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23 Cards in this Set
- Front
- Back
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Spirometry: Applications
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- determine the presence or absence of lung disease
• quantify known lung disease • measure the effects of treatment e.g. bronchodilators, steroids • monitor the effects of other diseases on lung function e.g. cardiac disease, neuromuscular disease • confirm the findings of other investigations e.g. chest x-ray • monitor the effects of environmental or occupational exposure e.g. smoking, dusts • assess patients pre-operatively Obstructive - Spirometric indices defines this impairment Restrictive -Spirometric indices may suggest this impairment |
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Forced vital capacity (FVC) and Forced expired volume in one second (FEV1)
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There are three important steps to follow in FVC maneuver for spirometry:
-Full inspiration -Forceful expiration -Full expiration FORCED (or FAST) VITAL CAPACITY FVC is the maximal volume of air exhaled with maximally forced effort from a maximal inspiration, i.e. vital capacity performed with a maximally forced expiratory effort, expressed in liters at body temperature and ambient pressure saturated with water vapor (BTPS). FORCED EXPIRED VOLUME IN ONE SECOND FEV1 is the maximal volume of air exhaled in the first second of a forced expiration from a position of full inspiration, expressed in liters at BTPS. |
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Flow volume curve: Applications
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Assess FVC maneuver effort
Assess for possible central airway obstruction |
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Normal, obstuctive, restrictive spirometry values
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Normal
-FEV1/FVC = 80% Obstructive -FEV1/FVC <75% Restrictive -FEV1/FVC = normal, but both FEV1 and FVC are lower |
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Reverence equations for spirometry
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Based on measures in "normal population" separated by:
-Gender -Height -Age -Ethnicity |
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Lower limit of normal
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Much theoretical evidence that 80% (or any fixed percentage) of the predicted value will incorrectly classify some individuals as abnormal
90% confidence interval for spirometric values will produce statistical error of 5% misclassification in a population Lower limit of normal (LLN) can be defined by mean predicted or reference value minus 1.64 X SEE |
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Interprative strategies for lung function tests
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FEV1/FVC > LLN?
-Yes or No If Yes is FVC > LLN? -Yes is normal spirometry -No suggests restrictive pattern --Is TLC > LLN? ---Yes is a normal test ---No is a restrictive pattern If no, it is an obstructive pattern. Is FVC > LLN? -Yes, pure obstruction -No, is TLC > LLN? --Yes, pure obstruction --no, combined obstruction and restriction |
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Bronchodilator response
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Metered dose inhaler (MDI) or small volume nebulizer (SVN) for drug delivery
Spacer preferred with MDI Dose should be specified Wait 15 min. after bronchodilator (BD) inhalation to retest Report only tests that meet acceptability and reproducibility criteria % Change = (Post BD value - pre BD value)/ pre BD value Suggested significance criteria: FVC at least increase of 12% and 200ml absolute change FEV1 at least increase of 12% and 200ml % change in FEV1 is a function of baseline airway obstruction Decision to use bronchodilators is a clinical one PEF values vary too much to be useful for BD testing If tests are not reproducible or acceptable, interpret with caution |
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Static lung volumes
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Four Methods:
Helium dilution Nitrogen washout Body plethysmography Chest x-ray measurements Volumes : 4 primary volumes by convention Do not overlap Cannot be subdivided Capacity : 4 capacities Each capacity is comprised of two or more primary volumes FRC = RV + ERV TLC = Vt + IRV VC = ERV + Vt + IRV IC = Vt + IRV The relationship between volumes obtained during a spirometric vital capacity (VC) maneuver and total lung capacity (TLC). Although spirometry measures VC and its components, it cannot measure absolute lung volumes, including residual volume (RV), functional residual capacity (FRC) or total lung capacity (TLC). |
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FRC, RV, TLC definitions
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F.R.C. (Functional residual capacity) : This is the volume of gas present in the lung and airways at the average end-expiratory level. It is the sum of expiratory reserve and residual volume : F.R.C. = E.R.V. + R.V. The latter can only be measured indirectly; the method of measurement as well as the measuring conditions should be specified. Expressed in liters.
