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Gas Transfer Measurement (Equipment & Instrumentation) Flashcards

1
Q

Draw a Vol/Time Trace for a Gas Transfer Manoeuvre

A

Whiteboard

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2
Q

Draw a Gas Conc Trace for a Gas Transfer Manoeuvre

A

Whiteboard

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3
Q

What are the acceptability criteria for exhalation?

A
  • Should be collected in less than 3 seconds

- For low VC (1.5-2L) - washout/sample volumes may need to be reduced

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4
Q

What is the washout sample?

A

A volume of gas (washout volume) must be expired to clear the total anatomical and equipment dead space volume

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5
Q

What must the washout volume be?

A

0.75-1L (BTPS)

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6
Q

What happens of VC<2L?

A

Reduce washout volume may be reduced to 0.5L

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7
Q

Explain how to measure the JMBHT?

A

The Jones-Meade Breath hold Time (Go to panopto and use whiteboard to practice)

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8
Q

What does the Gas Mixture Contain?

A
  • CO 0.28-0.3%

-Inert/Tracer Gas (He/CH4)
Helium = 9-14%
Methane = 0.3%

-Air

Oxygen = 18-21%
Nitrogen = Balance
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9
Q

What do commercial systems use for inspired Oxygen?

A

FiO2
(between 0.18 and 0.21)

And FiO2 will effect TLCO measurement

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10
Q

How long should supplemental Oxygen be discontinued for?

A

10 mins prior to testing

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11
Q

Why do we use Carbon Monoxide CO? (6)

A
  • High affinity of CO for Hb
  • Membrane diffusion coefficient and rate of reaction of CO with Hb are similar to O2
  • Safe to breathe at low concentrations
  • Binds to same sites as Oxygen on Hb Molecule
  • Easy to measure at low concentrations

(IR and Electrochemical)

-Low CO present in bloodstream at start of test and so facilitates gas uptakes

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12
Q

Describe the Inert gas component: (3)

A
  • Commonly Methane (CH4) or Helium (He)
  • Inert/relatively insoluble
  • Does not cross the lung membrane
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13
Q

What are the uses of an inert gas component?

A
  • Gives a measure of VA (Alveolar Volume)
  • VA used in calculation of TLCO
  • Calculation of gas transfer per unit volume (KCO)
  • Quality Assurance
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14
Q

How do you calculate TLCO

A

TLCO = VA x KCO

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15
Q

What type of gas analyser and is the clinical use for:

CO

A
  • Infra Red

- Electrochemical

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16
Q

What type of gas analyser and is the clinical use for:

He

A

Thermal Conductivity

17
Q

What type of gas analyser and is the clinical use for:

CH4

18
Q

What are the properties of the Ideal Gas Analyser?

RALSSOGC

A
  • Rapid
  • Accurate
  • Linear
  • Stable
  • Specific to gas being analysed
  • Operate with a small volume of gas
  • Gas requires minimum preparation before reaching analyser
  • Calibration and maintenance -simple and easy
  • Cost effective
19
Q

What factors affect gas analysis?

A
  • Delay Time
  • Response Time
  • Leaks/Blockages in samples
  • Exhausted Water Vapour/CO2 Absorbers
  • Improper mechanical zeroing (calibration)
  • Exhaustion of fuel cells
  • Inadequate warm up time
20
Q

What is the delay time?

A
  • Time taken for a gas to travel from sample site to the analyser
21
Q

What is the response time?

A
  • Time taken for an analyser to make measurement and display a change in concentration
22
Q

How is the response time expressed?

A

Often expressed as the time taken to produce a 90-95% response to a step

23
Q

What are the key points of an IR analyser? (5)

A
  1. IR radiation reflected through sample and reference tube to detector
  2. Detector has 2 compartments with pure gas (CO or CH4) separated by diaphragm
  3. Absorption of the radiance emitted from the sample and reference tubes takes place in the detector
  4. Gas is heated and expands and the flexible diaphragm assembly becomes distorted resulting in a change in capacitance which is amplified electronically
  5. Signals produced are proportional to the concentration of gas being analysed
24
Q

Describe electrochemical analysis:

A

A type of fuel cell that produces a current related to CO present.

25
Q

What are the 3 sensors in a liquid electrolyte?

A
  • Reference electrode
  • Counter Electrode
  • Working Electrode (Platinum)
26
Q

How does a fuel cell work?

A
  • Working electrode (Platinum) backed by a gas permeable membrane
  • CO diffuses through membrane
  • Pt Electrode catalyses the oxidation of CO to O2
  • Electrons flow from Working electrode to external circuit producing an output signal
27
Q

Define thermal conductivity:

A

The rate at which heat is conducted by a gas

-Helium has a much higher thermal conductivity than other gases

28
Q

Name 2 other Gas Transfer techniques:

A
  • Intrabreathing

- Rebreathing

29
Q

What should occur daily with machines?

A
  • Daily - volume calibration check with a 3 litre calibration syringe
  • Discharged at least 3 times to give a range of flow rates between 0.5 and 12 L per second
  • BioQC

R+S phys (17 decks)

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