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Asthma: Use of Spirometry

Created by the Asthma Coalition of Texas Jay Peters M.D David Weldon M.D. Terry LeGrand PhD.

Disclaimer: Information contained in this educational tool (module) is based on the "Guidelines for the Diagnosis and Management of Asthma," developed by the 2002 and 2007 National Asthma Education and Prevention Program (NAEPP) and the 2008 ACOG Update of these Guidelines. The content contained in this module is intended for education, information and communication purposes only, and does not constitute medical advice or product endorsement by the Asthma Coalition of Texas. The Asthma Coalition of Texas shall not be held liable for any damages related to the user's decision to use any material(s) or information contained within this module

Why Use Office Spirometry

Physicians and patients underestimate severity of asthma Evaluate reversibility

Determine if therapy is optimal ­ Assessment of compliance with medications

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Determine when therapy can be "stepped down" Determine when therapy should be "stepped up" Evaluate smokers >45 years old for obstructive lung disease

Peak Flow Meters: Advantages and Disadvantages

Advantages

Measurements within 1-2 minutes ­ Inexpensive (cost < $20) ­ Simple and Safe

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Disadvantages

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Very effort dependent Insensitive to obstruction of smaller airways Large intersubject and intrasubject variability Much less accurate than spirometers Considered monitoring tool rather than diagnostic tool

Spirometers: Advantages and Disadvantages

Advantages

Evaluates large and small airways ­ Diagnostic test as well as management tool ­ Relatively easy to use and maintain

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Disadvantages

Cost: $400-$2000 (for office spirometer) ­ Requires some training (usually ½ - 1 day course) ­ Requires time to perform Ten minutes for 3 maneuvers (longer in children) Additional 15 minutes for bronchodilator testing

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Office Spirometry*

Screening tool; may be diagnostic Measures only FEV1; FEV6 Advantages

­ Less expensive (Approx. $35-50/test) ­ Easy interpretation ­ Technically easier; more reproducible

*FEV6 is a substitute for FVC in screening spirometry (more reproducible in office practice) Note: Not considered diagnostic by some since no flow volume loop or measurement of small airways is obtained.

DETERMINANTS OF EXPIRATORY AIRFLOW (LUNG FUNCTION) AS COMPARED WITH THE DETERMINANTS OF BLOOD PRESSURE

Blood Pressure Sphygmomanometry SBP/DBP (120/80) Cardiac output Peripheral resistance Blood volume Blood viscosity Renin-angiotensin

Lung Function Spirometry FEV1/ FVC (3.0/4.0) Elastic recoil Airways resistance Large airways Small Airways Muscular effort and coordination

Adapted with permission: T. Petty M.D.

Definitions in Spirometry*

FEV1 = amount of air exhaled in 1 sec. FVC= total amount of air exhaled FEV6 = amount of air exhaled in 6 sec. (substitute for FVC; more reproducible) FEV1/FVC or FEV1/FEV6 < 70-75% used to define obstruction (or below LLN for the age, sex,& ethnicity of subject)**

· *All measurements done with forced exhalation · ** LLN = lower limit of normal by NHANES III and

represents the lower 5% of that population

Interpretation of Office Spirometry (ATS Standards)

Ensure test quality good Use NHANES III reference values

FEV1, FEV6 ­ Airway obstruction Good quality test FEV1, FEV1/FEV6 below lower limits of normal (LLN = 75%; range = 73-76% based on age) ­ Severity of obstruction FEV1= LLN ­ 60% predicted (mild) FEV1 = 40-59% predicted (moderate) FEV1 <40% predicted (severe)

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Spirometers: Automated Quality Controls Built into Spirometer

Expiratory time <6 seconds; "blow out longer" Time to peak flow >120 ms; "blast out faster" PEFR values not within 1L/s; "blast out harder" FEV6 or FVC values not within 150 ml; "breath deeper" Back extrapolated volume >150 ml; "don't hesitate" After 2 acceptable maneuvers, the message is "good test session"

