Evie Summers
Thermistors and pflow (nasal pressure monitoring) are both used to monitor sleep and detect sleep disorders. Thermistors are temperature-sensitive transducers that detect changes in temperature, while pflow responds to changes in pressure. Thermistors have traditionally been used to determine airflow during polysomnographic studies, but nasal pressure monitoring is becoming more popular due to its higher sensitivity to small changes in airflow. However, thermistors are still used to score apneas, and according to AASM rules, apnea events are scored using thermal sensors, while hypopneas are scored using pressure sensors.
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What You'll Learn
- Thermistors are temperature-sensitive transducers made of compressed sintered metal oxides
- Thermistors are composed of materials that change electrical resistance when exposed to temperature changes
- Thermistors are used to detect sleep-disordered breathing (SDB) during polysomnography
- Thermistors are less sensitive than nasal pressure transducers for detecting airflow limitation
- Thermistors are more expensive than conventional thermocouples
Thermistors are temperature-sensitive transducers made of compressed sintered metal oxides
Thermistors are temperature-sensitive transducers that change their resistance with changes in temperature. They are made of compressed sintered metal oxides, such as nickel, manganese, cobalt, copper, or iron. The name "thermistor" is a combination of the words "thermal" and "resistor", reflecting its ability to change resistance in response to temperature fluctuations.
Thermistors are constructed using metal oxides in powdered form, which are then compressed and sintered. This process involves heating the powdered metal oxides to a temperature below their melting point, causing the particles to fuse together. The resulting material exhibits a negative temperature coefficient, meaning that its resistance decreases as the temperature increases. This behaviour is described by the Steinhart-Hart equation, a widely used third-order approximation.
Thermistors are available in various shapes, including small beads, rods, plates, and large disks. They are commonly used to monitor airflow by detecting changes in temperature, such as the cool air that flows during inspiration and the warm air during expiration. This is achieved by placing a thermistor between the nose and mouth, where it records changes in electrical resistance. Thermistors have been traditionally used to determine airflow during polysomnographic studies (PSG) and to score apneas.
However, thermistors have limitations, including a slow response time due to their thermal mass, which results in smoothed average waveforms that may not accurately represent the patient's actual airflow patterns. Additionally, they may have lower accuracy in detecting hypopneas compared to other methods, such as nasal prong pressure (NPP) measurements.
Despite these limitations, thermistors offer certain advantages. They are long-lasting, accurate, and inexpensive. Thermistors can also be used in various applications beyond temperature measurement, such as controlling electrical currents and measuring blood temperature to calculate cardiac output.
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Thermistors are composed of materials that change electrical resistance when exposed to temperature changes
Thermistors are temperature-sensitive transducers made of materials that change electrical resistance when exposed to temperature changes. They are composed of compressed sintered metal oxides that exhibit a negative temperature coefficient, meaning their resistance decreases as temperature increases. The most common types of thermistors are constructed using oxides of iron, copper, or nickel. These oxides form a ceramic body with terminals composed of conductive metals such as silver, nickel, and tin.
Thermistors are available in two types: those with Negative Temperature Coefficients (NTC) and those with Positive Temperature Coefficients (PTC). NTC thermistors are the most common type and are used for temperature measurement. They are characterised by their base resistance at room temperature (25°C), which provides a convenient reference point. As the temperature increases, the resistance of an NTC thermistor will increase in a non-linear fashion, following a particular "curve". The shape of this resistance vs. temperature curve is determined by the properties of the materials that make up the thermistor.
PTC thermistors, on the other hand, are primarily used for circuit protection. Their resistance increases as temperature rises, due to increased thermal lattice agitations, particularly of impurities and imperfections. PTC thermistors are commonly installed in series with a circuit to protect against overcurrent conditions, acting as resettable fuses.
Thermistors are typically pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass. They are long-lasting, accurate, and cost-effective for temperature measurement. However, they have a slow response time due to their thermal mass, which can result in a smoothed average of the actual changes in airflow temperature.
Thermistors have been traditionally used to determine airflow during polysomnographic studies (PSG) and to score apneas. However, they have low accuracy in detecting hypopneas, and nasal prong pressure (NPP) measurements are becoming a more popular alternative for quantifying respiratory events during sleep.
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Thermistors are used to detect sleep-disordered breathing (SDB) during polysomnography
Thermistors are temperature-sensitive transducers made of compressed sintered metal oxides such as nickel, manganese, or cobalt. They change their electrical resistance when exposed to temperature changes. Thermistors are placed under a patient's nose or in front of their mouth to detect the temperature changes that occur during inhalation and exhalation.
