Fast Response Humidity Sensor Research Articles

A fast response humidity sensor based on MXene-SWCNTs for the monitoring of respiration

Two-dimensional materials have attracted great interest in humidity sensing due to their excellent sensitivity and response time. Herein, we propose a humidity sensor consisting of MXene and single-walled carbon nanotubes (SWCNTs), using the Marangoni effect to self-assemble two-dimensional materials on the liquid surface, and then preparing them on the interdigital substrate through the layer-by-layer dip-coating method. Due to the expanded interlayer spacing of MXene and more exposed hydrogen active sites provided by SWCNTs, the sensor showed an excellent dynamic property with the response and recovery time of 2 s and 1.75 s Besides, the sensitivity is 0.53 pF/% RH (10–60% RH) and 7.6 pF/% RH (60–90% RH), the maximum humidity hysteresis is 6% of full scale (60% RH), and the reproducibility is ＞200cycles. Then, a flexible humidity breathing detection system has been developed based-on the sensor. Result demonstrated that it can detect human respiration and be successfully used to distinguish different human respiratory patterns. This work not only optimizes the dynamic property of sensors, but also provides a solution for the production of high-performance flexible humidity monitoring systems on this basis.

Fast-response humidity sensors based on all-inorganic lead-free Cs2PdBr6 perovskite integrated with bulk acoustic wave resonators for motions monitoring

Halide perovskites have arisen extensive concerns due to their distinguished achievements in optoelectric fields. However, the intrinsic toxicity of lead and instability have limited their applications in humidity sensing. Herein, all-inorganic lead-free Cs2PdBr6 perovskite incorporated with a bulk acoustic wave resonator for humidity detection is demonstrated for the first time. The proposed sensor exhibits faster response and recovery speed than most other perovskite-based humidity sensors, indicating its potential utilization in real-time monitoring of body movements. Apart from that, the perovskite-based sensor shows remarkable logarithmic linearity response as well as superior repeatability and stability in the relative humidity range of 11%-85%. Owing to its fast response and good stability, the sensor is successfully applied in finger movements monitoring, suggesting the potential of application in human–machine interactions. Furthermore, the underlying sensing mechanism of the sensor is analyzed by the Langmuir adsorption model and density functional theory. Therefore, above results have demonstrated the feasibility of perovskite for humidity detection and more perovskites with similar structures could be also be utilized for further exploration.

High-Sensitivity and Fast-Response Humidity Sensor Based on a Simple Fiber-Tip Interferometer With Thin Agarose Gel Coating

High-Sensitivity and Fast-Response Humidity Sensor Based on a Simple Fiber-Tip Interferometer With Thin Agarose Gel Coating

Fast response humidity sensor based on hyperbranched zwitterionic polymer for respiratory monitoring and non-contact human machine interface

Non-contact humidity sensing is a prospective method for gathering biomedical information and realizing the non-screen-contact human–machine interaction. However, humidity sensors with both fast response and recovery are still considered a significant challenge. This study proposes to develop a humidity sensor based on hyperbranched zwitterionic polymer (PTS). The sensors are featured with fast response and recovery (3 s/3 s) as well as outstanding repeatability in the range of 11%-98% RH. The excellent sensing performance of PTS benefits from the rational regulation of molecular interactions. LiCl is then employed to dope the PTS to fabricate PTS/LiCl composite sensitive materials. The introduction of conductive ions further improves the sensing performance, and the modified humidity sensor exhibits an ultrafast response (0.2 s). The PTS/LiCl sensors demonstrate robust long-term stability and good anti-interference capability. Sensors are also developed into masks for respiratory status monitoring. A gesture monitoring keyboard is constructed by integrating sensor array panels with control circuits to recognize non-contact gestures. The results prove that hyperbranched zwitterionic polymers offer a promising perspective as humidity sensing materials for the application of biomedical monitoring and human machine interfaces (HMI).

