Essentia / Devices / Spirometer

Device Lab 53

Spirometer

40 mm in radius and 40 mm long, held above the dew point by a small heater. Gas passing the bundle produces a pressure drop across it that is proportional to the flow, because each capillary is running laminar; two small-bore lines carry that difference back to a differential transducer, and the flow signal is integrated in software to produce a volume. The head sits on a handle at mouth height with a one-way barrier filter and a disposable mouthpiece in front of it.

Also called: Spirometry. Arabic: مقياس التنفس. Device Lab 53 of 69 in BMEssentia Medical City, 2 configurations.

Overview: the configurations

How it works: the main parts

What each part does, from the Spirometer lessons in the 3D Device Lab.

Disposable mouthpiece and the lip seal

A short flanged tube of moulded plastic, twenty-five millimetres in the bore and thirty-five long, with a rim the lips close on and a flange the teeth sit behind. It is thrown away after one patient.

One-way barrier filter and the resistance it adds

A flat cylindrical cartridge about forty-one millimetres across, with a pleated medium inside it, a coloured rim at each end and an arrow moulded on the side. It is fitted between the mouthpiece and the machine, it is changed for every patient, and it is the largest single resistance anywhere in the breathing path.

The volume between the lips and the sensing element

Not a part. The enclosed gas inside the mouthpiece, the filter housing and the adapter, added together: forty-eight point nine one millilitres.

Nose clip and the leak it exists to close

A sprung wire with two soft pads on it, pinching the nose closed. It costs almost nothing, it is the least technical object in the room, and it is the only thing preventing a parallel path around the entire instrument.

Ambient temperature, pressure and humidity sensing

A small module on the trolley top with a grille and three sensing elements behind it: a thermistor, a barometric element and a humidity element. It reports the state of the air in the room, and it is the only instrument in the room that measures the room.

Bench BTPS board and the conditions nobody breathed at

A board on a stand carrying two bars, a dial with a needle that moves, and a screen. It exists because the largest single number in this instrument is applied invisibly in software, and it says so on itself: no instrument of either class shows you this factor.

Signal conditioning, anti-alias filtering and the sample rate

A board inside the host enclosure carrying an instrumentation amplifier, a handful of capacitors that form a low-pass filter, and the clock that decides when the converter is read. The last of those three is the one that turns up in the arithmetic.

Analogue-to-digital converter and its least significant bit

A chip a centimetre and a half square with a voltage reference beside it. It turns a continuous voltage into a whole number, and the size of one step in that whole number is the finest distinction the instrument can make about anything.

Explore it in the Device Lab

• Two gains whose product is exactly one: Leave every instrument alone and read two numbers off the bench error board: the integrator gain and the differentiator gain, at a tenth of a hertz, at one hertz, at five and at fifty. Multiply the two together at each frequency before reading on.
• A constant, integrated, with no ceiling: This experiment needs the configuration that measures flow. Set the zero offset to the declared default of ten millilitres a second and read what it represents as a flow. Then read the volume error it becomes at one second, at six, at fifteen, and across the whole session.
• A count, differentiated, multiplied by a hundred: Now the configuration that measures volume. Read the volume worth of one encoder count, which is the drawn seal area times the declared pitch and comes to six hundred and thirty-six microlitres. Then read what one count of jitter between two consecutive samples represents as a flow.
• A correction of ten per cent that nothing displays: Read the correction factor on the BTPS board at twenty degrees, then at twenty-four, then at thirty-four, then at thirty-seven. Write the four figures down before reading on.
• Infection control, in centimetres of water: This experiment is about a consumable and it is the only one here that is about the patient rather than the arithmetic. Read the device total resistance with the barrier filter fitted and with it removed, then read the pressure the filter consumes at the declared peak flow.

Common faults and what to check

Most reported device problems (FDA MAUDE)

Raw counts of adverse event reports for this device type (FDA product code BZG), all years. Not adjusted for the number of units in use, so they show what gets reported, not failure rates. Report text is never copied.

Planned maintenance checks

From the BMEssentia procedure library: every 12 months, about 30 minutes, electrical class II, applied part type BF.

Test instruments: 3 L calibration syringe.

Recent FDA recalls

From the FDA recall database (openFDA), newest first, imported 2026-10-22. 1 recalls on record for this device type. Recall text is the FDA's public text; each recall links to the official record.

Learn it, see it in 3D, ask about it

• Ask Essentia about the Spirometer: answers from named sources, with the device open in its 3D Device Lab beside the answer.
• The Spirometer on the BMEssentia Platform: the Device Library course, 13 sections from physics to maintenance.
• BMEssentia Medical City: Device Lab 53, the Spirometer fully assembled in 3D, with lab tasks and the simulations.

Previous: Pulse Oximeter. Next: Blood Pressure Monitor. All 69 devices.