Respiratory Physiology: L2 - Respiratory mechanics and lung volumes

Flashcards for Respiratory Physiology Lecture 2

Inspiration

Movement of air into the lungs from the atmosphere.

Expiration

Movement of air out of the lungs into the atmosphere.

External respiration

O₂ diffuses from the lungs to the blood, and CO₂ diffuses from the blood to the lungs.

Transport of respiratory gases

The cardiovascular system transports gases using blood as the transporting fluid.

Internal respiration

O₂ diffuses from blood to tissue cells, and CO₂ diffuses from the tissue cells to blood.

Beginning of Inspiration

Contraction of muscles & increase of thoracic volume, expansion of lungs & Increase in alveolar volume, decrease in the intrapulmonary pressure below atmospheric pressure, and air flows in the lungs.

End of Inspiration

Alveoli and thorax stop expanding, air flow into the lungs causes Patm = Palv, and no more movement of air occurs

Transmural pressure gradient across lung wall

Intra-alveolar pressure minus intrapleural pressure.

Natural tendency for lungs to recoil

Tendency for lungs to recoil due to water surface tension and elastic fibres.

Inspiration Steps

Inspiratory muscles contract, thoracic cavity volume increases, intrapulmonary (lung) volume increases, intrapulmonary pressure decreases, and air flows in until pressure equalises

Expiration Steps

Inspiratory muscles relax, thoracic cavity volume decreases, elastic lungs recoil passively, intrapulmonary volume decreases, intrapulmonary pressure rises, and air flows out of lungs

Pneumothorax

Air in pleural cavity; causes intrapleural pressure to become equal to intrapulmonary pressure, resulting in lung collapse.

Airway resistance

Friction of air against walls or airways; depends mostly on the diameter of the airway.

Alveolar surface tension

Tendency to collapse alveoli; resist alveoli inflation

Surfactant

Secreted by type 2 alveolar cells, breaks the surface tension of water, reduces the lung’s tendency to recoil, increases pulmonary compliance, and maintains lung stability

Compliance

How easy it is to stretch the lungs

Elastic recoil (Elastance)

Ability for lungs to rebound; a key driving force during expiration

Tidal Volume (TV)

Amount of air inhaled or exhaled with each breath under resting conditions

Inspiratory Reserve Volume (IRV)

Amount of air that can be forcefully inhaled after a normal tidal volume inspiration

Expiratory Reserve Volume (ERV)

Amount of air that can be forcefully exhaled after a normal tidal volume expiration

Residual Volume (RV)

Amount of air remaining in the lungs after a forced expiration

Total Lung Capacity (TLC)

Maximum amount of air contained in lungs after a maximum inspiratory effort

Vital Capacity (VC)

Maximum amount of air that can be expired after a maximum inspiratory effort

Inspiratory Capacity (IC)

Maximum amount of air that can be inspired after a normal tidal volume expiration

Functional Residual Capacity (FRC)

Volume of air remaining in the lungs after a normal tidal volume expiration

FVC

Forced Vital Capacity

FEV1

Forced Expiratory Volume in 1 second

PEF

Peak Expiratory Flow rate

PIF

Peak Inspiratory Flow rate

Minute ventilation

Two factors contributing to volume of air breathe in and out per minutes

Airway dead-space volume

Volume of air that does not participate in gas exchange

Efficient respiration

Requires matching ventilation (V) with perfusion (Q)

V/Q < 1

Airway dilation + vasoconstriction

V/Q > 1

Airway constriction + vasodilation