Airflow And Gas Exchange Flashcards
(26 cards)
What is the normal respiratory rate for animals and then horses
Animals = 20-30brpm
Horses = 10-12brpm
What do these terms mean
Eupnoea
Tachypnoea
Hyperpnoea
Dyspnoea
Apnoea
Eupnoea = normal breathing
Tachypnoea = increased RR
Hyperpnoea = increased respiratory depth
Dyspnoea = increased respiratory effort
Apnoea = absence of breathing
What is inspiration and expiration
Inspiration = diaphragm and external intercostals contract
Expiration = usually passive. Can be active in some species and during exercise in this case internal intercostals and abdominal muscles contract
What is compliance and what does it depend on
Degree to which a decrease in transpulmonary pressure leads to an increase in volume of the lung
C = change in volume/change in pressure
Depends on elasticity (of lungs and thoracic cage) and surface tension (in the alveoli)
Why are alveoli lined with fluid
To facilitate dissolution and diffusion of gases
How is surface tension created and and does it do
Water molecules form hydrogen bonds at water-air interface
Surface tension resists expansion of lungs
Higher surface tension = lower lung compliance
What does surfactant do
Surfactant acts to reduce surface tension of the fluid film lining in the alveoli
O2 and CO2 do not dissolve in the surfactant they dissolve in water
What does pressure inside the alveolus depend on
It’s radius and surface tension inside it
P=2T/R
The total amount of surfactant inside an alveolus is the same regardless of size.
What does airway resistance depend on and what is the Pouseille’s equation
Resistance is dependent on the radius and length of a tube and the viscosity (n) of the substance travelling through it
Pouseille’s equation = 8Ln/Pie x r to the power of 4
When and where is resistance present
Lower airways are always distended in inspiration resistance therefore greater during expiration
Upper airways resistance higher during inspiration
Most of resistance from upper airways
What is smooth muscle in the walls of the airways innervated by
Autonomic nervous system.
Sympathetic B2 adrenoreceptors (relaxation of smooth muscle = dilation of airways)
Parasympathetic (contraction of smooth muscle = constriction of airways)
Disease states e.g. asthma
When does turbulence increase
Increasing speed of flow
What is tidal volume and minute ventilation
Tidal volume = the volume of air moved during a respiratory cycle 10ml/kg in a normal resting dog
Minute ventilation = Tidal volume x Respiratory rate
Must increase when oxygen requirement increases
What is the fraction of gas in normal animals
FO2 in normal air is 21% (0.21)
What is the normal partial pressure of air
PO2 in normal air is 0.21 x atmospheric pressure
Atmospheric pressure at sea level = 760mmHg
0.21x760mmHg = 160mmHg
How does gas exert pressure
Gas molecules move around and collide with surfaces creating pressure.
Size of molecule is immaterial
Gas exchange along their own gradient
What are the solubilities of O2 and CO2
CO2 is more soluble than O2
In contact with water gas molecules dissolve. More dissolve if the partial pressure of the gas increases.
Molecules can also come out of solution and re-enter the gas phase.
When the number of molecules of given gas entering and leaving solution during a given unit of time is equal this is a dynamic equilibrium.
At this point the partial pressure of the gas molecules in solution can be said to equal that of the molecule in gas phase
What happens to air when it’s inhaled
Inhaled air is warmed and humidified as it moves through the upper airways. Water vapour is added
We must account for this in terms of the PO2 in the air by the time it reaches the distal airway.
PH2O at the alveolus is about 50mmHg
PO2 = (atmospheric pressure - PH2O) x 0.21
= (760-50) x 0.21 = 149mmHg
What is the exchange of gases at the alveolus like
It is constant and ongoing
Only a small proportion of alveolar gas is exchanged with each breath.
PAO2 will always be lower than PO2 in the airways
PACO2 will always be higher than PCO2 in the airways
What is the correct exchange of gases reliant on
The correct ventilation and perfusion of the alveolus
What are alveoli with low ventilation to perfusion ratio
Overperfused and under ventilated
What are alveoli with a high ventilation and perfusion ratio
Under perfused and over ventilated
Can the ventilation and perfusion ratio alter
There is a ratio range in the normal lung
The caudal dorsal lung lobes are preferentially perfused in the dog for example changes to systemic arterial gas tensions will only occur if a significant proportion of alveoli have abnormal ratio
What is hypocapnia
Hyperventilation will cause excess loss of CO2 leading to a drop in PaCO2
