Physiology Flashcards
(18 cards)
What are the key Figures for airflow obstruction?
- Airflow obstruction: FEV1: FVC <70%
- Severity based on FEV1
- Mild = >80%
- Moderate = 50-79%
- Severe = 30-49%
- Very severe = <30%
Describe the key points for limits of normality (What, when and why used, and key values)
- What - LLN = lower limit of normality, ULN = upper limit of normality
- When - should be used in deciding if an individual’s results are within normal range or not
- Why - with just a 70% cut-off we underdiagnose some younger patients and overdiagnose some older patients with airflow obstruction
- If falls within SR (standardised residual) of +/- 1.65 then results within normal limits for that patient
What are some key features and examples of an obstructive flow volume loop?
- Key features:-
i. Normal PEF (as large airways often unaffected)
ii. Low FEV1 and FEF25-75 (due to smaller airway obstruction)
iii. Concave F/V loop
iv. FVC normal (early stage of disease)
v. Normal inspiratory loop - Examples: COPD, asthma
What are some key features and examples of an restrictive flow volume loop?
- Key Features:-
i. Normal FV loop (as airways unaffected)
ii. FVC is low
iii. PEF can be normal or low - Examples: ILDs, asbestosis
What are some key features and examples of a variable intrathoracic obstructive flow volume loop?
- Features:-
i. Flattening of inspiratory loop (obstruction near intrathoracic part of trachea sucked outwards during inspiration
ii. Normal inspiratory loop - Examples: main bronchus/lower tracheal tumours, tracheomalacia
What are some key features and examples of a variable extrathoracic obstructive flow volume loop?
- Features:-
i. Normal expiratory loop (obstruction pushed outwards by force of expiration)
ii. Flattening of inspiratory loop (obstruction sucked into trachea) - Examples: vocal cord paralysis, extrathoracic goiter, laryngeal tumours
What are some key features and examples of fixed large airway obstruction on the flow volume loop?
- Features:-
i. Flattened inspiratory and expiratory flow loops - Examples: both intrathoracic + extrathoracic – tracheal stenosis (circular tracheal tumour, intubation)
Describe the Different Lung Volume Measurements
- TV (tidal volume) = inspiration and expiration at rest
- IRV (inspiratory reserve volume) = max inspiratory volume beyond TV
- ERV (expiratory reserve volume) = max expiratory volume beyond TV
- RV (residual volume) = residual volume within lungs at max expiration
- IC (inspiratory capacity) = TV + IRV
- FRC (functional respiratory capacity) = ERV + RV
- VC (vital capacity) = IRV + TV + ERV
- TLC = VC + RV
What are the main methods of measuring lung volumes, and key differences in diagnostic values
Inert gas dilution (ie helium) and box bethysmography
- Body plethysmography will include poorly ventilated areas (bullae/small airway obstruction/pneumothorax) within the volumes, whereas helium won’t reach these areas.
What are some key findings of pathology in lung volumes
- Restrictive = reduced TLC (all volumes reduced). RV/TLC ratio unchanged or reduced
- Muscle weakness = raised RV
What are the key points in understanding gas transfer
- TLCO (Transfer capacity of the Lung for CO) = VA (Alveolar Volume ie size of lungs during the test) x KCO (CO Transfer Coefficient ie uptake of gas)
- A decrease in transfer factor is due to:-
- Decrease in VA
- Decrease in KCO
- Decrease in both KCO and VA
What would cause reduced VA and reduced KCO?
ILD
What would cause normal VA with reduced KCO?
Vasculitis
What would cause reduced VA with normal or slightly raised KCO?
Pneumonectomy or mechanical restriction (eg obesity/chest wall deformity)
What would cause reduced VA with raised KCO?
Pulmonary haemorrhage
What would cause a reduced KCO with normal TLCO
Respiratory muscle weakness, pulmonary haemorrhage (ie normal/raised VA with reduced KCO)
What tests are used for respiratory muscle weakness, and what values are diagnostic?
Lying/Standing VC
* Simplest clinic test for measuring respiratory muscle weakness (specifically diaphragm)
* Abdominal contents will push a paralysed diaphragm up on lying supine (obesity can have a similar effect)
* Values:-
- VC fall <10% - probably normal
- VC fall 10-20% - suspicious of diaphragmatic paralysis
- VC fall >20% - suggests significant (usually bilateral) diaphragmatic paralysis
Other tests:-
* Pressure meter (highly effort dependent)
* Sniff (rough and ready test for inspiratory weakness)
* Transdiaphragmatic pressures (reproducible measure of diaphragm function, need good patient cooperation and effort)
What is the A-a Gradient and when is it significant?
A-a gradient = PIO2 – (PaO2 + PaCO2/0.8)
* PIO2 = 100-7 x FiO2 (where 100 is atmospheric pressure, 7 is subtracted for water vapour pressure due to humidification of inspired air)
* 0.8 = Respiratory quotient
Significance = V/Q mismatch
- 1-2 kPa normal in young and middle-aged
- 2-3 kPa normal in elderly
- >2 kPa in young/middle-aged or >3 kPa in elderly –> V/Q mismatch
