Lecture 4 Lung Diagnostics Klassen LUNG FUNCTION: … · 2018. 4. 7. · Minimum of 3 tests (reliability) Maximum of 8 acceptable FVC maneuvers Good “start of test” o Rapid start

Lecture 4 Lung Diagnostics Klassen LUNG FUNCTION:

Tidal Volume (VT): volume of air moved in or out of lungs at rest (~ 500 mL) – involuntary stage

Inspiratory Capacity (IC): amount of air that can be inhaled from the resting expiratory level

Vital Capacity (VC): maximum volume of air expelled after maximum inspiration to full exhalation – used in diagnostic testing

Residual Volume (RV): volume of air remaining in lungs after maximal exhalation

Total Lung Capacity (TLC): total amount of air in the lungs after maximal inhalation (TLC = VC + RV)

DIAGNOSTIC TESTING

Endoscopy

Imaging

Pulmonary Function Testing (Spirometry)

Identify respiratory abnormalities

Categorize lung disease

Measure severity of lung dysfunction

Monitor disease progression

Quantify measured response to therapy

BRONCHOSCOPY/ENDOSCOPY

Visualize the inside of the airways

Tissue/specimen sampling if needed

Cannot use at respiratory airways to avoid damage

IMAGING Chest X-ray: radio dense material

(fluid, bone absorb X-rays)

Dx: pneumonia, pulmonary edema

Pulmonary angiography: pulmonary blood vessels are injected with radio-constrat dye and x-rayed

Dysfunction of perfusion Spiral CT scan: helical movement of scanner takes cross sections through body & reconstructs anatomy

Increased 3D resolution

Ventilation/Perfusion Scan: imaging is based on the inhalation of radionucleotide gas & the injection of contrast media

Normal adult V/Q ratio = 1/1

V/Q mismatch – ratio is uneven o No ventilation = SHUNT (high V/Q) o No perfusion = DEAD SPACE (dead tissue) (low V/Q)

SPIROMETRY Indications:

At risk individuals: >40 & current or ex-smoker

Pts complaining of sx (coughing, SOB)

Pts with concerns about their lung health because of environmental exposures or family history

Pts with already diagnosed lung disease to monitor lung function and response to medication

Refer pts with abnormal test results

Contraindications:

Hemoptysis of unknown origin

Pneumothorax, thoracic, abdominal or cerebral aneurysms

Recent eye, thorax, or abdomen surgery

Unstable cardiovascular status (recent MI or pulmonary embolus)

Inability due to age, confusion, etc

Suspected TB or other contagious respiratory infection

Predicted values:

Gender

Age

Height

Ethnic origins

Always verify these are accurately entered

Test results interpreted by comparing the values with the reference (predicted) values for that patient

Defines the Lower Limit of Normal & Range of Normal

General procedure 1. Maximal inspiration 4. Get 3 readings – within 5% or 100 mLs of each other 2. Maximal expiration (“blast expiration) 5. Use best values for FEV1, FVC & FEV1 3. Continued exhalation until max air exhaled (RV) 6. Introduce bronchodilator & repeat for assessment

(6 seconds in adults) of reversibility 15 minutes later

Lecture 4 Lung Diagnostics Klassen

SPIROMETRY MEASUREMENTS: assess dynamic flow within the airways – airway calibre & lung compliance

Maximal expiratory flow is highly reproducible – HAS DIAGNOSTIC UTILITY

FEV1 – Forced Exhalation Volume: max. volume of air exhaled in 1 second with maximally forced effort from a position of maximal inspiration

FVC – Forced Vital Capacity: max. volume of air exhaled from lungs with maximally forced effort from a position of maximal inspiration

FEV1/FVC % (Tiffeneau-Pinelli Index): proportion of vital capacity

Healthy persons generally exhale at least 80% of their VC in 1 second

FLOW-VOLUME GRAPH: flow plotted on vertical axis and volume plotted on horizontal axis

Exhalation: area above horizontal axis

Inhalation: area below horizontal axis

Tidal breathing (prior to max. exhalation): small circle in middle of graph

Inspired flow: down Inspired volume: moves to left

Expired flow: up Expired volume: moves to the right

PEFR – Peak Expiratory Flow Rate: the volume of air that can be forcibly exhaled from max. inhalation to max. exhalation

SPIROMETRY CRITERIA:

Acceptability criteria

Minimum of 3 tests (reliability)

Maximum of 8 acceptable FVC maneuvers

Good “start of test” o Rapid start to rise time (good PEF) o No hesitation or pause o Extrapolated volume < 5% of FVC or 150 mL (whichever is greater) o No cough, especially during first second

Satisfactory exhalation: min. exhalation of 6 seconds for adults & children > 10 yrs; 3 seconds for children < 10 yrs

