• ventilation
• perfusion (movement and distribution of blood through pulmonary circulation)
• diffusion (mov't of oxygen and carbond dioxide across air-blood barrier)
• control of breathing- process of regulation of gas exchange to meet the metabolic needs of the moment

Phases of ventilation

inspiratory

expiratory

• fresh atmospheric air breathed in (rich in oxygen)
• delivered to alveolar reservoir
• oxygen and carbond dioxide exchanged between the air and blood across the gas exchange membrane

• carbon dioxide moved out of the alveolar reservoir to the atmosphere

• strength of pump (muscles of inspiration)
• airway resistance (frictional resistance to flow of air through the pipes)
• elastance/compliance (distensibility/stiffness of lungs and chest wall)
• tissue resistance (friction created by mov't of lungs and chest)
• inertance (energy expended to set system in motion)

Structure of lung

• gas exchange membrane
• gas reservoir
• two sets of delivery pipes
  • bronchial tree for air
  • pulmonary vessels for blood

Forces that must be overcome to ventilate the lungs

• stiffness/elastic recoil of both lungs and chest wall
• fricitional resistance in airways as air moves through them
• inertance of entire system

• diaphragm
• external intercostals
• accessory muscles
  • SCM
  • scalenes
  • small muscles of neck, head

Accessory muscles of expiration

• internal intercostals
• abdominal muscles

EXPIRATION IS PASSIVE, SO YOU SHOULD NOT BE USING MUSCLES UNLESS ACTIVE EXPIR.

• attachment poins
  • sternal- inner pt of xiphoid process
  • costal- inner surface of lower six ribs
  • lumbar- upper 2-3 lumbar vertabrae
  • central tendon

• alter shape and volume of thoracic cavity
  • increase diameter
  • increase intrathoracic volume
• push abdominal contents downward

Describe the state of lungs in relation to the chest wall

• remember, lung is sealed against chest wall and diaphragm by a small amount of pleural fluid between pleural membranes that line thoracic cavity and cover the external surface of lung
• this create a vacuum within thoracic cavity created by the pull of the lung against the chest wall
  • neither lung or ches wall is in relaxed state when coupled across the pleural state

• contraction will pull against chest wall at its poins of insertion, changing the configuration of the thoracic cavity by increasing its vertical dimension
• lung is pulled down as diaphragm moves
  • this contributes to a more negative pressure within thorax

• you break the vacuum seal
• this will lead to lung collapse inward and chest wall springing out
• so the elastic elements of both are stretched when they are linked within thoracic cavity and are trying to pull apart in opposite directions to release the tension

• external intercostals- during inspiration, they elevate ribs (pull up and forward)
• internal intercostals- during active expiration, they depress ribs (pull down and inward)

• if you notice the pressure-volume loop of the lung, there is a difference in compliance of the lung during inflation (more stiff) and deflation (less stiff)

• used apparatus with moveable barrier and force tranducer
• the moveable barrier is moved across the surface with the detergent added
• as you increase surface area, surface tension rose
• as you decrease surface area, the surface tension decreased

Describe CT structure of lung

• arranged in such a way to allow lung to be stretched (called tissue forces)
• peripheral (in btw alveoli)
• septal and axial

interupts polar attraction of water molecules

 Chemical structure of detergents/surfactant

• amphipathic
• these molecules repel from each other

• responsible for phenomenon of hysteresis
• promote stability of alveoli of differing sizes and prevents alveolar collapse

Effect of reducing surface tension on compliance

• leads to increase compliance, reducing work of expanding lungs with each breath

• surfactant produced by Type II pneumocytes
• location- line surface of alveoli

Symptoms of neonatal RDS

• atelectasis
• difficulty inflating lungs
• hypoxemia

Test for ADS

ratio of lecithin: sphingomyelin in amniotic fluid (if more than 2, its mature)

Effect of surfactant on surface tension

• lungs- collapsing force
• chest- expanding force

At rest, both forces are equal and opposite, so neither system wants to collapse or expand.

• high compliance, emphysema
• low compliance, fibrosis

• laminar
• turbulent
• tracheobronchial

• fast air flow
• P = K X V squared

Equation for airflow resistance

• very high in beginings of conducting zone
• decreases gradually as you move through the conducting zone
• very very minimal as you enter the respiratory zone

• very low in conducting zone
• exponentially higher in respiratory zone

NT's that cause bronchoconstriction and its affect on alveolar carbon dioxide pressure

• parasympathetic (vagal)- ACh, methacholine, histamine
• decreases alveolar carbon dioxide pressure

beta-2 adrenergic receptors (stim. by epi from adrenal medulla)

Although there is no DIRECT sympathetic innervation of the lungs.

Role of tissue resistance in movement of lung

• 20% of total resistance/pulmonary resistance
• must overcome the viscous forces within the tissues as they slide over each other

• involves resistance and compliance

Pressure = (volume/compliance) + (flow x resistance)

• intrapleural pressure decreases (becomes MORE NEGATIVE)
• alveolar pressure decreases

Pressure gradient allow for air to flow into the lungs

Effect of expiration on alveolar pressure and intrapleural pressure

• alveolar pressure increase (becomes greater than atmospheric, leading to expiration)
• intrapleural pressure increases (become LESS NEGATIVE)

• elastic forces
• airway resistance
• tissue resistance

• cerebral cortex gives you the volition
• medulla gives you the drive