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Chapter 9Pulmonary Function Testing

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Overview

PFT includes: Spirometry Flow volume loop (FVL) before and after

bronchodilator inhalation Lung volume studies Diffusing capacity (DLCO) Airway resistance (Raw) Arterial blood gas (ABG) measurements Pulmonary response to exercise and bronchial

provocation

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Purpose of PFT

Evaluate cause of pulmonary symptoms Evaluate abnormalities seen on the CXR

and/or CT scan Follow course of disease and response to

treatment Evaluate perioperative risk for pulmonary

complications Rule out pulmonary pathology in people

with high risk for pulmonary dysfunction Evaluate disability

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Normal Values

PFT normal values vary with age, height, gender, and race

Height the most important factor predicting lung volumes The taller the person, the larger the values

Weight important when BMI >30 = restrictive

Gender: males have larger lungs Race: African Americans, Asians, East

Indians have 12% smaller lung volumes

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PFT Equipment

American Thoracic Society standards Spirometer: routine flows and volume Body plethysmograph: TLC and airway

resistance studies Diffusion system: lung diffusion Gas analysis (carbon dioxide, carbon

monoxide, helium, nitrogen, and oxygen) Nebulizer equipment for albuterol and

methacholine

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Arterial blood gas analyzer Treadmill or bicycle for exercise evaluation Laboratories with smaller volumes of tests

Multifunction device that measures lung volumes, flow rates, diffusing capacity, and response to bronchial provocation

all spirometric values obtained under ambient conditions convert to

Body temperature, ambient pressure, saturated (BTPS)

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Measures of Lung Function

Tidal volume (VT) Residual volume (RV) Expiratory reserve volume (ERV) Inspiratory reserve volume (IRV) Minute volume (VE) Vital capacity (VC) Total lung capacity (TLC) Functional residual capacity (FRC) Inspiratory capacity (IC) Maximal voluntary ventilation (MVV)

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Measures of Lung Function (cont’d)

Tidal volume Volume during quiet breathing Adults: 350 to 600 ml Stiff lungs: small volumes at higher rate Obstruction: normal volume at slower rate

Minute volume Rate x volume 4 to 8 L/min

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Measures of Lung Function (cont’d)

Vital capacity: maximal volume exhaled Measured after deepest breath possible Slow vital capacity (SVC) Forced vital capacity (FVC)

Proper coaching is essential Phases

Maximal inspiratory effort Initial expiratory blast Forceful emptying of lungs

<20 ml/kg: risk for complications

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Measures of Lung Function (cont’d)

Total lung capacity Sum of SVC and RV Normal % predicted is 80% to 120% Increased in obstructive diseases due to air

trapping Obtained by body plethysmography, open-

circuit nitrogen washout, closed-circuit helium dilution, XR planimetry

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Body Plethysmography

Boyle’s law Pressure and volume of a gas vary inversely if

temperature is constant

Accurate but body box is expensive A Calibrated 3l sirynge is use to

determine the accuracy of a water-sealed spirometer in measuring lung volumes

Used to measure Lung Volumes

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Nitrogen Washout

To determine distribution of ventilation Patient breathes 100% oxygen Nitrogen analyzer measures diminishing

N2 concentration from lungs Well-ventilated units empty first Uneven pattern common in obstructive

lung disease

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Nitrogen Washout

Oxygen 100% for 7 minutes or until nitrogen is washed out of patient’s lungs, by putting an amount of know oxygen volume we can estimate lung volume, 79% of RV is NITROGEN.

