Control of Breathing

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Control of Breathing
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Control of Breathing

• Central control
• Breathing is controlled by neurons located in the
  pons and the medulla.
• Sensors
• They are located in
• Respiratory and Cardio vascular systems
• Muscles and tendons
• Skin
• Viscera and brain
• Pulmonary receptors
• Sensors in the respiratory system.
• 3 groups
• Pulmonary stretch receptors
• Pulmonary irritant receptors
• Type-J receptors

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Control of Breathing

• 1. Pulmonary stretch receptors
• Inflation of lung stimulates
• Located in the tracheal and bronchial smooth
  muscle
• Response results in decrease of Rf and
  bronchodilation
• 2. Irritant Receptors
• Located in the epithelium of the larynx and URT.
• Chemical or mechanical irritation of airways can
  stimulate
• coughing
• hypernea and
• bronchoconstriction.

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Control of Breathing

• 3. Type-J Receptors are thought to be responsible
  for the hypernea that accompanies pulmonary
  embolism or pulmonary vascular congestion.
• It is thought that these receptors are located in
  the walls of the pulmonary capillaries.

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Control of Breathing

• Chemoreceptors
• Are sensors that detect changes in arterial blood
  gases or chemical composition.
• Two types
• Peripheral located in the carotid bodies of the
  bifurcation of the common carotid arties and
  aortic body.
• They are sensitive to changes in arterial O2 PP.
• Central located near the ventral aspect of the
  medulla.
• Responds to changes in the interstitial tissue
  fluid pH.

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Lung Volumes and Ventilation
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Respiratory System

• Ultimate importance of the pulmonary ventilatory
  system is to continually renew the air in the gas
  exchange areas of the lungs
• where the air is in the proximity to the
  pulmonary blood.
• These areas include
• alveoli alveolar sacs alveolar ducts and
  respiratory bronchioles.

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Respiratory System

• Main respiratory processes involved in gas
  exchange are
• Ventilation movement of gas(es) into and out of
  the lungs
• Perfusion flow of blood per unit volume of
  tissue
• Ventilation/perfusion ratio (V/Q) how matching
  of air and blood in the lung influences gas
  exchange.

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Respiratory System

• Diffusion how gas gets across the air- blood
  barrier.
• Gas transport how gases are moved from lungs
  to the tissues.
• Mechanics of breathing how the lungs are
  moved.
• Control of breathing how the supply of gas
  exchange is adjusted to the demand.

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Ventilation

• How much air goes in and out
• Lung Volumes
• The volume of air inhaled or exhaled during a
  normal breath is termed tidal volume (VT).
• Also known as the depth of a breath
• In a healthy resting athletic horse its about 12
  ml/kg of body weight (5-6 liters).
• Respiratory frequencies (Rf) the number of
  complete breaths taken per minute
• Expired minute volume (VE)
• tidal volume x respiratory frequency

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Ventilation

• Exercise imposes a potent stress on the
  ventilatory pump
• Minute ventilation (MV) increases almost
  linearly.
• Which is the volume of gas that enters or leaves
  the airways in any minute.
• The expired minute ventilation (VE) which
  averages 80 l/min at rest may reach values in the
  vicinity of 1800 l/min during heavy exercise.

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Ventilation

• To accommodate the change in minute ventilation
  a horse can alter its
• tidal volume (VT)
• respiratory frequency (Rf)
• or both
• In Trotter horses increase in MV is achieved by
  both (VT and Rf) at low exercise and increase
  respiratory frequency at high exercise
  intensities.
• Values as high as 133 breaths/ min have been
  reported on treadmills.

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Ventilation

• In galloping horses respiratory and the
  locomotion are coupled.
• Step and respiratory frequencies average 110 to
  130 per minute with max. values of 148 per
  minute.
• Therefore increase ventilation with increasing
  speeds is due mainly to the increase in tidal
  volume (12 - 15 liters).

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Ventilation

VO2max
15
Ventilation
liters
VT
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Ventilation

• Alveolar and Dead Space Ventilation
• Only a part of the inspired volume reaches the
  area of the lung where gas exchange takes place
  Alveolar ventilation (VA).
• The remaining part of the minute ventilation is
  wasted in the regions of lung where no gas
  exchange occurs Physiologic dead space
  ventilation (VD).
• Which includes the conducting airways and alveoli
  that ventilated but do not perfuse

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Alveolar Ventilation

• Rate of Alveolar Ventilation
• Alveolar ventilation per minute is the total
  volume of new air entering the alveoli each
  minute.
• Its equal to the respiratory rate (Rf) times the
  amount of new air that enters the alveoli with
  each breath.

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Ventilation

• On expiration the air in the dead space is
  expired first before any of the air from the
  alveoli reaches the atmosphere.
• The dead space is equally disadvantageous for
  removal of the expiratory gases from the lungs.

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Ventilation
liters
Value
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Ventilation

• Exercise-induced changes in VA and VD to VT ratio
  in horses depend on the type of exercise.
• During mild to moderate exercise
• The dead space volume does not change
  significantly
• If exercise is prolonged at a constant rate
• The dead space ventilation will increase by a
  simultaneous increase in Rf and in VD to VT ratio
• During intense efforts
• There is a decrease in the same ratio from 60 to
  20
• In absolute terms the physiologic dead space is
  reduced from 3.5 liters at rest to 2.5 liters
  during heavy exercise.

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Ventilation

• The dead space to tidal volume ratio averages 50
  to 60 in the resting horse.
• Studies have shown evidence that adequate gas
  exchange is maintained with very low tidal volume
  and very high respiratory frequency.

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Ventilation

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Ventilation

• For a given minute ventilation the lower the
  physiologic dead space ventilation
• The higher the alveolar ventilation and the
  better the gas exchange.

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Respiratory System

• From a functional standpoint the respiratory
  system can be divided into two major components
• Upper or extrathoracic respiratory tract
• URT
• Lower or intrathoracic respiratory tract
• LRT

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Respiratory System

• Distinction can be made by the neg. and pos.
  pressure experienced by the airways during
  breathing.
• Exercise magnifies these pressures and
• Enhances detrimental effects when disease and
  malfunction is present

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Respiratory System

• Elastic properties of the lung.
• The normal lung is a network of elastin and
  collagen fibers.
• Pressure-volume
• curve

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Elastic properties of the lung

• Compliance
• Measure of the distensibility of the lung.
• A measure of the ease w/ which a hollow viscus
  may be distended.
• Can be illustrated in the
• slope of either the inflation
• or deflation curve of the
• pressure-volume diagram.

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Elastic properties of the lung

• Surface tension
• Is responsible for helping to determine the
  elasticity and thus the compliance of the lung.
• If to high atelectasis may occur.
• Absence of gas from a part or the whole of the
  lungs
• Due to failure of expansion or resorption of gas
  from the alveoli

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Elastic properties of the lung

• Interdependence
• Is the phenomenon whereby alveoli are held open
  from support offered by neighboring lung units.
• Helps prevent atelectasis
• Also may play a role in exercise-induced
  pulmonary hemorrhage.