Generation Of Positive Pressure Research Articles

Experimental and computational comparison of freeze-thaw-induced pressure generation in red and sugar maple.

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 etal. (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.

Testing positive pressure delivered from commercial and WHO-style pediatric bubble CPAP devices

Background/aimLow-cost commercial bCPAP devices have been deployed in resource-limited settings to treat neonatal respiratory failure. The use of these devices has increased access to pediatric respiratory support for infants. However, constrained resources may result in substitution of recommended consumables and/or use in older age groups. We hypothesized that commercially available bCPAP devices, the standard WHO-style device and various improvised adaptations would all generate effective, safe positive pressure at the patient interface.MethodsPerformance of 2 commercially available bCPAP devices was tested against the standard WHO-style bCPAP device, as well as several improvised modifications of these devices, by measuring positive pressure delivered at the patient interface. Variables tested included different flow rates, patient interfaces and respiratory circuit tubing.ResultsBoth commercial devices utilized according to manufacturer recommendations generated the expected positive pressure at the patient interface. When testing the recommended WHO-style bCPAP device with recommended materials as well as other improvised modifications, we found variable and potentially unpredictable generation of positive pressure at the patient interface.ConclusionsModified or improvised bCPAP devices should be used with extreme caution as the support provided may be more or less than expected depending on respiratory tubing and flow rates employed. Our data support the effectiveness of bCPAP in newborns and young infants. But, to our knowledge, there are no bCPAP patient interfaces for older children effective with low liter flow devices. Therefore, based on these results, we recommend against using WHO-style bCPAP devices for non-infant patients with respiratory failure and instead recommend using standard oxygen therapy with nasal cannulae or face-masks, as well as early consideration of transfer to a higher level of care.

Inspiratory muscle activation via ventral lower thoracic high-frequency spinal cord stimulation.

In animals, high-frequency spinal cord stimulation (HF-SCS) applied on the ventral epidural surface at the T2 level results in negative airway pressure generation consistent with inspiratory muscle activation. In the present study, in anesthetized dogs, we found that ventral HF-SCS (500 Hz) applied at all thoracic levels resulted in negative airway pressure generation. In the region of the lower thoracic spinal cord, negative airway pressure generation was most pronounced at the T9 level. At this level, airway pressure generation was monitored: 1) during ventral HF-SCS over a wide range of stimulus amplitudes (0.5-15 mA) and frequencies (50-1,000 Hz) and 2) following spinal sections at C8 (to assess potential diaphragm activation) and subsequently at T6 (to assess potential intercostal muscle activation). The application of low stimulus currents between 1 and 2 mA and high stimulus frequencies (>300 Hz) resulted in the development of large negative airway pressure generation. Stimulation with 1 mA, 500 Hz resulted in a highest negative airway pressure generation of 47 ± 2 cmH2O. Increasing stimulus current was associated with progressive reductions in the magnitude of negative airway pressure generation. HF-SCS (500 Hz) with 15 mA resulted in a negative airway pressure generation of 7 ± 3 cmH2O. C8 section markedly reduced negative airway pressure generation, and subsequent T6 section resulted in positive airway pressure generation after HF-SCS. Our results indicate the existence of pathways with connections to both the phrenic and inspiratory intercostal motoneuron pools in the ventral part of the lower thoracic spinal cord. We speculate that the circuits mediating the previously described excitatory intercostal-to-phrenic reflex mediate the observed responses. NEW & NOTEWORTHY This study suggests that, in contrast to dorsal high-frequency spinal cord stimulation at the T9 spinal level, which results in positive pressure generation, ventral high-frequency spinal cord stimulation at the same spinal level results in large negative airway pressure generation with low stimulus currents. This method, therefore, may provide an alternative method to restore ventilation in ventilator-dependent spinal cord-injured patients.

High-flow nasal cannula therapy for adult patients.

High-flow nasal cannula (HFNC) oxygen therapy has several physiological advantages over traditional oxygen therapy devices, including decreased nasopharyngeal resistance, washing out of the nasopharyngeal dead space, generation of positive pressure in the pharynx, increasing alveolar recruitment in the lungs, humidification of the airways, increased fraction of inspired oxygen and improved mucociliary clearance. Recently, the use of HFNC in treating adult critical illness patients has significantly increased, and it is now being used in many patients with a range of different disease conditions. However, there are no established guidelines to direct the safe and effective use of HFNC for these patients. This review article summarizes the available published literature on the positive physiological effects, mechanisms of action, and the clinical applications of HFNC, compared with traditional oxygen therapy devices. The available literature suggests that HFNC oxygen therapy is an effective modality for the early treatment of critically adult patients.

Interaction between deglutition, tongue posture, and malocclusion: A comparison of intraoral compartment formation in subjects with neutral occlusion or different types of malocclusion.

