Background: Negative pressure wound therapy (NPWT) is an intensely investigated topic, but its mechanism of action accounts for one of the least understood ones in the area of wound healing. Apart from a misleading nomenclature, by far the most used diagnostic tool to investigate NPWT, the laser Doppler, also has its weaknesses regarding the detection of changes in blood flow and velocity. The aim of the present study is to explain laser Doppler readings within the context of NPWT influence. Methods: The cutaneous microcirculation beneath an NPWT system of 10 healthy volunteers was assessed using two different laser Dopplers (O2C/Rad-97®). This was combined with an in vitro experiment simulating the compressing and displacing forces of NPWT on the arterial and venous system. Results: Using the O2C, a baseline value of 194 and 70 arbitrary units was measured for the flow and relative hemoglobin, respectively. There was an increase in flow to 230 arbitrary units (p = 0.09) when the NPWT device was switched on. No change was seen in the relative hemoglobin (p = 0.77). With the Rad-97®, a baseline of 92.91% and 0.17% was measured for the saturation and perfusion index, respectively. No significant change in saturation was noted during the NPWT treatment phase, but the perfusion index increased to 0.32% (p = 0.04). Applying NPWT compared to the arteriovenous-vessel model resulted in a 28 mm and 10 mm increase in the venous and arterial water column, respectively. Conclusions: We suspect the vacuum-mediated positive pressure of the NPWT results in a differential displacement of the venous and arterial blood column, with stronger displacement of the venous side. This ratio may explain the increased perfusion index of the laser Doppler. Our in vitro setup supports this finding as compressive forces on the bottom of two water columns within a manometer with different resistances results in unequal displacement.

Sap exudation is the process whereby trees such as sugar (Acer saccharum Marsh.) and red maple (Acer rubrum L.) generate unusually high positive stem pressure in response to repeated cycles of freeze and thaw. This elevated xylem pressure permits the sap to be harvested over a period of several weeks and hence is a major factor in the viability of the maple syrup industry. The extensive literature on sap exudation documents competing hypotheses regarding the physical and biological mechanisms that drive positive pressure generation in maple, but to date, relatively little effort has been expended on devising mathematical models for the exudation process. In this paper, we utilize an existing model of Graf et al. (J Roy Soc Interface 12:20150665, 2015) that describes heat and mass transport within the multiphase gas-liquid-ice mixture in the porous xylem tissue. The model captures the inherent multiscale nature of xylem transport by including phase change and osmotic transport in wood cells on the microscale, which is coupled to heat transport through the tree stem on the macroscale. A parametric study based on simulations with synthetic temperature data identifies the model parameters that have greatest impact on stem pressure build-up. Measured daily temperature fluctuations are then used as model inputs and the resulting simulated pressures are compared directly with experimental measurements taken from mature red and sugar maple stems during the sap harvest season. The results demonstrate that our multiscale freeze-thaw model reproduces realistic exudation behavior, thereby providing novel insights into the specific physical mechanisms that dominate positive pressure generation in maple trees.

There is an elevated incidence of hypoxemia during the airway management of the morbidly obese. We aimed to assess whether optimizing body position and ventilation during pre-oxygenation allow a longer safe non-hypoxic apnea period (SNHAP).
Fifty morbidly obese patients were recruited and randomized for this study. Patients were positioned and preoxygenated for three minutes in the ramp position associated with spontaneous breathing without additional CPAP or PEEP (RP/ZEEP group) or in the reverse Trendelenburg position associated with pressure support ventilation mode with pressure support of 8 cmH2O and an additional 10 cmH2O of PEEP while breathing spontaneously (RT/PPV group) according to randomization.
The SNHAP was significantly longer in the RT/PPV group (258.2 (55.1) vs. 216.7 (42.3) seconds, p = 0.005). The RT/PPV group was also associated to a shorter time to obtain a fractional end-tidal oxygen concentration (FEtO2) of 0.90 (85.1(47.8) vs 145.3(40.8) seconds, p < 0.0001), a higher proportion of patients that reached the satisfactory FEtO2 of 0.90 (21/24, 88% vs. 13/24, 54%, p = 0.024), a higher FEtO2 during preoxygenation (0.91(0.05) vs. 0.89(0.01), p = 0.003) and a faster return to 97% oxygen saturation after ventilation resumption (69.8 (24.2) vs. 91.4 (39.2) seconds, p = 0.038).
In the morbidly obese population, RT/PPV, compared to RP/ZEEP, lengthens the SNHAP, decreases the time to obtain optimal preoxygenation conditions, and allows a faster resuming of secure oxygen saturation. The former combination allows a more significant margin of time for endotracheal intubation and minimizes the risk of hypoxemia in this highly vulnerable population.
NCT02590406, 29/10/2015.

