1. Mechanics of Breathing Overview 1. Inspiration 2. Expiration 3. Respiratory Volumes

2. 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

3. 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 animation 1animation 2

4. 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))

5. 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

6. 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

7. Respiratory Volumes

8.  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

9. 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