L2 Ventilation Flashcards
Spirometer
Device to measure depth of respiration
Tidal volume
Tidal= air has to go in and out same set of tubes
Inspiration
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
Capacity
Sum of two or more volumes
Volume
V
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
Flow
Vdot Lmin-1 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
=5.250L
much less than Minute volume (6-7.5 L) = due to dead space
Anatomic Dead-Space Volume
VD 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
