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Inflation (left panel) and deflation (right panel) P-V curves are shown for three patients. The open circles are the data points and the thick solid line is the equation curve-fitted to the data. The values for P mci,i and mean Pflex are shown for the inflation curves and the value for P inf,d is shown for deflation. These patients were chosen to illustrate a patient with no Pflex (top), a mean Pflex in the middle range (middle), and the maximum mean Pflex (bottom) of all of the 18 patients.
Source publication
To assess the interobserver and intraobserver variability in the clinical evaluation of the quasi-static pressure-volume (P-V) curve, we analyzed 24 sets of inflation and deflation P-V curves obtained from patients with ARDS. We used a recently described sigmoidal equation to curve-fit the P-V data sets and objectively define the point of maximum c...
Context in source publication
Context 1
... sets of inflation and deflation P-V curves were ob- tained from 18 patients. In four patients, P-V curves were re- peated at different times giving a total of 24 sets used for anal- ysis. The mean Murray Lung Injury Score for the 18 patients was 2.98 0.42 SD. P-V data were obtained at times ranging from 1 to 50 d postintubation (median, 6.5 d). All but three pa- tients had P-V curves done within 3 wk of intubation. In one inflation P-V curve, all seven clinicians agreed there was no Pflex. In two other inflation P-V curves, one of seven clini- cians and four of seven clinicians, respectively, reported no Pflex. All other curves had Pflex values 0 cm H 2 O for all clinicians. The diagnoses were pneumonia in nine, sepsis in eight, aspiration in five, pancreatitis in one, and lymphangitic spread of tumor in one. The sigmoidal Equation 1 had excel- lent fit (Figure 2), yielding R 2 values ranging from 0.9965 to 0.9999 for both inflation (mean, 0.9992 0.0005 SD) and de- flation (mean, 0.9993 0.0010 SD). When inflation and defla- tion data points (547 points) were pooled for all curves ana- lyzed and normalized by their corresponding curve-fitting parameters in a plot of (V a)/b versus (P c)/d, they clus- tered tightly along the sigmoidal curve, with an R 2 of 0.9992 ( Figure ...
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Citations
... Many anaesthesiologists increase PEEP to prevent collapse of the airways. The aim of a 'best PEEP concept' is to detect the optimal individual PEEP level to enable non-harming ventilation for lung compliance (LC) and to minimise the development of mechanical lesions due to ventilation [6]. ...
Objectives:
Robotic-assisted laparoscopic prostatectomy (RALP) is typically conducted in steep Trendelenburg position (STP). The aim of the study was to evaluate whether crystalloid administration and individual management of positive end-expiratory pressure (PEEP) improve peri- and post-operative pulmonary function in patients undergoing RALP.
Design:
Prospective randomised single-centre single-blinded explorative study.
Setting:
Patients were either allocated to a standard PEEP (5 cmH2O) group or an individualised high PEEP group. Furthermore, each group was divided into a liberal and a restrictive crystalloid group (8 vs. 4 mL/kg/h predicted body weight). Individualised PEEP levels were determined by means of preoperative recruitment manoeuvre and PEEP titration in STP.
Participants:
Informed consent was obtained from 98 patients scheduled for elective RALP.
Interventions:
The following intraoperative parameters were analysed in each of the four study groups: ventilation setting (peak inspiratory pressure [PIP], plateau pressure, driving pressure [Pdriv], lung compliance [LC] and mechanical power [MP]) and postoperative pulmonary function (bed-side spirometry). The spirometric parameters Tiffeneau index (FEV1/FVC ratio) and mean forced expiratory flow (FEF25-75) were measured pre- and post-operatively. Data are shown as mean ± standard deviation (SD), and groups were compared with ANOVA. A p-value of <0.05 was considered significant.
Results:
The two individualised high PEEP groups (mean PEEP 15.5 [±1.71 cmH2O]) showed intraoperative significantly higher PIP, plateau pressure and MP levels but significantly decreased Pdriv and increased LC. On the first and second postoperative day, patients with individualised high PEEP levels had a significantly higher mean Tiffeneau index and FEF25-75. Perioperative oxygenation and ventilation and postoperative spirometric parameters were not influenced by restrictive or liberal crystalloid infusion in either of the two respective PEEP groups.
