Mechanics of Breathing

Overview1. Inspiration

2. Expiration

3. Respiratory Volumes

Inspiration

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

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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