Spirometers: Quality Control Grades

A = At least 2 acceptable maneuvers; FEV1 and FEV6 within 100 ml B = FEV1 and FEV6 within 101-150 ml C = FEV1 and FEV6 within 151-200 ml D = Only one acceptable maneuver or FEV1 values >200 ml (no interpretation) F = No acceptable maneuvers (no interpretation) Note: D and F should be rejected

Spirometry Steps

Measure standing height in stocking feet Record age, gender, height, and ethnicity Explain and demonstrate the correct maneuver Coach and watch patient perform each maneuver Repeat until 2 acceptable maneuvers

Office Spirometry

Predicted values based on height, weight, and age Adjust for ethnicity Use of nose clip optional; must be consistent Sitting or standing but again consistent Values for FEV1,FVC should be within 5% (reproducibility)

Performance of Spirometry

Watch patient and graph (if available) for consistency in effort Delete poor attempts, cough artifact Watch for truncation of inspiratory loop with stridorous breath sounds Three reproducible attempts should be made for both pre and post bronchodilator

Office Spirometry: Quality Control

Diagnostic spirometry (Gold standard) Office spirometry calibration

­ 1 or 3 liter syringe ­ Plastic (Mylar) bag ­ "Self-calibrating spirometer" ­ Daily calibration ­ 3 liter syringe

Periodic calibration at local diagnostic lab Periodic testing of biologic control

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Healthy subject (>25 years old, no lung disease) FEV1, FEV6 daily x 10 days "Average value" calculated (range within 10%) Control subject tested each day patients tested (must be within 10% of "average value")

Resp Care 2000; 45(5)513-530

Diagnostic Approach to Spirometry

Normal FVC ­ 80% predicted Normal FEV1 ­ 80% predicted Normal FEV1/FVC = 70-75% predicted or above LLN Algorithm:

Low FVC = obstruction or restriction ­ Low FEV1 = obstruction or restriction ­ FEV1/FVC < 70-75% obstruction FEV 1 = 60-75% mild FEV 1 = 40-59% moderate FEV 1 < 40% severe

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Basics of Pulmonary Function Test

Obstructive Lung Disease = unable to get air out

FEV1/FVC < 70-75% (70% used in COPD) ­ The lower the ratio, the worse the obstruction

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Restrictive Lung Disease = unable to get air in

Low FVC; normal or elevated FEV1/FVC ­ Gold Standard: Low TLC

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Diagnostic Criteria for Obstruction and Restriction (ATS)

Diagnosis of obstruction: FEV1/FVC <70-75% = obstruction (Use LLN) Severity

­ FEV1: 60-75% = mild ­ FEV1: 40-59% = moderate ­ FEV1: <40% = severe

Diagnosis of Restriction:

­ Reduced FVC; normal FEV1and FEV1/FVC ­ Reduced total lung capacity (TLC)

"Gold standard" Requires plethysmography, helium dilution or nitrogen washout

PFT's Algorithm (GOLD Guidelines: COPD)

Is the PEF adequate?

yes no

Is the FEV1/FVC < 70% lower than predicted?

yes no

Interpretation may be limited by falsely low FVC

This is the definition of obstruction ­ FEV1 Mild Moderate Severe 80-100% 50-79% <50%

Is FVC reduced?

yes no

Restriction may be present; Need TLC to definitively diagnose restriction

Normal pulmonary mechanics

Lung volumes DLCO

Enright Algorithm: Office Spirometers

START Check maneuver quality No FEV1/FVC below LLN? Yes FEV1 above LLN? No FEV1 above 60% of predicted? No FEV1 above 40% No FVC below LLN? Yes FVC above 60% of predicted No FVC above 50% of predicted Yes Moderate restriction Severe restriction Yes Mild restriction No Yes Moderate obstruction Severe obstruction Normal spirometry Yes Mild obstruction Yes Borderline obstruction

