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
Decreased lung volumes
Lung parenchymal process: expansion of the interstitial space (water, scar or inflammation) or “airspace filling process”
Pleural disease
Chest wall disease
Weakness
focal or global
Nerve or muscle based
Elevated lung volumes - increased TLC
Increased TLC is called hyperinflation
Elevated lung volumes - increased RV
Increased RV is air trapping
Diffusing capacity
Measured as CO transfer factor
Perform a breath hold on a known concentration of an inhaled gas (CO) which is diffusion-limited
Amount of diffusion = inspired CO – expired CO
Gas exchange
Takes place at alveoli
Depends on adequate ventilation of alveoli
Influenced by alveolar surface area and thickness of respiratory membrane
Reduced CO transfer & disease - pulmonary
Decrease in
- Emphysema
- Lung infiltration
- Lobectomy
But…
High cardiac output
Pulmonary haemorrhage
Polycythaemia
Reduced CO transfer & disease - Cardiovascular /haematological disease
Decrease in
- Pulmonary hypertension
- Low cardiac output
- Pulmonary oedema
- Anaemia
But…
High cardiac output
Pulmonary haemorrhage
Polycythaemia