Conclusions:
Individualised high PEEP levels (≥14 cmH2O) during RALP improved intraoperative blood oxygenation and resulted in more lung-protective ventilation. Furthermore, postoperative pulmonary function was improved for up to 48 h after surgery in the sum of the two individualised high PEEP groups. Restrictive crystalloid infusion during RALP seemed to have no effect on peri- and post-operative oxygenation and pulmonary function.
... Спавшиеся альвеолы обладают низким комплаенсом, также низкий комплаенс имеют и перерастянутые альвеолы, оказывая высокое сопротивление дальнейшему растяжению. По сути, именно избегание подобных низких значений комплаенса и лежит в основе ряда методик, которые отличаются лишь выбором индикатора для установки уровня PEEP: от непосредственного анализа значений статического или динамического комплаенса [42,43], поиска точек перегиба на кривых вдоха или выдоха петли давление-объем [44][45][46], до сложных формул подсчета момента его максимального роста [47,48]. Идея поиска момента максимального комплаенса для установки уровня PEEP эволюционировала в идею оценки анализа повреждающей энергии потока в целом. ...
End-expiratory pressure remains one of the few parameters of mechanical respiratory support whose values have not been strictly regulated using the evidence-based approach. The absence of «gold standard» for end-expiratory pressure optimization together with its obvious significant contribution to the efficiency and safety of respiratory support has driven the search for the optimal method of choosing its values for several decades.
Aim of the review : to identify the optimal methods for determining the values of end-expiratory pressure based on the analysis of its positive and negative effects in the used strategies of mechanical respiratory support.
Material and methods . We analyzed 165 papers from the PubMed, Scopus, and RSCI databases of medical and biological publications. Among them we selected 86 sources that most completely covered the following subjects: respiratory support, end-expiratory pressure, recruitment, ventilation-perfusion relationships, metabolography, and gas analysis.
Results. We outlined the main positive and negative effects of the end-expiratory pressure with regard to both lung biomechanical characteristics and pulmonary perfusion. The evolution of views on the methods of determining optimal values of the end-expiratory pressure was reviewed with the emphasis on a certain «fixation» of the scientific community in recent decades concerning the opening of the alveoli. The promising techniques based on the analysis of the diffusion capacity of the lungs were presented.
Conclusion. Focusing on mechanical lung opening prevents the scientific community from advancing in the optimization of the end-expiratory pressure. Dynamic assessment of pulmonary diffusion efficiency provides a new perspective on the issue, offering additional ways to the development of «gold standard».
... from the following equations using sigmoidal 4 parameter relationships [46,47], adapted by Saraydın's approach, for binding ratio (Φ) and equilibrium concentration of solute (C); ...
The effects of crosslinker and dye type on swelling and S-type adsorption properties of crosslinked polyhydroxamates (CHP) were investigated. CHPs containing N,Nʹ-methylenebisacrylamide (N), or ethylene glycol dimethacrylate (E) were used in the swelling, diffusion, and adsorption experiments in solutions of oxazine dyes such as Brilliant Cresyl Blue, Nile Blue, and Cresyl Violet. Swelling and diffusion parameters of CHPs in dye solutions (such as equilibrium swelling, half time of swelling, swelling value at half time, network parameter, diffusion exponent, and diffusion constant) were calculated. It is understood from the time of swelling to reach equilibrium that CHPs swell very fast. CHP-E in all dyes solutions swelled considerably more than CHP-N. Dye solution diffusion into CHPs was determined to be of non-Fickian character. It has been observed that the swelling properties of hydrogels are highly influenced by the crosslinker type. The adsorption of oxazine dyes onto CHPs is similar to the S-type adsorption in the Giles classification system. When it was seen that the experimental data fit the Sigmoidal 4 parameter equation with a high correlation (r² > 0.995), the use of this equation determined the adsorption parameters such as the highest bonding rate or monolayer coverage, the transition point of the isotherm, the magnitude of the absorbent's absorbability and the slope parameter. Site-size, maximum fractional occupancy, the binding ratio at the transition point, binding constant, the initial binding constant, partition coefficient, and adsorption free energy values were also calculated by using the found adsorption values. Dye adsorption from all dyes solutions to CHP-E is considerably higher than CHP-N. An increasing linear relationship was found between swelling and adsorption. In conclusion, the sigmoidal equation approach can be a useful tool for chemists, chemical, agricultural and environmental engineers, polymer scientists to find the adsorption parameters of polymer adsorbents, and at the same time, it can be said that CHP can be used as a good sorbent in the removal of some chemical agents (such as dye molecules, organic molecules, biologically active molecules).
