Ins and outs of respiratory physiology

David Taylordcmt@liv.ac.uk

All illustrations and text © The University of Liverpool and David Taylor 2008

Why?

• ....Dr Al-Ghabra and the medical student with her, Sally Lawrence, review ventilation, gas exchange, and control of breathing related to anatomical landmarks on the film. ...

Why?

• ....Dr Al-Ghabra and the medical student with her, Sally Lawrence, review ventilation, gas exchange, and control of breathing related to anatomical landmarks on the film. ...

Expected outcomes of this

be able to.......• Explain the different respiratory tests that

could be used• Recognise, draw and label a lung volume

graph• Recognise normal volumes and flow rates• Understand the difference between

obstructive and restrictive lung disease

and

• Relate this new understanding to a patient with asthma

Explain the different respiratory tests that could be used

• Two things matter– Volumes– Flow rates

• But (vital capacity) differences due to– Age (younger>older– Gender (male>female)– Size (tall>short)– physical condition (thin fit>obese less active)

Volumes

Tidal volume 500ml

Time (each breath about 5s)

Minute volume500 x 12 = 6l min-1

Vital capacity

Maximum inspiration

Maximum expiration

InspiratoryReserve volume3000ml

Expiratory reserveVolume 1100ml

TV

Vital Capacity4600ml

And the others....

Residual volume1200ml

Expiratory reserveVolume 1100ml

Functional residual capacity2300ml

Total lung capacity 5800ml

Flow rate...Vital Capacity

Forced vital capacity

Expanded

Forced volumesFEV1 = Forced expiratory volume in 1 second

FVC=Forced Vital Capacity

In normal adultFEV1/FVC = 75%

This patientFEV1/FVC = 44%Obstructive lung disease

Chronic airflow limitation

• In (obstructive) diseases like asthma there is difficulty in breathing out.

• Over long periods of time this tends to lead to an increase in residual volume

Just for completeness

• If FVC is lower than predicted, then the patient has restrictive lung disease– Expansion of the lung is restricted• Fibrosis• Pneumonia• Pulmonary oedema• Pregnancy• pain

Simplest and cheapest test is

• Peak expiratory flow rate– Reproducible, but only measures flow over a few

milliseconds– And people don’t always try hard– But values over 500 lmin-1 in men– And 400 lmin-1 in women are in the right region– Best used for tracking changes (measure at same

time each day for several days)

510 l/min

Expected outcomes of this

be able to.......• Explain the different respiratory tests that

could be used• Recognise, draw and label a lung volume

graph• Recognise normal volumes and flow rates• Understand the difference between

obstructive and restrictive lung disease