Current protocols using liquid disinfectants to disinfect heat-sensitive hospital items frequently fail, as evidenced by the continued isolation of bacteria following decontamination. The contamination is, in part, due to biofilm formation. We hypothesize that mild positive pressure (PP) will disrupt this biofilm structure and improve liquid disinfectant/detergent penetration to biofilm bacteria for improved killing. Staphylococcus aureus biofilm, grown on polycarbonate coupons in the biofilm reactor under shear at 35 °C for 3 days, was treated for 10 min and 60 min with various dilutions of benzalkonium chloride without PP at 1 atmosphere (atm), and with PP at 3, 5, 7, and 10 atm. The effect on biofilm and residual bacterial viability was determined by standard plate counts, confocal laser scanning microscopy, and scanning electron microscopy. Combined use of benzalkonium chloride and PP up to 10 atm significantly increased biofilm killing up to 4.27 logs, as compared to the treatment using disinfectant alone. Microscopy results were consistent with the viability plate count results. PP improved disinfectant efficacy against bacterial biofilm. The use of mild PP is possible in many flow situations or if equipment/contaminated surfaces can be placed in a pressure chamber.

Drainage of a pleural effusion is done either by inserting an intercostal tube or by aspirating pleural fluid using a syringe. The latter is a time-consuming and labour-intensive procedure. The serious complications of pleural aspiration are the development of a pneumothorax and re-expansion pulmonary oedema. We describe an observation made during a pleural aspiration in a patient who was on positive pressure ventilation. We explain the physiological basis for the observation, the safety of the procedure and its potential to reduce complications by reviewing the literature. A 56-year-old Sri Lankan female patient with end-stage kidney disease presented with fluid overload and bilateral pleural effusions. She was found to have concurrent COVID pneumonia. The patient was on bilevel positive airway pressure, non-invasive ventilation when pleural aspiration was done. The pleural fluid drained completely without the need for aspiration, once the cannula was inserted into the pleural space. One litre of fluid drained in 15 min without the patient developing symptoms or complications. Positive pressure ventilation leads to a supra-atmospheric (positive) pressure in the pleural cavity. This leads to a persistent positive pressure gradient throughout the procedure, leading to complete drainage of pleural fluid. Pleural fluid drainage in mechanically ventilated patients has been proven to be safe, implying the safety of positive pressure ventilation in pleural fluid aspiration and drainage. It further has the potential to reduce the incidence of post-aspiration pneumothorax by reducing the pressure fluctuations at the visceral pleura. Re-expansion pulmonary oedema is associated with a higher negative pleural pressure during aspiration, and the use of positive pressure ventilation can theoretically prevent re-expansion pulmonary oedema. Positive pressure ventilation can reduce the re-accumulation of the effusion as well. We suggest utilizing positive pressure ventilation to assist pleural aspiration in suitable patients.

Beryllium is widely used in the manufacturing of precision instruments because of its high thermal and mechanical properties. However, because beryllium is expensive, and processing it generally uses subtractive manufacturing methods, the cost is high, the utilization rate of cutting the materials is low, and the processing is difficult. Additionally, it is extremely prone to cracking, brittle fracturing, and fracturing during the machining process. In this paper, a new method for manufacturing beryllium laser additives under a pressure atmosphere is proposed. Via the single-point and single-pass laser melting of beryllium materials in an inert gas (Ar) pressure atmosphere, the results of the experiments conducted in the pressure range of 1 to 30 bar indicated the following: (1) beryllium can absorb the laser and form a molten pool, and the contour area of the upper surface of the molten pool is approximately 80% of that of 304 stainless steel under the same energy input; (2) severe oxidation occurs on and near the molten pool surface under low pressure, and oxidation is eliminated when the pressure is increased; (3) as ambient pressure increases, the surface profile of the molten pool gradually exhibits an irregular shape, and the cracks on the surface of beryllium change from \"divergent\" to \"shrinkage\", which can eliminate cracking. At higher pressures, the \"small hole\" phenomenon in the molten pool disappears, forming a wide and shallow molten pool shape that is more conducive to stable deposition. The experimental results indicate that the laser-additive manufacturing of beryllium in a pressure atmosphere is a meaningful developmental direction for beryllium processing in the future.

