Spirometry
OVERVIEW
- Capacity = any combination of 2 or more volumes
LUNG VOLUMES
FLOW VOLUME LOOP
PARAMETERS
- VC = 70mL/kg
= IRV + TV + ERV - IRV = 45mL/kg
- TV = 10mL/kg – volume breathed in & out during a normal breath (without extra effort)
- ERV = 15mL/kg – extra volume beyond normal expiration
- RV = 15mL\kg (not measured by spirometer)
- TLC = 85L\kg
- FRC = 30mL\kg
- FEV1 = forced expiratory volume in 1 second (normally 4L)
- FVC = forced vital capacity (a little lower than VC because of dynamic airway closure; normally ~5L)
- PEFR = peak flow rate over an expiration (normally 500L/min)
- FEV1/FVC (normal = 80%)
– obstructive disease = FEV1 reduced more than FVC, low FEV1/FVC
– restrictive disease = FEV1 & FVC reduced but FEV1/FVC normal or increased
– after a relatively small amount of gas has been exhaled -> flow is limited by airway compression determined by (1) elastic recoil force of lung & (2) resistance of airways upstream of the collapse point. - FEF50%
- FIF50%
- FEF/FIF50 = if > 1 -> inspiratory flow is affected more than expiratory -> extrathoracic site of obstruction
OBSTRUCTIVE DISEASE
- flow rate very low in relation to lung volume (c/o resistance to flow – scooped out appearance often seen following the point of maximum flow)
- total lung capacity is large, but expiration ends prematurely c/o early airway closure from increased smooth muscle tone of bronchi (asthma) or loss of radial traction from surrounding parenchyma (emphysema).
- equal pressure point is close to the alveolus and the transmural pressure gradient can become negative quickly -> collapse.
- encroachment of VC by an increased RV caused by hyperinflation (‘air trapping’)
RESTRICTIVE DISEASE
- total volume exhaled and flow rate reduced
- inspiration limited by reduced compliance of lung/chest wall or weakness of inspiratory muscles
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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