Pressure-volume Curves Research Articles

Hydraulic properties and drought response of a tropical bamboo (Cephalostachyum pergracile)

Bamboo plants are an essential component of tropical ecosystems, yet their vulnerability to climate extremes, such as drought, is poorly understood due to limited knowledge of their hydraulic properties. Cephalostachyum pergracile, a commonly used tropical bamboo species, exhibited a substantially higher mortality rate than other co-occurring bamboos during a severe drought event in 2019, but the underlying mechanisms remain unclear. This study investigated the leaf and stem hydraulic traits related to drought responses, including leaf-stem embolism resistance (P50leaf; P50stem) estimated using optical and X-ray microtomography methods, leaf pressure–volume and water-releasing curves. Additionally, we investigated the seasonal water potentials, native embolism level (PLC) and xylem water source using stable isotope. We found that C. pergracile exhibited strong resistance to embolism, showing low P50leaf, P50stem, and turgor loss point, despite its rapid leaf water loss. Interestingly, its leaves displayed greater resistance to embolism than its stem, suggesting a lack of effective hydraulic vulnerability segmentation (HVS) to protect the stem from excessive xylem tension. During the dry season, approximately 49% of the water was absorbed from the upper 20-cm-deep soil layer. Consequently, significant diurnal variation in leaf water potentials and an increase in midday PLC from 5.87 ± 2.33% in the wet season to 12.87 ± 4.09% in the dry season were observed. In summary, this study demonstrated that the rapid leaf water loss, high reliance on surface water, and a lack of effective HVS in C. pergracile accelerated water depletion and increased xylem embolism even in the typical dry season, which may explain its high mortality rate during extreme drought events in 2019.

Compliant Aortic Annulus Sizing With Different Elliptical Ratios Through a Valvuloplasty Balloon Catheter.

Aortic stenos (AS) is a heart valve disease that commonly affects the elderly. Transcatheter aortic valve implantation is a minimally invasive treatment that allows to replace the function of the diseased native valve with a prosthetic device, relying on catheters for device implantation. According to the current clinical guidelines, the choice of the implanted device is based on preoperative sizing determined by image-based technology. However, this assessment faces inherent limitations that can lead to sub-optimal sizing of the prosthesis; in turn, this can cause major post-operative complications like aortic regurgitation or cardiac electrical signal disruption. By utilizing balloon pressure and volume data, this article proposes an intra-operative method for determining the dimension of the aortic annulus which takes into account its compliance and geometric irregularity. The intra-balloon pressure-volume curves were obtained using an Automated Balloon Inflation Device operating a commercially available valvuloplasty balloon catheter. A sizing algorithm to estimate the dimensions of the annulus was integrated via a validated analytical model and a numerical model for balloon free-inflation. Tests were performed on circular and elliptical idealised aortic phantoms. Experimental results confirm that the pressure-volume data processed with the sizing algorithm can be used to determine the circular annular diameter for all tissue rigidities. The measurement of stiffer elliptical annulus phantoms shows good accuracy and high repeatability. This work represents substantial progress toward improving the selection of TAVI devices by using balloon catheters to improve the sizing of compliant aortic annuli with complex geometry.

Abstract 16954: Sex Differences in Cardiac and Vascular Function With Healthy Aging: Implications for Greater Risk of HFpEF in Women

Introduction: Mechanisms mediating the disproportionate risk for heart failure with preserved ejection fraction (HFpEF) in women are poorly understood. Impaired stroke volume (SV) reserve, increased afterload, arterial and left ventricular (LV) stiffness contribute to exercise intolerance in HFpEF. It is unknown whether subclinical changes in these measures predispose women to HFpEF; therefore, we compared resting and exercise cardiovascular structure and function across age in healthy men and women. Methods: We studied 192 sedentary normotensive, non-obese adults (53% female; age: 58 ± 13 [20-90] years) at rest, during sub- and maximal exercise. We measured systolic blood pressure (SBP; electrosphygmomanometry) and aortic stiffness (carotid-femoral pulse wave velocity; aPWV). Myocardial stiffness was assessed as the slope of individual pressure-volume (right heart catheterization-echocardiography) curves generated by graded LV loading and unloading. SV was calculated from cardiac output (Q˙c; C 2 H 2 rebreathe)/heart rate to assess afterload (Ea; SBP/SV) and SV reserve (% change from rest) during exercise. Data were compared via two-way ANOVA (age*sex). Results: There was no significant age*sex interaction for aPWV, SV reserve, resting or maximal SBP, or myocardial stiffness; however, there was a main effect for sex with higher myocardial stiffness in women (Figure). aPWV and SV reserve were not different between sexes (p=0.349, p=0.940). Maximal exercise SBP was lower in women, but a similar proportion of each sex had an exaggerated maximal exercise SBP (Men: >210; Women: >190 mmHg; 28% vs 35%, χ 2 =0.290). Peak exercise afterload was higher in women (Figure) due to lower SV. Conclusions: Increased risk for HFpEF in women may be driven in part by greater myocardial stiffness throughout the aging process. Sex related abnormalities in afterload were most prominent with exercise in women, which may predispose to LV hypertrophy and increased stiffness.

