Exhaled Concentration Research Articles

Influence of Long Pressure and Short Suction Ventilation Parameters on Air Flow Field and Dust Migration in Driving Face

A combination of similar tests and numerical simulation was used to study the distribution of the air flow field and the dust field in the driving face under the conditions of long pressure and short suction ventilation. The results show that the air flow field is divided into return, jet, and vortex zones. When the distance (L) is 1.6 m, the wind speed (Va) is 8 m/s, and the ratio of pumped air volume to pressure air volume (Q) is 0.8, the total and exhaled dust concentration (Td, Rd, Tp, and Rp) at the driver’s and pedestrian’s position were the lowest. According to the grey correlation analysis, the importance of factors affecting Td and Tp is ranked as L > Va > Q, Rd is ranked as Va > L > Q, and Rp is as follows: Va > Q > L. The increase in Va and the decrease in L have a significant effect on the expulsion of exhaled dust.

Could exhaled methane be used as a possible indicator for hemodynamic changes in trauma induced hemorrhagic shock? Scientific basis supported by a case study

IntroductionIdentification of severe blood loss and hemorrhagic shock in polytrauma patients poses a key challenge for trauma teams across the world, as there are just a few objective parameters, on which clinicians can rely. We investigated the relationship between exhaled air methane (CH4) concentration and blood loss in a polytrauma patient. Decreased blood flow in the superior mesenteric artery (SMA) is one of the first compensatory responses to blood loss. Gases produced by the anaerobic flora of the intestinal segment supplied by the SMA are the primary source of exhaled CH4, which diffuses through the intestinal microvessels into the circulation and is finally eliminated through the lungs. We hypothesized that diminution of exhaled CH4 indicates blood loss and tested our theory in a severely injured patient. MethodsExhaled CH4 concentrations of a severely injured patient were measured using a photoacoustic spectroscope (PAS) attached to the exhalation side of the breathing circuit. The primary objective was to investigate the relationship between exhaled CH4 and conventional indicators of hemorrhage including hemoglobin (Hb) levels, base deficit (BD) values and vital parameters (heart rate and systolic blood pressure) in the early phase of in-hospital care (first 4 h). ResultsA severely injured patient was admitted with unstable hemodynamic parameters and incomplete left lower limb amputation, (Injury Severity Score: 38, 74/36 mmHg, 76 bpm). At the time of arrival, considerably lower CH4 levels were detected (22,800 PAU) in the exhaled air. During the first 4 h fluid and massive blood resuscitation, the exhaled CH4 levels were continuously rising in parallel with Htc and Hb values. Corresponding to these changes, BD values displayed a decreasing tendency. DiscussionOur study was conducted to characterize the changes in exhaled air CH4 concentration in response to hemorrhagic shock and to provide data on a viable clinical use of an experimental technique. According to our results, the real-time detection of exhaled air CH4 concentration is an applicable and promising technique for the early detection of bleeding and hemorrhagic shock in severely injured patients. Further research on large sample size and refinement of the PAS technique is required.

Design of an electronic device for detection of exhaled gas concentration

Design of an electronic device for detection of exhaled gas concentration

Using the phase III slope of exhaled methane during a single breath DLCO test to assess ventilation heterogeneity

BackgroundThe Phase III slope from a single breath nitrogen washout test provides information about ventilation heterogeneity (VH) in the lungs. PurposeTo determine if the Phase III slope from the exhaled tracer gas concentration during a standard, single breath DLCO test using rapid gas analysis provides similar information about VH. Basic proceduresRetrospective analysis of clinical pulmonary function laboratory data including spirometry, lung volumes, and DLCO. The normalized Phase III slope from the exhaled CH4 concentration (SnCH4) was compared among different patterns of physiologic abnormality and with VA/TLC as an indicator of VH. Main findingsSnCH4 was the steepest in the group with “Obstruction and Low DLCO”, with significant differences between this group and the “Normal”, “Obstruction with Normal DLCO”, “Mixed Obstruction and Restriction” and “Isolated Low DLCO” groups. SnCH4 was steeper in current and former smokers compared to non-smokers. Among the entire study sample, SnCH4 correlated with VA/TLC (Spearman rho = −0.56, p < 0.01) and remained a significant determinant of VA/TLC by regression modeling. Principal conclusionsThe SnCH4 derived from a standard, single breath DLCO test using rapid gas analysis varied among distinct patterns of physiologic abnormalities and was associated with VA/TLC as a measure of VH.