Fast response humidity sensor based on chitosan/graphene oxide/tin dioxide composite

In this paper, Chitosan(CS)/graphene oxide(GO)/SnO2 composite is proposed as the sensing material of an impedance-type humidity sensor. The composite was synthesized via a facile solution mixing method. And it was formed by adding CS and SnO2 to GO aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FT-IR) were executed to characterize the structure and morphology of the composite. At room temperature, the CS/GO/SnO2 composite shows more favorable humidity-sensing properties compared with the CS, CS/GO, and CS/SnO2 material. The resulted sensor exhibits high response (72683%), high sensitivity (402.5 kΩ/%RH), rapid response and recovery time (8 s/8 s). Moreover, small humidity hysteresis value (<7%) under maximum impedance difference, good repeatability and long-term stability are demonstrated. Therefore, the CS/GO/SnO2 composite is a promising candidate for humidity sensing.

Polypyrrole/reduced graphene oxide composite as a low-cost novel sensing material for fast-response humidity sensor

In this study, the polypyrrole/reduced graphene oxide (PrGO) composites' ability to detect humidity was investigated. Polypyrrole (PPy), a chemically produced oxidative polymer, was physically blended, for these observations in accordance with the feeding mass ratio of reduced graphene oxide (rGO). The Hummers process is utilized to produce graphene oxide (GO), which is then quickly and easily reduced to rGO by adding a small amount of selenium power. To determine the functional and morphological characteristics of the produced PrGO composites XRD, FTIR, RAMAN, SEM, and TEM characterisations were performed. To know about the humidity sensing performances, The thin film of PPy, Polypyrrole/Graphene oxide (PGO), and PrGO composites were prepared by wedging the sample on a basic glass plate using a low-cost spin coating approach. Among all the samples prepared, the PrGO composite demonstrated a sensing response of 99.99%, with a quick response and recovery time of 2 s and 4 s, respectively. The ideal characteristics such as high real sensitivity, lower limits of detection (LOD), minimal hysteresis, and perfect stability were established by PrGO composite. When compared to PPy and PGO composite, the physical properties of PrGO composite have significantly improved, including porosity, water content, and degree of swelling compare to other samples. A detailed discussion of the humidity sensing system has been made.

Renewable and fast response humidity sensors based on multiple construction of water graftable molecules highly sensitive surface

It is a challenge to solve the performance regeneration and reuse of humidity sensor. This paper presents a new strategy to effectively solve the performance regeneration of humidity sensors. A humidity sensor featuring high sensitivity and fast response is obtained by adsorption of the bipyridyl ruthenium molecule (N3) on the TiO2 film on the surface of interdigital electrode (IDE) to form a humidity-enhanced sensing material. At 11% to 97% RH, the impedance value is changed by over 2 orders of magnitude, with a fast response time of 5 s and a recovery time of 8 s as well as relatively small hysteresis (2.09%). Meanwhile, through continuous multiple erase/re-sensing techniques, the humidity sensor performance is regenerated up to 30 cycles with no significant change in sensor performance. The humidity sensing mechanism of this sensor is investigated utilizing impedance spectroscopy, which reveals the unique humidity sensing mechanism of TiO2/N3 humidity sensor. Compared with general sensors, the biggest advantage of the humidity sensor designed in this paper is that it can regenerate the performance of the sensor and the idea and technology of this work can also be applied to other sensor fields.