*LLN = Lower Limit of Normal

No

Pulmonary Function Test in Asthma

Reduced FEV1 and FEV1/FVC <75% or LLN Positive bronchodilator response (in adults)

Improvement in FEV1 > 12% ­ Increase in FEV1 > 200 cc

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Normal diffusion capacity (DLCO)

Spirometry: Poor Effort

Most common reason for misinterpretation of PFT Restrictive pattern on spirometry Determining poor effort:

% predicted PEFR < % predicted FEV1 ­ Time/volume curve ­ no plateau ­ Flow-volume loop ­ expiratory ascent not steep

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Lung Volumes

Vt 500-600 ml IRV 3,000 ml ERV 1,200 ml RV 1,200 ml

Time Volume vs. Flow Volume Loops

Normal Flow Volume Loop

Examples of Spirometry ­ Time/Volume Curves

Time (x-axis) vs Volume (y-axis) Does not determine inspiratory loop Most frequently used for OSHA and other occupational health tests Peak flow not determined from graph itself

Post bronchodilator

Pre bronchodilator

Lung Capacities

ml/kg

VC = IRV + Vt + ERV = 4,800 ml 70 IC = Vt + IRV = 3,600 ml 50 ml/kg FRC = ERV + RV = 2,400 ml TLC = IRV + Vt + ERV + RV = 6,000 ml

Expiratory Flow Volume Curve

Obstructive Disease

­ Lower PEF ­ More concave as disease

worsens ­ Improves with beta-agonist

Restrictive Disease

­ Normal shape but less wide ­ PEF nl. or decreased ­ FEF 25-75 reduced

Examples of Spirometry

Flow Volume Loop Tracing from normal patient Look for good peak flow and smooth tracing Inspiratory effort should look both deep and full

Examples of Spirometry

Mild obstructive pattern Peak flow may be low Decrease in FEV1 /FVC to less than 75% in adults Decreased FEF 25-75 (suggestive of small airways disease) Inspiratory loop not truncated

Examples of Spirometry

Mild reversible obstruction (dotted line) with significant improvement post bronchodilator (solid line) Pattern characteristic for partially reversible obstructive lung disease (asthma or COPD)

Examples of Spirometry

Severe obstructive pattern Low peak expiratory flow Severe decrease in FEV1/FVC and FEF25-75 Often seen in patients with emphysema or chronic, severe asthma

Examples of Spirometry

Pattern of Restrictive Lung Disease Decreased FVC Usually normal peak flow May have decreased FEF25-75 also Seen in interstitial lung disease; neuromuscular dz.

Examples of Spirometry

Truncation of Inspiratory Loop Seen in extrathoracic obstruction and vocal cord dysfunction (VCD) May be due to slow inspiratory effort ­ watch for this carefully May be accompanied by stridorous breath sounds May be accompanied by obstructive pattern

Upper Airway Obstruction

Truncation of expiratory or inspiratory flow loop Expiratory = intrathoracic Inspiratory = extrathoracic Both = fixed obstruction Causes:

­ Tumor

-Normal -Flat inspiratory loop

Tracheal stenosis ­ Vocal cord dysfunction

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Examples of Spirometry

Cough Artifact Typically will be seen as patient completes forced vital capacity (end exhalation) Saw tooth pattern may be seen with other disorders like Obstructive Sleep Apnea (OSA)

Office Spirometry

Advantages of Spirometer over Peak Flow Meter

Measures function of large and small airways More reproducible Diagnostic tool as well as monitoring tool Easy to operate Can screen for obstructive lung disease in smokers over 45 years old

Summary

Spirometry is a reproducible and inexpensive tool in the management of asthma Spirometry is useful in the diagnosis of asthma (demonstrations of reversibility) Spirometry measures both large and small airways function and can be used to monitor patients

Information

Asthma: Use of Spirometry

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