Fractional exhaled nitric oxide in idiopathic pulmonary arterial hypertension and mixed connective tissue disease complicating pulmonary hypertension

BackgroundFractional exhaled nitric oxide (FeNO) has been extensively studied in various causes of pulmonary hypertension (PH), but its utility as a noninvasive marker remains highly debated. The objective of our study was to assess FeNO levels in patients with idiopathic pulmonary arterial hypertension (IPAH) and mixed connective tissue disease complicating pulmonary hypertension (MCTD-PH), and to correlate them with respiratory functional data, disease severity, and cardiopulmonary function.MethodsWe collected data from 54 patients diagnosed with IPAH and 78 patients diagnosed with MCTD-PH at the Shanghai Pulmonary Hospital Affiliated to Tongji University. Our data collection included measurements of brain natriuretic peptide (pro-BNP), cardiopulmonary exercise test (CPET), pulmonary function test (PFT), impulse oscillometry (IOS), and FeNO levels. Additionally, we assessed World Health Organization functional class (WHO-FC) of each patient.Results(1) The fractional exhaled concentration of nitric oxide was notably higher in patients with IPAH compared to those with MCTD-PH. Furthermore, within the IPAH group, FeNO levels were found to be lower in cases of severe IPAH compared to mild IPAH (P = 0.024); (2) In severe pulmonary hypertension as per the WHO-FC classification, FeNO levels in IPAH exhibited negative correlations with FEV1/FVC (Forced Expiratory Velocity at one second /Forced Vital Capacity), MEF50% (Maximum Expiratory Flow at 50%), MEF25%, and MMEF75/25% (Maximum Mid-expiratory Flow between 75% and 25%), while in severe MCTD-PH, FeNO levels were negatively correlated with R20% (Resistance at 20 Hz); (3) ROC (Receiving operator characteristic curve) analysis indicated that the optimal cutoff value of FeNO for diagnosing severe IPAH was 23ppb; (4) While FeNO levels tend to be negatively correlated with peakPETO2(peak end-tidal partial pressure for oxygen) in severe IPAH, in mild IPAH they had a positive correlation to peakO2/Heart rate (HR). An interesting find was observed in cases of severe MCTD-PH, where FeNO levels were negatively correlated with HR and respiratory exchange ratio (RER), while positively correlated with O2/HR throughout the cardiopulmonary exercise test.ConclusionFeNO levels serve as a non-invasive measure of IPAH severity. Although FeNO levels may not assess the severity of MCTD-PH, their significant makes them a valuable tool when assessing severe MCTD-PH.

Evaluating the Accuracy of Patient State Index for Measuring Anaesthetic Depth in Patients Undergoing Propofol-Sevoflurane Anaesthesia

Abstract Processed electroencephalographic indices such as the Patient State Index (PSi) have been proposed as a method of monitoring the depth of general anaesthesia. However, in order to establish the validity of PSi, it is necessary to compare its accuracy to other techniques, such as the isolated forearm technique (IFT). 30 ASA (American Society of Anaesthesiologists classification) I–III patients were administered standard propofol-sevoflurane anaesthesia with PSi monitoring. Before each dose of muscle relaxant, the forearm contralateral to the intravenous cannula was isolated for 30 minutes. PSi, hand movements, and exhaled sevoflurane concentrations were recorded during the induction of anaesthesia, intubation, throughout the surgical procedure, prior to extubation, and patients’ responses to commands were classified as positive or negative. The Brice questionnaire was used to assess intraoperative awareness after the patient regained consciousness. All patients completed the study without memory of the surgery or IFT commands, 53.3% of patients showed a response to IFT commands during intubation. PSi values ranged around 26 (23.5; 30) in IFT non-responders and 33.5 (26; 42) in responders (p = 0.15). The best cut-off value for PSi to predict IFT response was 55, with a sensitivity of 60% and specificity of 85.2%, which led to the conclusion that PSi is not a fully reliable tool for monitoring the depth of anaesthesia.

