eLFH - Lung Function Tests Flashcards
Lung function test examples
Peak expiratory flow rate
Spirometry
Diffusing capacity
Types of spirometry
Benedict Roth Spirometer
Vitalograph trace
Flow volume curves
Peak flow meter description
Telescopic tube with a piston that expands as gas is blown into it, with longitudinal gas escape slot
Best of 3 measurements are taken
Conditions which have reduced PEFR
Obstructive lung conditions:
- Asthma
- COPD
PEFR prediction tables description
Gives predicted PEFR based on height and gender
Needs correction for ethnic groups that are not Caucasian
Predicted PEFR correction in Afro-Caribbean population
Reduce values by 13%
Predicted PEFR correction in Asian population
Reduce values by 7%
Limitations of predicted FVC and FEV1 values
Less established for patients aged 70 years and older
Calculation for predicted FVC in females over 70 years old
FVC = (0.0443 x height in cm) - (0.026 x age) - 2.89
SD +/- 0.43 L
Calculation for predicted FEV1 in females over 70 years old
FEV1 = (0.0395 x height in cm) - (0.025 x age) - 2.60
SD +/- 0.38 L
Calculation for predicted FVC in males over 70 years old
FVC = (0.0576 x height in cm) - (0.026 x age) - 4.34
SD +/- 0.61 L
Calculation for predicted FEV1 in males over 70 years old
FEV1 = (0.043 x height in cm) - (0.029 x age) - 2.49
SD +/- 0.51 L
Benedict Roth Spirometer use
Measures static lung volumes
Measures Tidal volume and vital capacity
Can then calculate Inspiratory reserve volume and Expiratory reserve volume
Method to measure functional residual capacity
Helium dilution
or
Body plethysmography
Volumes which can be calculated from FRC + other spirometry
Residual volume
Total lung capacity
Tidal volume definition and volume
Volume of air inspired and expired with each breath
6-8 ml/kg
Inspiratory reserve volume definition
Additional volume of air that can be forcibly inhaled after normal tidal volume inspiration
Expiratory reserve volume definition
Additional volume of air that can be forcibly exhaled after normal tidal volume expiration
Vital capacity definition
Maximal volume of air that can be exhaled after maximal inspiration
VC = TV + IRV + ERV
Residual volume definition
Volume of air remaining in lungs after maximal expiration
RV = FRC - ERV
Functional residual capacity definition
Volume of air remaining in lungs at the end of normal expiration
FRC = RV + ERV
Total lung capacity definition
Total volume of air in lungs after maximal inspiration
TLC = FRC + TV + IRV
or
TLC = VC + RV
Spirometry volumes and capacities graph and which cannot be calculated from it
Residual volume (and therefore also FRC and TLC) cannot be calculated from graph as lungs cannot be fully emptied
Vitalograph definition
Plots time on x axis against forces expiratory volume (FEV) on y axis
FEV1 definition
Volume of air forcefully exhaled in first second
Reduced in obstructive lung disease
Forced vital capacity definition
Volume of air that can be forcefully exhaled after maximal inspiration
Reduced in restrictive lung disease
High risk factor for general anaesthesia from vitalograph
FEV1 < 1L
Flow volume curve definition
Derived from pneumotachograph studies of whole respiratory cycle
Air flow is plotted against lung volume during forced inspiration and forced expiration
Normal flow volume curve
On expiration - rapid rise to maximal expiratory flow, followed by steady decline
Flow volume curve in obstructive lung disease
Expiration flow rate is low, with rapid decline after maximal flow giving scooped out appearance
Flow volume curve in restrictive lung disease
Maximal flow rate reduced
Flow volume curve with variable extra-thoracic obstruction e.g. goitre
Inspiratory part of curve is flattened, but expiratory part is preserved
Flow volume curve with variable intra-thoracic obstruction e.g. tracheomalacia
Expiratory part of curve is flattened but inspiratory part is preserved
Flow volume curve with fixed extra-thoracic obstruction
Flattening of curve in both inspiration and expiration
Abnormal spirometry results by each measurement definition
Below are all considered abnormal results:
FEV1 < 80% predicted
FVC < 80% predicted
FEV1/FVC < 0.7
Diagnosis of obstructive lung disease
FEV1 < 80%
and
FEV1/FVC < 0.7
Differentiating between COPD and Asthma on spirometry
Reversibility with bronchodilators
Diagnosis of restrictive lung disease on spirometry
FEV1 < 80%
FVC < 80%
FEV1/FVC > 0.7
Spirometry findings obstructive vs restrictive lung disease
Diffusing Capacity of Lung for Carbon Monoxide (DLCO) alternate name
Transfer factor
Diffusing Capacity of Lung for Carbon Monoxide (DLCO) definition
Test of the integrity of the alveolar-capillary surface area for gas transfer
Normal carbon monoxide transfer limiting factor
CO rapidly taken up by Hb in blood
Therefore transfer of CO mainly limited by diffusion and used to measure gas transfer
Conditions where DLCO is reduced
COPD
Interstitial lung disease
Multiple PEs
Anaemia
Normal partial pressure changes in pulmonary capillary blood for N2O, O2, and CO
N2O is perfusion limited
CO is diffusion limited
O2 can be perfusion limited or partially diffusion limited
Pathogenesis of Cor pulmonale or P pulmonale
Lung disease results in hypoxic pulmonary vasoconstriction
Pulmonary hypertension results in right heart failure