If air trapping is present this technique will underestimate total intrathoracic volume

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Closed-System Helium Dilution

Helium is inhaled and not significantly absorbed from lungs by blood

Helium is diluted in proportion to size of lung volume being measured

Equilibrium takes 7 minutes

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RV, ERV, and FRC

Residual volume (RV) Gas left after exhalation Obtained from TLC studies TLC-SVC or FRC-ERV Increased in air trapping

Expiratory reserve volume (ERV) Maximal gas exhaled from resting status

Functional residual capacity (FRC) Gas left after full exhalation at resting status 3 way of measuring FRC are Helium, body

box, and Nitrogen Washout

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Indices of Flows

Forced expiratory volume at 1 sec (FEV1) Forced expiratory volume at 3 sec (FEV3) Forced expiratory flow, mid-expiratory

(FEF25%-75%) Peak expiratory flow (PEF)

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FEV1

Maximal volume exhaled during 1st second of expiration

It is a forced maneuver Varies with age, gender, race, and height The % predicted is 80% to 100% Reduced in obstructive and restrictive lung

disease

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FEV3

3-second point of the expiratory curve Not as reproducible as FEV1

Reported as % of the FVC (normal ~95%) FEF25%-75%

Average flow rate during middle half of expiratory curve

Normal 65% to 100% More sensitive to airway obstruction than FEV1

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Peak Expiratory Flow

Maximum flow rate achieved during FVC maneuver

Effort dependent Peak flowmeters are inexpensive Asthma action plans

Green zone: 80% to 100% of personal best Yellow zone: 50% to 80% Red zone: <50% = urgent physician

intervention

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Maximal Voluntary Ventilation

Patient breathes as rapidly and deeply as possible for 12 to 15 seconds

Extrapolated to obtain MMV in 1 minute MMV reflects:

Status of respiratory muscles Compliance of thorax-lung complex Airway resistance

Patient motivation and ability to move air Important in the preoperative patient

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Flow Volume Curves (Loops)

Volume plotted on horizontal axis and flow on vertical axis

Fixed or variable upper airway obstruction COPD/asthma Restrictive lung disease Pre- and postbronchodilator curves

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PFT Before and After Bronchodilators

FVC, FEV1, FEF25%-75% and FVL to assess reversibility

Amount of change required to qualify as improvement FVC >10% FEV1 >200 ml or >15% FEF25%-75% >20% to 30%

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Diffusion Capacity (DL)

Determinants of gas exchange Surface area of membrane Thickness of membrane Hemoglobin and blood flow in capillaries Measures crossing of co from Alveoli to cap

and back Pt breaths in mixture of 4% CO and 16%

Helium. Holds breath for 10-12 sec. Machine reads time of CO crossing membrane and back.

DLCO-SB Normal: 80% to 120% predicted

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Bronchoprovocation Testing

Diagnosis of occult asthma Provoking agents

Inhaled histamine or methacholine Exercise Cold air

A 20% decrease in FEV1 indicates hyperreactive airways

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Other Applications of PFT

Smoking cessation Surgery Sleep apnea Environmental lung disease

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Obstructive and Restrictive Disorders

Obstructive Expiratory flow <80% predicted TLC >80% predicted (air trapping) Obstruction changes flow volume loop (FVL) Fixed: flattened expiratory and inspiratory limbs

of FVL Restrictive

Lung volume <80% predicted

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Approach to PFT Interpretation

If FVC >80% predicted = no restrictive <80% predicted = look at TLC

If TLC >80% predicted = no restrictive <80% predicted = restrictive

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Approach to PFT Interpretation (cont’d)

FEV1 and FEF25%-75%

FEV1 normal and FEF25%-75% <65% predicted = mild obstructive disease

Response to bronchodilator If FVC, FEV1, FEF25%-75% improve = response

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Approach to PFT Interpretation (cont’d)

FVL Scooping of expiratory limb = obstructive Flattening inspiratory and expiratory limbs =

fixed or variable large airway obstruction DL >80% predicted is normal

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Pattern Recognition

Asthma Low FEV1 and FEF25%-75%; normal TLC; normal

DL; response to bronchodilator Emphysema

Low FEV1 and FEF25%-75%; normal TLC; low DL; no response to bronchodilator

Pulmonary fibrosis Low FVC; low FEV1 but normal FEV1/FVC;

small TLC, low DL; no response to bronchodilator