An ultra-small integrated CO2 infrared gas sensor for wearable end-tidal CO2 monitoring

Human physiological metabolic status can be obtained by monitoring exhaled CO2 concentration, but current CO2 sensors have disadvantages such as large size, high power consumption, and slow response time, which limit their application in wearable devices and portable instruments. In this article, we report a small size, good performance, and large range CO2 infrared gas sensor that integrates a high emissivity MEMS emitter chip, a high detectivity thermopile chip, and a high coupling efficiency optical chamber to achieve high efficiency optical-thermal-electrical conversion. Compared with typical commercial sensors, the size of the sensor can be reduced by approximately 80% to only 10mm×10mm×6.5mm, with the advantages of low power consumption and fast response speed. Further, a monitoring system for end-tidal CO2 concentration installed on a mask was developed using this sensor, and good results were achieved.

Origin of breath isoprene in humans is revealed via multi-omic investigations

Plants, animals and humans metabolically produce volatile isoprene (C5H8). Humans continuously exhale isoprene and exhaled concentrations differ under various physio-metabolic and pathophysiological conditions. Yet unknown metabolic origin hinders isoprene to reach clinical practice as a biomarker. Screening 2000 individuals from consecutive mass-spectrometric studies, we herein identify five healthy German adults without exhaled isoprene. Whole exome sequencing in these adults reveals only one shared homozygous (European prevalence: <1%) IDI2 stop-gain mutation, which causes losses of enzyme active site and Mg2+–cofactor binding sites. Consequently, the conversion of isopentenyl diphosphate to dimethylallyl diphosphate (DMAPP) as part of the cholesterol metabolism is prevented in these adults. Targeted sequencing depicts that the IDI2 rs1044261 variant (p.Trp144Stop) is heterozygous in isoprene deficient blood-relatives and absent in unrelated isoprene normal adults. Wild-type IDI1 and cholesterol metabolism related serological parameters are normal in all adults. IDI2 determines isoprene production as only DMAPP sources isoprene and unlike plants, humans lack isoprene synthase and its enzyme homologue. Human IDI2 is expressed only in skeletal-myocellular peroxisomes and instant spikes in isoprene exhalation during muscle activity underpins its origin from muscular lipolytic cholesterol metabolism. Our findings translate isoprene as a clinically interpretable breath biomarker towards potential applications in human medicine.

Octane in exhaled breath to diagnose acute respiratory distress syndrome in invasively ventilated intensive care unit patients.

The concentration of exhaled octane has been postulated as a reliable biomarker for acute respiratory distress syndrome (ARDS) using metabolomics analysis with gas chromatography and mass spectrometry (GC-MS). A point-of-care (POC) breath test was developed in recent years to accurately measure octane at the bedside. The aim of the present study was to validate the diagnostic accuracy of exhaled octane for ARDS using a POC breath test in invasively ventilated intensive care unit (ICU) patients. This was an observational cohort study of consecutive patients receiving invasive ventilation for at least 24 h, recruited in two university ICUs. GC-MS and POC breath tests were used to quantify the exhaled octane concentration. ARDS was assessed by three experts following the Berlin definition and used as the reference standard. The area under the receiver operating characteristic curve (AUC) was used to assess diagnostic accuracy. 519 patients were included and 190 (37%) fulfilled the criteria for ARDS. The median (interquartile range) concentration of octane using the POC breath test was not significantly different between patients with ARDS (0.14 (0.05-0.37) ppb) and without ARDS (0.11 (0.06-0.26) ppb; p=0.64). The AUC for ARDS based on the octane concentration in exhaled breath using the POC breath test was 0.52 (95% CI 0.46-0.57). Analysis of exhaled octane with GC-MS showed similar results. Octane in exhaled breath has insufficient diagnostic accuracy for ARDS. This disqualifies the use of octane as a biomarker in the diagnosis of ARDS and challenges most of the research performed up to now in the field of exhaled breath metabolomics.

A preclinical study on online monitoring of exhaled ciprofol concentration by the ultraviolet time-of-flight spectrometer and prediction of anesthesia depth in beagles

