chapter 2 oft equipment Flashcards
primary volume
bell is measured directly bell that collects volume bellow collects volume piston collects volume flow is indirectly determine: flow=volume/time
primary flow
flow is directly measure pneumotachometer thermal anemometer volume is indirectly determine volume = flow x time
primary volume spirometer: water seal
history the oldest and accurate
large bell suspended in the water
separate inspiratory and excretory into and out of the interior bell
kymograph
pen
valve- turns patient in and out of the system
very accurate
also must be counterweight
if the bell is heavy, inertia may limit the measured of subtle flow changes
they are quite large
bellow spirometer
wedge type is most common type
as bellow expands a pen records the volume change on calibrated paper
may having a moving chart for the time element
advantages: small size and portable
disadvatages: less accurate the extremes of flow measurement
dry rolling spirometer
a piston collects the volume and is sealed with thin flexible plastic that folds and unfolds with movement of piston
this type offer very little resistance and minimum frictional loss
horizontal mounting negates the need for counter weight
most use a potentiometer to convert piston motion to an anolog electrical signal
advantages: smaller than type seal types
respond well to flow changes
disadvatages: unless well maintain friction losses can increase
chain compensated and stead wells spirometer
bell must be counter weight pen is attached to counter weight kymograph speeds 32 mm/min slow vital capacity 160 mm/min maxima voluntary ventilation 1920 mm/min forced vital capacity disadvantages- since bell has a greater mass may inertia may negate measurement of sublet flow changes
stead wells spirometer
use light weight plastic bell inertia effect less on results pen attached directly with bell kymograph speeds 32 mm/min slow vital capacity 160 mm/min maxima voluntary ventilation 1920 mm/min forced vital capacity
vane type respirometer
common use in bedside assessment vital capacity spontaneous parameters vc minute volume tidal volume
vane type respirometer operation
gas flow through directional vanes
a flexible mica vane spins wit exhaled gas flow
a gear set turns with vane as it spins, recording volume and inner workings are similar to a mechanical watch
spirometer has flow limitation which can influence accuracy of your results
most accurate between 10 -20 L/min
screen type pneumotachometer
a screen or capillary grid in the flow path through the spirometer causes a pressure drop
pressure proximal to the screen or capillary grid is greater than the pressure distal to it
the pressure difference is proportional to the flow
strain gage transducer
has a wire coil attached to diaphragm. As the diaphragm expands the coils changes in length electrical resistance
electrical flow to the change
variable reluctance transducer
a stainless steel diaphragm separate two wire wounds coils
one coil is energized with alternating current causing a magnetic force to be created
movement of diaphragm causes the air space surrounding the coil to change. This changes magnetic reluctance or flux
a change in flux results in change in the induced current in the uncharged coil
current fluctional on the output fails are proportional to pressure change
these are most sensitive type of pressure transducer and can measure incredibility small change in pressure
venturi pneumotachometer
employ a venturi tube with pressure port distal to the throat and the throat of venturi
as flow increase pressure decrease at the throat
pressure difference is proportional to flow
thermal anemometer
gas is passed over heat bead and maintain constant temperature
gas flowing over the heated elements cools
as the element cools additional current is require to maintain the set temperature
current flow is proportional to flow
mass flow sensor( Sensormedics)
uses two heated elements in series with one another
heated to different temperature
by using two elements gas composition and humidity don not effect the accuracy
the temperature changes due to gas flow causing a change in current require to heat the elements