To test the null hypothesis of no significant difference in terms of intraoral pressure curve characteristics assessed simultaneously at the subpalatal space (SPS) and the vestibular space (VS), during different oral postures, between four groups with either an Angle Class II/1 (II1), Angle Class II/2 (II2), anterior open bite (O) malocclusion, or a neutral occlusion control group (I). Intraoral pressure recordings were performed simultaneously in the VS and SPS of 69 consecutive subjects (nII1 = 15; nII2 = 17; nO = 17; nI = 20; mean age/standard deviation 18.43/6.60 years). Assessments included defined sections of open mouth posture (OMP, 30 seconds), anteriorly closed mouth condition (60 seconds), dynamics by a tongue-repositioning maneuver (TRM, 60 seconds), swallowing, and positive pressure generation (PP, 10 seconds). Interactions of malocclusion, compartment location, and posture on pressure curve characteristics were analyzed by Kruskal-Wallis and Mann-Whitney U-tests, adopting an α level of 5%. Globally significant group differences were detected at the VS (plateau duration and median peak heights during TRM; area under pressure curve [AUC] during PP) and SPS (AUC during TRM and PP). Subjects with anteriorly nonopen dental configurations (groups I and II2) were able to keep negative pressure levels at the VS for longer time periods during TRM, compared to groups O and II1. The null hypothesis was rejected for mean VS plateau durations and peak heights and for SPS AUC. Negative pressures at the VS may stabilize outer soft tissues passively and may explain the dental arch form shaping effect by mimic muscles.

Effort of Breathing in Children Receiving High-Flow Nasal Cannula

High-flow humidified nasal cannula is often used to provide noninvasive respiratory support in children. The effect of high-flow humidified nasal cannula on effort of breathing in children has not been objectively studied, and the mechanism by which respiratory support is provided remains unclear. This study uses an objective measure of effort of breathing (Pressure. Rate Product) to evaluate high-flow humidified nasal cannula in critically ill children. Prospective cohort study. Quaternary care free-standing academic children's hospital. ICU patients younger than 18 years receiving high-flow humidified nasal cannula or whom the medical team planned to extubate to high-flow humidified nasal cannula within 72 hours of enrollment. An esophageal pressure monitoring catheter was placed to measure pleural pressures via a Bicore CP-100 pulmonary mechanics monitor. Change in pleural pressure (ΔPes) and respiratory rate were measured on high-flow humidified nasal cannula at 2, 5, and 8 L/min. ΔPes and respiratory rate were multiplied to generate the Pressure.Rate Product, a well-established objective measure of effort of breathing. Baseline Pes, defined as pleural pressure at end exhalation during tidal breathing, reflected the positive pressure generated on each level of respiratory support. Twenty-five patients had measurements on high-flow humidified nasal cannula. Median age was 6.5 months (interquartile range, 1.3-15.5 mo). Median Pressure,Rate Product was lower on high-flow humidified nasal cannula 8 L/min (median, 329 cm H2O·min; interquartile range, 195-402) compared with high-flow humidified nasal cannula 5 L/min (median, 341; interquartile range, 232-475; p = 0.007) or high-flow humidified nasal cannula 2 L/min (median, 421; interquartile range, 233-621; p < 0.0001) and was lower on high-flow humidified nasal cannula 5 L/min compared with high-flow humidified nasal cannula 2 L/min (p = 0.01). Baseline Pes was higher on high-flow humidified nasal cannula 8 L/min than on high-flow humidified nasal cannula 2 L/min (p = 0.03). Increasing flow rates of high-flow humidified nasal cannula decreased effort of breathing in children, with the most significant impact seen from high-flow humidified nasal cannula 2 to 8 L/min. There are likely multiple mechanisms for this clinical effect, including generation of positive pressure and washout of airway dead space.

The role of oral soft tissues in swallowing function: what can tongue pressure tell us?

Tongue pressure data taken from healthy subjects during normal oral activities such as mastication, speech and swallowing are providing us with new ways of understanding the role of the tongue in craniofacial growth and function. It has long been recognized that the sequential contact between the tongue and the palate plays a crucial role in the oropharyngeal phase of swallowing. However, because the focus of most research on intraoral pressure has been on the generation of positive pressure by the tongue on the hard palate and teeth, generation and coordination of absolute intraoral pressures and regional pressure gradients has remained unexplored. Ongoing research in our laboratory has uncovered highly variable individual pressure patterns during swallowing, which can nonetheless be divided into four stages: preparatory, primary propulsive, intermediate and terminal. These stages may further be sub-classified according to pressure patterns generated at the individual level as tipper or dipper patterns in the preparatory stage, roller or slapper in the primary propulsive and monophasic or biphasic during the intermediate stage. Interestingly, while an increase in bolus viscosity can result in significant changes to pressure patterns in some individuals, it has little effect in others. Highly individual responses to increased viscosity are also observed with swallowing duration. The above, together with other findings, have important implications for our understanding of the aetiology of widely differing conditions such as protrusive and retrusive malocclusions, dysphagia and sleep apnoea, as well as the development of novel food products.