... Therefore, CWC in the decubitus position keeps the intrapleural pressure at EELV negative and does not cause airway and alveolar collapse. LIP is created at the beginning of the inspiration of P-V loops of ARDS with an increasing point of sudden compliance by collapsed alveolar expansion 12) . Also, because LIP suggests collapsed alveolar presence 13) , it is recommended that the level of positive end-expiratory pressure is set just above the LIP in ARDS/ALI. ...
[Purpose] This study aimed to investigate the difference in intrapleural pressure between the supine and lateral decubitus positions during manual chest wall compression. [Participants and Methods] Eight healthy males participated in this study. The same physiotherapist performed chest wall compression on participants lying supine, and on their right and left sides. We noted changes in intrapleural pressure and lung volume in each participant during quiet breathing and chest wall compression. [Results] During chest wall compression, intrapleural pressure at the end-expiratory lung volume and the end-inspiratory lung volume were lower in the right and left decubitus positions than in the supine position. We observed the following low inflection points in the pressure-volume loops during chest wall compression: all participants in the supine position, no participants in the right decubitus position, and two participants in the left decubitus position. [Conclusion] Chest wall compression in the bilateral decubitus positions may not cause excessive intrapleural pressure on the airway and alveoli as compared to chest wall compression in the supine position.
... The pH was estimated by the chemical shift of the Pi signal relative to the PCr signal. Signals in 31 P NMR spectra were determined quantitatively by fitting the peak in question (after phase and baseline corrections) to a Lorentzian function, using the LCModel method [25,26]. Differences in chemical shift between the γ, α and β-phosphorus nuclei of ATP were used to assess the amount of Mg 2+ ions bound to ATP and to estimate their levels. ...
... One of the most outstanding characteristics of the complaints of patients with COPD is the reduction of exercise tolerance, caused in part by the structural and functional deterioration of the skeletal muscles [27]. Previous results published by our group show how chronic exposure to cigarette smoke induces increased oxidative stress levels in their gastrocnemius, greater oxidative modifications on muscle proteins and systemic inflammation [26]. Proteins involved in ATP production were carbonylated in limb muscles and blood tumor necrosis factor (TNF)alpha levels were significantly greater in cigarette smoke mice than in control animals [28]. ...
Skeletal muscle dysfunction is a common complication and an important prognostic factor in patients with chronic obstructive pulmonary disease (COPD). It is associated with intrinsic muscular abnormalities of the lower extremities, but it is not known whether there is an easy way to predict its presence. Using a mouse model of chronic cigarette smoke exposure, we tested the hypothesis that magnetic resonance spectroscopy allows us to detect muscle bioenergetic deficit in early stages of lung disease. We employed this technique to evaluate the synthesis rate of adenosine triphosphate (ATP) and characterize concomitant mitochondrial dynamics patterns in the gastrocnemius muscle of emphysematous mice. The fibers type composition and citrate synthase (CtS) and cytochrome c oxidase subunit IV (COX4) enzymatic activities were evaluated. We found that the rate of ATP synthesis was reduced in the distal skeletal muscle of mice exposed to cigarette smoke. Emphysematous mice showed a significant reduction in body weight gain, in the cross-sectional area of the total fiber and in the COX4 to CtS activity ratio, due to a significant increase in CtS activity of the gastrocnemius muscle. Taken together, these data support the hypothesis that in the early stage of lung disease, we can detect a decrease in ATP synthesis in skeletal muscle, partly caused by high oxidative mitochondrial enzyme activity. These findings may be relevant to predict the presence of skeletal bioenergetic deficit in the early stage of lung disease besides placing the mitochondria as a potential therapeutic target for the treatment of COPD comorbidities.
