What does a pulmonary function test measure quizlet?

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Indications for Pulmonary Function Tests

Diagnose Pulmonary disease
Asymptomatic smokers
Preoperative evaluation
Monitor occupational exposures
Evaluate severity of respiratory disease Evaluation of impairment or disability
Evaluate therapeutic interventions

Pulmonary function tests must always be analyzed within the context of the patient being tested

-Age, height, weight, race, and sex directly affect the results which one would predict for a given individual.
-Diseases which the patient may have or drugs which they are taking may be important in the interpretation of the patient's test. For instance, in a patient taking amiodarone for atrial fibrillation, the finding of a restrictive PFTs, particularly if they are new, is very significant

Spirometry

The four volumes we will be concerned with are:
1) total lung capacity (TLC) or the total volume of air contained in the lungs;
2) functional residual capacity (FRC) or the volume of air left at the end of normal expiration;
3) residual volume (RV) the volume of air left in the lungs at the end of forced expiration;
4) vital capacity (VC) the difference between the largest(TLC) and the smallest (RV) lung volumes which can be obtained. RV is the amount of air left in the lungs that cannot be breathed out.

categories of information which can be obtained with routine pulmonary function testing

1) Lung volumes which can allow us to measure the maximum volume of the lungs as well as sub-compartments.
2) Flow rates which measure the maximum flow of gas out of and into the lungs.
3) Diffusing capacity which measures the transfer of gas from the alveolar space into the capillary blood stream.
4) Maximal inspiratory and expiratory pressures which measure the applied strength of the respiratory muscles.

Total lung capacity

-determined by the ability of the inspiratory pump (brain, nerves, muscle) to expand the chest wall and lungs which in turn have a strong tendency to recoil inwards at high lung volumes.
-Any breakdown in the ability of the pump to function will result in a smaller total lung capacity (restrictive lung disease). Neuromuscular disease is an example of this, as is severe kyphoscoliosis.
-Diseases which increase inward recoil of the lung (pulmonary fibrosis) will lead to a smaller TLC.
-Diseases which lead to a reduction in inward recoil of the lung (emphysema) result in an increase in TLC know as hyperinflation (due to air trapping).

Residual volume (RV)

-determined in healthy younger individuals by a competition between the strength of the expiratory muscles and compressibility of the chest wall.
-By the onset of middle age or in obstructive lung disease residual volume appears to be determined by a flow limitation; expiratory flow rates at low lung volumes are so low that expiration is prolonged and is not completed down to the original RV by the time the subject gives up the effort and takes another breath. (Please remember that determining RV takes special testing)

Vital capacity (VC)

-determined by the difference between TLC and RV and changes in variations between these two.
-FRC is the relaxation volume at the end of expiration. It is not a reliable measurement.
-In patients with obstructive lung disease FRC may be elevated. This imposes a significant extra load on the inspiratory muscles which can result in muscle fatigue

Obstructive lung diseases are characterized by KNOW THIS

resistance to expiratory flow

When we measure expiratory flow what parameters are we looking at?

1.) Forced vital capacity FVC
2.) FEV1- the volume if gas exhaled in the 1st one second
3.) FEF25-75- the flow of gas exhaled during the middle half of the vital capacity

extrathoracic obstruction

-tracheomalacia ( a softening of the cartilage after prolonged intubation. It has also been reported in patients who have never been intubated)
-During inspiration the softened trachea is sucked into the upper airway causing it to partially collapse.
-During expiration the expiratory pressure is high enough to push the trachea open. Thus you only see the obstruction on the inspiratory side of the flow-volume loop.
-Vocal cord paralysis gives the same type of pattern.
-A tracheal stenosis is a fixed lesion and therefore will be present on both the inspiratory and expiratory side of the flow-volume loop

Pulmonary function test examples

Expiratory flows

-Measuring expiratory flows is the key to determining the presence of airflow obstruction.
-In obstruction all expiratory flows are reduced but FEV1 more so than FVC.
-FEV1: the maximum volume of air that can be exhaled during the first second of a forced vital capacity (FVC)

Obstructive lung disease is defined as?

FEV1/FVC< 70% defines obstruction.

Restrictive Lung Disease

-Small lungs with increased stiffness from parenchymal disease or problems with nerves or chest wall.
-FEV1 and FVC are each decreased. However, decreased proportionately so FEV1/FVC ratio is preserved.
-TLC < 80% predicted= Restrictive Lung Disease

Lung Volumes

Residual volume (RV) is estimated
Can be done by Helium Dilution
Nitrogen washout
Body plethysmography
RV + VC = Total Lung Capacity (TLC)
TLC < 80% predicted= Restrictive Lung Disease

DLCO Determination

-Linear Diffusion of Carbon Monoxide
-"Transfer Factor" in Europe
-The test is easy to do but the machine is very expensive and needs maintenance and calibration. It is usually only found in hospitals.
-What you are actually measuring on DLCO is the ability of carbon monoxide to cross the alveolar-capillary membrane
-A reduced DLCO implies a loss of effective capillary surface and interface
-There are many indications for DLCO and no contraindications that I know of. It must be ordered separately from PFT (if you order PFT it will not include DLCO)

Whats DLCO good for?

-DLCO is a sensitive test for measuring the amount of lung involvement in smokers with COPD.
-Anatomically the lower DLCO the more lung involvement

Smokers with airway obstruction on PFT but normal DLCO have what?

chronic obstructive bronchitis NOT COPD

Patients with an obstructive pattern on PFT but DLCO is normal or high?

Have asthma

DLCO is used to differentiate restrictive lung disease

-If you do flow-volume loop and have reduced vital capacity and reduced total lung capacity you are thinking of restrictive lung disease ⟹ If the DLCO is also low it suggests interstitial lung diseasee*.
-It helps differentiate between interstitial lung disease (where the DLCO is low) from the other restrictive lung disease such as kyphoscoliosis, neuromuscular problems, obesity, pleural effusion or pleural thickening (where the DLCO is normal).

If you have a patient with cough or shortness of breath you will want to order what?

-pre and post bronchodilator.
-If you have a patient that you highly suspect has asthma but the PFT is normal ⟹ methacholine challenge test might be indicatedd*.

The difference between an obstructive and restrictive pattern.

Obstructive vs restrictive

PFT Obstructive vs restrictive

Flow volume loops Obstructive vs Restrictive

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