Question

A 17 year old student complained of wheezing and shortness of breath, especially at night. He was known to be allergic to feathers and house dust. Physical examination revealed inspiratory and expiratory rales and hyperresonance with percussion of the chest but no cyanosis. Radiologic examination suggested over-inflation of the lungs, but no localized disease. The following laboratory and pulmonary function test values were obtained:

Vital Capacity                                     2,800 ml (decreased)

Functional Residual Capacity                        4,420 ml (increased)

Total Lung Capacity                           7,050 ml (normal)

Tidal Volume                                      600 ml (normal)

Respiratory Rate                                16 breaths/minute (increased)

Arterial PO2                                        62 mmHg

Arterial O2 saturation                                   90%

Arterial O2 saturation                                   100%

(breathing 100% oxygen)

Arterial pCO2                                     38 mmHg

Arterial Blood pH                               7.44

Maximum voluntary ventilation       60 L/min (decreased)

Maximum inspiratory flow rate        220 L/min

Maximum expiratory flow rate         50 L/min

After administration of an isoproterenol aerosol, epinephrine subcutaneously and aminophylline intravenously, the following values were obtained:

Vital capacity                                      3,640 ml

Maximum voluntary ventilation       110 L/min

Arterial O2 saturation                                   97%

1.         Explain the shortness of breath, wheezing, and rales in terms of the functional deficit. What does the change in pulmonary function after therapy indicate?

Answer 1

Answer:1

This patient is suffering from Bronchial asthma.

Bronchial asthma is a condition characterised by symptoms of cough, breathlessness and chest tigthness associated with variable airflow obstruction. In this condition, there is inflammation of the airways. This leads to swelling of the airways and bronchospasm. This bronchospasm is reversible with bronchodilator therapy.

He has the following features suggestive of asthma:

1. Wheezing, shortness of breath.
2. Nighttime symptoms - this suggests poor control of asthma
3. History of allergies.
4. Percussion revealed - hyper resonance - this indicates air-trapping. In asthma due to expiratory airflow obstruction, there is incomplete exhalation. This causes incomplete emptying of the alveoli. This traps the air in the alveoli
5. Auscultation revealed inspiratory and expiratory rales - Rales may be produced due to the snap opening of small airways. NOTE -This patient didn't have rhonchi. The absence of rhonchi doesn't rule out asthma. Rather the absence of rhonchi ( also known as the silent chest) is a red flag sign (dangerous sign)
6. Chest X-ray revealed hyperinflation - This is another indication of air-trapping ( which is characteristic of asthma)
7. The pulmonary function test is also suggestive of asthma.
   • Let us calculate forced expiratory volume at the end of the first sec (FEV1) and FEV1/VC ratio .

maximal voluntary ventilation (MVV) = forced expiratory volume at the end of the first sec (FEV1)* 35

let us put in the values

60,000 ml = FEV1 * 35

FEV1 = 60,000/35 = 1,714 ml (Pre bronchodilator FEV1)

let us calculate the FEV1/VC ratio = 1,714 ml / 2,800 ml = 0.61

If the ratio of FEV1/VC is less than 0.70, it indicates an obstructive abnormality in lung functions. Obstructive abnormality is seen in bronchial asthma.

• Reduced pre-bronchodilator capacity which improved by 840 ml after bronchodilator drugs like epinephrine ( beta agonist), aminophylline (non-selective phosphodiesterase inhibitor)and isoproterenol ( beta 1 and 2 agonists). This indicates reversible airflow obstruction. This is a feature of asthma

• Functional residual capacity is increased due to air-trapping. Air trapping is caused due to expiratory airflow obstruction.

Answer 2:

The FEV1/VC ratio of less than 0.70, improvement in vital capacity and maximal voluntary ventilation after bronchodilator therapy are consistent with the diagnosis of Bronchial asthma.