Gas Exchange Flashcards
Physiology
explain the difference between pulmonary ventilation and alveolar ventilation and the significance of the anatomical dead space
pulmonary ventilation -
volume of air breathed in and out per minute
to increase pulmonary ventilation (e.g. during exercise) both the depth (tidal volume) and rate of breathing (RR) increase
(L) = tidal volume (L/breath) x respiratory rate (breath/min)
volume of air breathed in and out per minute
alveolar ventilation -
the volume of air exchanged between the atmosphere and alveoli per minute (represent new air available fr gas exchange with blood)
is less than pulmonary ventilation because of the presence of anatomical dead space
= (tidal volume - dead space volume) x respiratory rate
anatomical dead space - some inspired air remains in the airways where it is not available for gas exchange
because of dead space, it is more advantageous to increase the depth of breathing
explain the basic principles of ventilation perfusion matching
the transfer of gases between the body and atmosphere depends upon;
ventilation - the rate at which gas is passing through the lungs
perfusion - the rate at which blood is passing through the lungs
both blood flow and ventilation vary from bottom to top of the lung - the result is that the average arterial and alveolar partial pressures of oxygen are not exactly the same. Normally this effect is not significant but it can be in disease.
describe the significance of alveolar dead space
the match between air in the alveoli and the blood in the pulmonary capillaries is not always perfect
ventilated alveoli which are not adequately perfused with blood are considered as alveolar dead space
explain that the alveolar dead space could increase in disease conditions
in healthy people, the alveolar dead space is very small and of little importance
physiological dead space = anatomical dead space + alveoli dead space
the alveolar dead space could increase significantly in disease
describe and explain the local controls which operators to match ventilation and perfusion in the lung
local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
accumulation of CO2 in alveoli as a result of increased perfusion decreases airway resistance leading to increased airflow
increase in alveolar oxygen contraption as a result of increased ventilation causes pulmonary vasodilation which increases blood flow to match larger airflow
area in which perfusion (rate of blood flow) is greater than ventilation (rate of airflow); carbon dioxide increases in the area dilation of local airways airflow increases oxygen decreases in area constriction of local blood vessels blood flow decreases
area in which ventilation is greater than perfusion; carbon dioxide decreases in area constriction of local airways airflow decrease oxygen increases in area dilation of local blood vessels blood flow increases
identify and explain the four factors which influence gas transfer across the alveolar membranes
partial pressure gradient of oxygen and carbon dioxide;
rate of transfer increases as partial pressure increases (has major influence in the rate of gas transfer)
diffusion coefficient for oxygen and carbon dioxide;
rate of transfer increases as diffusion coefficient increases (diffusion coefficient of carbon dioxide is 20 times that of oxygen)
surface area of alveolar membrane;
rate of transfer increases as surface area increases (exercise increases surface area - deeper breathing expands alveoli and pulmonary capillaries open up when cardiac output increases. surface area decreases with e.g. emphysmema, lung collapse, pneumonectomy)
thickness of alveolar membrane;
rate of transfer decreases as thickness increases (thickness increases with e.g. pulmonary oedema, pulmonary fibrosis, pneumonia)
explain the Dalton’s law of partial pressures
the total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
explain that gases move by partial pressure gradient
the partial pressure of a gas determines the pressure gradient for that gas
the partial pressure of gas in a mixture of gases that don’t react with each other is;
the pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
know the alveolar gas equation and how to calculate the partial pressure of oxygen in the alveolar air if the partial pressure of carbon dioxide is measured in the arterial blood
alveolar gas equation;
PAO2 = PiO2 - [PaCO2/0.8]
PAO2 - partial pressure of oxygen in alveolar air
PiO2 - partial pressure of oxygen in inspired air
PaCO2 - partial pressure of carbon dioxide in arterial blood
0.8 - respiratory exchange ration
the air in the respiratory tract is saturated with water
the water vapour pressure contributes about 47 mm Hg to the total pressure in there lungs
explain the clinical significance of a big gradient between the partial pressure of oxygen in the alveolar air and the partial pressure of oxygen in the arterial blood
a small gradient between alveolar PO2 (PAO2) and arterial PO2 (PaO2) is normal (ventilation perfusion match s not usually perfect)
a big gradient between PAO2 and PaO2 would indicate problems with gas exchange in the lungs or a right to left shunt in the heart
explain the role of diffusion coefficient on gas transfer across membranes
partial pressure gradient for carbon dioxide is much smaller than the partial pressure gradient for oxygen
carbon dioxide is more soluble in membranes than oxygen
the solubility of gas in membranes is known as the diffusion coefficient for the gas
the diffusion coefficient for carbon dioxide is 20 times that of oxygen
explain the effects of membrane surface area and the membrane thickness on gas transfer, with Fick’s Law of diffusion
the lungs provide a very large surface area with thin membranes to facilitate effective gas exchange
the airways divides repeatedly to increase the surface area for gas exchnage
the small airways form out pockets (the alveoli). This helps increase the surface area for gas exchange in the lungs
the lungs have a very extensive pulmonary capillary network
the pulmonary circulation receives the entire cardiac output
ficks law of diffusion
the amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
describe the respiratory membranes and how gas trainer is affected by disease
alveoli;
thin walled inflatable sacs
function in gas exchange
walls consist of a single layer of flattened type I alveolar cells
pulmonary capillaries;
circle each alveolus
narrow interstitial space
identify the non-respiratory functions of the respiratory system
route for water loss and heat elimination
enhances venous return (cardiovascular physiology)
helps maintain normal acid-base balance (respiratory and renal physiology)
enables speech, singing, and other vocalisations
defends abasing inhaled foreign matter
removes, modifies, activates, or inactive various materials passing through the pulmonary circulation
nose serves as the organ of smell
