Question

Respiratory Case Histories - Case 13

A 150 lb., 62-year-old man had a chronic productive cough, exertional dyspnea, mild cyanosis, and marked slowing of forced expiration. His pulmonary function and laboratory tests follow:

Frequency	16 breaths/min
Alveolar ventilation	4.2 L/min
Vital capacity (VC)	2.2 L
Functional residual capacity (FRC)	4.0 L
Total lung capacity (TLC)	5.2 L
Maximum inspiratory flow rate	250 L/min
Maximum expiratory flow rate	20 L/min
PaO2	62 mm Hg
PaCO2	39 mm Hg

Pulmonary function tests after bronchodilator therapy:

Frequency	16 breaths/min
Alveolar ventilation	4.35 L/min
VC	2.4 L
FRC	4.0 L
TLC	5.2 L
Maximum inspiratory flow rate	250 L/min
Maximum expiratory flow rate	23 L/min
PaO2	62 mm Hg
PaCO2	38 mm Hg

1. What is the disorder of this 62-year-old man?

2. Is this primarily a restrictive or an obstructive disorder? Why?

3. Why is the bronchodilator therapy ineffective in this man?

4. What causes the hypoxemia?

6. What is the cause of this altered RV?

7. Calculate the tidal volume (TV) for this person before and after the bronchodilator therapy.

8. Is each TV normal or altered?

9. Calculate the minute ventilation (MV) for this person before and after the bronchodilator therapy.

10. Is each MV normal or altered?

Answer 1

This patient is likely to be suffering from chronic obstructive airway disease.

Explanation:

1. History -
   1. Productive cough (as airways are inflamed)
   2. Exertional dyspnea
2. Signs - cyanosis -
3. Pulmonary function:
   1. Reduce forced expiration (FEV)
   2. Reduced expiratory flow rate - which improved with bronchodilator therapy
   3. Reduced vital capacity which improved with bronchodilator therapy
   4. Functional residual volume is high

All these factors point towards an expiratory airflow obstruction. This expiratory airflow obstruction doesn't improve much with bronchodilator therapy. This is seen with Chronic obstructive airway disease. In asthma the response to a bronchodilator is good.

Answer 2 - Obstructive: because

Explanation:

1. History -
   1. Productive cough (as airways are inflamed)
   2. Exertional dyspnea
2. Signs - cyanosis -
3. Pulmonary function:
   1. Reduce forced expiration (FEV)
   2. Reduced expiratory flow rate - which improved with bronchodilator therapy
   3. Reduced vital capacity which improved with bronchodilator therapy
   4. Functional residual volume is high

All these factors point towards an expiratory airflow obstruction.

Answer 3:

Bronchodilator response is less because the some changes might have occurred in the airways that have reduced the bronchodilator response. This includes fibrosis in the airways

Answer 4:

The cause of hypoxemia is acute bronchospasm

Answer 6: The residual volume is increased. This is because of expiratory airflow obstruction. As a result, less air is expired and air gets trapped in the lungs.

Answer 7:

The formula of minute ventilation = TV x RR ( frequency)

Prebronchodilator

• minute ventilation ( alveolar ventilation) = 4.2 L/min
• frequency = 16 breath /min
• minute ventilation = Tidal volume x frequency
• 4.2 L/min = TV x 16 breath /min
• TV = 4.2 / 16 = 0.263 L = 262 ml

Post bronchodilator -

• minute ventilation ( alveolar ventilation) = 4.35 L/min
• frequency = 16 breath /min
• minute ventilation = Tidal volume x frequency
• 4.35 L/min = TV x 16 breath /min
• TV = 4.35 / 16 = 0.272 L = 272 ml

Answer 8: The tidal volume is reduced

Normal tidal volume = 7ml /kg

The patient weight = 150 lb = 150 / 2.2 = 68 kgs

Therefore Tidal volume = 68 x 7 = 477 ml

So the tidal volume (predicted)for this patient is 477 ml. The measured Tidal volume ( pre and post) both is less for this patient