Characterizing and Quantifying Material Fatigue of the Artificial Urinary Sphincter Pressure Regulating Balloon

ObjectiveTo characterize and quantify changes in elastic properties and in vivo pressure characteristics of pressure regulating balloons (PRB) over time, we conducted an analysis of the mechanical characteristics of the PRB after removal from patients for revision surgery. MethodsPressure and elasticity characteristics of new and used 61-70cmH20 PRBs were analyzed. Pressure-volume curves were generated using commercially available urodynamics equipment. PRB pressures were measured at a standard fill volume (23cc). Elastance was calculated by the slope of the tangent line at the inflection point of the pressure-volume curve. Tests were repeated 5 times per PRB and intraclass correlations were used to gauge test-retest reliability. Regression models were used for continuous variables based on data distribution. ResultsTwenty-seven used PRBs were analyzed after excluding three for alternative pressure ratings and two for occult pinpoint leaks. Time from AUS placement to removal ranged from 0.02 to 17.6 years (median 8.4, IQR 5.7-10.0). The mean pressure of all extracted PRBs: 58.8cmH2O (±7.4), 17 (62.9%) below the standard operating range. Each year of use in-vivo was associated with 1.09cmH20 pressure loss on linear regression (p<0.01 CI -1.52 to -0.65). PRB pressures were not significantly different according to indication for removal (one-way ANOVA p=0.11). Loss of elastance was non-linear, decreasing by 1.9% per year on Poisson regression (p<0.01, CI -0.03 to -0.01). When accounting for PRB age, PRB pressure was independently associated with detrusor overactivity. ConclusionsIn PRBs tested for pressure-volume characteristics, increasing PRB age was associated with decreased pressure and elasticity.

Leaf hydraulic distance is a good predictor of growth response to climate aridity within and across conifer species in a Taiga ecosystem

Despite inter-specific differences in hydraulic traits at broad scale have been comprehensively studied, intra-specific hydraulic variability in situ is less well known. Which hydraulic traits can better predict whole-plant performance in field both within and across species remains largely ambiguous. In the study, we conducted a field investigation on branch radial growth, leaf and branch anatomical traits related to hydraulics, as well as leaf pressure–volume curve parameters of two dominant conifer species (Larix sibirica and Picea obovata) at four sites over an aridity gradient across the Altay Mountain range, which locates at the southern edge of Taiga ecosystem, one of the largest and the most sensitive terrestrial biomes to climate change. L. sibirica is a generalist deciduous conifer species, while P. obovata is a specialist evergreen conifer species. It was found that: 1) P. obovata showed ten times higher slope of branch radial growth (RGRbranch) fitted to aridity than L. sibirica; 2) the hydraulic distance from the bundle sheath to the stomata (DMC) can predict the growth rate both within and across species; 3) earlywood and latewood anatomies showed different relations to RGRbranch within and across species; 4) leaf saturated osmotic potential (Ψsat) but not turgor loss osmotic potential (Ψtlp) was significantly and positively related to RGRbranch within species. Our results support the hypothesis that specialists are more sensitive in growth to climate change than generalists. Further, the results highlight DMC as a pivotal role in water transport and associated carbon assimilation both within and across species in Taiga ecosystem, therefore at the core of the structural adjustments to climate change in this largest and the most sensitive terrestrial biome.