Biopolymer Derived Thin Carbon Film As a Novel Sensing Material for Low-Cost Resistive and Fast-Response Humidity Sensors

Introduction Recently, fast response humidity sensors are an active area of research for applications such as industrial, agricultural and point of care devices. Among various types of humidity sensor materials, thin film based resistive humidity sensors have been actively studied because those exhibit high surface area and the sensor configuration is simple. However, most of these sensors are relatively slow with long response time (over 60 seconds) and narrow detection limits (30-50 RH%), making them difficult to use in many applications [1-2]. Besides, the need of an external heater for fast response increases power consumption and complicates the manufacturing process of the sensor. Functionalized graphene, the most popular humidity sensor material, offers significant advantages due to its unique 2D structure and oxygen-containing functional groups, providing a large surface reaction site. However, it also has limitations such as poor stability in a moist environment due to its hydrophilic nature and weak adhesion with the substrate, complex synthesis procedure, makes it difficult to develop practical sensing devices.Here, we developed the low-cost and fast-response humidity sensors by integration of thermally decomposed carbon (TDC) thin film and carbon nano-sized interdigitated electrodes (IDEs). Carbon IDEs were used as a sensor platform due to its excellent thermal compatibility with TDC films and it provides low-cost wafer-level fabrication of three-dimensional nanoelectrodes [3], resulting in the miniaturized sensor configuration at a wafer level. Shellac, a low-cost biopolymer, was used as a precursor for synthesizing TDC films via single-step pyrolysis. The obtained film showed conformal coating with no grain boundaries or defects and formed high sp2 hybridized carbon network on the carbon nano-sized IDEs, thus providing excellent stability, rapid response/recovery and low power consumption as a room temperature humidity sensor. Our results demonstrate the potential application of TDC film as an alternative sensing material for environmental humidity, instant calibration for gas sensing measurements and human respiration in real time. Methods We integrated a nanometer-thick TDC film onto the carbon nano-IDEs, using two-step process, to facilitate a simple and cost-effective humidity sensor. Firstly, microscale interdigitated polymer patterns were fabricated using photolithography and then pyrolyzed into nanoscale carbon IDEs due to volume reduction in pyrolysis. The interdigitated carbon nanoelectrodes were annealed at 1000 °C using a rapid thermal annealing process to enhance the electrical conductivity. The next step is the integration of a TDC film on the carbon IDEs. For that, shellac solution (4 wt.%) was uniformly spray-coated on the carbon IDEs and air-dried (1 hour). This shellac film was pyrolyzed at 600 °C to obtain a uniform TDC thin film. Results and Conclusions Figure a shows a scanning electron microscopy (SEM) image of the TDC coated nano-sized carbon IDEs (width = 800 nm, height = 300 nm, gap = 2.5 μm). The film displays a conformal coating with no signature of defects or grain boundaries. The electrical properties of TDC film were evaluated using a two-probe I-V technique (Figure b), which indicated the excellent ohmic contact with carbon IDEs. Raman spectra of the TDC film (Figure c) indicated the presence of local intrinsic defects and disorder (intense D band) due to the presence of oxygen functional groups, especially at the edges and basal plane of the TDC film. X-ray photoelectron spectroscopy (XPS) for carbon (Figure d) also confirmed the presence of oxygen-containing functional groups (C-OH and C=O) and a high sp2 hybridized carbon network. Higher dynamic response (40 %) is attributed to the presence of oxygen functional groups (Figure e), whereas sp2 carbon network induce hydrophobicity, which lowers the condensation of water molecules without using any external heating source, resulted in fast response (37s) and recovery time (8s) (Figure f), compared to previously reported rGO-based sensors [4]. The obtained thin film humidity sensor also displayed the linear response over the wide humidity range (10-90 RH%), with high sensitivity > 0.7/RH%. The dynamic response of the sensor revealed that the protonic conduction mechanism is dominant in TDC film.

