Mechanics of Breathing Flashcards
How does inspiration occur?
Contraction of inspiratory muscles
How does expiration occur?
Elastic recoil of lungs
What 3 things does contraction of the inspiratory muscles cause?
Expands thoracic cavity -> decreases intrapleural pressure -> helps lungs expand
What pressure does the expansion of lungs decrease intrapulmonary pressure to?
Sub atmospheric level - air from atmosphere is sucked in
Define Boyle’s Law.
Pressure (P) exerted by a constant number of gas molecules in an enclosed space is inversely proportional to the volume (V) of the container
P1V1 = P2V2
How does air move?
In bulk flow from low pressure to high pressure
What is flow (F) equal to?
Pressure difference between 2 points (∆P)
What is flow inversely proportional to?
Resistance
What is the equation for flow?
F=∆P/R
What 2 things cause changes in alveolar pressure?
Changes in volume of chest wall and lungs
What is pulmonary ventilation achieved by?
Repeated cyclical process of inhalation and exhalation, efficiently exchanging air between the environment and the alveoli
What are the 2 main muscles for inspiration?
Diaphragm and external intercostal muscle
What are the 3 main muscles for expiration?
Internal intercostal
Pectoral
Abdominal muscle
What happens to the abdominal contents and ribs with diaphragm contraction?
Abdominal contents - forced downwards and forwards (increases vertical dimensions)
Ribs - margins are lifted and move outwards (increases transverse dimensions)
Where are external intercostal muscles present?
Obliquely between ribs in a forward and downward direction
How does contraction of external intercostal muscles raise the lower ribs?
Attachment to lower ribs is more forward from the axis of rotation
What 2 effects does the contraction of external intercostal muscles have on the thoracic cavity?
Bucket handle effect - increases transverse diameter
Pump-handle effect - increases vertical diameter
When are accessory muscles used for inspiration?
Only during forced inspiration
What do the scalene muscles attach?
Attach cervical vertebrae to first and second rib
What do the pectoralis muscle attach?
Attach thoracic cage to upper limb
What are the 2 accessory muscles?
Scalene muscles
Pectoralis major
What are the 3 types of scalene muscles?
Scalenus anterior
Scalenus medius
Scalenus posterior
What is the action of the pectoralis major?
Increases antero-posterior diameter when arm is fixed
When are expiratory muscles used?
During forced expiration
