Table 3

Which of the following statements best explains the cause of this patient's symptoms?

Figure 1

Table 4

Guidelines

JACC Journals on ACC.org

Membership

About ACC

Clinical Topics

Latest in Cardiology

Education and Meetings

Tools and Practice Support

Heart House