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)
