Respiratory Physiology

Respiratory Physiology

Respiratory physiology is the branch of human physiology focusing upon respiration.

Topics include:


  • lung volumes
  • vital capacity
  • functional residual capacity
  • dead space
  • spirometry
  • body plethysmography
  • peak flow meter


Inhalation (breathing in) is usually an active movement. The contraction of the diaphragm muscles cause a pressure variation, which is equal to the pressures caused by elastic, resistive and inertial components of the respiratory system. In contrast, expiration (breathing out) is usually a passive process.

<br />
\begin{align}<br />
P &= P_{el} + P_{re} + P_{in} \\<br />
P &= EV + R\dot{V} + I\ddot{V}<br />
\end{align}<br />

Where Pel equals the product of elastance E (inverse of compliance) and volume of the system V, Pre equals the product of flow resistance R and time derivate of volume V (which is equivalent to the flow), Pin equals the product of inertance I and second time derivate of V. R and I are sometimes referred to as Rohrer's constants.

  • Anatomy: pleural cavity, thoracic diaphragm, Intercostales externi muscles, Intercostales interni muscles
  • inhalation and exhalation
  • lung, pulmonary alveolus
  • With insufficient pulmonary surfactant, the pulmonary alveoli collapse, causing atelectasis (in infants, infant respiratory distress syndrome)
  • the law of Laplace,
  • compliance (physiology) - decreased with fibrosis, increased with emphysema
  • Poiseuille's law
  • asthma and COPD
  • hysteresivity

Circulation, ventilation, and perfusion

  • pulmonary circulation
  • positive pressure ventilation
  • hypoxic vasoconstriction
  • ventilation (physiology), perfusion, ventilation/perfusion ratio (V/Q), and ventilation/perfusion scan
  • shunts: right-to-left (tetralogy of fallot), left-to-right (patent ductus arteriosus)
  • respiratory rate and respirometer

Gas exchange/transport (primarily oxygen and carbon dioxide)

  • gas exchange
  • Dalton's law
  • hemoglobin
  • oxygen-hemoglobin dissociation curve, Bohr effect, Haldane effect
  • carbonic anhydrase
  • oxyhemoglobin
  • respiratory quotient
  • arterial blood gas

Control and response

  • control of respiration
  • reticular formation
  • pons (apneuistic and pneumotaxic)
  • chemoreceptors (medulla, carotid body, aortic body)
  • Hering-Breuer reflex
  • involuntary control of respiration
  • exercise
  • hyperoxia
  • hypoxemia (hypoxic hypoxia)


  • altitude sickness
  • asthma
  • carbon monoxide poisoning
  • chronic obstructive pulmonary disease
  • emphysema
  • infant respiratory distress syndrome
  • pulmonary edema
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