Mechanics of Ventilation Flashcards
primary function of the lungs?
animals require oxygen for aerobic metabolism
oxygen then delivered to tissues to meet metabolic demands
Remove carbon dioxide from the tissues (waste product of metabolism)
what do land-based animals use their lungs for?
use lungs as a means of interfacing oxygen in the air with the blood
air drawn through the airways (from nose/mouth) - what is the journey from trachea to alveoli?
trachea, bronchi, bronchioles, respiratory bronchioles, alveolar duct, alveolar sac and alveoli
what is the conducting zone?
this is where air passes through - it is dead space
respiratory zone?
oxygen can enter the blood, carbon dioxide can leave the blood
why can conducting zone be called dead space?
as no gas exchange occurs
anatomic dead space?
conducting zone of airway
alveolar dead space?
alveoli with poor perfusion (e.g. a heavy animal lying on its side)
equipment dead space?
something to be aware of when anaesthetising animals and using an endotracheal tube
what are the types of dead spaces in the airway?
anatomic dead space
alveolar dead space
equipment dead space
what does tidal volume do?
dead space plus alveolar gas exchange space and it not only ventilates alveoli but also conducting the airways
dead space is important for?
thermoregulation
this is when they are panting
what is physiologic dead space?
alveolar dead space plus anatomic dead space is referred to collectively as physiological dead space
what is the equation for the fact that tidal volume has a dead space component and an alveolar (gas exchange) component?
VT = VD+ VA
Always have some air in lungs apart from at birth - what is this?
residual air
total lung capacity?
maximum amount of air that lungs can hold
inspiratory reserve volume?
volume of air in a maximal inspiration after normal lung fill
expiratory reserve volume?
volume of air in the lungs at the end of normal passive respiration that can be further expelled
what is residual volume?
min volume of air remaining in lungs even after max expiration
vital capacity?
max volume of air that can be moved out during a single breath following a max inspiration
what is ventilation defined as?
as the movement of air in and out of the lungs - breathing
minute ventilation?
volume of air breathed per minute (VE)
tidal volume?
volume of air in each breath (VT)
frequency of ventilation?
number of breaths per minute
what is the minute ventilation determined by?
determined by each breath and the number of breaths per minute
inspiration?
movement of gas into lungs
expiration?
movement of gas out of lungs
what is alveolar ventilation?
it is the movement of air into and out of alveoli
equation including the minute ventilation, tidal volume and frequency?
VE = VT x f
what are the major inspiratory muscles?
the diaphragm and external intercostal muscles
describe the state of the muscles before the beginning of inspiration?
the muscles are relaxed, no air is flowing
intra-alveolar pressure is equal to atmospheric pressure
at the onset of inspiration, what happens to the resp muscles?
they are stimulated to contract, which enlarges the thoracic cavity
contraction of the diaphragm causes it to what?
causes it to move caudally and flattens
contraction of the external intercostal muscles causes them to what?
pull the ribs cranially and laterally
what is Boyle’s law?
when volume increases, pressure decreases and vice versa
how are pressure and volume related?
they are inversely related
how are pressure and volume inversely related?
as lungs distend, alveolar pressure decreases
intra-alveolar pressure becomes less than atmospheric pressure
pressure difference propels air through the airways into alveoli until P is equalised (alveolar pressure equals atmospheric pressure)
what happens when the inspiratory muscles contract?
the ribcage expands
volume of thorax increases
intra-alveolar pressure decreases
higher atmospheric pressure pushes air into the lungs
what pressures help accomplish ventilation?
atmospheric pressure
intra-alveolar pressure
intrapleural pressure
transpulmonary pressure
atmospheric pressure?
pressure exerted by the weight of the air in the atmosphere on objects on Earth’s surface
intra-alveolar pressure?
pressure inside the alveoli (intrapulmonary pressure)
intrapleural pressure?
pressure outside the lungs but within the thoracic cavity (between visceral and parietal pleura = within pleural sac)
transpulmonary pressure?
difference between intra-alveolar and intrapleural pressure (transmural pressure gradient)
transpulmonary pressure is ………………. as pulmonary pressure?
NOT THE SAME
describe how the intrapleural pressure decreases?
pleural cavity contains small amount of fluid
hydrostatic pressure in the pleural cavity is always slightly negative relative to atmospheric pressure
this small negative pressure causes a pulling force to keep the lungs expanded
as volume of thoracic cavity increases, intrapleural pressure decreases which creates a suction that pulls the lungs outwards decreasing the intra-alveolar pressure
what is the connection between the intrapleural space and the alveoli?
there is no direct connection
P alv is always greater than P pl
P t varies with respiratory phase
what does P t measure?
it measures elastic recoil of the lung and represents the pull that keeps lungs distended
at the onset of expiration, what do the resp muscles do?
they relax, returning the thoracic cavity to its previous size by elastic recoil
type II alveolar cells aka?
type II epithelial cells
type II mamacyte cells (search it up)
always have same amount of surfactant irrelevant of whether the alveolus is small or big
high lung compliance means?
