Question

Patricia Jones, age 50 years, was diagnosed with idiopathic pulmonary fibrosis (IPF) two years ago. IPF is a chronic, progressive lung disease with no cure. It results in fibrotic scarring and thickening of lungs tissue, impairing oxygen delivery. Despite her diagnosis, patricia continues to work full time at her job, taking the commuter train daily. However, over the past few weeks the demands of activities of daily living have become increasingly difficult. She complains of being tired, persistent dry cough, and extreme shortness of breath when climbing a flight of stairs. She had to take a medical leave from her job. The following information was obtained at her recent physical examination.

Arterial Blood Gases At Rest
PaO2	76 mm Hg
PaCO2	37 mm Hg
% Hgb Saturation	97%

Results of Pulmonary Function Tests at Rest
Total Lung Capacity	Decreased
Functional Residual Capacity	Decreased
Residual Volume	Decreased
FEV1/FVC	Increased

FEV₁ = volume of air expired in the first second of forced expiration; FVC, forced vital capacity

After these results were obtained at rest, Sue was asked to exercise on a stair climber. After only 2 minutes, she became extremely fatigued and had to discontinue the test. The arterial blood gas measurements were repeated, with the following results.

Arterial Blood Gases During Exercise
PaO2	58 mm Hg
PaCO2	36 mm Hg
% Hgb Saturation	90%

1. Idiopathic pulmonary fibrosis is a restrictive pulmonary disease. Define lung compliance and explain how lung fibrosis affects lung compliance. Use this information to explain Patricia's decreased total lung capacity, decreased functional residual capacity (FRC), and decreased residual volume at rest.

Answer 1

Lung compliance is the ablity of lungs to expand and contract based on changes in pressure, it is a measure of lungs ablity to stretch and expand.

Lung fibrosis or pulmonary fibrosis is associated with reduced lung compliance. In a condition like fibrosis, the lungs elastin fibrin are replaced by collagen, these collagen are less elastic, so they decrease the compliance of lungs. Low compliance means stiff lungs.

Lung capacity refers to volume of air in lungs, normaly it is around 6 liters. In a condition like pulmonary fibrosis, the lungs are stiff so it makes it harder for oxygen to pass through the air sacs of the lungs, which reduces the amount of oxygen passing into blood stream, thereby reducing lung capacity.

Functional residual capacity is the volume of air present in the lungs at the end of passive expiration, pulmonary fibrosis can prevent your lungs from adequately expanding, because of which there is reduced lung volume, which in turn decreases FRC.

Residual volume at rest, it is the air that is left after a forced exhalation, because in fibrosis there is reduced lung capacity, residual volume also decreases.