High sensitive and fast response humidity sensor based on polymer composite nanofibers for breath monitoring and non-contact sensing

A rapid and stable polymeric humidity sensor is demonstrated using electrospun sulfonated poly (ether ether ketone)/polyvinyl butyral (SPEEK/PVB) composite nanofiber and applied in breath monitoring and non-contact sensing for the first time. First, SPEEK was fabricated into thin film sensor by drip casting and nanofiber sensor by electrospinning, respectively. By comparing the humidity sensing characteristics of the two sensors, it is found that the hysteresis and response/recovery time of the nanofiber humidity sensor have been significantly improved. To further improve its sensing performance, we incorporated different contents of polyvinyl butyral (PVB) to the electrospinning solution to prepare SPEEK/PVB composite nanofiber humidity sensors. The morphology and diameter of nanofibers with different PVB contents were observed by Scanning Electron Microscope. The composite nanofiber humidity sensor exhibited high sensitivity, wide working range of relative humidity, small hysteresis (2.68 %), fast response time (<1 s), rapid recovery time (5 s) and stable sensing performance when the ratio of SPEEK to PVB is 1:3. In addition, the breath monitoring and non-contact sensing performance of SPEEK/PVB = 1:3 composite nanofiber humidity sensor was also studied. This work indicates that electrospun SPEEK/PVB nanofibers have good application prospects as humidity sensors for real-time humidity monitoring and non-contact sensing devices.

Fast response humidity sensor based on graphene oxide films supported by TiO2 nanorods

This paper suggests a novel humidity sensor based on graphene oxide sensing film supported by TiO2 nanorods which are grown between Au electrodes via hydrothermal method. The supported structure allows water molecules to pass through TiO2 nanorods and spread to the lower surface of the sensing film, which increases the utilization of the lower surface of graphene oxide (GO) film for humidity detection. Hence, water molecules can diffuse rapidly on both sides of GO film, which will assist in reducing the response time of the sensor. The SEM morphology characterization shows that the supported structure is feasible, and the response curve proves that the response speed of the humidity sensor is improved. The complex impedance spectra (CIS) results are utilized to analyse the response characteristics of the sensor at low humidity level.

High-Precision Humidity Sensor Response Time Measurement Based on the Switchable Chamber With the Hydrophobic Interface

A high-precision humidity response time measurement has been urgently needed for the fast response humidity sensor in some special situations, for instance, when the quadcopter performs the meteorological observations in the atmospheric boundary layer, the relative humidity changes drastically as it flies into the cloud. So it is essential to gain the accurate response time for these sensors. However, owing to the uncontrollable errors, the conventional methods are difficult to carry out an accurate measurement. Herein, for meeting the requirements above, we designed an accurate measurement method based on a type of switchable chamber and a humidity generator. Among, the chamber was designed through surface molecular dynamics analysis and verified by experiments. It is proved that the switchable chamber with the hydrophobic surface and low water molecule content, combined with the surface to volume ratio S/V = 0.2 can achieve the realistic humidity response time of the sensor. For a commercial sensor (SHT20) at 25 °C, the time corresponding to the 63% and 90% complete responses are 7 s and 49 s measured in this way, which is extraordinarily improved than those traditional ways (51 s and 140 s). As a result, this measurement method could gain the accurate response time for the special situation applications.

Biopolymer Derived Thin Carbon Film As a Novel Sensing Material for Low-Cost Resistive and Fast-Response Humidity Sensors

