Pulmonary Ventilation, Boyles Law and Muscles of Breathing

What is pulmonary ventilation?

the exchange of gasses between the atmosphere and lungs

(PV) Inspiration/ inhalation 

moving air INTO the lungs 

(PV) Expiration/exhalation

moving air OUT of the lungs

What is pulmonary ventilation based off of?

Boyle’s law 

What is Boyle’s law?

at a constant temperature the pressure of a gas in a closed container is inversely proportional to the size of the container 

BL applied: As the volume of the lung increases?

the pressure of gas decreases

BL applied: As the volume of the lung decreases?

the pressure of gas increases

What are the types of inhalation?

quite breathing - pons + medulla are controlling

strenuous inhalation - forced

(I) Muscles of Quiet Breathing: 

• functions

diaphragm: contracts and flattens out

internal intercostals: pulls the rib cage up

(I) Muscles of Strenuous Inhalation: 

• functions

sternocleidomastoid: elevates the sternum and clavicle 

scalenes: elevates ribs 1+2

pectoralis minor: elevates ribs 3-5

diaphragm: contracts even MORE to push on abdomen 

Boyles law applied in inhalation

when the muscles contract it creates more volume for the lungs to expand, decreasing the pressure of the lungs and thoracic cavity lower than atmospheric pressure

air moves from an area of high pressure to low pressure allowing air to flow inside the lungs 

(I) BL simplified

once pressure inside lung is less than atmospheric pressure the air moves into the lung

Pressure changes during inhalation: Atmospheric pressure 

• before and after inhalation 

remains at 760, does not change 

Pressure changes during inhalation: Interpleural pressure 

• before and after inhalation 

Before: 756 (because of vacuum)

After: 754

Pressure changes during inhalation: alveolar pressure 

• before and after inhalation 

before: 760

after: 758 

In interpleural and alveolar pressure inhalation, it moves? 

diaphragm moves?

500 ml of air into lungs

1 cm

What are the types of exhalation/expiration 

normal (quiet) expiration and forced expiration 

(E) Muscles of Normal (quiet) Expiration

• functions

passive process where inspiratory muscles relax 

(E) Muscles of Forced Expiration

• functions?

abdominal group: pulls the ribcage down and compresses the abdomen 

internal intercostals: pulls down of ribs further 

(E) Boyle’s law applied

when the muscles relax/contract and push on the abdomen and thoracic cavity, it decreases the volume of the lung + thoracic cavity, increasing the pressure above atmospheric pressure, allowing air to be expelled 

E) Boyle’s law applied, simplified

lung pressure becomes greater than atmospheric pressure, air wants to move from an area of HP→ LP