Hydraulic Traits in Populus simonii Carr. at Stands of Categorized Ages in a Semi-Arid Area of Western Liaoning, Northeast China

Poplar plantations can acclimate to drought stress in semi-arid areas, where the variation of stand age may result in varied water adaptation strategies presented as hydrodynamic performance. In this study, nine mature Populus simonii Carr. individuals were targeted as sampling objects in plantations characterized to three stand ages: young (9 yr), middle-aged (17 yr), and near-mature (29 yr) stages in a semi-arid area of western Liaoning, Northeast China. Hydraulic traits were investigated as parameters of leaf pressure-volume curves, xylem embolism vulnerability curves, hydraulic structure, and wood density (WD). Results showed that osmotic potential (Ψtlp) and relative water content at the turgor loss point and cell-wall bulk elastic modulus were lowest in middle-aged stands (−2.19 MPa; 86.71%; 13.75 MPa). Stem and leaf-specific hydraulic conductivity (Ks and LSC) were all the highest in middle-aged stands. Xylem embolism vulnerability (P50) and lethal water potential of trees (P88) increased with the growth of stand age. Young stands faced minimal risk of hydraulic failure according to the stomatal safety margin (SSMtlp, Ψtlp minus P50), which was consistent with the comprehensive evaluation results of the principal component analysis. WD was related to P88 (R2= 0.51; p &lt; 0.05). P50 was related to drought avoidance traits Ψtlp (r = 0.76; p &lt; 0.05) but not to xylem efficiency (Ks). Overall, WD can be an excellent proxy for hydraulic safety monitoring. Young and middle-aged Populus simonii populations are more adaptable to drought conditions than near-mature populations, and near-mature stands should receive intermediate cuttings to avoid exposure to drought stress.

Leaf structure and water relations of an allotetraploid Mediterranean fern and its diploid parents.

Allopolyploidy is a common speciation mechanism in plants; however, its physiological and ecological consequences in niche partitioning have been scarcely studied. In this sense, leaf traits are good proxies to study the adaptive capacity of allopolyploids and diploid parents to their respective environmental conditions. In the present work, leaf water relations (assessed through pressure-volume curves) and structural and anatomical traits of the allotetraploid fern Oeosporangium tinaei and its diploid parents, Oeosporangium hispanicum and Oeosporangium pteridioides, were studied under controlled conditions in response to a water stress (WS) cycle. O. hispanicum showed the lowest osmotic potential at turgor loss point (πtlp ) and leaf capacitance, together with higher leaf mass per area (LMA), leaf thickness (LT), leaf density (LD), and leaf dry matter content (LDMC), whereas O. pteridioides presented the opposite set of traits (high πtlp and capacitance, and low LMA, LT, LD, and LDMC). O. tinaei showed an intermediate position for most of the studied traits. The responsiveness (osmotic and elastic adjustments) to WS was low, although most of the traits explained the segregation of the three species across a range of drought tolerance according to the rank: O. hispanicum > O. tinaei > O. pteridioides. These trait differences may underlie the niche segregation among coexisting populations of the three species in the Mediterranean basin.

Urinary bladder phantom mimicking mechanical properties and pressure during filling

Objective. Phantoms that mimic healthy or diseased organ properties can complement animal models for surgical planning, training, and medical device development. If urodynamic studies rely on pressure-volume curves to assess lower urinary tract symptoms, there is an unsatisfied need for a bladder phantom that accurately mimics the bladder stretching capabilities and compliant behaviour during physiological filling. Approach. We demonstrate the suitability of water-soluble 3D-printed moulds as a versatile method to fabricate accurate phantoms with anatomical structures reconstructed from medical images. We report a phantom fabricated with silicone rubber. A wire net limits the silicone expansion to model the cystometric capacity. A mathematical model describes the pressure increase due to passive hyperelastic properties. Main results. The phantom reproduces the bladder’s mechanical properties during filling. The pressure-volume curve measured on the phantom is typical of cystometric studies, with a compliance of 25.2 ± 1 The root-mean-square error between the theoretical model and experimental data is 2.7 The compliance, bladder wall thickness, cystometric capacity and pressure near the cystometric capacity of the phantom can be tuned to mimic various pathologies or human variability. Significance. The manufacturing method is suitable for fabricating bladder and other soft and hollow organ phantoms. The mathematical model provides a method to determine design parameters to model healthy or diseased bladders. Soft hollow organ phantoms can be used to complement animal experimentations for developing and validating medical devices aiming to be anchored on these organs or monitor their activity through pressure and strain measurement.