Introduction Recently, fast response humidity sensors are an active area of research for applications such as industrial, agricultural and point of care devices. Among various types of humidity sensor materials, thin film based resistive humidity sensors have been actively studied because those exhibit high surface area and the sensor configuration is simple. However, most of these sensors are relatively slow with long response time (over 60 seconds) and narrow detection limits (30-50 RH%), making them difficult to use in many applications [1-2]. Besides, the need of an external heater for fast response increases power consumption and complicates the manufacturing process of the sensor. Functionalized graphene, the most popular humidity sensor material, offers significant advantages due to its unique 2D structure and oxygen-containing functional groups, providing a large surface reaction site. However, it also has limitations such as poor stability in a moist environment due to its hydrophilic nature and weak adhesion with the substrate, complex synthesis procedure, makes it difficult to develop practical sensing devices.Here, we developed the low-cost and fast-response humidity sensors by integration of thermally decomposed carbon (TDC) thin film and carbon nano-sized interdigitated electrodes (IDEs). Carbon IDEs were used as a sensor platform due to its excellent thermal compatibility with TDC films and it provides low-cost wafer-level fabrication of three-dimensional nanoelectrodes [3], resulting in the miniaturized sensor configuration at a wafer level. Shellac, a low-cost biopolymer, was used as a precursor for synthesizing TDC films via single-step pyrolysis. The obtained film showed conformal coating with no grain boundaries or defects and formed high sp2 hybridized carbon network on the carbon nano-sized IDEs, thus providing excellent stability, rapid response/recovery and low power consumption as a room temperature humidity sensor. Our results demonstrate the potential application of TDC film as an alternative sensing material for environmental humidity, instant calibration for gas sensing measurements and human respiration in real time. Methods We integrated a nanometer-thick TDC film onto the carbon nano-IDEs, using two-step process, to facilitate a simple and cost-effective humidity sensor. Firstly, microscale interdigitated polymer patterns were fabricated using photolithography and then pyrolyzed into nanoscale carbon IDEs due to volume reduction in pyrolysis. The interdigitated carbon nanoelectrodes were annealed at 1000 °C using a rapid thermal annealing process to enhance the electrical conductivity. The next step is the integration of a TDC film on the carbon IDEs. For that, shellac solution (4 wt.%) was uniformly spray-coated on the carbon IDEs and air-dried (1 hour). This shellac film was pyrolyzed at 600 °C to obtain a uniform TDC thin film. Results and Conclusions Figure a shows a scanning electron microscopy (SEM) image of the TDC coated nano-sized carbon IDEs (width = 800 nm, height = 300 nm, gap = 2.5 μm). The film displays a conformal coating with no signature of defects or grain boundaries. The electrical properties of TDC film were evaluated using a two-probe I-V technique (Figure b), which indicated the excellent ohmic contact with carbon IDEs. Raman spectra of the TDC film (Figure c) indicated the presence of local intrinsic defects and disorder (intense D band) due to the presence of oxygen functional groups, especially at the edges and basal plane of the TDC film. X-ray photoelectron spectroscopy (XPS) for carbon (Figure d) also confirmed the presence of oxygen-containing functional groups (C-OH and C=O) and a high sp2 hybridized carbon network. Higher dynamic response (40 %) is attributed to the presence of oxygen functional groups (Figure e), whereas sp2 carbon network induce hydrophobicity, which lowers the condensation of water molecules without using any external heating source, resulted in fast response (37s) and recovery time (8s) (Figure f), compared to previously reported rGO-based sensors [4]. The obtained thin film humidity sensor also displayed the linear response over the wide humidity range (10-90 RH%), with high sensitivity > 0.7/RH%. The dynamic response of the sensor revealed that the protonic conduction mechanism is dominant in TDC film.

Fast-response humidity sensor based on laser printing for respiration monitoring.

Respiration monitoring equipment has wide applications in daily health monitoring and modern medical diagnosis. Despite significant progress being made in humidity sensors for respiration monitoring, the fabrication of the humidity sensors with low-cost, simple manufacturing process and easy integration remains a challenge. This work reports a facile and inexpensive laser printing fabrication of PEDOT:PSS micron line as a humidity sensor for respiration monitoring. Laser printing technology can process any material into an arbitrary pattern. The PEDOT:PSS micron line humidity sensor has a fast response–recovery time (0.86 s/0.59 s), demonstrating excellent performance for real-time monitoring of human respiration. Furthermore, the PEDOT:PSS micron line humidity sensor can also monitor the respiration of rats under different physiological conditions along with the drug injection. The PEDOT:PSS micron line humidity sensor features simple manufacturing process with commercial materials, and easy integration with wearable devices. This work paves an important step in real-time monitoring of human health and further physiology and pharmacology study.