In patients with extrinsic tracheal stenosis caused by a mediastinal mass, an airway stent is a palliative measure to relieve airway obstruction. However, the self-expanding force of the stent may be insufficient to force a rigid stenosis. Our goal was to report a simple strategy to indirectly estimate the rigidity of the stenosis and predict airway patency after inserting the stent. Before the procedure, the inspiratory and expiratory flows and their ratio were evaluated under spontaneous breathing and after positive pressure ventilation generated by a facial mask. In patients with stenosis successfully treated with a stent (n = 11), we found significant changes in expiratory (2.3 ± 0.7 vs 2.8 ± 0.7; p = 0.03) and inspiratory (1.5 ± 0.6 vs 2.5 ± 0.9; p = 0.001) flows and a reduction of their ratio (1.4 ± 0.3 vs 1.1 ± 0.2; p = 0.01) whereas no significant changes were observed in patients (n = 2) whose stent failed to force the stenosis. In these cases, a tracheostomy was performed to assure ventilation. Our simple strategy may help physicians predict airway patency after stenting or plan alternative treatments in patients with rigid stenosis difficult to force by stenting.

Two orotracheal extubation techniques are described in the literature: the traditional technique and the positive-pressure technique. Although prior studies reported better clinical outcomes with the positive-pressure extubation technique, its superiority has not been extensively studied yet. This study was to determine whether the positive-pressure orotracheal extubation technique, compared with the traditional orotracheal extubation technique, reduces the incidence of major postextubation complications (up to 60 min) in critically ill adult subjects.
This was a multi-center randomized clinical trial. Subjects age > 18 y, requiring invasive mechanical ventilation through an endotracheal tube, who met the orotracheal extubation criteria were included and randomized to traditional extubation group (removing the endotracheal tube by applying continuous endotracheal suctioning during the entire procedure) or positive-pressure group (application of pressure support mode at 15/10 cm H2O during cuff deflation and extubation). The primary measure was postextubation major complications, defined as the clinical evidence of at least one of the following: desaturation, upper-airway obstruction, or vomiting.
A total of 725 subjects was randomly assigned to the traditional extubation group (n = 358) and positive-pressure group (n = 367). Seventeen subjects were eliminated and not included in the per-protocol analysis. Of 708 subjects, 185 (26.1%) developed at least one major complication. The incidence was 27.8% (96/345) in the traditional group compared with 24.5% (89/363) in the positive-pressure group. No statistically significant differences were observed between the 2 groups (absolute risk 3% [95 CI -3 to 10]; relative risk, 0.88 [95 CI 0.69-1.13], P = .32).
Despite the trend toward the positive-pressure group, no statistically significant differences were observed. Our findings agree with the literature in that positive-pressure extubation is a safe procedure; therefore, both techniques may be used during extubation in critically ill adult patients.

One of critical technologies in a non-invasive positive airway pressure respirator is to output the airflow for meeting the requirement of respiratory patient in breath. In order to develop a safe and reliable blower driving system, a circuit based on the special chips MC33035 and MC33039 was designed. The linear relationship between the input control voltage and the output air flow was achieved. This designed circuit will be embedded in the non-invasive ventilator system as a module. And based on this circuit, the secure and controllable ventilation flow can be performed.

COVID-19 has caused a huge impact on people\'s daily life and has made great damage on national economy. All the epidemic situation not only require the improvement of medical science, but also the corresponding auxiliary research field, e.g. the improve of protective clothing for medical use (MUPC). Developing a new kind of MUPC with portable cooling devices to improve medical workers\' thermal comfort and protection performance of MUPC is imminent. In this paper, an integrated MUPC with a portable vortex tube cooling device was studied with experimental method. In a phytotron, a manikin wearing the MUPC was experimentally studied in terms of the influence of environment temperature and cool air supply conditions. On the basis of experiments, the MUPC inside air temperature and relative humidity, skin temperature of human body was studied with simulation method. Overall thermal sensation vote (TSV) and local TSV of human body were calculated, based on simulation results, to evaluate human thermal sensation. The results showed that, first, 50 L/min cool air flowrate with 18-20 °C supply temperature can create a good MUPC inside thermal sensation environment, for both head supply and body supply conditions. Both body supply condition and head supply condition cannot create a uniform MUPC inside thermal sensation environment. Second, MUPC inside air relative humidity is around or lower than 60% for most body parts, except for air supply position and body parts that air is difficult to reach. Thirdly, with cool air supplied into MUPC, a micro-positive pressure environment can be obtained, and the protection performance of MUPC can be improved.