Wrights Respirometer + Pneumotachograph Flashcards
What is the accuracy of Wrights respirometer?
For clinical use, the respirometer accurately reads the tidal volume and minute volume (+/- 5 to 10 %) within the flow range of 4-24 L/min.
A minimum flow of 2 L/min is required for the respirometer to function accurately.
What can be used to measure inhaled and exhaled volumes?
Wrights respirometer or pneumotachograph
When does a Wrights respirometer under-read values?
Wright’s respirometer under-reads at low tidal volume due to friction. It also under-reads at low flow rates.
When does a Wrights respirometer over-read values?
It over-reads at high tidal volume due to momentum. Over-reading also occurs at high flow rates, such as a high peak flow at the beginning of expiration.
What can affect accuracy of Wrights respirometer?
- It is not accurate if used to measure a continuous flow.
- Water condensation from the expired gases causes the pointer to stick, thus preventing it from rotating freely, and can lead to corrosion.
What is a pneumotachograph used for?
The pneumotachograph is a device used for measuring gas flow, from which gas volume can be calculated.
How does a pneumotachograph work?
In principle, it consists of a tube through which a laminar flow of gas passes over a small and fixed resistance.
The changes in pressure across the resistance are detected by two sensitive pressure transducers located on either side of the resistor.
Although the pressure change is only very small, it is linearly proportional, over a certain range, to the flow rate of gas passing through the resistor. Thus, an accurate measurement of gas flow can be achieved.
Is a pneumotachograph used for inspiration or expiration?
It is bi-directional so it can do both.
How does water vapour affect a pneumotachograph?
Water vapour condensation at the resistor can occur. This causes a turbulent flow affecting the accuracy of the measurement. This can be controlled by heating the resistor.
How does a Fleisch Pneumotachograph vary from standard pneumotachograph?
In the Fleisch pneumotachograph, a bundle of small capillary tubes, arranged in parallel to the direction of the flow, provide the small and fixed resistance.
These tubes ensure laminar flow through the sensor body, thereby producing a nearly linear relationship between flow and differential pressure.
What are the disadvantages of the fleisch pneumotachograph?
- it can be easily contaminated by sputum and water condensate.
- due to its relatively large surface area or dead space, it is often not suited for continuous respiratory monitoring.
- This type of pneumotachograph is heavy, costly and difficult to clean.
What is unique about a Lilly pneumotachograph?
The flow head uses a metal mesh as the flow restrictor.
Some designs use three screens as the flow restrictor to create a linear flow/differential pressure relationship.
What type of equipment allows the most accurate measurement of inspiratory and expiratory volumes?
The combined pneumotachograph and pitot tube allows more accurate measurement, even in neonates and infants.
Such a combination allows the calculation and measurement of compliance, airway pressures and resistance, gas flow and pressure/volume and flow/volume loops.
Where should the pneumotachograph be placed in the breathing system?
When monitoring patients, the sensor should be placed between the breathing system Y-piece and the tracheal tube.
In an electronic version of Wrights respirometer, what type of radiation is used?
Infra red light.