Drawn a facile sensor: A fast response humidity sensor based on pencil-trace

Developing a facile and low cost way for fabricating high performance humidity sensor is one of significant strategies to enhance its practical applications. The pencil-trace is emerging in novel electronic devices due to its excellent properties, low cost and facile fabrication method. Here, the commercial pencil is used to fabricate humidity sensor by drawing the sensing layer on the ceramic substrate with interdigital electrodes. It is found that the drawing times of pencil-trace on ceramic substrate strongly affect the conductivity of the sensing layer which is related to the humidity sensing properties of the sensor. The humidity sensor with good humidity sensing properties can be obtained by adjusting the drawing times. The impedance variation of the humidity sensor with drawing two times is about four orders of magnitude within the whole humidity range from 11% to 95% relative humidity at 100 Hz and the response time is as short as 1 s. The humidity sensor is of good linearity (R2 = 0.9913), small humidity hysteresis (3% RH) and long-term stability. Given the facile fabrication way, low cost and high performance, the humidity sensor based on pencil-trace may be of extensive and practical application values.

Black P/graphene hybrid: A fast response humidity sensor with good reversibility and stability

Black phosphorus (BP) materials have attracted considerable attention owing to their ultra-sensitive humidity sensing characteristics because of the natural absorption of water (H2O) molecules on the BP surface caused by the specific 2D layer-crystalline structure. On the other hand, the BP-based humidity sensor is less repeatable due to the instability of BP with water molecules and the stability of the sensor is reduced. In this study, this limitation of the BP-based humidity sensor was overcome by preparing a BP/graphene hybrid as a novel humidity sensing nanostructure. The BP/graphene interface improved the stability of the humidity sensor after a few weeks with a linear response within the relative humidity (RH) range of 15–70%. The sensor’s response/recovery speed of the humidity sensor was extremely fast within few seconds. The response (S) of the humidity sensor based on the BP/graphene hybrid is 43.4% at RH = 70%. The estimated response and recovery time of the sensor is only 9 and 30 seconds at RH = 70% at room temperature. The experimental investigation reveals that the BP/graphene hybrid not only improves the reversibility and hysteresis factors but also enhances the stability of the humidity sensor.

A facile and one step synthesis of W doped SnO2 nanopowders with enhanced humidity sensing performance

High sensitivity and fast response humidity sensor based W doped SnO2 nanopowders were prepared by hydrothermal method. The structural, morphological and optical properties of the films nanopowders were analysed by using powder X-ray diffraction (XRD), Transmission electron microscope (TEM), UV–Vis transmission spectra, Fourier transform infra-red spectra and photoluminescence spectra analysis. XRD results suggest that both pure and W doped samples had a tetragonal rutile type structure and the results are in good agreement with the standard JCPDS data (card no# 41-1445). The uniform distribution and well crystalline elongated spherical shaped rod like morphology was observed by TEM micrographs. UV and PL results confirmed the optical property of pristine SnO2 was significantly improved by W doping. Humidity sensor set up was fabricated and tested for relative humidity (RH) variation from 10 to 90%. The 10 wt% doped W sample showed high sensitivity fast response and recovery time as compared to other samples. The humidity sensing results showed that W–SnO2 can be used as active nanostructures for humidity sensors. The humidity sensing mechanism was also discussed in detail.

Rapid response and recovery humidity sensor based on CoTiO3 thin film prepared by RF magnetron co-sputtering with post annealing process

The fast-response humidity sensor based on CoTiO3 thin film was prepared by RF magnetron co-sputtering using TiO2 and Co2O3 targets followed by post-annealing process. The effects of annealing temperature and target sputtering power ratio on the preparation and humidity sensing properties of CoTiO3 films were thoroughly investigated. The results show that an annealing treatment is beneficial for the crystallization and (100) preferred orientation of CoTiO3 film. The sputtering power ratio of Co2O3 to TiO2 affects the phase composition and morphology of the films. The most sensitive CoTiO3 film with fastest response/recovery is prepared by employing co-sputtering power of 100W and 400W for Co2O3 and TiO2, respectively, as well as the post-annealing at 650°C for two hours. The sensitivity value of the as-prepared CoTiO3 film is 17.02 towards 95% RH, and the response/recovery time is as short as 1s. This fast response is attributed to (100) preferred orientation and the fine-established-net morphology.