基于AIBN材料的微流体驱动用微型正压源

In order to provide the driving force for the collection and transport of the micro liquid in a microfluidic chip developed by our research group in earlier research,this paper presents a micro positive pressure generator based on the released gas by thermal decomposition of azobisisobutyronitrile(AIBN).The AIBN is fixed to a micro-heater and heated to 70 ℃ to produce a certain amount of positive pressure.Experimental measurements show that this micro positive pressure generator can obtain 182 kPa pressure with heating 8.7 mg of AIBN by a heating current of 900 mA.The designed micro positive pressure generator is a smaller size,pressure controllable and easy to produce,and obtained pressure can satisfy the requirements of transdermal interstitial fluid(ISF) extraction.

High flow nasal oxygen generates positive airway pressure in adult volunteers

The use of non-invasive ventilation (NIV) as an alternative to intubation in respiratory failure is associated with better outcomes in certain conditions. NIV is often poorly tolerated by patients hence precipitating the need for invasive ventilation. High flow nasal (HFN) oxygen delivery is a potential alternative to NIV as it delivers air and oxygen via a humidified circuit at flows greater than those traditionally used with a nasal interface. BODY: Studies of paediatric patient using high flow nasal oxygen therapy have been shown to have similar efficacy as nasal continuous positive airway pressure (CPAP). Although the degree of positive pressure and the effect of different flow rates on positive pressure generation have not been well defined or studied in the adult intensive care population. St. Vincent's Health Human Research and Ethics Committee granted approval to this study and also awarded a $3000 grant. Volunteers were fitted with the Fisher & Paykel high flow nasal interface (RT034) and pharyngeal pressures were recorded with flows from 0 to 60L/min. Expiratory pressures with the mouth closed were higher than those with the mouth open and this was statistically significant (<0.001). Expiratory pressures were higher with the mouth closed and were statistically different (p<0.001). EPPs were higher amongst female subjects compared to male subjects and were statistically different between genders for both open (p<0.05) and closed (p<0.001) measurements. This study has demonstrated that high flow nasal therapy is associated with the generation of significant positive airway pressure in volunteers. In conclusion there is a degree of CPAP generated with the HFN therapy, which is flow dependent and also dependent on whether the person is breathing with mouth open or closed.

The Nature of Feeding in Infants with Unrepaired Cleft Lip and/or Palate Compared with Healthy Noncleft Infants

Feeding difficulties are reported widely in infants with cleft lip and/ or palate. There is, however, a paucity of objective information about the feeding patterns of these infants. This study compared patterns of feeding in infants with unrepaired cleft lip and palate with healthy noncleft infants of a similar age. North Thames Regional Cleft Centre. The noncleft cohort was recruited from West Middlesex University Hospital, a general hospital with similar demographics. Fifty newborn infants with nonsyndromic complete unilateral cleft lip and palate or a cleft of the soft and at least two thirds of the hard palate who were referred to the North Thames Regional Cleft Centre participated. Parents of 20 randomly selected, noncleft infants agreed to participate. Feeding patterns were rated using the Neonatal Oral Motor Assessment Scale. Additional objective information was collected using the Great Ormond Street Measurement of Infant Feeding (Masarei et al., 2001; Masarei, 2003). Infants with nonsyndromic complete unilateral cleft lip and palate or a cleft of the soft and at least two thirds of the hard palate had less efficient sucking patterns than their noncleft peers had. They used shorter sucks (mean difference, 0.30 second; p < .0005), a faster rate of sucking (mean difference, 34.20 sucks/second; p < .0005), higher suck-swallow ratios (mean difference, 1.87 sucks/swallow; p < .0005), and a greater proportion of intraoral positive pressure generation (mean difference, 45.97% positive pressure; p < .0005). This study demonstrated that the sucking patterns of infants with nonsyndromic complete unilateral cleft lip and palate or a cleft of the soft and at least two thirds of the hard palate differ from those of their noncleft peers.

Microprocessor-controlled ventilator monitor with pre-evaluation of preset variables and graphic simulation: a preliminary clinical impression.

The prototype of a fully computerized servoventilator monitor was successfully used to support ventilation in 25 adult patients during a total of 2030 patient hours. This prototype is volume-cycled in active inspiration and time-cycled in the inspiratory pause. During time-cycled expiration, it functions as a constant atmospheric pressure generator, or constant positive-pressure generator if positive end-expiratory pressure is applied. From the information received through a pneumotachometer placed near the patient's airway, a microprocessor controls the mode of ventilation, and monitors and processes the ventilatory data. This computerized device has a high-security keyboard and a visual display screen. Ventilatory data are stored in a timed memory and presented on the screen. By measuring compliance and airway resistance with a standardized cycle, it is possible to define the patient's ventilatory mechanics by a mathematical model and predict the result of any proposed change in preset variables.