What is the next step in managing a patient with vomiting on exertion and a normal abdominal ultrasound, considering potential cardiac or pulmonary causes?

Cardiopulmonary Exercise Testing for Vomiting on Exertion with Normal Abdominal Ultrasound

The next step is cardiopulmonary exercise testing (CPET) to differentiate cardiac versus pulmonary causes of exertional symptoms, as this patient's presentation suggests unexplained exertional intolerance that requires systematic evaluation of the cardiovascular and pulmonary systems. 1

Why CPET is the Definitive Next Step

CPET possesses the unique ability to comprehensively assess the independent and integrated exertional responses of the cardiovascular and pulmonary systems, making it the most important assessment for unexplained exertional symptoms. 1 The primary goal should be to reproduce the patient's exertional vomiting during testing to optimally detect any coinciding physiological abnormalities. 1

Key CPET Parameters to Measure

The following variables must be assessed during testing to distinguish cardiac from pulmonary causes 1:

Cardiac causes show:

• Reduced peak VO2 with normal pre-exercise pulmonary function tests 1
• SpO2 remains ≥90% throughout exercise 1
• No change in FEV1 or peak expiratory flow post-exercise 1
• May have reduced cardiac output 1
• VE max <80% of maximal voluntary ventilation 1

Pulmonary causes show:

• Reduced peak VO2 with abnormal pre-exercise pulmonary function tests (obstructive or restrictive pattern) 1
• SpO2 may drop below 90% during exercise 1
• ≥15% decrease in FEV1 or peak expiratory flow post-exercise (suggests exercise-induced bronchospasm) 1
• VE max ≥80% of maximal voluntary ventilation 1

Critical Testing Protocol Details

Pulmonary function testing must be performed both before and after CPET, with post-exercise measurements at 1,3,5,7,10,15, and 20 minutes into recovery, as exercise-induced bronchospasm responses typically worsen several minutes after exercise cessation. 1

Pulse oximetry (SpO2) must be continuously monitored at rest, throughout exercise, and into recovery. 1 A drop in SpO2 below 90% during exercise indicates a pulmonary limitation. 1

Maximal voluntary ventilation should be directly measured prior to exercise rather than estimated using FEV1 × 40. 1

Additional Cardiac Evaluation Considerations

While CPET is being arranged, consider these cardiac-specific evaluations 2:

• Transthoracic echocardiography is mandated when cardiac cause is suspected to assess for structural abnormalities including hypertrophic cardiomyopathy, valvular disease, or cardiomyopathies. 2
• Brain natriuretic peptide (BNP) levels can help exclude heart failure. 2, 3
• ECG monitoring during CPET may confirm exertion-induced supraventricular or ventricular tachycardia in individuals with suggestive history. 1

Common Pitfalls to Avoid

Do not assume gastrointestinal pathology simply because the primary symptom is vomiting. Exertional vomiting can be a manifestation of severe cardiac or pulmonary limitation causing exercise intolerance. 1

Do not perform extensive gastrointestinal workup before ruling out cardiopulmonary causes when symptoms are strictly exertional. 4, 5 The temporal relationship to exertion is the critical diagnostic clue pointing toward cardiopulmonary etiology.

Do not rely on estimated maximal voluntary ventilation (FEV1 × 40) as this can be inaccurate - direct measurement is essential for proper interpretation. 1

Do not stop pulmonary function monitoring immediately after exercise cessation - continue for at least 20 minutes as exercise-induced bronchospasm may not manifest until several minutes into recovery. 1

Risk Stratification During Testing

Abnormal hemodynamic response, abnormal ECG response, or heart rate recovery <12 beats at 1 minute post-exercise provide evidence of poor prognosis and greater disease severity. 1

Report of unusual dyspnea (severely difficult, patient cannot continue) as the primary subjective symptom eliciting test termination indicates increased adverse event risk. 1