BackgroundExhaled air has been demonstrated as a reliable medium for monitoring propofol concentration. However, online monitoring of exhaled ciprofol have not been reported. MethodsThirty-six beagles undergoing mechanical ventilation were divided into 6 groups, including bolus injection of low (Group BL, n = 6), medium (Group BM, n = 6), and high dose of ciprofol (Group BH, n = 6) groups; as well as 1 h continuous infusion of low (Group IL, n = 6), medium (Group IM, n = 6), and high dose of ciprofol (Group IH, n = 6) groups. The ciprofol concentration in exhaled air (CE) was determined by the ultraviolet time-of-flight mass spectrometer (UV-TOFMS). The correlations of CE and plasma concentration (Cp), CE and the bispectral index (BIS) were explored. Additionally, the pharmacokinetics (PK) models of CE and Cp, the pharmacodynamics (PD) models of CE and BIS were also established. ResultsOnline monitoring of exhaled ciprofol can be achieved with the UV-TOFMS instrument. The CE of ciprofol in beagles was found at parts per billion by volume (ppbv) level. The linear correlation of CE and Cp was weak in bolus injection groups (R2 = 0.01) nonetheless moderate in continuous infusion groups (R2 = 0.53). The i.v. bolus PK model of CE and Cp can be fitted with the non-compartment models. Additionally, the the PD models of CE and BIS can be well fitted with the inhibitory sigmoid Emax model with the estimate values of IC50 = 0.05 ± 0.01 ppbv, γ = 4.74 ± 1.51, E0 = 81.40 ± 3.75, Imax = 16.35 ± 4.27 in bolus injection groups; and IC50 = 0.05 ± 0.01 ppbv, γ = 6.92 ± 1.30, E0 = 83.08 ± 1.62, Imax = 12.58 ± 1.65 in continuous infusion groups. ConclusionsOnline monitoring of exhaled ciprofol concentration in beagles can be achieved with the UV-TOFMS instrument. Good correlations can be observed between exhaled ciprofol concentration and its cerebral effects reflected by the BIS value, demonstrating the potential of exhaled ciprofol monitoring for titrating depth of anesthesia in future clinical setting.

Bed-level ventilation conditions in daycare centers

In Dutch daycare centers, most often, semi-enclosed beds are used in bedrooms. Given that air usually does not mix completely in a ventilated room, there are concerns about whether room-level ventilation would be enough to keep the air clean inside semi-enclosed beds. No studies into the bed-level ventilation conditions in daycare centers have been identified. Therefore, a field survey was performed in 17 Dutch daycare centers to collect bedroom ventilation conditions and occupants’ characteristics. Based on that information, a full-scale bedroom identical to that of typical daycare centers was constructed in a climate chamber. The bed-level ventilation conditions were investigated by examining the dispersion and inhalation of CO2 gas exhaled by a breathing thermal baby model while sleeping in a bed. The effect of three variables, i.e., sleep positions (supine, lateral-to-wall, lateral-to-corridor), baby ages (12- and 30-month-old), and ventilation rates (55 and 250 m3/h), were studied. The results showed that excess exhaled CO2 concentration was accumulated inside the semi-enclosed bed in most cases. This indicates that bed-level ventilation conditions are not sufficient enough when only relying on the room-level mixing ventilation mode. The inhaled CO2 concentration of infants sleeping inside the bed was remarkably high, on average, three times higher than the measured values in the room exhaust. The study provides knowledge on the bed-level ventilation conditions in miniature semi-enclosed sleeping spaces under a mixing ventilation mode at room level and highlights the need to improve the air quality inside the baby bed.

Quartz tuning fork (QTF) coating enhanced Mid-Infrared laser Induced-Thermoacoustic spectroscopy (LITES) for human exhaled methane detection

Human exhaled methane (CH4) has essential significance in detecting intestinal flora. In this study, a high-precision quartz tuning fork (QTF) based light-induced thermoelastic spectroscopy (LITES) system was developed, a mid-infrared interband cascade laser (ICL) and a QTF detector coated with polydimethylsiloxane (PDMS) and reduced graphene oxide (rGO) were employed for the CH4 detection. Experimental results indicate that the composite coating resulted in a 3-fold increase in 2f signal amplitude and signal-to-noise ratio (SNR), when compared to the bare QTF detector. The system has achieved a minimum detection limit (MDL) of 58.65 ppbv (part per billion volume) and a normalized noise equivalent absorption coefficient (NNEA) of 2.069 × 10−10 cm−1·W·Hz−1/2, Allan deviation analysis indicates that the optimal measurement accuracy is 36.85 ppbv. 24 healthy college students and 10 overweight/obese students were recruited to measure the CH4 concentration in the exhaled breath. The results show that exhaled CH4 concentrations of healthy individuals range from 0.5 to 3 ppmv (part per million volume), with slightly higher levels in males than females, and higher levels in the obese individuals than those in the normal individuals. The mid-infrared LITES CH4 measurement system holds promise as a new non-invasive method for assessing human metabolic states, with potential applications in medical and life sciences.

