1- gas exchange Flashcards
(40 cards)
what is anatomical dead space in airways?
where some inspired airways remain in airways and isn’t available for gas exchange
how do you calculate pulmonary ventilation?
tidal volume x respiratory rate
e.g. 0.5 L x 12 breaths/min = 6 L/min under resting conditions
is alveolar ventilation or pulmonary ventilation lower?
alveolar is less because of presence of anatomical dead space
how to calculate alveolar ventilation?
(tidal volume - dead space volume) x respiratory rate
e.g 0.5-0.15 x 12 = 4.2 L/min
what is the effect of dead space volume on exchange of tidal volume between atmosphere and alveoli?
dead space volume means that even though 500 ml of air moves in and out between atmosphere & respiratory system, only 350 ml is actually exchanged between atmosphere & alveoli
what is pulmonary ventilation?
volume of air breathed in and out per minute
what is alveolar ventilation?
volume of air exchanged between atmosphere & alveoli per minute
why is alveolar ventilation more important than pulmonary ventilation?
alveolar represents new air available for gas exchange with blood
what about your breathing should be increased to increase pulmonary ventilation for example during exercise?
pulmonary ventilation = volume of air breathed in and out per minute
- to increase pulmonary ventilation increase both depth (tidal volume) and rate of breathing
= because of dead space, it’s more advantageous to increase depth of breathing
what is normal tidal volume, respiratory rate, dead space volume? and how do they change in
a) deep slow breathing
b) shallow rapid breathing
tidal volume = 0.5 L
respiratory rate = 12 breath/min
dead space volume = 0.15 L
a) tidal volume increases to 1.2 L and rate decreases to 5 breaths/min
b) tidal volume decreases to 0.15 L and respiratory rate increases to 40 breaths/min
*dead space volume doesn’t changes
what is ventilation?
rate at which gas is passing through the lungs
what is perfusion?
rate at which blood is passing through the lungs
how does blood flow and ventilation vary from bottom to top of lungs?
higher in bottom of lungs than top with blood flow higher than ventilation at bottom and ventilation higher than blood flow at top
which means average arterial and alveolar partial pressures of O2 are not exactly the same
what is alveolar dead space?
Ventilated alveoli which are not adequately perfused with blood
when does alveolar dead space become significant?
in normal healthy people it’s small and not very important but it can increase significantly in disease
how does accumulation of carbon dioxide in alveoli impact and airflow?
accumulation of CO2 as a result of increased perfusion = decreased airway resistance = increased airflow
*since more perfusion is more blood flow which means enhanced lung compliance - expansion & contraction
how does increase in alveolar oxygen concentration affect airflow?
increased oxygen as a result of increased ventilation = pulmonary vasodilation = increases blood flow to match larger airflow
what happens in area in which perfusion is greater than ventilation?
perfusion = blood flow, ventilation = airflow
perfusion greater means oxygen leaving more so decreased and CO2 arriving so increased
CO2 increased = dilation of local airways = airflow increased
O2 decreased = constriction of local blood vessels = blood flow decreases
what happens in area in which ventilation greater than perfusion?
perfusion = blood flow, ventilation = airflow
increased ventilation means more oxygen breathed in and less CO2 arriving back from blood vessels
CO2 decrease = constriction of local airways = airflow decrease
O2 increase = dilation of local blood vessels = blood flow increases
what is effect of decreased O2 and increased O2 on
a) pulmonary arterioles
b) systemic arterioles
a) decreased O2 = vasoconstriction, increased O2 = vasodilation
b) decreased O2 = vasodilation, increased O2 = vasoconstriction
what are the 4 factors that influence rate of gas exchange across alveolar membrane?
- Partial Pressure Gradient of O2 and CO2
- Diffusion Coefficient for O2 and CO2
- Surface Area of Alveolar Membrane
- Thickness of Alveolar Membrane
what is total pressure exerted by gaseous mixtures a sum of?
a sum of partial pressures of each individual component in gas mixture
what determines the pressure gradient for each specific gas?
the partial pressure for that gas
what is partial pressure?
- pressure that gas 1 would exert if it alone occupied the entire volume of the gas mixture, in the absence of other gases.
- Example: If we have a mixture of gases and the total pressure of the mixture is 100 kPa, and half of the mixture is made up of gas 1, then the partial pressure of gas 1 would be 50 kPa.
