Understanding the Basics of Spirometry It s not just about yelling blow Carl D. Mottram, RRT RPFT FAARC Technical Director - Pulmonary Function Labs and Rehabilitation Associate Professor of Medicine - Mayo Clinic College of Medicine Prevalence of COPD and Heart Disease in Smokers Centers for Disease Control Lancet Vol 370, p765 773, 1 September 2007 Measuring and Monitoring Lung Function 1
John Hutchinson MD Surgeon and Master Violinist Coined the term Vital Breath later changed to Vital Capacity based on his observations that it accurately predicted the capacity to live Hutchinson J. On the capacity of the lungs and on the respiratory function with a view of establishing a precise and easy method of detecting disease by the spirometer. Med Chir Tr (London) 1846; 29: 137. Spirometers Spirometers Single component of a complex PFT testing system 2
How to Guidelines and Standards American Thoracic Society/European Respiratory Society 2005 ATS/ERS Spirometry Standards 2007 ATS/ERS PFT Testing in Preschool Children ATS Pulmonary Function Laboratory Management and Procedure Manual 3 rd Edition 2016 Clinical Practice Guidelines National Asthma Education and Prevention Program Clinical Practice Guidelines Spirometry required to establish the diagnosis of COPD 3
Clinical Indications Diagnostic To evaluate symptoms, signs, or abnormal laboratory tests Symptoms: dyspnea, wheezing, orthopnea, cough, phlegm production, chest pain Signs: diminished breath sounds, hyperinflation, expiratory slowing, cyanosis, chest deformity, unexplained crackles Abnormal laboratory tests: hypoxemia, hypercapnia, polycythemia, abnormal CXR Clinical Indications Monitoring To assess therapeutic interventions Bronchodilator therapy Steroid treatment for asthma, interstitial lung disease, etc. Other (antibiotics in cystic fibrosis etc.) Surgical intervention Spirometry Measurements FVC - the volume of air expired forcefully after a maximal inspiration FEV 1 - the maximal volume of air exhaled with maximally forced effort in 1 second FEV 1 /FVC ratio Alphabet soup 4
Spirometry graphs Volume-Time Curve Spirometry graphs Flow-Volume Loop ATS/ERS Standards General Considerations Pre-test instructions Medications Eating Exercise Smoking Questionnaire Height* and weight Equipment quality assurance program 5
ATS/ERS Standards General Considerations Height and weight Measured in indoor clothes without shoes Patients with deformities of the thoracic cage should have their arm span measured Regression equations Ht = arm span/1.06 2005 ATS/ERS Standards General Laboratory ATS/ERS Standards General Considerations Personnel qualifications Minimum requirements include sufficient education and training to assure that the testing staff are competent Mayo PFL Quality Assurance Program NIOSH spirometry training 6
ATS/ERS Standards Standardization of Spirometry Test Procedure There are three distinct phases to the FVC maneuver: 1. maximal inspiration 2. a blast of exhalation 3. continued complete exhalation to the end of test (EOT) ATS/ERS Standards Standardization of Spirometry Maximizing Effort Use words like: Blast it out!, Snap it out! Coaching 7
ATS/ERS Standards Standardization of Spirometry ATS/ERS Acceptability Unacceptable Cough in the First Second ATS/ERS Acceptability Unacceptable Hesitation/Back Extrapolation 8
ATS/ERS Acceptability Unacceptable Suboptimal Blast ATS/ERS Acceptability Unacceptable Early Termination or Glottis Closure ATS/ERS Acceptability Unacceptable Negative Sensor Drift 9
ATS/ERS Acceptability Unacceptable Positive Sensor Drift ATS/ERS Acceptability Unacceptable Sneak Breath ATS/ERS Acceptability Spirometry Test Results 10
ATS/ERS Standards Standardization of Spirometry Between Maneuver Evaluation Minimum of 3 maneuvers Acceptable repeatability is achieved when the difference between the largest and the next largest FVC is 0.150 L or less AND the difference between the largest and next largest FEV 1 is 0.150 L or less. For those with an FVC of 1.0 L or less both these values are 0.100 L. What is Your Predicted Normal? Factors Affecting Lung Volumes & Flow Rates Height Age Sex Race These measurements are very critical since the predicted normal values (reference values) are based on these. Weight does NOT affect predicted normals! 11
Men have larger lung volumes than women. Blacks & Asians have lower predicted values than Caucasians. What is considered abnormal? What reference values are you using? Knudson (1976) Knudson (1983) Morris Crapo NHANES III (Hankinson, et. al., 1999) Global Lung All Age (3-95yrs) Quanjer, Stocks, et al., 2012 12
What is Considered Abnormal? Lower Limit of Normal (LLN) Threshold below which a value is considered abnormal (Of a Normal population--95% will be above and 5% will be below the LLN) Rules of thumb : 80% of predicted for FVC & FEV 1 70% for actual FEV 1 /FVC ratio Global Initiative for Obstructive Lung Disease (GOLD) Recommends FEV 1 /FVC < 70% (after bronchodilator) as diagnostic of COPD obstruction 70% cut-off results in increased false negatives and false positives with potential for misclassification GOLD Misclassification Mottram CD Ruppel s Manual of Pulm Func 11 th 2017 13
Interpretation Guidelines Official Statements of the American Thoracic Society and the European Respiratory Society Obstructive Pattern COPD/Asthma Restrictive Pattern osis, chest wall, weakness 14
Basic Spirometry Interpretation Algorithm FEV₁/FVC% Normal? Obstruction No (<LLN) Yes Yes Normal FVC Normal? No (< LLN) Restriction Example #1 Pred LLN Actual %Pred FVC 4.97 ( 4.12 ) 6.00 120.7% FEV 1 4.08 (3.36 ) 4.80 117.6% FEV 1 /FVC 81.9% (72.2%) 80.0% 97.7% A. Normal B. Obstruction C. Restriction Example #2 Pred LLN Actual %Pred FVC 4.97 (4.12) 3.00 60.4% FEV 1 4.08 (3.36) 3.00 73.5% FEV 1 /FVC 81.9% (72.2%) 100.0% 122.1% A. Normal B. Obstruction C. Restriction D. Unacceptable 15
Example #3 Pred LLN Actual %Pred FVC 4.97 (4.12) 1.80 36.2% FEV₁ 4.08 (3.36) 1.78 43.6% FEV₁/FVC 81.9% (72.2%) 99.0% 120.9% A. Normal B. Obstruction C. Restriction Example #4 Pred (LLN) Actual %Pred FVC 4.97 (4.12) 3.20 64.4% FEV 1 4.08 (3.36) 0.89 21.8% FEV 1 /FVC 81.9% (72.2%) 27.8% 33.9% A. Normal B. Obstruction C. Restriction Example #5 Pred (LLN) Actual %Pred FVC 4.97 (4.12) 4.45 89.5% FEV 1 4.08 (3.36) 3.00 73.5% FEV 1 /FVC 81.9% (72.2%) 67.4% 82.2% A. Normal B. Obstruction C. Restriction D. Neuromuscular weakness or suboptimal blast 16
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