The effect of activity and face masks on exhaled particles in children.

Despite the high burden of respiratory infections among children, the production of exhaled particles during common activities and the efficacy of face masks in children have not been sufficiently studied. To determine the effect of type of activity and mask usage on exhaled particle production in children. Healthy children were asked to perform activities that ranged in intensity (breathing quietly, speaking, singing, coughing, and sneezing) while wearing no mask, a cloth mask, or a surgical mask. The concentration and size of exhaled particles were assessed during each activity. Twenty-three children were enrolled in the study. Average exhaled particle concentration increased by intensity of activity, with the lowest particle concentration during tidal breathing (1.285 particles/cm3 [95% CI 0.943, 1.627]) and highest particle concentration during sneezing (5.183 particles/cm3 [95% CI 1.911, 8.455]). High-intensity activities were associated with an increase primarily in the respirable size (≤ 5 µm) particle fraction. Surgical and cloth masks were associated with lower average particle concentration compared to no mask (P = 0.026 for sneezing). Surgical masks outperformed cloth masks across all activities, especially within the respirable size fraction. In a multivariable linear regression model, we observed significant effect modification of activity by age and by mask type. Similar to adults, children produce exhaled particles that vary in size and concentration across a range of activities. Production of respirable size fraction particles (≤ 5 µm), the dominant mode of transmission of many respiratory viruses, increases significantly with coughing and sneezing and is most effectively reduced by wearing surgical face masks.

A2M Serves as Promising Biomarker for Chronic Obstructive Pulmonary Disease.

Chronic obstructive pulmonary disease (COPD) often associated with cigarette smoking. However, increasing evidence suggests that non-smoking COPD is much higher than previously thought. This study aims to identify a nonsmoking COPD biomarker and examined its value in diagnosis and prediction of acute exacerbation. A total of 35 stable COPD patients, 70 acute exacerbation chronic obstructive pulmonary disease (AECOPD) patients and 35 healthy control subjects were included. Plasma α 2 macroglobulin (A2M) and matrix metalloproteinase-9 (MMP-9) levels were measured using the enzyme-linked immunosorbent assay (ELISA) method on all participants. Their association with clinical characteristics and lung function parameters were determined by regression analysis. Receiver operating characteristic (ROC) curve was used to determine the diagnostic sensitivity and specificity. Correlation coefficients were evaluated using Pearson's correlation. Plasma A2M concentration was decreased and MMP-9 concentration, MMP-9/A2M ratio were elevated in stable COPD patients compared with control groups. And MMP-9 expression was significantly higher in AECOPD patients. A2M level was increased in AECOPD patients with infection compared with those without. In addition, there was no statistical difference in A2M levels between smokers and nonsmokers COPD or healthy control subjects. Furthermore, A2M, MMP-9 and MMP-9/A2M were correlated with forced expiratory volume in one second (FEV1)%, FEV1/ forced vital capacity (FVC), CAT and mMRC score in COPD patients, but had no correlation with fraction of exhaled nitric oxide (FeNO) and concentration of alveolar nitric oxide (CaNO). A2M is altered in peripheral blood of COPD patients and correlated with severity and infection. Moreover, there was no significant correlation between the change in A2M and smoking, FeNO and CaNO, suggesting A2M may reflect the overall rather than local inflammation in COPD patients and serve as a potential biomarker for nonsmoking COPD patients.

Accurate evaluation of inhalation exposure based on CFD predicted concentration in the breathing zone towards personalized and smart control

Considering pollutants sourced from one's own exhaled air and skin as well as ambient air, this study adopts CFD technology to explore accurate evaluation method of inhalation exposure based on the pollutant concentration in the breathing zone. To do so, the concentration data extracted from the surfaces of mouth/nose openings and various sampling points close to mouth/nose openings is analyzed. The distribution of exhaled pollutants on one's own face is subsequently revealed and the re-inhalation ratio is quantified. If only point data is available (e.g., experimental context), the inhalation exposure to one's own exhaled pollutants can be evaluated based on the data at the center of the upper lip when inhaled through the mouth and at a location of 0.005 m away from the center of the nose openings when inhaled through the nose. If surface data is available (e.g., numerical context), the data on the whole mouth/nose openings should be used to evaluate the exposure. The distribution of exhaled pollutant concentration on one's own face changes periodically and asymmetrically over time. Based on the data obtained on face, the inhalation exposure to pollutants from one's own exhaled air would be underestimated. Depending on breathing mode, the re-inhalation ratio is mostly in a range of 0.3–1.0%. These findings can contribute to a more accurate evaluation of inhalation exposure and provide information for the development of personalized air quality control systems and smart wearable devices.

