Lecture 9 2/1/24 Flashcards
Which processes are involved with delivering gases within the body?
-ventilation
-circulation
-perfusion
-diffusion
What is ventilation?
movement of gas into and out of the lung
What is minute ventilation?
total volume of air breathed per minute
What is tidal volume?
the volume of each breath
What is respiratory frequency?
the number of breaths per minute
What are the characteristics of pulmonary circulation?
-receives total output of right ventricle
-low pressure and low resistance
-involved in gas exchange
What is perfusion?
delivery of blood in capillaries surrounding the alveolar space in the lungs
What is a V/Q ratio?
comparison of ventilation to perfusion
What is diffusion?
flow of particles from a region of high pressure to a region of low pressure
Where does gas movement take place?
-within alveoli: air to air
-across alveoli into blood: air to liquid
-from blood into tissues: liquid to tissues
What are the general characteristics of conducting airways?
-conduits to get air to alveoli
-no gas exchange occurs
Which spaces comprise anatomic dead space?
-nasal cavity
-pharynx
-larynx
-trachea
-bronchi
-bronchioles
What are the characteristics of alveolar dead space?
-caused by poor perfusion of alveoli
-prevents gas exchange
-blood flow is disrupted/absent while alveolus is ventilated
What is physiologic dead space?
alveolar dead space + anatomic dead space
Why is it important to minimize the amount of plastic tubing when ventilating a patient?
decrease the amount of dead space contributed by the tubing
What is the importance of calculating the tidal volume minus the dead space volume?
it represents the actual volume of gas available for gas exchange
What are the characteristics of minute ventilation?
-amount of fresh gas entering lungs per minute
-estimated by resp. rate x tidal vol. in simplest form
What is alveolar ventilation?
amount of fresh gas reaching the alveoli per minute
How can alveolar ventilation be increased?
-increase tidal volume
-increase respiratory rate
Why is it possible to measure alveolar ventilation?
-no gas exchange occurs in the anatomic dead space, thus all CO2 must come from alveolar gas
-measuring CO2 in clinic can provide a measure of alveolar ventilation
What are the characteristics of the dead space/tidal volume ratio?
-identifies the fraction of each breath that ventilates dead space
-can change with disease and exercise
-changes tend to reflect alveolar/physiologic dead space changes
What is the purpose of dead space?
-warming and moistening of air
-particle clearance
What are the general steps of inhalation?
-resp. muscles contract
-thorax expands
-lung stretches
-neg. pressure forces air into lungs
What are the general steps of expiration?
-resp. muscles relax
-thoracic volume decreases
-lung compresses
-increased pressure forces air out of lungs
What are the characteristics of exhalation?
-does not require muscular effort in normal animals at rest
-can be assisted by muscle contraction during exercise or due to disease
Why are horses unique in terms of exhalation?
they have an activate phase of contraction when normal and at rest
What are the characteristics of the diaphragm?
-most important inspiratory muscle
-innervated by phrenic nerve
-contraction pulls diaphragm caudally to expand thoracic cavity
What is the main function of external intercostal contraction?
pull ribs rostral and outward to expand thoracic cavity volume
What is the main function of the abductor muscles?
prevent collapse of the nares/upper airways during inspiration
How does the pressure in the alveolar space differ based on the phase of respiration?
-pos. pressure for expiration
-neg. pressure for inspiration
What is the resting pressure of the pleural space?
-4 cmH2O
What happens as the lungs deflate and fall away from the chest wall?
generates negative pressure
What is the inspiratory pressure of the intrapleural space?
-8 cmH2O
What are the characteristics of transpulmonary pressure?
-difference between pressures within the airways and the pleural pressures
-driving force behind expanding and contracting lungs
What is distensibility?
the ability of the lung to stretch
What is elasticity?
the capability of a strained body to recover its size and shape after deformation
What is compliance?
change in the dimension of a structure for a change in applied force
What is the relationship between compliance and elasticity?
compliance is the inverse of elasticity
What is residual volume?
air that remains in the lung after it is exposed to atmospheric pressure
What is functional residual capacity?
air left in the lung at the end of normal expiration
What is total lung capacity?
maximum amount of air that can be in the lungs
What are the limiting factors of total lung capacity?
-collagen in pleural surface
-rib cage
What is surface tension?
elastic tendency of a fluid surface to acquire the least surface area possible
Why is surface tension important in the alveolus?
-water molecules have tendency to go towards alveolar membrane
-makes water layer in alveolus thinner, favoring collapse
Which alveoli are more likely to collapse due to surface tension?
those with a smaller radius
What are the characteristics of surfactant?
-produced by type II pneumocytes
-has hydrophilic and hydrophobic ends
-opposes natural attraction between the water molecules
-reduces surface tension
Why is surfactant important to the alveolus?
-promotes alveolar stability
-increases lung compliance (makes inflation of lungs easier)
What determines lower airway resistance?
-length
-radius
How does inspiration impact airway resistance?
-increased radius
-decreased resistance
How does contraction of bronchial smooth muscle impact airway resistance?
-decreased radius
-increased resistance
Which breath function is more exaggerated during resp. distress?
expiration
Which portion of the nervous system stimulates airway muscle contraction?
parasympathetic system
Which type of receptor mediates airway dilation?
beta-2 adrenergic receptor
