Pulmonary function Flashcards
Tidal volume
Dead space
500ml
150ml
Total minute ventilation
6L/min (alveolar VE 4L/min)
23 generations of alveoli
Conducting (1-16) and respiratory zones (17-23)
Cartilaginous (1-4) and membranous airways (5-23)
All (1-22)airways have smooth muscle
Pneumotachograph
measures flow; converts to volume
Pulmonary function testing
Spirometry
Lung volume testing
Diffusion capacity
Modern spirometry
Vital capacity can be done slowly or “forced”
FVC manoeuvre
FEV1 manoeuvre
FEV1/FVC ratio: should exhale > 70% of FVC in first second
If FEV1/FVC < 0.7, then obstruction is present
Spirometry
Lung volumes and airflow rates are a function of GENDER + AGE + HEIGHT + RACE
No defined absolute normal or absolute abnormal values
Compare actual values to predicted values. Abnormal result often defined as % predicted < 80.
Exception is for FEV1/FVC ratio, which is expressed and evaluated as an absolute ratio.
Bronchodilator responsiveness
Albuterol/Salbutamol -> 15 minutes
Positive response: INCREASE in FEV1 (and/or FVC) by 12% and 200mL. This indicates reversible obstruction.
The lack of a bronchodilator response in the laboratory does not preclude a clinical response to bronchodilator therapy in real life.
Flow rates during forced expiration
Effort-dependent phase: increasing effort = increased flow rates
Effort-independent phase: increasing effort does not change flow rates
In the effort-dependent phase, flow rates decrease with decreasing effort, or with increased resistance.
They also decrease if starting a lower than TLC volumes
Peak Expiratory Flow Rate
Measured during spirometry in the PFT lab
But also can be performed with separate hand held device at home
Do ~ same time each day (morning dips)
Useful for patients with asthma:
Picking up exacerbations
Assessing response to treatment
Effort independent flow
Airway resistance causes a pressure drop from alveoli to mouth
When Ppl = Pairway, compression starts. This is called the equal pressure point (EPP).
EPP and dynamic airway collapse
Cartilage-free bronchioles act as starling resistors.
Bronchioles re-open when (positive) Ppl builds up enough to > Pairway. On/off flow for this phase of forced exhalation.
Increased effort will cause similar increases in alveolar pressure and pressure at the EPP. Pressure difference and flow will be unchanged.
Methacholine test
Methoacholine -> increase dose every 5 minutes
Assess for significant decline in flow
Positive test result = DECREASE in FEV1 by 20%. This indicates hyper-reactive airways (suggestive of but not specific for asthma)
Lung volume + restriction
Restriction should lead to reduction in RV, FRC, and TLC
Measuring lung volumes
Restriction should lead to reduction in RV, FRC, and TLC
Approach to determined lung volumes:
measure tidal volume, ERV and IRV
Indirectly measure the FRC
Calculate the TLC and RV (and IC) from this
None of these values not be obtained from spirometry
Methods of measurement of lung volumes:
Currently: Plethysmography, aka “Body Box”
Prior: helium dilution
