Respiratory physiology Flashcards
- Draw a graph describing lung volumes, label it including values
- What is the difference between a volume and a capacity?
- Which volumes/capacities can not be measured by spirometry?
- TC 6000ml
IRV 2500ml
TV 500ml
ERV 1500ml
RV 1500ml
FRC 3000ml
VC 4500ml
- A capacity is the some of two volumes
- RV can not be measured by spiromerty and therefore capacities containing it (FRC and TLC) can not be measured. They require helium dilution and body plethysomgraph
Name the ways that lung volumes can be measured
- Water-sealed spirometer
- Dry spirometer
- Body plethysmograpgh
- Helium dilution
- Nitrogen washout
Describe how a water spirometer works
Involves breathing into a closed chamber that is partially submerged in water.
Breathing in and out of the chamber causes the water to be displaced. This is recorded by the movement of a pen on a sheet of paper.
Only gas volumes uo to few litres can be measured. As it is not possible to exhale below RV this can not be measured
How does a dry spirometer work?
The simplest example is a bellows driven device e.g. vitalograph.
This contains a set of belows which are attached to a pen. As the patient exhales the belows expand and collapse, moving the pen
- Describe how body Plethsmography works
- How are lung volumes and FRC calculated via this method?
The subject is placed in an upright box and air pressure (P1) and Volume (V1) are measured. The subject then inhales and exhales to a particular lung volume (normally FRC) though a mouthpiece.
A shutter then drops across the breathing tube and the subject continues breathing against a closed shutter. This causes their chest volume to increase and thus causes the vol in the box to decrease.
According to Boyle’s law (PV=k) the pressure in the box must increase (P2).
Airway pressures at the mouth are also measured
- P1xV1= P2x(V1-change in lung volume)
To calc FRC:
Inital airway pressure x intial lung volume= inspiratory airway pressure x insp volume of chest
Where inital lung volume= FRC, and inspiratory volume of the chest=change in lung vol +FRC
This measurement of FRC (unlike helium dilution) includes lung unitsthat are collapsed or with poor air entry
Describe how Helium dilution works
The subject breaths air containing a known concentration of helium in a closed system containing a spirometer.
The CO2 produced during the test is absorbed by soda lime andreplace by O2
The helium is distributed throughout the subjects lungs (although not into obstructed lung units) and the equipment.
Helium is used becuse of its very low solubility, which means a minimal amount is lost through absorption into the bloodstream.
Describe how nitrogen washout method works
How does it compare to the helium diluation method
What does Fowler’s method measure?
The subject breaths 100% O2 from the end of a normal expiration through a closed brearthing circuit connected to a spirometer
After several minutes the N2 conc and vol of gas within the equipement are measured. This will be equal to the amount of nitrigen that was initally present. =FRCx79% (atmospheric conc of nitrogen)
As with helium dilution, poorly or non-ventilated lung units will not be included
A SINGLE breath nitrogen washout curve (FOWLER’S method) employs a different technique used to measure anatomical dead space and closing capacity
- Define
- Typical volume
- Function
- How does pre-oxygention work?
- The volume of the lungs at the end of a normal expiration, with the subject in the standing position. Sum of RV and ERV. It can be considered the volume in the lungs when the elastic recoil of the lungs is equal to the outward recoil of the chest wall and diaphragm tone.
- 2500ml
3.
- Oxygen reservoir and maintainance of oxygenation during expiration and breathholding
- Prevention of airway collapse
- Optimal compliance
- Optiaml pulmonary vascualr resistance (PVR)
- There is de-nitrogenation of the lungs, alveolar oxygen content can be increased to around 90%, therefore FRC now contains 2500x0.9=2250ml of 02 so a reserve of 2250/250= 9 mins (typical O2 consumption is 250ml/min)
Why does this occur?
What is Closing Capacity?
List some causes
How can FRC be maintained in the supine anaesthetised patient?
Occurs when FRC equals the closing capacity.
Closing capacity (CC) is the sum of closing volume and RV.
In young fit patients CC is always less than FRC so no airway collapse occurs during TV ventilation.
If FRC is freduced it may reach CC and airways collpase. Alternatively CC can increase.
Causes:
- Smoking
- Asthma
- Age
In anaesthetised supine patients the FRC can be maintained above CC with PEEP created by maintaining a positive airway pressure during expiration (normally 5-15cm H20
Draw a graph and describe the relation between Lung volume and Transpulmonary pressure.
Draw what happens if FRC is reduced
Graph showing the relationship between LV and Transpulmonary pressure where FRC is reduced. The slope of the line represents lung compliance
The FRC normally correspondes to the stepest part of the curve, this is where lung compliance is greatest
If FRC is reduced the patient breaths from a point of the curve that is flatter, this is assoc with a fall in compliance and increase WOB.
Draw a graph to show the relationship between pulmonary vascular resistance and Lung volume
PVR is lowest at FRC allowing for optiamal pulmonary blood flow
- What is dead space?
- What types of dead space are there?
- Dead space is the vol of insp air that does not take part is gas exchange and typically makes up 30% of normal TV ventilation
Alv Vent (Va)= TV-Dead space volume (Vd)
2.
- Apparatus: vol of external equipement inc HME, mainstrem capnography, face mask etc
- Anatomical: this is made upof gas in the larger, conducting airways
- Alveolar: this is gas from alveoli that are poorly pefused. That is alveoli with high V/Q ratios
- Physiological Dead Space= Anatomical Dead Space + Alveolar Dead space
