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Flashcards in L2 Ventilation Deck (29):


Device to measure depth of respiration


Tidal volume

Tidal= air has to go in and out same set of tubes



Activates muscles of inspiration and hence develops force
Increases volume of Thorax
Decrease in pressure (subatmospheric)
-if glottis is open air will enter
Total Lung capacity= max deep breath


Residual volume

Cannot expel more air without assistance


Functional Residual Capacity

functional amount of air in lung between each breath


What do you need to o in order to get air into the lung?

Overcome lung compliance
Overcome resistance to air flow



Sum of two or more volumes



L Litres
Gas volumes are temperature-Dependant
Measured Gas volumes are atmospheric Pressure Dependant
"Correction" to Standard Temperature and Pressure
V(STP) = V(ATP) x (273/(273+T)) x (Pb/760)
Expired air is water-saturated
The saturation vapour pressure of water is temperature-dependant
V(STPD) = V(ATPS) x (273/(273+T)) x ((Pb-PsatH2O)/760)


Volumes Pressure Dependant

Measured Gas volumes are atmospheric Pressure Dependant
"Correction" to an agreed Standard Pressure (760mmHg) (101 kPa) is required
V(SP) = V (AP) x Pb/760
Pb (pressure at which the volume was measured)


Volumes Temperature Dependant

Gas volumes are temperature-Dependant
"Correction" to agreed Standard Temperature (0 Degrees) is required
Measure are under Ambient conditions but correct to standard temperature
V(ST)= V(AT) x 273/(273+T)


Water Saturated Expired Air

Expired air is water-saturated
The saturation vapour pressure of water is temperature-dependant
-air is dry in the winter
"Correction" to DRY conditions is required
V(STPD) = V(ATPS) x (273/(273+T)) x ((Pb-PsatH2O)/760)


Ambient vs Standard values for Temperature, Saturation Vapour Pressure and Pressure

Temperature (C): Ambient=20 degrees. Standard=37 Degrees
Saturation Vapour Pressure(mmHg): Ambient= 20mmHg. Standard=47mmHg
Pressure (kPa): Ambient=2.7kPa. Standard=6.3kPa



V. = (dV)/(dt)
Rest: 6Lmin-1 = Minute Volume
Minute volume= magnitude of pulmonary ventilation = V. = VT x freq.


Minute Volume

Rest: 6Lmin-1 = Minute Volume
Minute volume= magnitude of pulmonary ventilation
V. = VT x freq.= Tidal volume x Freq = 500ml x 12 = 6L


Alveolar Ventilation

amount of fresh air entering the alveoli
much less than Minute volume (6-7.5 L) = due to dead space


Anatomic Dead-Space Volume

Respiratory Tubing --> 17/20division
= all tubing w/o substantial gas exchange
Volume of Conducting Airways
In Healthy individuals = about 2mL/kg


Physiological consequence of Dead Space

4x 150ml Aliquots
Inhale 450mL air
One way system = First air that enters alveoli is old dead space air from previous breath (not fresh air)
Inspired air in alveoli= 150mL Deadspace air + 300mL fresh
Exchange 450mL, only 300mL made it down to an area of value
Have no choice but to inspire dead space air and expire fresh air
V.A= f x (VT-VD)


Measurement of Anatomical Dead Space

Written calculations
-can readily measure FECO2 with carbon dioxide analyser
-harder to measure FACO2 as hard to get sample of air from deep out of alveoli
Approximation1: Pgas ~ Fgas
Approximation2: PaCO2 ~ PACO2


Hold your breath

Fraction of CO2 in lung is steadily rising
Cardiovascular system still bringing blood back to lungs regardless if lungs are changing their volume at the time
-Continuously produce CO2 independant of status of respiratory system


Estimation of dead space Volume

Clinically used for patient having trouble breathing
-increase in dead space volume


Bohr equation

Fraction of the Tidal volume that is dead space volume
VD/VT = (PaCO2 - PECO2)/PaCO2


Bohr equation in practice

Initial air exhaled contains negligible amounts of CO2
Then alveolar air and dead space air comes out mixed (CO2 fraction increases)
Hold breath: CO2 continues to increase as tissues continue to respire, producing CO2, blood brings CO2 back to lungs (limited air exchanged but still rising)
Jaggard line= not a square wavefront of CO2 coming out of the lungs, but is blended as it rises


Requirement for flow

In order for flow to occur, there must be a gradient of Pressure
High --> Low Pressure
V. = PA - PB / r = delta P /R
Proportional to pressure gradient
Inversely proportional to resistance


Distribution of air-flow resistance in the lungs

Distribution of air flow in the lungs ISNT uniform
as the resistance to airflow isnt uniform
Trachea --> alveoli, total cross sectional area doesnt change much until 10th generation until skyrocket until final alveoli branching
-vessels are smaller but So many more
-increase in total cross sectional area = decrease in resistance (small as parallel resistance even though resistance is individually higher in tiny vessels)


Topographical variation of air-flow in the lungs

Inhale small aliquot of radioactive Xenon 133Xe
Radiation counters placed along height of the thorax
Ventilation is most effective at the lower part of the lung
and diminishes pretty rapidly when getting to the upper zone


Laminar and Turbulent Flow

Smoke initially Laminar --> then becomes highly turbulent
Turbinate bones in nose breaks up airflow


Poiseuille-Hagen Law

Flow is in Laminae = in Layers
=results in Parabolic Profile in Flow (not an abrupt change inc carbon dioxide, there is some mixing from alveoli to outside air)
Arrows= velocity profile
Laminar flow has essentially no velocity at the edges of the tube
Highest velocity = in centre


Quantitative Comparison of Laminar and Turbulent Flow

Laminar Flow: V. propn deltaP
-rate of change of volume is proportional to different in pressure
R propn (n (viscosity) x l (length))/r^4
-small change in radius has a large change in resistance inversely
Turbulent flow: V. propn square root of delta P
-must apply a larger amount of pressure to maintain same flow


Difference b/w a and b in diagram

a=pure nasal breathing
b= nasal and mouth breathing