Thermistors have traditionally been used to determine airflow during polysomnographic studies, but they have low accuracy in detecting hypopneas, which is a major drawback. Nasal prong pressure (NPP) measurements are becoming more popular for quantifying respiratory events during sleep as they are more sensitive and reliable for detecting SDB.
Despite the limitations of thermistors in detecting subtle SDB, they are still recommended for evaluating apneas during PSG. This is because the thermistor channel is insensitive to partial flow obstruction, making it suitable for detecting the complete absence of airflow in apnea events.
In summary, thermistors are used to detect SDB during PSG by measuring airflow changes through temperature detection. While they have limitations in detecting subtle SDB events, they are useful for evaluating apneas due to their insensitivity to partial flow obstruction.
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Thermistors are less sensitive than nasal pressure transducers for detecting airflow limitation
Thermistors are temperature-sensitive transducers made of compressed sintered metal oxides (such as nickel, manganese, or cobalt) that change their resistance with temperature. They are commonly used to monitor airflow by detecting changes in temperature (cool air flows during inspiration and warm air flows during expiration). Thermistors are placed between the nose and mouth to record changes in electrical resistance.
Nasal pressure transducers, on the other hand, detect pressure changes during inspiration and expiration to monitor airflow. They respond very quickly to changes in pressure and hence do not suffer from the slow response time associated with thermistors. This fast response time allows nasal pressure transducers to display subtle changes in airflow, such as those associated with RERAs and flow limitation, which thermistors cannot detect.
The slow response time of thermistors due to their thermal mass is a significant disadvantage. The waveforms produced by thermistors are a smoothed average of the actual changes in airflow temperature that occur as the patient inhales and exhales. This means that subtle changes in airflow, such as those associated with RERAs, cannot be detected by thermistors.
Studies have shown that nasal pressure transducers have higher sensitivity than thermistors in detecting hypopneas and diagnosing sleep-disordered breathing in both adults and children. In a study comparing thermistors to nasal prong pressure (NPP), it was found that more events were nearly always detected using NPP compared to thermistors.
In conclusion, thermistors are less sensitive than nasal pressure transducers for detecting airflow limitation due to their slow response time and inability to detect subtle changes in airflow. Nasal pressure transducers are better suited for detecting subtle changes in airflow and have higher sensitivity in detecting hypopneas and sleep-disordered breathing.
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Thermistors are more expensive than conventional thermocouples
Thermistors and thermocouples are both temperature sensors used to monitor airflow by detecting changes in temperature. Thermistors are temperature-sensitive transducers made of compressed sintered metal oxides that change their resistance with temperature. Thermocouples, on the other hand, are composed of dissimilar metals that generate a voltage difference when exposed to different temperatures.
Thermistors are generally more expensive than conventional thermocouples due to their external power source and circuitry. While thermistors can be more accurate and sensitive to temperature changes, they are limited by their temperature range, typically ranging from -50°C to 300°C. They are also less durable and may not be suitable for harsh environments.
Thermocouples, on the other hand, are more durable and versatile. They can withstand high-vibration and corrosive conditions, and they have a wider temperature range, typically from -200°C to 1750°C. Thermocouples are self-powered, generating their own voltage signal, which eliminates the need for an external power source. This makes them more cost-effective and suitable for remote or inaccessible locations.
When choosing between thermistors and thermocouples, it is important to consider the specific requirements of the application. Thermistors are ideal for applications that require high accuracy and sensitivity in temperature monitoring, such as in life safety applications like fire detectors and thermometers. Thermocouples, on the other hand, are more commonly used in industrial settings due to their durability and lower cost. They are widely used in various industries, including furnaces, ovens, and temperature measurement in high-temperature environments.
In the context of sleep scoring, both thermistors and nasal pressure monitoring (NPM) techniques are used to detect respiratory events during sleep. Thermistors have traditionally been used to determine airflow during polysomnographic studies (PSG), but they have low accuracy in detecting hypopneas. NPM, on the other hand, responds quickly to changes in pressure and provides accurate waveforms that represent air pressure changes associated with breathing.
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Frequently asked questions
A thermistor is a temperature-sensitive transducer made of compressed sintered metal oxides that exhibit a negative temperature coefficient, meaning their resistance decreases as temperature increases.
Pflow, or NPP, is short for nasal prong pressure. It is a more sensitive method for detecting respiratory events during sleep compared to thermistors.
Thermistors and pflow, or NPP, work together to score sleep by detecting changes in temperature and pressure, respectively. While thermistors are good at detecting complete airflow cessation (apnea), pflow provides quantitative measures of airflow for hypopnea detection.