... Significant inter-and intra-observer variability in identifying the lower inflection point in P-V curves obtained from patients with ARDS has been noted, with maximum differences up to 17 cm H 2 O between observers for the same patient's curve. 49 This may partly be explained by the fact that alveolar recruitment does not happen uniformly and instantaneously, especially in a heterogeneous disease such as ARDS. In a uniformly recruited lung, the lower inflection point should be well defined and sharp; however, a very sharp lower inflection point may represent the airway opening pressure rather than lung recruitment, which can further complicate interpretation of the lower inflection point of the P-V curve. ...
Mechanical ventilation is an indispensable form of life support for patients undergoing general anesthesia or experiencing respiratory failure in the setting of critical illness. These patients are at risk for a number of complications related to both their underlying disease states and the mechanical ventilation itself. Intensive monitoring is required to identify early signs of clinical worsening and to minimize the risk of iatrogenic harm. Pulse oximetry and capnography are used to ensure that appropriate oxygenation and ventilation are achieved and maintained. Assessments of driving pressure, transpulmonary pressure, and the pressure-volume loop are performed to ensure that adequate PEEP is applied and excess distending pressure is minimized. Finally, monitoring and frequent adjustment of airway cuff pressures is performed to minimize the risk of airway injury and ventilator-associated pneumonia. We will discuss monitoring during mechanical ventilation with a focus on the accuracy, ease of use, and effectiveness in preventing harm for each of these monitoring modalities.
... Prior research indicates that recruitment rate with increasing pressure follows an exponential decay. 1,5,15,24,25,33,34,[37][38][39]46,58,60 This new model challenges the assumption that recruitment models must also be exponential since recruitment over pressure is a complex mechanical behaviour that is not driven solely by pressure and volume. Sensitivity analyses of the new model assesses the robustness of model parameter choices and assumptions. ...
Mechanical ventilation is a life-support therapy for intensive care patients suffering from respiratory failure. To reduce the current rate of ventilator-induced lung injury requires ventilator settings that are patient-, time-, and disease-specific. A common lung protective strategy is to optimise the level of positive end-expiratory pressure (PEEP) through a recruitment manoeuvre to prevent alveolar collapse at the end of expiration and to improve gas exchange through recruitment of additional alveoli. However, this process can subject parts of the lung to excessively high pressures or volumes. This research significantly extends and more robustly validates a previously developed pulmonary mechanics model to predict lung mechanics throughout recruitment manoeuvres. In particular, the process of recruitment is more thoroughly investigated and the impact of the inclusion of expiratory data when estimating peak inspiratory pressure is assessed. Data from the McREM trial and CURE pilot trial were used to test model predictive capability and assumptions. For PEEP changes of up to and including 14 cmH2O, the parabolic model was shown to improve peak inspiratory pressure prediction resulting in less than 10% absolute error in the CURE cohort and 16% in the McREM cohort. The parabolic model also better captured expiratory mechanics than the exponential model for both cohorts.
... Static compliance has been reported to change significantly with both tidal volume and PEEP [133][134][135][136]. The local maxima of compliance at a patient-specific PEEP was noted to be dependent on the ventilated tidal volume and explained in terms of position on the static pressure-volume (PV) curve [133][134][135][136]. ...
... Static compliance has been reported to change significantly with both tidal volume and PEEP [133][134][135][136]. The local maxima of compliance at a patient-specific PEEP was noted to be dependent on the ventilated tidal volume and explained in terms of position on the static pressure-volume (PV) curve [133][134][135][136]. In general, higher tidal volumes reduce the PEEP of maximum compliance [133][134][135][136], and equally, higher PEEP at a fixed tidal volume can have a similar effect [105]. ...
... The local maxima of compliance at a patient-specific PEEP was noted to be dependent on the ventilated tidal volume and explained in terms of position on the static pressure-volume (PV) curve [133][134][135][136]. In general, higher tidal volumes reduce the PEEP of maximum compliance [133][134][135][136], and equally, higher PEEP at a fixed tidal volume can have a similar effect [105]. ...