Results of Analysis of Volatile Organic Compound (VOC) Measurements Using Breath Analyzer on Coronavirus Disease 2019 (COVID-19) Confirmed Patients with Healthy People

Background/aim: The analysis of VOCs through respiration has been used for biomarker analysis for the detection of novel coronaviruses and has found mainly six VOCs by breath analysis by GC-IMS are ethanol, octane, acetone, cluster mixture of acetone/butanone and methanol. Previous research found exhaled methanol concentrations were lower in COVID-19 patients. The aim of this study was to analyze differences in VOC concentration in Covid-19 patients with healthy people. Methods: This Case Control study used 93 confirmed case samples of Covid-19 and 42 healthy people. Demographic and clinical data taken from anamnesis and/or medical records. VOC’s data of respiratory track are taken through the exhalation air in a bag and analyzed with breath analyzer. Statistical analysis was conducted using Mann-Whitney test. Results: VOC compound measured include CO2, C7H8, CH2O, NH4, TVOC, NO2, PM1.0, CO, NH3, and Acetone. Analysis between Covid-19 patients and healthy people showed significant differences in all VOC components CO2 (p=0,000), C7H8 (p=0,000), CH2O (p=0,000), NH4 (p=0,001), TVOC (p=0,000), NO2 (p=0,000), PM1.0 (p=0,000), CO (p=0,000), NH3 (P=0,000), Acetone (p=001). Logistic regression analysis was obtained no meaningful influence on each component of the VOC with covid/healthy people conditions of patients with components CO2 (p=1,000), C7H8 (p=1,000), CH2O (p=0,999), NH4 (p=1,000), TVOC (p=1,000), NO2 (p=1,000), PM1.0 (p=0,999), CO (p=0,999), NH3 (P=0,999), Acetone (p=1,000). Conclusion: There is a significant difference between the VOC results of confirmed COVID 19 patients and healthy people Keywords: breath analyzer, coronaviruses, COVID-19, healthy people, volatile organic component

Calibration and validation of ultraviolet time-of-flight mass spectrometry for online measurement of exhaled ciprofol.

Ciprofol (HSK 3486, C14H20O), a novel 2,6-disubstituted phenol derivative similar to propofol, is a new type of intravenous general anaesthetic. We found that the exhaled ciprofol concentration could be measured online by ultraviolet time-of-flight mass spectrometry (UV-TOFMS), which could be used to predict the plasma concentration and anaesthetic effects of ciprofol. In this study, we present the calibration method and validation results of UV-TOFMS for the quantification of ciprofol gas. Using a self-developed gas generator to prepare different concentrations of ciprofol calibration gas, we found a linear correlation between the concentration and intensity of ciprofol from 0 parts per trillion by level (pptv) to 485.85 pptv (R2 = 0.9987). The limit of quantification was 48.59 pptv and the limit of detection was 7.83 pptv. The imprecision was 12.44% at 97.17 pptv and was 8.96% at 485.85 pptv. The carry-over duration was 120 seconds. In addition, we performed a continuous infusion of ciprofol in beagles, measured the exhaled concentration of ciprofol by UV-TOFMS, determined the plasma concentration by high-performance liquid chromatography, and monitored the anaesthetic effects as reflected by the bispectral index value. The results showed that the exhaled and plasma concentrations of ciprofol were linearly correlated. The exhaled ciprofol concentration correlated well with the anaesthetic effect. The study showed that we could use UV-TOFMS to provide a continuous measurement of gaseous ciprofol concentration at 20 second intervals.

