Pulmonary Function Tests

Question 1

Major components of pulmonary function testing

Answer 1

• lung volumes
• expiratory airflow
• gas exchange

Question 2

Technique of lung volume measurement in pulmonary function testing

Answer 2

• measured by spirometer, helium dilution method or body plethysmography
• LV should = 80-120% of predicted total lung capacity
• If residual volume is elevated ==> air trapping

Question 3

Technique of expiratory airflow measurement

Answer 3

• measured by spirometer
• expiration for at least 6 seconds w/curve plateau of at least 1 sec

Question 4

Technique of gas exchange measurement

Answer 4

• measured by DLCO
• determined by surface area, membrane thickness, diffusion gradient, presence of hemoglobin

Question 5

Characterisctics of volumes

Answer 5

• Volumes: can be measured or estimated
• On spirogram (right) upward deflection are inspiratory and downward deflections are expiratory
• Tidal volume (VT): volume of normal, even respirations at rest
• Expiratory reserve volume (ERV): Volume of gas remaining in the lung after a normal, tidal expiration that can be exhaled
• Inspiratory Reserve volume (IRV): Volume of gas that can be inhaled above that inhaled with a normal tidal inspiration
• Residual Volume (RV): Volume of gas remaining in the lung at the end of a maximum expiration

Question 6

Characteristics of capacities

Answer 6

• Capacities: sums of at least 2 volumes
• Functional residual capacity (FRV): Where the tendency for the chest to expand and the lungs to contract are at equilibrium. Volume of gas remaining in the lung at the end of a tidal expiration”. Sum of ERV and RV.
• Inspiratory capacity (IC): Volume of gas that can be maximally inspired from FRC. Sum of VT and IRV
• Vital Capacity (VC): Volume of gas that can be maximally inspired from RV. Sum of ERV, VT, and IRV
• Total Lung Capacity (TLC): Total volume of gas in the lung. Sum of RV, ERV, TV, and IRV

Question 7

Determinants of FRC (aka TGV)

Answer 7

• “functional residual capacity” (aka “thoracic gas volume”)
• Expiratory Reserve Volume + Residual Volume

Question 8

Obstructive vs. Restrictive Pulmonary Function Test Results

Answer 8

• Obstructive: FEV1/FVC ratio tells if you have this or not, should be 0.7 - 0.8; < 0.7 is obstructive.
  
  • Asthma
  • COPD (emphysema, bronchitis)
  • Bronchiolitis
• ​Restrictive: Can’t diagnose with spirometry - ratio can be preserved or elevated. Trouble with the chest wall expansion or elastic recoil
  
  • ​Pulmonary edema
  • ILD
  • Neuromuscular weakness
  • Pleural disease
  • Obesity

Question 9

Major factors contributing to D_LCO

Answer 9

• 1. amount of hemoglobin
• 2. surface area
• 3. membrane thickness

Question 10

D_LCO definition

Answer 10

• diffusion capacity of carbon monoxide
• gas used to quantify gas exchange
• anything that alters the ability of gases to diffuse will alter this measurement

Question 11

Factors that increase/decrease D_LCO

Answer 11

• Increased DLCO:
  
  • Polycythemia
  • Interstitial edema​
  • asthma
  • Alveolar hemorrhage
• ​Decreased DLCO:
  
  • ​Emphysema
  • Pulmonary vascular disease
  • Interstitial lung disease
  • anemia
  • pulmonary edema
  • pneumonia

Question 12

P-V curves in abnormal pulmonary function tests

Answer 12

• Relative to the normal curve:Recall that the emphysemic curve is on the left and up (more compliance).
• Asthma is slightly up and to the left, much less dramatic
• f

ibrotic lung disease curve is on the right and down (less compliance)

• decreased chest wall compliance curve (obesity) is slightly down and to the right.
• slopes of chest wall compliance and asthma curves is more or less the same as that of the normal curve, while the slopes of emphysema and fibrosis are steeper and flatter respectively.

Question 13

Major disease process PFT patterns

Answer 13

• Interstitial lung disease or fibrosis decreases diffusion capacity
• Water in lung increases diffusion distance and decreases surface area
• Pulmonary vascular disease decreases blood flow to lungs
• Intra or extra thoracic obstructions limit airflow

Question 14

Bronchoprovocation characteristics

Answer 14

• used as a test in asthma <==usually diagnosed on spirometry ==> obstructive pattern w/relief w/bronchodilator
• sometimes require impetus for bronchoconstriction to help dx asthma
• example: metacholine challenge

Question 15

Metacholine challenge characteristics

Answer 15

• metacholine challenge: pt inhales progressively higher concentrations of nebulized methacholine (or histamine), which stimulates bronchoconstriction
• In asthmatics, the concentration required to reduce airflow by 20% (PC20) is several orders of magnitude lower than in healthy subjects.
• measurement of the PC20 can help diagnose asthma in patients with normal spirometry and no response to bronchodilator