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

Explain the reason for the elevated functional residual capacity in terms of airway resistance during inspiration and expiration.

Answer 1

Patient are allergic to dust cause asthmatic reaction, incresed airway secretion, mucous secretion, Inflammation and edema in airway.

These conditions cause Hypoventilation in lungs, retention of CO2, hypercapnia, hypoxia. Due to hypoxia incresed effort by lungs for improving oxygen level cause Incresed airway resistance.

The main reason is lungs Hypoventilation which condition lungs try to effort more oxygen so incresed airway resistance and functional residual capacity because heart need more oxygen for pumping the blood cause more pressure on lungs.