Background
Mechanical ventilation is an essential therapy to support critically ill respiratory failure patients. Current standards of care consist of generalised approaches, such as the use of positive end expiratory pressure to inspired oxygen fraction (PEEP–FiO2) tables, which fail to account for the inter- and intra-patient variability between and within patients. The benefits of higher or lower tidal volume, PEEP, and other settings are highly debated and no consensus has been reached. Moreover, clinicians implicitly account for patient-specific factors such as disease condition and progression as they manually titrate ventilator settings. Hence, care is highly variable and potentially often non-optimal. These conditions create a situation that could benefit greatly from an engineered approach. The overall goal is a review of ventilation that is accessible to both clinicians and engineers, to bridge the divide between the two fields and enable collaboration to improve patient care and outcomes. This review does not take the form of a typical systematic review. Instead, it defines the standard terminology and introduces key clinical and biomedical measurements before introducing the key clinical studies and their influence in clinical practice which in turn flows into the needs and requirements around how biomedical engineering research can play a role in improving care. Given the significant clinical research to date and its impact on this complex area of care, this review thus provides a tutorial introduction around the review of the state of the art relevant to a biomedical engineering perspective.
Discussion
This review presents the significant clinical aspects and variables of ventilation management, the potential risks associated with suboptimal ventilation management, and a review of the major recent attempts to improve ventilation in the context of these variables. The unique aspect of this review is a focus on these key elements relevant to engineering new approaches. In particular, the need for ventilation strategies which consider, and directly account for, the significant differences in patient condition, disease etiology, and progression within patients is demonstrated with the subsequent requirement for optimal ventilation strategies to titrate for patient- and time-specific conditions.
Conclusion
Engineered, protective lung strategies that can directly account for and manage inter- and intra-patient variability thus offer great potential to improve both individual care, as well as cohort clinical outcomes.
... Similarly, at relatively high pressures, the work of breathing would also increase because of the effect of hyperinflation on diaphragmatic contractility, which thus left an optimal ventilation zone in-between these 2 extremes. 27 Our study highlighted that the majority of convalescent prematurely born infants would be in this zone at a distending pressure of 6 cm H 2 O. ...
Background:
CPAP improves respiratory function in prematurely born infants by establishing and maintaining functional residual capacity, but the level of CPAP that optimizes respiratory function has not been adequately described. We compared ventilation efficiency and respiratory muscle function at different levels of CPAP.
Methods:
We studied spontaneously breathing, intubated convalescent premature infants at King's College Hospital NHS Foundation Trust and calculated the ventilation efficiency index and the respiratory muscle time constant of relaxation (τ) at the end of 3 consecutive 5-min periods at 4, 6, and 8 cm H2O of CPAP delivered in random order.
Results:
Between February 2016 and August 2016, 38 infants with a median gestational age of 27 (interquartile range [IQR], 25-30) weeks and a median birthweight of 0.88 (IQR, 0.73-1.02) kg were studied. At a CPAP level of 6 cm H2O, the median ventilation efficiency index was higher (1.52 [IQR, 1.02-2.27]) and median τ was lower (15.6 [IQR, 10.1-21.3]) s/cm H2O] compared with the median ventilation efficiency index (0.75 [IQR, 0.56-1.03]) and median τ (23.3 [IQR, 15.4-35.2] sec/cm H2O) at CPAP of 4 cm H2O (P < .001 for both). At a CPAP level of 8 cm H2O, median ventilation efficiency index was significantly lower (1.27 [IQR, 1.04-1.91]) and median τ was not significantly different (11.2 [IQR, 8.3-18.9] s/cm H2O) compared with ventilation efficiency index and τ at CPAP of 6 cm H2O (P < .001 and P = .12, respectively). After multiple logistic regression, the level of CPAP was independently associated with the ventilation efficiency index (adjusted P < .001) and τ (adjusted P = .003).
Conclusions:
Increasing the level of CPAP from 4 to 6 cm H2O was associated with enhanced ventilation efficiency and respiratory muscle function in convalescent premature infants on ventilation, but there was no further benefit from increasing the pressure >6 cm H2O.
... (3) Operability difference; it is difficult to precisely determine the LIP of the P-V curve. Harris et al. found that the differences between observers can be as high as 6-11 cmH 2 O when judging the LIP [14]. ...
