Pulmonary Function Measurements

Why PFTS?1. To detect the presence or absence of

pulmonary disease.

2. To classify disease as obstructive or restrictive

3. To quantify severity, progression, and reversibility.

Why PFTs1. To quantify therapeutic effectiveness

2. To assess risk for post-operative complications

3. Health Screening

4. To determine pulmonary disability – Federal requirements

Lung Volumes

IRV

TV

ERV

• 4 Volumes

• 4 Capacities– Sum of 2 or

more lung volumes

RV

IC

FRC

VC

TLC

RV

Factors that affect lung volumes

• Age• Sex• Height• Weight• Race• Disease• The main factor in determining reference

range is?

Lung Volumes

Tidal volume (VT)

Inspiratory reserve volume (IRV)

Expiratory reserve volume (ERV)

Residual volume (RV)

Tidal volume

• The amount of air inhaled and exhaled with each breath during normal breathing.

• Normal is 5 to 7 ml/kg

• Often calculated by measuring Ve and dividing by the RR

Inspiratory Reserve Volume (IRV)• The amount of air that can be inhaled

beyond the tidal volume.

Expiratory Reserve volume(ERV)

• The amount of air that can be forcibly exhaled after a normal expiration.

Residual Volume - RV• The amount of air still in the lungs after a

forced ERV

Lung Capacities

Vital capacity (VC)

Inspiratory capacity (IC)

Functional residual capacity (FRC)

Total lung capacity (TLC)

Vital Capacity - VC• The maximal amount of air that can be exhaled

after a maximal inspiration.

• Can be an FVC or a SVC

• Normal value 50-70 ml/kg/Acceptable 10-15 ml/kg

• VC = IRV + TV + ERV

Inspiratory Capacity (IC)• The volume of air that can be inhaled after a

normal exhalation.

• Normal or predicted values obtained from a nomogram.

• Average range 2400-3600 ml

• Used very often in bedside Respiratory Care in the form on an incentive spirometer.

Lung expansion Therapy - IS

Functional Residual Capacity – (FRC)

• The amount of air remaining in the lungs after a normal exhalation.

• FRC = ERV + RV

• Important physiologically for oxygenation and complaince

• Explain why

Normal Lung Volumes and Capacities

Figure 3-1.

LUNG VOLUMES & CAPACITIES

18

• Restrictive vs Obstructive Disorders

Obstructive Lung Disorders

Figure 3-2.

Restrictive Lung Disorders

Figure 3-3.

Methods to measure Total Lung Volume/RV

•Helium dilutionBased on fact that known amount of helium will be

diluted by size of patient’s RV

•Nitrogen washoutBased on fact that 79% of RV is nitrogenVolume of nitrogen exhaled ÷ 0.79 = RV

•Body boxApplies Boyle’s law to measure RV

BODY PLETHYMOGRAPHY

23

• Review the 3 techniques to measure total lung volume in your text books.

Pulmonary Mechanics

–In addition to measuring volumes and capacities, we also measure rate at which gas flows in and out of lungs

• Expiratory flow rate measurements provide data on integrity of airways and severity of airway impairment

• Indicate whether patient has large or small airway obstruction

Measurement of the pattern of air movement into and out of the lungs during controlled ventilatory maneuvers.

Often done as a maximal expiratory maneuver

Spirometry

Pulmonary Mechanics Measurements

Forced vital capacity (FVC)

Forced expiratory volume timed (FEVT)

Forced expiratory volume1sec/forced vital capacity ratio (FEV1/FVC ratio)

Forced expiratory flow25%-75% (FEF25%-75%)

Pulmonary Mechanics Measurements

• Forced expiratory flow200-1200 (FEF200-1200)

• Peak expiratory flow rate (PEFR)

• Maximum voluntary ventilation (MVV)

• Flow-volume loop

FVC

• Maximum volume of gas that can be exhaled as forcefully and rapidly as possible after maximal inspiration.

• Most commonly performed PFT – effort dependent

• Additional measurements made from FVC

FVC

Figure 3-4.

Forced Expiratory Volume Timed (FEVT)

• Maximum volume of gas that can be exhaled within specific time period– Measurement obtained from FVC

– Most frequently used time period:• 1 second

FEVT

Figure 3-5.

Normal FEVT

• Normal percentage of total FVC exhaled during these time periods:– FEV0.5

• 60 percent

– FEV1

• 83 percent

– FEV2

• 94 percent

– FEV3

• 97 percent

Forced Expiratory Volume1sec/Forced Capacity Ratio (FEV1/FVC Ratio)

• Comparison of amount of air exhaled in 1 second to total amount exhaled during FVC maneuver

• Commonly referred to as forced expiratory volume in 1 second percentage (FEV1%)

FVC, FEV1, and the FEV1%

• Collectively, most commonly used pulmonary function measurements to:

– Distinguish between obstructive and restrictive lung disorder

– Determine severity of patient’s pulmonary disorder

Pulmonary Function Differences Between Obstructive and Restrictive

Lung Disorder• In obstructive lung disorders, both FEV1 is

decreased

• In restrictive lung disorders, FEV1 normal or increased

FEV1

• Interpretation of % predicted:

–>75% Normal–60%-75% Mild obstruction–50-59% Moderate obstruction–<49% Severe obstruction

Forced Expiratory Flow (FEF)25%-75%

• Average flow rate that occurs during middle 50 percent of FVC measurement

FEF25%-75%

Figure 3-7.

Interpretation of % predicted:

>60% Normal40-60% Mild obstruction20-40% Moderate obstruction<10% Severe obstruction

FEF 25-75

FEF200-1200

Figure 3-9.

Peak Expiratory Flow Rate (PEFR)

• Maximum flow rate that can be achieved during FVC maneuver.

• Can be done a single test with a peak flowmeter to assess severity of airway obstruction in asthma and look at bronchodilator response.

PEFR

Figure 3-11.

Peak Flow Meter

Maximum Voluntary Ventilation (MVV)

• Largest volume of gas that can be breathed voluntarily in and out of lung in 1 minute

MVV

Figure 3-13.

Flow-Volume Loop

• Graphic presentation of FVC maneuver

• Plots flow and volume rather than flow and time.

FVC

Normal Flow-Volume Loop

Figure 3-14.

Figure 3-15.

Figure 3-9. Flow-volume loop demonstrating the shape change that results from an obstructive lung disorder. The curve on the right represents

intrathoracic airway obstruction.

Figure 3-16.

Figure 3-10. Flow-volume loop demonstrating the shape change that results from a restrictive lung disorder. Note the symmetric loss of flow and volume..

Factors Affecting Predicted Normal Values

• Height– Taller subjects have greater pulmonary function

values

• Weight– In general, as weight increases, lung volumes

decrease

Factors Affecting Predicted Normal Values

• Age– After age 25, lung volumes, expiratory flow rates,

and diffusing capacity values decrease

• Gender– Males typically have greater lung volumes,

expiratory rates, and diffusing capacities

Factors Affecting Predicted Normal Values

• Race– Blacks and Asian subjects tend to have lower

pulmonary function values than subjects of European-descent origin

Specialized Tests

• Airway Resistance• Lung and Chest Wall Compliance• Airway Hyperresponsiveness• Bronchoprovocation Testing• FeNO

Exercise Tests

• 6-minute walk test

• Cardiopulmonary Exercise Testing

Diffusion Capacity of Carbon Monoxide (DLCO)

• Measures the amount of carbon monoxide (CO) that moves across the alveolar-capillary membrane

• The average DLCO value for the resting male is 25 mL/min/mm Hg

• Decreases in lung disorders that affect the A-C Membrane. Give some examples