Flow Volume Loops


  • provide a graphical analysis of inspiratory and expiratory flow from various inspired lung volumes
  • breathing across a pneumotachograph subjects inhale to TLC -> FEC manoeuvre -> rapidly inhale back to TLC.
  • airflow from TLC is maximal at the beginning of forced exhalation where:
    1. elastic traction of alveolar septa on airway is greatest
    2. expiratory muscle strength is greatest
    3. airway resistance is lowest
  • airway resistance increases as forced expiration proceeds due to progressive reduction in airway calibre and is maximal at RV (effort independent part of curve – flow limited by dynamic compression)
  • circular in spontaneously breathing patients
  • squared but set at an angle in PC and PS breaths

Information Gathered

  • peak inspiratory flow rate
  • peak expiratory flow rate
  • tidal volume
  • type of lung and airway pathology
  • leaks or air trapping
  • water or secretions in circuit


Flow limitation can arise from 3 factors:

(1) decreased maximal static expiratory pressure (neuromuscular disease)
(2) increased airway resistance (asthma)
(3) decreased lung elastic recoil pressure (emphysema)

A = lower airway obstruction (COPD/asthma)
B = fixed upper airway obstruction (tracheal stenosis)
C = variable intrathoracic upper airway obstruction (tumour in lower trachea)
D = variable extrathoracic upper airway obstruction (vocal cord tumour or paralysis, enlarge thyroid)

  • restrictive lung disease (pulmonary fibrosis)

Leaks or Air Trapping

  • loop will not meet at left side where inspiration and expiration end

Jagged Loop

  • water of secretion build up

CCC 700 6

Critical Care


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.

| INTENSIVE | RAGE | Resuscitology | SMACC

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