Question

A 155 lb., 60-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 15 breaths/min Alveolar ventilation 4.1 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 252 L/min Maximum expiratory flow rate 21 L/min PaO2 63 mm Hg PaCO2 38 mm Hg Pulmonary function tests after bronchodilator therapy: Frequency 15 breaths/min Alveolar ventilation 4.25 L/min VC 2.4 L FRC 4.0 L TLC 5.2 L Maximum inspiratory flow rate 252 L/min Maximum expiratory flow rate 24 L/min PaO2 63 mm Hg PaCO2 37 mm Hg

6. What is the cause of this altered RV?

7. Calculate the tidal volume (TV) for this person before and after the bronchodilator therapy. TV = AV/f + patient body weight. Hint: TV is calculated in mL, so you will need to convert L to mL before completing the equation.

8. Is each TV normal or altered?

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

10. Is each MV normal or altered?

Answer 1

Information provided

Symptoms -

1. Chronic productive cough
2. Exertional dyspneo
3. Mild cyanosis
4. Reduced forced expiration

Pulmonary function test result

	Pre bronchodilator	Post bronchodilator
respiratory rate ( aka frequency)	15 breaths /min	15 breaths /min
Alveolar ventilation	4.1 l/min	4.25 l/min
Vital capacity (VC)	2.2 L	2.4 L
Functional residual capacity (FRC)	4.0 L	4.0 L
Total lung capacity	5.2 L	5.2L
Maximum inspiratory flow rate	252 L/min	252 L/min
Maximum expiratory flow rate	21 L/min	24 L/min
PO2	63 mmHg	63 mmHg
PCO2	38 mmHg	37 mmHg

From the PFT it is clear that after bronchodilator therapy, there is an improvement in alveolar ventilation, vital capacity, and maximal expiratory flow rate.

Base on these observations and the history of the patient - it seems that the patient is suffering from airway disease. As the bronchodilator response was not profound - it seems to be a case of chronic obstructive pulmonary disease

Question 6:

residual volume is that volume of air that remains in the lung after forceful expiration -

Formula - Total lung capacity - vital capacity

Pre bronchodilator residual volume=

5.2 L - 2.2 L= 3 L

Post bronchodilator residual volume =

5.2 L - 2.4 L = 2.8 L

therefore, we can conclude that there is a decrease in the residual volume after bronchodilator therapy. The reason for this is:

1. COPD is airway inflammation and there is alveolar destruction.
2. As a result of this, there is an increase in expiratory airflow obstruction.
3. Therefore, the airway collapse of the airways prematurely during expiration.
4. As a result, the air gets trapped in the lungs.
5. This leads to an increase in residual capacity
6. After bronchodilator therapy, some of the bronchoconstriction is reduced.
7. This allows the trapped air to escape during breathing.
8. This in turn reduces the residual volume.

Answer 7 :

The formula for tidal volume is - Alveolar ventilation/frequency + the weight of the patient

Before we calculate the Tidal volume, please understand why we are subtracting the patient's weight

the Alveolar ventilation = ( tidal volume - physiological dead space ) / frequency

The physiological dead space is that part of the air which lies in the airways and doesn't participate in gas exchange. The estimate physiological dead space = 2 ml x weight in Kg or the weight of the patient in pounds

Coming back to the problem, inserting all values ( for pre-bronchodilator)-

TV = 4.1 x 1000 / 15 + 155 = 428 ml ( we have converted the alveolar volume into ml)

Post bronchodilator:

TV -= 4.25 x 1000 / 15 + 155 = 438 ml

Therefore the prebronchodilator tidal volume is 428 ml and post-bronchodilator tidal volume is 438ml

Answer 8

• Normal tidal volume is 500 ml
• In our patient, it is reduced.
• Administration of bronchodilator has brought about a slight improvement of 10ml
• Therefore, the tidal volume is altered not normal

Answer 9

Minute ventilation formula = tidal volume x frequency

Pre-bronchodilator value = 428 ml x 15 = 6420 ml = 6.420 L/min

Post-bronchodilator value = 438 ml x 15 = 6570 ml = 6.570 L/min

Answer 10

Normal minute ventilation is = 5 - 8 L/min

So the minute ventilation is normal. The patient has responded to reduced tidal volume by increasing his respiratory rate. This has allowed the patient to maintain a normal minute ventilation