Part II - Respiratory Physiology

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Part II - Respiratory Physiology
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4 distinct events

• Pulmonary ventilation air is moved in and out
  of the lungs
• External respiration gas exchange between blood
  and alveoli
• Respiratory gas transport CV system transports
  oxygen and carbon dioxide between lungs tissues
  (discussed in Blood chapter)
• Internal respiration gas exchange between blood
  tissue cells
• Definition Cellular respiration actual use of
  oxygen production of carbon dioxide in the
  cells
• (this is why we have to breathe!!)

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Pulmonary Ventilation
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External Respiration
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Resp. Gas Transport
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Internal Respiration
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Cellular Respiration
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Mechanics of Breathing
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Pulmonary Ventilation Event 1

• Pulmonary ventilation - Moving air into and out
  of the lungs
• Depends on pressure changes
• Breathing
• Inspiration moving air into the lungs
• Expiration moving air out of lungs

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Pressure Relationships

• Intrapulmonary pressure
• Pressure within the alveoli (lungs)
• Changes with phases of breathing
• Always equalizes itself with atmospheric pressure
• Intrapleural pressure
• Pressure within intrapleural space (between the
  pleural membranes )
• Always 4 mmHg less than intrapulmonary pressure

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Atalectasis

• Any conditions that causes intrapulmonary
  pressure to equal intrapleural pressure will
  cause the lungs to collapse
• This means they lose the ability to move air
  since there is NO more pressure difference

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Atelectasis

• term for lung collapse

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Pneumothorax

• Air in the intrapleural space due to trauma
  causes lung collapse

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Pulmonary ventilation

• Question Why does breathing happen?
• ONLY acceptable answer The RULE Volume changes
  lead to pressure changes which lead to the flow
  of gases to equalize the pressure

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Diaphragm Structure
Boyles Law Pressure Volume have an INVERSE
relationship.
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Pressure differences cause gas to flow from high
to low
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When the diaphragm contracts, the muscle fibers
shorten so muscle comes down
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Inspiration

• Main inspiratory muscles
• Diaphragm external intercostals
• Thoracic dimensions change to increase volume of
  thoracic cavity by 0.5 liters
• Intrapulmonary pressure drops 1-3 mmHg and air
  rushes info normal quiet inspiration
• A deep forced (active) inspiration requires
  activation of accessory muscles see diagram in
  notes

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Expiration

• A passive process dependent on natural lung
  elasticity
• lungs recoil when inspiration stops so alveoli
  compress which leads to a volume
• decreases -causing intrapulmonary pressure to
  rise - gas outflows to equalize the pressure with
  atmospheric pressure
• Forced (active) expiration requires contraction
  of abdominals, etc see diagram

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What doctors listen for

• Bronchial sounds produced by air rushing
  through trachea bronchi
• Vesicular sounds produced by air filling alveoli

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Respiratory Sounds

• Wheezing whistling sound
• Rales rasping sound

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Hear the sounds

• Basic Lung Sounds Bronchial
• Auscultating The Lungs - Reference Guide

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Physical factors influencing

• Pulmonary ventilation can be influenced by 4
  physical factors
• Respiratory passage resistance
• Lung compliance
• Lung elasticity
• Alveolar surface tension forces

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Respiratory passage resistance

• Resistance due to increased friction as air moves
  through passages
• Smooth muscle bronchoconstriction Disorders such
  as asthma when bronchi constrict
• Local accumulations of mucus, infectious
  material, and tumors also block air passage

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Asthma
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Lung compliance

• The ease with which lungs can readily expand
• Affected by the elasticity of the lungs and the
  thoracic cage which can be diminished by 2 main
  factors
• Fibrosis of the lung tissue
• Ossification and/or muscle paralysis impairs
  flexibility of the thoracic cage

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Lung fibrosis
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Lung Elasticity

• Essential for normal expiration
• Emphysema tissue becomes less elastic and more
  fibrous
• loss of elasticity increase in fibrous tissue
  causes enormous effort to exhale at end stages,
  alveolar walls break down and surface area is
  lost for gas exchange

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Alveolar Surface Tension forces

• Surface tension is caused by the tendency of
  polar molecules such as water to stick to each
  other with hydrogen bonds
• this can cause the walls of the alveoli to stick
  together like plastic wrap every time you exhale.
• Large amounts of energy /effort will be required
  to simply re-expand the lungs and allow you to
  inhale (IRDS)

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Alveolar Surface Tension Forces

• Surfactant interferes with cohesion of water
  molecules so less energy needed to expand lungs
  this is one of the things that keeps our lungs
  partially expanded at all times. (the other thing
  is the pressure difference previously discussed)
• Secreted by Type II cells in lungs

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Alveoli Surface Tension
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IRDS Infant Respiratory Distress Syndrome

• AKA Hyaline Membrane Disease
• Caused by lack of surfactant due to prematurity
• 28 weeks of gestation is considered

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Nonrespiratory Air Maneuvers

• Reaction or reflex response
• Cough
• Sneeze travels up to 40 miles per hour
• Hiccup phrenic nerve irritation causes
  diaphragm to spasm
• Yawn saturates alveoli with fresh air
• Need for increased oxygen

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Control of Breathing

• Neural
• Medulla oblongata sets rate of breathing
• Pons fine-tunes rate and transition

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Hering-Breuer Reflexes

• Stimulation is sent
• Inflation reflex- prevents overexpansion via
  receptors around bronchioles
• Deflation reflex inhibits expiratory centers
  and stimulates inspiratory centers.
• Receptors in alveolar walls
• Usually during forced activity

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Control of Breathing Chemical Factors

• Central chemoceptors monitor pH levels in
  cerebrospinal fluid.
• High levels of CO2 increase hydrogen level in
  blood therefore pH decreases.
• Peripheral chemoreceptors located in aorta and
  carotid arteries monitor blood oxygen level.
• Mechanoreceptors located in muscles and joints
  detect muscle contraction and force increased
  ventilation.

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Lung Volume

• Static Lung Volume
• Instructed to perform following breathing
  maneuvers
• Tidal volume amount inhaled during normal
  breathing
• Vital capacity breath in maximum, followed by
  maximum expiration

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Lung Volume

• Residual volume volume of air that never leaves
  the lungs
• Important for continual gas exchange

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Lung Volume

• Dynamic Lung Volume

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End of Quiz 2 Material