Physics MCQ 7 Flashcards
Which device can measure CO2 in the blood? O2 in the blood?
Severinghaus electrode
Clark electrode measures O2 in the blood
What values do you need to calculate shunt fraction (Q’s/Qt)?
- Pulmonary end capillary O2 content (same as alveolar O2)
- Arterial O2
- Mixed venous O2 content
Qs - blood flow through the shunt/min
Qt - total cardiac output/min
Measurement of peak expiratory flow:
1. Does it reveal normal diurnal variation?
- What are the readings for a normal adult?
- Reveals a normal diurnal variation of less than 10%
2. Reading of 450 - 650 litres.min-1
Can electrically isolated circuits eliminate the risk of electrocution?
No, even if the patient comes into contact with the earth this does not prevent electrocution.
What is relative humidity?
The ratio of mass of water vapour present in a given volume of air to the mass required to SATURATE the same volume of air at the same temperature.
How is relative humidity calculated?
SVP at dew point / SVP at ambient temperature.
How does a hair hygrometer respond to temperature?
Hair in the hair hygrometer lengthens as humidity rises.
How does a Renaults hygrometer work?
Works by bubbling air through a silver tube of ether. The ether cools, and condensation appears on the surface of the silver tube.
The temperature at which the condensation appears is known as dew point.
In a manometer:
7.5mmHg is equivalent to how many cm H2O and kPa?
7.5mmHg = 10.2cm H2O = 1kPa.
What is different in the way mercury manometers and mercury barometer is sealed?
A manometer used to measure BP is open top, it has a gas permeable top which is open to atmospheric pressure. Measures gauge pressure.
(Michelle - open - engaging)
The barometer is sealed with vacuum above the surface of the liquid, which allows full absolute pressure to be recorded.
(Barak - closed - absolute)
In the Bain co-axial breathing system is fresh gas flow equivalent to the patients minute ventilation?
Fresh gas flow is 2-4 timess the patients minute ventilation to maintain normocapnia in a spontaneously breathing patient.
What classification of Mapleson does Bains function under?
Mapleson D
In the Bain coaxial system how is fresh gas flow delivered?
What can cause an increase in dead space?
Fresh gas flow is delivered through the inner tube and if this becomes disconnected it can hugely increase the dead space.
What temperature do hot water humidifiers usually operate?
40-45 degrees C
How can ultrasonic nebulisers produce fluid overload?
Because they produce very fine water droplets, those at 5microns deposit in the trachea and 1 micron in the alveoli.
Relative humidities > 100% can be produced which may lead to fluid overload or pulmonary oedema in children.