Graphene quantum dots as a novel sensing material for low-cost resistive and fast-response humidity sensors

A room temperature graphene quantum dots (GQDs) based sensing material for relative humidity monitoring is presented. GQDs are synthesized by pyrolysis of citric acid and are deposited on a metallic interdigitated microelectrodes by drop-casting technology. GQDs are nanosheets around 20nm in average lateral size and an average height of 2.7±0.9nm. The response time is around few seconds and the sensitivity shows an exponential relation between 15 and 80% of RH, in resistive configuration device working at room temperature. The electrical changes as a function of the RH are related to the capillary condensation produced on the surface of the GQDs. Due to this physical behavior, a resistive path is formed between the microelectrodes and the condensed water vapor, and the resistivity of the system diminishes as the RH increases. A comparison on real time between the sensor developed and a commercial device corroborates the potential application of the novel sensor presented in this work.

A Method to Measure the Dynamic Characteristics of Microhumidity Sensors

The method of measuring the dynamic characteristics of microhumidity sensors is becoming a bottleneck in developing fast-response humidity sensors. This paper introduces a method for measuring the dynamic characteristics of microhumidity sensors. In this method, two environments with different relative humidity (RH1 and RH2) are established using different saturated aqueous solutions of salt. There is independent air circulation for each environment. These loops of air circulation are connected to the test cell, where the tested sensor is located. Air coming from the RH1 environment always flows over the tested sensor until the valves controlling the air circulation of the RH2 environment operate. Then, the air humidity of the test cell is quickly changed from RH1 to RH2. By decreasing the time needed to change the humidity of the air in the test cell, the response time of the tested sensor can be obtained more precisely. A prototype based on this method is built, and it is tested by measuring the dynamic behavior of a parallel plate capacitance humidity sensor based on polyimide. The analytical results show that the response time of the prototype is less than 250 ms. The response time of the prototype can be improved greatly by enhancing the response time of the subassemblies used in the prototype.

Novel Portable Device Measures Preoperative Patient Metabolic Gas Exchange

Indirect calorimetry (IC), the measurement of airway CO2 elimination (VCO2), O2 [corrected] uptake (VO2) [corrected], and respiratory exchange ratio (RER = VCO2/VO2), is a noninvasive modality for the assessment of body metabolism. In anesthesia, IC can signal critical events and onset of acute metabolic derangements. We have previously demonstrated the accuracy and precision of a new IC measurement system designed for mechanically ventilated patients, comprised of a new clinical bymixer, fast response humidity and temperature sensor, and a flowmeter. However, measurement of IC during spontaneous breathing is challenging because of unstable tidal volume, frequency, and functional residual capacity (FRC). A new device for IC measurements, designed specifically for spontaneous breathing, was validated against a metabolic lung simulator bench setup. In a second study, the same device was used to conduct preoperative measurements of VCO2 and VO2 in 15 patients. Our measurements showed excellent correlation and agreement with metabolic lung simulator values: The average (+/-SD) percent error for airway VCO2 was -4.7% +/- 3.31%; the average (+/-SD) percent error for airway VO2 was -0.30% +/- 5.25%. Average values of VCO2 and VO2 in the patient study (3.01 +/- 0.56 and 3.44 +/- 0.69 mL x kg(-1) x min(-1), respectively) were in agreement with previously reported values. We have shown that the new, portable bymixer-flow device, using a bymixer and a fast response humidity sensor, provided accurate and convenient bedside measurement of VCO2 and VO2. We believe that it can contribute in the future to preoperative assessment and baseline reference value for perioperative management.