Dohongsamul-tang inhibits cardiac remodeling and fibrosis through calcineurin/NFAT and TGF-β/Smad2 signaling in cardiac hypertrophy

Ethnopharmacological relevanceDohongsammul-tang (DH) is a Korean traditional herbal medicine used to alleviate symptoms caused by extravasated blood. It is known to protect against cardiovascular diseases and promote blood circulation by activating blood circulation to dispel blood stasis. The DH based on the characteristics of its medicinal properties has discovered the potential of alleviating cardiac hypertrophy. Therefore, this study was performed to verify the pharmacological effect of DH on improving cardiovascular disorders and to demonstrate its mutual improvement effect on renal function. Furthermore, aim of this study is founding the new potential beyond the traditional medicinal efficacy of DH, a traditional medicine. Aim of the studyIn cardiovascular disease, cardiac hypertrophy refers to a change in the shape of the heart's structure due to pressure overload. It is known that an increase in myofibrils causes thickening of the heart, resulting in high blood pressure. Therefore, suppressing cardiac hypertrophy may be a major factor in lowering the morbidity, mortality, and heart failure associated with cardiovascular disease. Therefore, the study was performed to investigate whether DH, traditionally used, has effects on improving and alleviating cardiac injury and fibrosis caused by cardiac hypertrophy. Materials and methodsDohongsamul-tang was composed of 6 herbal medicine and each material were boiled with 4 L distilled water for 2 h. The mixture for dohongsamul-tang centrifuged at 3000 rpm for 10 min and concentrated. The concentrated dohongsamul-tang extraction freeze-dried and sotred at 70 °C. The powder of dohongsamul-tang was diluted with distilled water and administered orally. In this study, pressure overload was induced by tying the transverse aortic arch, which is connected to the left ventricle, to the thickness of a 27G needle by performing a surgical operation. The resulting cardiac hypertrophy and heart remodeling was induced and maintained for 8 weeks. ResultsThe study administered propranolol and dohongsamul-tang orally for 10 weeks to investigate their effects on cardiac hypertrophy induced by transverse aortic contraction (TAC) surgery. Results showed that TAC group increased the left ventricle weight and decreased cardiac function, but dohongsamul-tang treatment attenuated these effects. The pressure-volume curve experiment revealed that dohongsamul-tang improved cardiovascular function, which was worsened by TAC group. Dohongsamul-tang treatment also downregulated collagen I and III through the TGF-β/Smad2 signaling pathway and improved hematological biomarkers of cardiac hypertrophy. In addition, dohongsamul-tang treatment improved renal function-related biomarkers, such as blood creatinine, blood urea nitrogen, and neutrophil gelatinase-associated lipocalin, which were increased by TAC-induced cardiac hypertrophy. ConclusionsTaken together, dohongsamul-tang treatment inhibited cardiac remodeling due to pressure overload in the TAC-induced cardiac hypertrophy model, and this effect is thought to be manifested by improving the functional and morphological changes through the calcineurin/NFATc4 and reducing the cardiac fibrosis by suppressing TGF-β/Smad2 signaling pathways.

Fluid phase equilibria of Brazilian presalt crude oil – CO2 systems at high pressure and high temperature

This paper aims to conduct an experimental investigation of the fluid phase behavior of a highly opaque Brazilian pre-salt crude oil-CO2 system, specifically focusing on the occurrence of highly dispersed liquid-liquid transitions. The study involves examining the phase behavior of five global mole compositions [zCO2= (37.9, 50.0, 76.6, 80.6, and 84.2) mol%] by using conventional PVT techniques as light scattering, pressure-volume curve, and direct fluid observation through sapphire windows. When other techniques were ineffective, a high-pressure microscope coupled with a short-wave infrared apparatus (SWIR camera and light source) was used for complex fluid inspection.

Use of positive end-expiratory pressure titration and recruitment maneuvers in pediatric intensive care unit – A narrative review

Mechanical ventilation is a lifesaving support for patients suffering with acute respiratory distress syndrome. This modality is likely to cause ventilator-induced lung injury if not used judiciously and appropriately. Lung protective ventilation strategy is routinely practiced in adult and pediatric intensive care units. Positive end-expiratory pressure (PEEP) and recruitment maneuvers (RMs) are used in “Open Lung Ventilation” strategy and to keep the lung open. PEEP is applied to recruit collapsed alveoli to improve oxygenation, compliance, reduce tidal stress, and strain on the lungs and to promote homogenous lung ventilation. There is no agreement on methods to set “Best PEEP” for a particular patient. There are many approaches described in published literature to optimize PEEP. PEEP titration may be done with PEEP/FiO2 grid, targeted compliance, driving pressure, by using pressure-volume curve and stress index. Esophageal manometry and measurement of end-expiratory lung volume may be used if special equipment, machines, and expertise are available. No single method of PEEP titration has been shown to improve outcome. RM is characterised by sudden transient increase in transpulmonary pressure. Different RMs including high-frequency oscillator ventilation and prone position ventilation have been studied in adults and pediatric patients with very conflicting results and inconsistent survival benefits. Serious complications, hemodynamic instability, air leak syndrome, transient, or no improvements in oxygenation are reported. In this narrative review, we have discussed different methods of PEEP titration and RMs and available evidence for each especially in children.