Towards an accurate CFD prediction of airflow and dispersion through face mask

Given the difficulty of experimental measurement of respiratory airflow and dispersion through a face mask, accurate numerical simulation is an important method to increase the understanding of the health effect of face masks and to develop high-performance ones. The objective of this study is to develop such an accurate modeling framework based on computational fluid dynamics (CFD) theory and method. For model validation, the flow characteristics through the face mask were tested experimentally, and the air speed and exhaled pollutant concentration in the breathing zone were measured with human subjects. The influence of gird division, time step size, and turbulence model on simulation accuracy were investigated. The result shows that the viscous resistance coefficient and inertial resistance coefficient of face masks (surgical masks) were 3.65 × 109 and 1.69 × 106, respectively. The cell size on the surface of face masks should not be larger than 1.0 mm; the height of the first layer cells near the face masks should not be larger than 0.1 mm; and the time step sizes discretizing the breathing and coughing periods should not be more than 0.01 s and 0.001 s, respectively. The results given by LES model show closer agreement with the experimental data than RANS models, with approximately 10% relative deviation for the air speed near the face mask. Overall, the SST k-ω model performs the best among the RANS models, especially for the air speed. The findings obtained form a CFD modeling framework for an accurate prediction of airflow and dispersion problems involving face masks.

In vitro model for investigating aerosol dispersion in a simulated COVID-19 patient during high-flow nasal cannula treatment.

The use of high-flow nasal cannula in the treatment of COVID-19 infected patients has proven to be a valuable treatment option to improve oxygenation. Early in the pandemic, there were concerns for the degree of risk of disease transmission to health care workers utilizing these treatments that are considered aerosol generating procedures. This study developed an in vitro model to examine the release of simulated patient-derived bioaerosol with and without high-flow nasal cannula at gas flow rates of 30 and 50 L/min. Aerosol dispersion was evaluated at 30 and 90 cm distances. Reduction of transmission risk was assessed using a surgical facemask on the manikin. Results indicated that the use of a facemask facilitated a 94-95% reduction in exhaled aerosol concentration at 30 cm and 22-60% reduction for 90 cm distance across both gas flow rates. This bench study confirms that this in vitro model can be used as a tool to assess the risk of disease transmission during aerosol generating procedures in a simulated patient and to test factors to mitigate the risk.

Analgesic efficacy of ultrasound-guided transversus abdominis plane block in dogs undergoing ovariectomy.

In medicine, the transversus abdominis plane (TAP) block has been shown as an effective method of analgesia in several surgical procedures. In this context, this prospective, randomized, blinded study aimed to evaluate the analgesic efficacy of TAP block, guided by ultrasound in female dogs submitted to ovariectomy. Therefore, 32 animals randomly assigned in two groups (n = 16) were used. Groups consisted of TAP block control (TBC) which received water injection (0.2 ml kg-1 point), and TAP block bupivacaine (TBB) which received bupivacaine (0.2 ml kg-1 point at 0.25%); both groups were submitted to four-point approach. Animals were pre-medicated with acepromazine (0.03 mg kg-1) and meperidine (2 mg kg-1) IM, propofol was used as anesthetic induction (3-5 mg kg-1) IV, and isoflurane was used to maintain. To standardize groups, the animals received a continuous infusion of remifentanil (0.2μg kg-1 min) and rocuronium (0.6 mg kg-1) IV in the intraoperative period. Variables measured were the heart and respiratory rates, blood pressure, temperature, peripheral oxyhemoglobin saturation, exhaled carbon dioxide concentration, exhaled isoflurane concentration, serum cortisol, analgesia, and sedation. Before the pre-anesthetic medication (Baseline) and 1, 2, 4, 6, and 8 h after extubation, pain and sedation were assessed using a numeric rating scale (NRS), Glasgow composite measure pain scale (GCMPS-SF), and sedation scale. Moreover, serum cortisol was measured at different moments. The results show that in the intraoperative period, there was no significant difference between groups. After surgery, in TBC, 13 out of 16 animals required analgesic rescue, whereas, in TBB, this occurred only in one animal. Regarding the measurement of serum cortisol, the TBC group showed a significant difference when compared to the baseline time in the traction of the first ovary (p < 0.0001), 2 h (p = 0.0441), and 8 h (p = 0.0384) after extubation. In TBB, cortisol showed a significant increase only in the traction of the first ovary and 2 h after extubation (p < 0.0001). The technique using ultrasound-guided TAP block in two points approach by hemiabdomen with 0.2 ml kg-1 bupivacaine 0.25% was effective in providing post-operative analgesia in dogs undergoing ovariectomy.