Transcript Mechanics of Breathing

Mechanics of Breathing
Overview
1. Inspiration
2. Expiration
3. Respiratory Volumes
Inspiration
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An active process requiring muscle contraction
Diaphragm and ext. Intercostal muscles contract
Thoracic cavity expands
Pleural cavity pressure decreases
Lung surface is pulled outward
Alveolar pressure decreases below atmospheric
pressure causing air to rush in
Expiration
 Expiration is a passive process, no muscle
contraction required
 Diaphragm and external intercostals relax
 Thoracic cavity decreases in size
 Pleural pressure increases
 Alveolar press. Greater than atmospheric
 Air flows out
animation 1
animation 2
Pulmonary Ventilation
 The total amount of air moved in and out
of the lungs each minute is called
Pulmonary Ventilation
– depends upon 2 factors:
• The size of each breath (tidal volume: TV)
• The number of breaths/minute (respiratory
frequency: BR (breathing rate))
Respiratory Volumes
 Tidal Volume (TV)- amount of air
exchanged in normal breathing
 Inspiratory Reserve Volume (IRV) amount of air that can inhaled forcibly over
tidal volume
 Expiratory Reserve Volume (ERV) - amt.
of air that can be forcibly exhaled after a
tidal expiration
Respiratory Volumes
 Residual Volume (RV): air remaining in
lungs after a forced expiration
 Vital Capacity (VC): total amt. of
exchangeable air (TV + IRV +ERV)
 Total Lung Capacity: VC + RV = air
contained in fully inflated lung
Respiratory Volumes
Respiratory Volumes
 Under normal resting conditions
– Pulmonary ventilation
15 breaths/min X 0.5 L/breath = 7.5 L/min
 During exercise we can increase tidal volume by
expanding both inspiration and expiration
– Extra inspiratory reserve volume (IRV) is about 2.5
litres for each breath
– Extra expiratory reserve volume (ERV) is about 1.5
litres for each breath
Breathing During Exercise
 The body’s ability to deliver oxygen is usually
the limiting factor in exercise capacity.
– During exercise; intercostal muscles and
muscles supporting sternum further expand
chest cavity.
– Pulmonary Ventilation
• Rest = 7.5 L/min.
Exercise = 220 L/min