Week 3- RCP 110 {PFT}
Introduction to Pulmonary Function Studies (PFTs)
Define Pulmonary Function Studies (PFTs):
PFTs encompass a range of tests that assess the physiological function of the lungs.
Major Role of PFTs in Assessment of Lung Disease
Evaluate causes of pulmonary symptoms:
Dyspnea (shortness of breath)
Cough
Wheezing
Exercise tolerance
Distinguish between obstructive and restrictive lung disorders
Assess severity of the condition
Monitor trends over time to follow disease progression
Evaluate the effectiveness of therapy, such as bronchodilators
Assess patient lung function pre-operative (pre-op)
Importance of Predicted Normal Values in PFTs
Predicted normal values are crucial as they allow for comparison against measured values:
Deviations from normal predictions indicate the severity and type of lung disease.
Major factors influencing predicted normal values include:
Height
Age
Gender
Race
Height is deemed the most significant variable.
Variables Impacting Normal Values
Height
The most critical determinant of lung volume:
Taller individuals possess larger predicted lung volumes.
Weight
Weight's impact on lung volume is minimal unless the individual is obese:
Obesity can lead to smaller lung volumes.
Gender
Males typically exhibit larger lung volumes compared to females, assuming they are of the same height.
Age
Maximum lung function is generally reached by ages 20-30.
Healthy non-smokers without harmful exposures start to lose lung function in late 30s and 40s.
The trend indicates a gradual decline in lung function with advancing age.
Race
African Americans, Asians, and East Indians tend to have approximately 12% smaller lung volumes than Caucasians.
Hispanics and American Indians have moderately reduced lung volumes but do not require correction in lung volume predictions.
Race is considered one of the lesser factors in assessing predicted lung volumes.
Ranges for Normal PFT Values
Normal lung function is typically assessed between 80% to 120% of predicted values.
Lung function measurements are effort-dependent, requiring accurate assessment by PFT technicians who may coach patients for maximum effort during tests.
Lung Volumes and Capacities
Each lung volume and capacity provides specific insights into lung function:
Definitions of Lung Volumes
Total Lung Capacity (TLC):
The volume of gas in the lungs after maximal inspiration.
Tidal Volume (VT):
The volume of air inhaled and exhaled with each breath.
Expiratory Reserve Volume (ERV):
The maximum volume of air that can be exhaled from the resting end-expiratory level.
Residual Volume (RV):
The volume of air remaining in the lungs after maximal expiration regardless of starting lung volume.
Inspiratory Reserve Volume (IRV):
The volume of gas that can be inhaled after a normal inspiration, measured from a complete expiration without forced effort.
Vital Capacity (VC):
The total amount of air that can be forcibly exhaled following maximal inhalation.
Functional Residual Capacity (FRC):
The volume of air left in the lungs after a normal expiration.
Forced Expiratory Flow Rate and Volume Measurements
Forced Vital Capacity (FVC)
Definition:
The total volume of gas expelled forcefully and rapidly after a maximal inhalation.
Average normal FVC is approximately 4800 ml.
Clinical significance:
A decreased FVC suggests an obstructive lung disorder.
A normal or increased FVC points towards restrictive lung disorder.
A normal individual typically takes 4-6 seconds to complete exhalation during the FVC maneuver.
Obstructive diseases can lead to FVC being lower than VC due to increased airway resistance and air trapping despite a strong effort in administering the test.
Common Test Instruction
The patient should be informed, “In this test we are going to see how big your lungs are.”
Assess lung health via group discussion based on specific test outcomes, such as a 10-second timed exhalation (TET).
Additional Values Derived from FVC
Forced Expiratory Volume (FEVT):
This measures the maximum volume of air exhaled over specified time frames, usually recognized at intervals of 0.5, 1.0, 2.0, 3.0, and 6.0 seconds.
FEV1 (volume exhaled in the first second) is typically used, with a normal value being around 4200 ml (or 80% predicted or higher).
An FEV1 decrease indicates an obstructive lung disease while remaining normal for most restrictive disorders.
Percentage of total volume exhaled over time for healthy adults shows:
FEV0.5: 60%
FEV1: 80%
FEV2: 94%
FEV3: 97%
FEV1/FVC Ratio
Definition:
The FEV1/FVC Ratio compares the volume of air exhaled in 1 second to the total volume exhaled during FVC maneuver.
Normal findings indicate that the ratio should be ≥ 80%.
A ratio greater than 80% may suggest a restrictive disorder, while a ratio < 70% is often indicative of an obstructive disorder, with FEV1 determining the severity.
Clinical Application of PFT Scores
Factors to consider when evaluating patient pulmonary disorders:
Assessment of disease severity
Determining if the disorder is obstructive or restrictive
The primary differentiation based on these scores between obstructive and restrictive disorders highlights that:
In obstructive disorders, both FEV1 and FEV1/FVC ratio are decreased.
In restrictive disorders, FEV1 may be normal or increased, while the FEV1/FVC ratio is also increased.
Test Yourself Section (PFT Concepts)
Clinical assessments based on scenarios like pulmonary fibrosis to identify expected PFT results:
Understand that TLC may appear normal or larger, while expiratory flows will be decreased, implying expected findings in restrictive conditions.
Peak Expiratory Flow Rate (PEFR)
PEFR represents the maximum flow rate achieved during an FVC maneuver.
Importance:
Assesses large upper airway function and the degree of bronchospasm on a daily basis.
Measured in L/second or L/min:
Normal PEFR is around 10 L/second or 600 L/min.
A decreased PEFR indicates obstructive disease, while an increase may suggest restrictive disease.
Flow-Volume Loop
Description:
The flow-volume loop visually represents the results of both FVC and forced inspiratory volume maneuvers.
The upper section indicates exhalation; the lower section reflects inhalation.
Value extraction includes multiple metrics such as FVC, FEVT, and PEFR depending on the thoroughness of the equipment in use.
Pulmonary Diffusion Capacity
Carbon Monoxide (DLCO) measures the amount of carbon monoxide that diffuses across the alveolar-capillary membrane.
Normal DLCO averages around 25 ml/min/mmHg.
Clinical findings related to DLCO in different lung disorders:
In obstructive lung disorders, usually normal or decreased.
In restrictive lung conditions, the DLCO may be decreased with moderate to severe alveolar atelectasis or consolidation.
Summary of PFT Findings
PFTs comprise various measurements like spirometry, lung volumes, diffusion capacity, and airway resistance.
Normal measurements vary based on height, age, gender, and race.
Key distinctions:
Obstructive conditions demonstrate low expiratory flows.
Restrictive lung diseases display low lung volumes.
Review Questions
Identify the critical factor for predicting normal PFT values:
(A) Age
(B) Height
(C) Weight
(D) Race
Define total volume of air forcefully exhaled after maximal inspiration:
(A) MVV
(B) FEV1
(C) PEFR
(D) FVC
Determine the normal percentage of volume that can be exhaled in 1 second in a healthy adult:
(A) 68%
(B) 90%
(C) 80%
(D) 70%
Review obstructive disease characteristics:
(A) Both FEV1% and FEV1 decreased
(B) FVC increased
(C) FVC decreased with normal FEV1
(D) Both FEV1% and FEV1 increased
Identify diseases with hallmark decreased DLCO:
(A) Chronic Bronchitis
(B) Asthma
(C) Emphysema
(D) Pulmonary Edema