Plateau at end of exhalation (i.e. flow <0.025 L in 1 sec will be determined by spirometer)

No Valsalva maneuver (glottic closure)

No leak (lips are sealed)

Reproducibility: select data from acceptable curves only

2 largest FVC should not vary by more than 150 mL (5%)

2 largest FEV1 should not vary by more than 150 mL (5%)

In children & adults with small lung volumes, if FVC < 1.0 – 2 L, largest FVC & FEV1 must be within 100 mL

SPIROMETRY IN DISEASE DIAGNOSIS:

Obstructive lung disease: obstruction of airflow in/out

Bronchoconstriction, inflammation, mucus secretion, SMALL AIRWAY DISEASE, asthma, COPD

FEV1 <80% predicted

FVC usually reduced but to lower extent than FEV1

FEV1/FVC ratio reduced (<0.7)

Restrictive lung disease: restrict (LIMIT) expansion of lung = less ventilation and/or more effort to ventilate

Pneumothorax (punctured lung), atelectasis (collapsed lung), pulmonary fibrosis, obesity

FEV1 <80% predicted

FVC <80% predicted

FEV1/FVC ratio normal (>0.7)

Lecture 4 Lung Diagnostics Klassen

SPIROMETRY IN ASTHMA: BD = bronchodilator

Improvement after BD = reversibility NOTE: inhalation not affected

Diagnosis of asthma: variable airflow limitation

Confirm presence of airflow limitation

Document that FEV1/FVC is reduced (at least once when FEV1 low)

FEV1/FVC ratio normally >0.75-0.80 in adults, and >0.90 in children

Confirm variation in lung function is greater than in healthy individuals

Greater variation or more times variation occurs = % dx is asthma

Excessive BD reversibility (increase in FEV1 > 12% (or >200 mL increase in volume for adults))

Significant increase in FEV1 or PEF after 4 wks of controller txt

If initial testing is negative:

Repeat when pt is symptomatic, or after withholding BDs

Refer for additional tests (esp. children ≤ 5 years, or elderly)

GINA Classification of Asthma Severity Symptom/Day Symptoms/Night PEF or FEV1 PEF

variability

STEP 1 Intermittent

<1 time/wk

Asymptomatic & normal PEF between attacks

≤ 2 times/month ≥ 80% < 20%

STEP 2 Mild persistent

>1 time/wk but <1 time/day

Attacks may affect activity

> 2 times/month ≥ 80% 20-30%

STEP 3 Moderate persistent

Daily

Attacks affect activity

> 1 time/wk 60-80% > 30%

STEP 4 Severe persistent

Continuous

Limited physical activity

Frequent ≤ 60% > 30%

SPIROMETRY IN COPD Diagnosis and Assessment

COPD considered in any pt w/ dyspnea, chronic cough or sputum production, history of exposure to risk factors

Spirometry is REQUIRED to make diagnosis: presence of post-bronchodilator FEV1/FVC <0.70 confirms presence of persistent airflow limitation = COPD o Short-acting inhaled BD minimized variability o Values should be compared to age-related normal

values to avoid overdiagnosis of COPD in elderly

GOLD Classification of Asthma Severity: in patients with FEV1/FVC < 0.70 (based on post-BD FEV1)

GOLD 1: Mild FEV1 ≥ 80% predicted

GOLD 2: Moderate 50% ≤ FEV1 < 80% predicted

GOLD 3: Severe 30% ≤ FEV1 < 50% predicted

GOLD 4: Very Severe FEV1 < 30% predicted

SPIROMETRY IN ACOS: Overlap between Asthma and COPD Spirometric variable Asthma COPD ACOS

Normal FEV1/FVC pre- or post-BD

Compatible with asthma Not compatible with diagnosis

Not compatible unless other evidence of chronic airflow limitation

Post-BD FEV1/FVC <0.7 Indicates airflow limitation; may improve

Required for diagnosis by GOLD criteria

Usual in ACOS

FEV1 ≥ 80% predicted Compatible with asthma (good control, or interval between sx)

Compatible with GOLD category A or B if post-BD FEV1/FVC < 0.7

Compatible with mild ACOS

FEV1 < 80% predicted Compatible with asthma. A risk factor for exacerbations

Indicates severity of airflow limitation and risk of exacerbations and mortality

Post-BD increase in FEV1 > 12% and 200 mL from baseline (reversible airflow limitation)

Usual at some time in course of asthma; not always present

Common, and more likely when FEV1 is low

Post-BD increase in FEV1 > 12% and 400 mL from baseline

High probability of asthma. Unusual in COPD. Consider ACOS.

Compatible with diagnosis of ACOS.