they expand easily
what is lung compliance normally due to?
lung elasticity but this disappears with age
ventilation in birds?
very big sternum
no diaphragm
sternum moved ventrally by inspiratory muscles
lungs are rigid
no alveoli - microstructure consists of air capillaries radiating from cylindrical parabronchi
airflow in lungs is unidirectional
what happens at the onset of expiration?
the respiratory muscles relax, returning the thoracic cavity to its previous size by elastic recoil
what does relaxation of the diaphragm allow?
it allows the abdominal pressure (from internal organs) to push the diaphragm cranially and become more dome shaped
what does relaxation of the external intercostal muscles mean?
means that the ribs recoil caudally and medially
working with the elastic recoil of the lungs is naturally a … what… process?
It is a passive process
how is forced expiration possible?
it is possible with contraction of abdominal muscles to force viscera against the diaphragm and contraction of internal intercostal muscles to pull ribs caudally and medially
P atm?
atmospheric pressure
P alv?
intra-alveolar pressure
P pl?
intrapleural pressure
P t?
transpulmonary pressure
how is pressure related to volume?
it is inversley related
so, as the volume decreases, what happens to the intra-alveolar pressure?
it increases
P pl is always more negative than P alv - why?
so the lungs do not collapse
how are horses an exception to the phases of the inspiratory/expiratory cycles?
because inspiratory and expiratory phases of the cycles are generally smooth and symmetrical whereas horses have an active phase to exhalation even at rest
species difference in inspiratory/expiratory cycles may be due to?
due to a time delay in the firing of the late inspiratory neurons (located in the medulla oblongata)
In running mammals, how is the ventilation linked to the gait?
ventilation is synchronised with gait in the canter and gallop but not walk or trot
Breathing of galloping animals is synchronised with the stride cycle
spine extension helps too
what are the factors influencing ventilation?
changes in atmospheric pressure
changes in resistance
changes in intrapleural pressure
changes in resistance is a factor influencing ventilation - give examples of these resistances:
airway resistance: diameter of bronchioles
surface tension of the alveoli
lung compliance
how do changes in atmospheric pressure influence ventilation?
lower atmospheric pressure at altitude
pressure difference gets progressively harder to achieve
proportion of oxygen the same (21%) but much less quantity in each breath
how do changes in airway resistance influence ventilation?
diameter of bronchioles:
Resistance may increase w/ disease e.g. bronchitis/asthma
least resistance during inspiration (as thoracic cavity expands), airways expand a little too
most resistance during expiration
autonomic nervous system can adjust airflow to suit animals’ needs
increased sympathetic activity (β2 adrenergic receptors) leading to bronchodilation, helps reduce resistance to airflow
how do changes in resistance influence ventilation - airway resistance: diameter of bronchioles and air flow resistance?
resistance to flow increases w/ a decrease in tube radius (diameter) to the fourth power
*Hagen-Poiseuille law
*check slide 26/38 for equation - yr1 sem2 wk 7
what are the two types of air flow?
two types of air flow:
turbulent - increases w/ increasing flow speed
laminar - minimal friction between molecules, gases behave like fluids
what is flow resistance?
air flows from a region of higher pressure to a region of lower pressure
relationship of flow to pressure?
flow (Q) is proportional to pressure difference (AP)
(Pretend A is a triangle)
how does flow resistance influence ventilation?
when air flows, it is subject to friction or Resistance (R) from the tubular wall and from other gas molecule
Q = AP/R
(pretend A is triangle)
how does surface tension (changes in resistance) within the alveoli influence ventilation?
inner surfaces of the alveoli are lined with a fluid
at an air-water interface, the water molecules at the surface are more attracted to each other than to air above
this unequal attraction produces a force known as surface tension at the surface of the liquid
this surface tension opposes expansion of alveoli
how do the lungs overcome surface tension?
pulmonary surfactant
great amount of surface tension of pure water is normally counteracted by pulmonary surfactant
detergent-like mixture of lipids, proteins and ions secreted by the type-II alveolar cells
amount surfactant - does it change?
the amount of surfactant is the same, despite change in alveolar size
hence smaller alveoli have more surfactant
surface tension is indirectly related to size
this allows small alveoli to be connected to larger ones w/o collapsing (Law of Laplace)
how does surfactant help with balancing pressures in the alveoli?
surfactant reduces surface tension in the alveoli
prevents alveolar collapse
continuously released
how does lung compliance (changes in resistance) influence ventilation?
distensibility of the lungs - transpulmonary pressure keeps the lungs distended
high lung compliance means lungs will expand easily
related to distensibility of lung tissue, thoracic cage and surfactant
normally high due to high elasticity of the lung tissue - deteriorates with age
alveolar surface tension
how do changes in intra-pleural pressure influence ventilation?
intrapleural is pressure normally negative relative to atmosphere
trauma that allows pressure to equalise –> pneumothorax
expansion of the ribcage no longer inflates the lungs
