Ventilation and Lung Volumes Flashcards
describe the total lung capacity and name its components.
the max volume of gas that the lungs can contain.
tidal volume, inspiratory reserve volume, expiratory reserve volume and residual volume.
what is the tidal volume?
the volume of gas that flows into and out of the lung in one breath
what are the inspiratory reserve volume and expiratory reserve volume?
IRV- max gas that can be inhaled from end tidal inspiratory position
ERV- max gas that can be exhaled from the end titdal expiratory position
what is the residual volume?
the volume of gas contained in the lungs after a max forced expiration
what is the vital capacity? what is it made up of?
the max volume of gas that can be exhaled after max inspiration
IRV+ERV+tidal volume
what is the inspiratory reserve capacity? what is it made up of?
the max volume of gas that can be inhaled from resting position
tidal volume+IRV
what is the functional residual capacity?
the volume of gas in the lungs when the diaphragm and chest muscles are relaxed
why can’t FRC be measured with a spirometer?
because it is impossible to exhale the residual capacity
what effect does compliance have on FRC? how does this change during aging?
increased compliance increases FRC (decrease resistance of lung to pull of chest)
compliance and FRC increase during aging
what does the open-circuit nitrogen washout test measure?
the FRC
what is the equation that is used by the open circuit nitrogen washout test?
FRC=(fraction N2 sp x volume sp)/ fraction N2 lung
sp->spirometer
how are the values for the nitrogen washout test collected?
fraction N2 lung=0.8 (same as in atmosphere)
V sp-> measure of all of the air expired in the test
fraction N2 sp-> measured from the expired gas
how is the nitrogen washed out of the lung in the open circuit nitrogen washout test?
the patient breathes in 100% oxygen for at least 7 min and all of the expired gas from the test is collected.
in practice, what is different about the equation compared to the fractional equation?
there is a correction made for the amount of nitrogen brought to the lungs from the blood during the washout
what would not be measured during the nitrogen washout test? what would this due to the result?
any regions of the lung that contain trapped air, underestimating the actual FRC
describe the initiation of use for a body plethysmograph.
the subject sits in a gas tight chamber and breathes through a tube leading outside until temp and humidity are equilibrated
during testing for FRC using a body plethysmograph, what is the protocall?
the breathing line is closed when the lung is at FRC and the subject makes an expiratory effort against a pressure transducer
what is measured while in the body plethysmograph?
the pressure transducer blocking expiration measures the lung pressure and there is a second transducer records the pressure change of the box.
what equation is employed when calculating the FRC from values measured in the plethysmograph?
FRC= -Pt (deltaV/deltaP)
what happens to the pressure in the lungs and in the plethysmograph with the forced expiration?
the pressure in the lungs increases because the volume is being compressed. this compression of volume increases the volume within the plethysmograph, decreasing the pressure
what makes up the anatomic dead space?
the conducting zone
why does the last portion of each inspired breath not participate in gas exchange?
because the last amount of air only interacts with the anatomic dead space and never reaches the respiratory zone
what is the alveolar ventilation?
total ventilation - dead space ventilation
frequency of breathing x (total volume-dead space volume)
what is the rough approximation for anatomic dead space volume in an individual?
1 lb body weight=1 ml dead space (used in clinical practice)
what is the result of hypoventilation?
alveolar hypercapnea and hypoxia (decreased O2 and increased CO2)
why does hyperventilation result in alveolar hypocapnea and hyperoxia?
because the rate of gas diffusion into and out of the capillaries is small compared to the rate of influx of oxygenated air and efflux of CO2 containing air
what is the equation for CO2 ventilation at steady state?
ventilation of CO2= alveolar ventilation x alveolar fraction of CO2
what is the equation for alveolar partial pressure of CO2? based on this equation what happens if the alveolar ventilation is increased?
P CO2 alveolar= (ventilation CO2 x total pressure)/ alveolar ventilation
ventilation increased, alveolar CO2 partial pressure decreases
based on the equation for partial pressure of CO2, what two factors would increase the partial pressure of CO2 in the alveoli at steady state?
increasing CO2 production and decreasing alveolar ventilation
based on the equation for partial pressure of O2 in the alveoli, what three factors would increase alveolar oxygen?
increasing alveolar ventilation, decreasing oxygen consumption and increasing the partial pressure of oxygen in the inspired gas
what is the equation for partial pressure of O2 in the alveoli?
P O2 alveoli= (P O2 inspired- P CO2 alveoli)/ R
R= ventilation of CO2/ ventilation of O2
what percentage of total lung capacity does the tidal volume represent? what does this imply?
only ~10%
implies that the volume going in and out of the lung in each breath is a small fraction of the volume of air present in the lung
what is the magnitude of the partial pressure differences of CO2 and O2 during inspiration and expiration in the alveoli?
1-2 mmHg
why does the partial pressure of O2 fall and the partial pressure of CO2 rise during the beginning of inspiration?
because there is still gas transfer in the alveoli while air is traveling through the dead space to the alveoli
describe the protocall for using the single breath analysis of anatomic dead space.
a subject inspires air (negligible CO2) and then exhales into a spirometer while the fraction of CO2 is being measured
what is the principle of the fowler method of single breath analysis of anatomic dead space?
that expired CO2 comes exclusively from the alveoli and not from the anatomic dead space
on the fraction of CO2 graph, what point reveals the time when all of the dead space air would be expired if there was a sharp boundary between alveolar and dead space air?
at the point of concavity change in the sigmoidal shaped curve. the volume of expired air at this time corresponds to the volume of dead space
why is the curve of fraction of exhaled CO2 sigmoidal?
because there is a mixing of air free of CO2 from the dead space and air with a considerable amount of CO2 in the alveoli
