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
What are the 4 rib depressors?
Internal intercostal
Innermost intercostal
Subcostals
Transverse thoracis
What are the 4 anterior abdominal wall muscles?
External oblique
Internal oblique
Transversus abdominis
Rectus abdominus
How many layers form the anterior abdominal wall?
3 layers of muscles running in different directions - increases strength
Where does the 4th muscle lie?
In the sheath of the 3 muscle layers (rectus abdominus)
What are the muscles of the anterior abdominal wall attached to?
Sternum, costal cartilages, ribs and hip bones
What forms the linea alba of the anterior abdominal wall?
Aponeourosis of the 3 muscles on both sides fuse together
What is the action of the anterior abdominal wall?
Compression of abdominal viscera to help ascent of diaphragm (forced expiration)
What is the anterior abdominal wall’s nerve supply?
Lower intercostal nerves (T7-T11), subcostal nerve (T12) and 1st lumbar nerve
What are the 3 pressures in the thoracic cavity?
Intrapleural
Transpulmonary
Alveolar
What is intrapleural pressure?
Pressure in pleural space - around -2.5 to -4mm of Hg during expiration
-6mm of Hg during inspiration
What happens in loss of intrapleural pressure?
Lung collapse and barrel-shaped chest
What is transpulmonary pressure?
Pressure difference between alveolar space and intrapleural space - keeps lungs inflated
What is alveolar pressure?
Pressure inside alveoli - change moves air in and out