R.V. (Residual volume) : The volume of gas remaining in the lung at the end of a full expiration. It is calculated by subtracting the expiratory reserve volume from the functional residual capacity : R.V. = F.R.C. – E.R.V., or R.V. = T.L.C. – I.V.C. Expressed in liters. T.L.C. (Total lung capacity) : The volume of gas in the lung at the end of a full inspiration. It is either calculated from : T.L.C. = R.V. + I.V.C., or from : T.L.C. = F.R.C. + I.C. (the latter is the preferred method in body plethysmography). Expressed in liters. It can also be measured directly by the radiologic technique. The method of measurement (gas dilution, body plethysmography, radiology) should be specified. A low T.L.C. occurs in restrictive lung disease. |
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Obstructive ventilatory defect vs Restrictive ventilatory defect
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OVD = obstructive ventilatory defect (i.e. FEV1/FVC < LLN)
-TLC increased or the same -VC decreased -FRC increased -RV greatly increased RVD = restrictive ventilatory defect (i.e. TLC < LLN) -TLC decreased -VC decreased -FRC decreased -RV decreased or the same |
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Causes of reduced total lung capacity: a restrictive defect
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Intrapulmonary:
Pneumonectomy Collapsed lung Consolidation Edema Fibrosis Extrapulmonary: Pleural disease (effusion, fibrosis, pneumothorax) Rib cage abnormality (scoliosis, thoracoplasty) Respiratory muscle weakness Gross abdominal distention Severe obesity |
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Elevation of residual volume: "air trapping"
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Hyperinflation of RV. In both elderly healthy adults and
individuals with obstructive lung disease, early closure or compression of small airways during expiration is considered a key determinant of the frequently observed elevations of RV |
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Causes of increased residual volume
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Intrapulmonary:
Generalized airway obstruction Pulmonary vascular congestion Mitral stenosis Extrapulmonary Expiratory muscle weakness -Spinal injury -Myopathy |
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DLCO Diffusing capacity of the lung for carbon monoxide
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Transfer factor of the lung for carbon monoxide (TLCO)
Is used to evaluate the transfer of gas from the distal air spaces into the pulmonary capillaries. It can be measured when known and very low concentrations of carbon monoxide (CO) are inspired. The rate of CO disappearance is calculated from the ratio of the CO concentrations of the inspired and expired gas and then expressed as a function of the driving pressure. DLCO =V CO / (PACO - PcCO) Where: V CO is the uptake of CO in ml of CO at STPD conditions per minute PACO is the average partial pressure of CO in alveoli PcCO is the average partial pressure of CO in the pulmonary capillary plasma Transfer of CO requires: -Perfused alveoli -Ventilated alveoli -Hemoglobin (to bind CO) |
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Hemoglobin, carboxyhemoglobin, PIO2 (inspired oxygen pressure) effects on DLCO
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Hemoglobin
-As hemoglobin increases, DLCO increases -As hemoglobin decreases, DLCO decreases Carboxyhemoglobin -As carboxyhemoglobin concentration increases, DLCO decreases (and vice versa) PIO2 -As PIO2 increases, DLCO decreases (and vice versa) |
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Interpretation of DLCO
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LOW DLCO WITH OBSTRUCTION
Emphysema Cystic fibrosis Bronchiolitis LOW DLCO WITH RESTRICTION Diffuse parenchymal lung disease Pneumonitis/alveolitis OTHER Carboxyhemoglobulinemia Altitude Anemia Pulmonary embolism Pulmonary arterial hypertension A high DLCO is associated with asthma , obesity and intrapulmonary hemorrhage |
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DLCO testing
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DLCO testing involves 2 steps:
1) measure rate of uptake of CO into blood 2)estimating the driving pressure for CO from alveoli to capillary blood. thus; DLCO = VCO / (PACO - PcCO) Inhaled test gas usually contains: 10% He, 0.3%CO, 21%O2, balance N2 Subject inhales test gas from RV to TLC and holds breath for 9 to 11 sec Inhalation should be moderately fast, not slow. After breath, hold exhale moderately fast, collect alveolar sample when 0.75 to 1.0 L exhaled. |
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Interprative strategies for lung function tests
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From spirometry
If normal -DLCO > LLN -Yes, normal -No, pulmonary vascular disorder If Restricted -DLCO > LLN -Yes chest wall and neuromuscular disorder -No, interstitial lung disorder, Pneumonitis If Obstructive -DLCO > LLN -Yes, Asthma, chronic bronchitis -No, Emphysema |
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Flow volume curves in airway obstruction
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Normal
-Sail for expiration -Half oval for inspiration Fixed -Half oval for expiration and inspiration Variable extrathoracic -Normal sail for expiration -Truncated oval for inspiration Variable intrathoracic -Truncated expiration -Elongated oval inspiration |
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Maximal respiratory pressures
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Maximal respiratory pressures (MIP)
-indicated with an unexplained decrease in vital capacity -respiratory muscle weakness is suspected clinically MIP is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece Maximal expiratory pressure (MEP) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation -measured using a simple mechanical pressure gauge connected to a mouthpiece -MIP measures the ability of the diaphragm and the other respiratory muscles to generate inspiratory force, reflected by a negative airway pressure -average MIP and MEP for adult men are -100 cmH2O and +170 cmH2O, respectively -adult women are about -70 cmH2O and +110 cmH2O, respectively -lower limit of the normal range is about two-thirds of these values Repeated measurements of MIP and MEP -useful in following the course of patients with neuromuscular disorders -slow vital capacity may also be followed, but it is less specific and usually less sensitive. |
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Obstructive, restriction, and mixed defect diagnosis
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Obstruction
-FEV1/VC or FEV1/FVC < 5th percentile of predicted (i.e. <LLN) Restriction -TLC< 5th percentile of predicted (<LLN) -A reduced FVC or VC does not prove a restrictive pulmonary defect. It may be suggestive of lung restriction when FEV1/VC ratio is normal or increased Mixed defect -FEV1/VC and TLC< 5th percentile of predicted (i.e. <LLN) |
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Degree of severity of decrease in diffusing capacity for carbon monoxide (DLCO)
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Mild
-DLCO >60% and <LLN Moderate -40-60% Severe -<40% |
