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In its simplest form, spirometry is the measurement of how much air a person can breathe out in one forced breath, known as forced expiratory vital capacity (FVC). Different parameters can be measured from the flows that occur during the FVC maneuver. Healthcare professionals interpret volume and flow data alongside graphs showing volume/time and flow/volume to assess lung health.
Vitalograph has investigated many different precision technologies for measuring flows and volumes. Today, the preferred technology used in Vitalograph diagnostic spirometers for flow measurement is the Fleisch Pneumotachograph, and for volume measurement is the Rolling Seal. We use Lilly-type screen pneumotachographs in our lab spirometers and stator-rotor flow measuring technology in our monitoring and screening devices.
Fleisch pneumotachograph flow measuring technology is the most accurate, precise and reliable flow measuring technology. The linear signal is simple to process and the spirometry device is extremely robust as it has no moving parts. Even with a Bacterial Viral Filter (BVF), essential for effective hygiene between the patient and the measuring system, the system flow impedance is low even at high flow rates and well within the requirements of the current spirometer standard ISO26782:2009. Fleisch flowmeters may be heated or unheated, but in office spirometry flowmeters are generally unheated for safety, speed of use and accuracy. Vitalograph spirometers use an unheated Fleisch Pneumotachograph.
Small and lightweight, the simple digital signal produced by the spin of the rotor provides accurate results for monitoring and screening of respiratory parameters such as PEF, FEV1 and FEV6. On Vitalograph devices, a simple LCD screen provides immediate results and the device stores several hundred tests that can be downloaded to view trends in patient data. This spirometric measuring technology is often referred to as a ‘turbine’, although a true turbine has a curved blade and requires no stator.
View our range of monitors and screeners which use this technology.
Direct determination of volume has the advantage of being absolute and measured at ambient conditions during both inspiration and expiration. This high accuracy makes the rolling seal well suited to routine clinical testing, research and as an accuracy reference for other non-volumetric spirometers. Volumetric devices are also ideal for training where direct determination of volume provides a clear platform for demonstration and explanation of technique and results.
Launching soon! The Gold Standard, our new rolling seal spirometer, Talk to us to learn more.
Lilly screen pneumotachographs measure flow in a similar way to Fleisch technology, employing a fine wire mesh screen with low resistance to air flow. Flow is calculated by measuring the pressure differential across a screen or series of screens. This type of device is very accurate and stable. A screen pneumotachometer is slim, allowing space in the flowhead for other features e.g. demand valves and other gas inputs and outputs making it suitable for lab spirometry requiring additional gases for tests such as DLCO and nitrogen washout.
The screen used in a Lilly-type Pneumotachograph is very easy to clean and service. The heated screen provides stable measurement for protracted periods of testing, although the additional electronic components in the flowhead render it less suitable for office spirometry than Fleisch flowhead technology.
While this technology is very sensitive, Vitalograph does not use ultrasonic flow measuring technology as it is prone to errors before measurement with low flow profiling from ambient air movement and does not measure low flows accurately3. Accuracy depends on a developed flow profile that is not found in turbulent expired air, therefore flow rates must take into account the turbulent gas flow profile; in ultrasonic technology this is corrected by software algorithms based on Gaussian probability. Turbulent airflow is overcome in Fleisch, Screen and Stator-Rotor and turbine measuring technology by design elements that manage airflow i.e. the swirl induced by the stator in stator-rotor devices, laminar flow induced by capillaries in the Fleisch and the mesh in Lilly technology.
Hygiene in ultrasonic devices is dependent on expensive disposable flow tubes with additional filters required for infection control.
3 Perera, A., Friedrich, P., & Ledermüller, R. (2018). Novel hot-wire based spirometry is highly accurate at low flow rates, Current Directions in Biomedical Engineering, 4(1), 513-515.
Hot wire measuring technology is used in lab spirometer systems as it is capable of measuring flow using gases other than room air by applying conversion factors and it can give very stable, accurate measurements. However the requirement for delicate electrical wires within the flowhead means that the technology is unsuited to portable applications and can be unreliable. Vitalograph does not use hot wire measuring technology due to its fragility and the added complexity of patient safety incurred by including electrical parts within the flowhead.