The Spirometer

Spirometer

• instrument which measures the volume of air which enters and leaves the lungs

what kind of flow do lungs have

• tidal flow → moves back and forth

  • air cant leave from alveoli has to go back the same way it came from

tidal volume

• the amount of air that moves in and out during one breath when we are at rest

Inspiratory Reserve volume

• the amount of air which can be taken in after tidal inspiration - we can breathe more deeply then our tidal volume

Expiratory Reserve Volume

• total volume of air which can be exhaled after tidal inspiration

  • we can exhale more air then what we do during tidal

Vital Capacity

• combined tidal volume inspiratory and expiratory reserve volumes

• Maximum amount of air which can be exchanged during a breath in and out

facts about vital capacity

• non athlete is lower

• decreases with age

• clinically important → shows damage to alveoli in some pulmonary disorders

residual volume of air

• air remaining in the lungs after forceful exhalation

Total Lung Capacity

• vital capacity + residual volume

anatomical dead space

• volume of air which doesnt reach lungs but remains in bronchi and bronchioles

• 30% of air

tidal volume and anatomical dead space volume

• 150ml

• 500ml (tidal)

limitations of tidal breathing

• partial pressure gradient of oxygen due to mixing with stale air is diluted

• pauses between inhalation and exhalation o2 in alveoli is getting used up partial p gradient gets smaller

Setup of Spirometer

• air filled chamber suspended over water (doesnt let air escape)

• co2 is absorbed by soda lime

• oxygen is added in at the same rate the person is using it (keeping the volume constant)

• counterbalance makes chamber rise or fall with inhalation and exhalation

• pen is attached to the chamber - writes on a kymograph

What can be read using the spirometer

• metabolic rate → o2 needed per gram of body

• tidal volume

• rate of breathing

• o2 consumption

Pulmonary Ventilation

• volume of air exchanged between person and outside every minute

how to calculate PV

breathing rate x tidal volume

What happens if o2 is not replaced in the spirometer

• the chamber begins to drop as oxygen is used up

• oxygen consumption is determined as the overall drop in the chamber over a period of time

diagram of spirometer