Low baseline intraspecific variation in leaf pressure-volume traits: biophysical basis and implications for spectroscopic sensing.

Intra-specific trait variation (ITV) plays a role in processes at a wide range of scales from organs to ecosystems across climate gradients. Yet, ITV remains rarely quantified for many ecophysiological traits typically assessed for species means, such as pressure volume (PV) curve parameters including osmotic potential at full turgor and modulus of elasticity, which are important in plant water relations. We defined a baseline "reference ITV" (ITVref ) as the variation among fully exposed, mature sun leaves of replicate individuals of a given species grown in similar, well-watered conditions, representing the conservative sampling design commonly used for species-level ecophysiological traits. We hypothesized that PV parameters would show low ITVref relative to other leaf morphological traits, and that their intraspecific relationships would be similar to those previously established across species and proposed to arise from biophysical constraints. In a database of novel and published PV curves and additional leaf structural traits for 50 diverse species, we found low ITVref for PV parameters relative to other morphological traits, and strong intraspecific relationships among PV traits. Simulation modeling showed that conservative ITVref enables the use of species-mean PV parameters for scaling up from spectroscopic measurements of leaf water content to enable sensing of leaf water potential. This article is protected by copyright. All rights reserved.

The role of ultrasound in assessment of positive end-expiratory pressure-induced lung recruitment in acute respiratory distress syndrome patients

Abstract Background In the case of critically sick patients, acute respiratory distress syndrome (ARDS) may be life-threatening and necessitates the need for ICU admission. Continuous monitoring is required for mechanical ventilation and recruitment movements as necessary. In this research, the goal is to investigate the use of ultrasonography in the evaluation of positive end exhalatory pressure-induced lung recruitment in ARDS patients. Patients and methods A total of 25 ARDS patients were included in this research, which was done in the hospital’s respiratory care unit. All of the patients were seen by a doctor, had a chest radiograph, and had laboratory tests. Mechanical ventilation was used in the care of all patients. Using positive end-expiratory pressure (PEEP) values of 5 and 15, we measured pressure–volume (PV) and lung ultrasound tracings. The PV curve approach was used to assess PEEP-induced lung recruitment. Between PEEP 5 and PEEP 15, there was an extremely strong positive connection between reaeration score and the change in lung volume (r=0.737, P=0.001). Results Between PEEP 5 and PEEP 15, there was a substantial (r=0.577, P=0.003) positive association between the reaeration score and the decrease in PaO2. There was a substantial negative association between reaeration score and mortality (rpb=-0.842, P=0.001), in which mortality reduces as the score increases. Conclusion For quantitative evaluation of PEEP-induced lung recruitment, bedside lung ultrasound is equal to the PV curve approach. In patients with ARDS, PEEP-induced lung recruitment may be assessed using ultrasonography.

Pressure-volume mechanics of inflating and deflating intact whole organ porcine lungs

Pressure-volume curves of the lung are classical measurements of lung function and are impacted by changes in lung structure due to disease or shifts in air-delivery volume or cycling rate. Diseased and preterm infant lungs have been found to show heterogeneous behavior which is highly frequency dependent. This breathing rate dependency has motivated the exploration of multi-frequency oscillatory ventilators to deliver volume oscillation with optimal frequencies for various portions of the lung to provide more uniform air distribution. The design of these advanced ventilators requires the examination of lung function and mechanics, and an improved understanding of the pressure–volume response of the lung. Therefore, to comprehensively analyze whole lung organ mechanics, we investigate six combinations of varying applied volumes and frequencies using ex-vivo porcine specimens and our custom-designed electromechanical breathing apparatus. Lung responses were evaluated through measurements of inflation and deflation slopes, static compliance, peak pressure and volume, as well as hysteresis, energy loss, and pressure relaxation. Generally, we observed that the lungs were stiffer when subjected to faster breathing rates and lower inflation volumes. The lungs exhibited greater inflation volume dependencies compared to frequency dependencies. This study’s reported response of the lung to variations of inflation volume and breathing rate can help the optimization of conventional mechanical ventilators and inform the design of advanced ventilators. Although frequency dependency is found to be minimal in normal porcine lungs, this preliminary study lays a foundation for comparison with pathological lungs, which are known to demonstrate marked rate dependency.

Non-invasive pressure-volume analysis by 3-dimensional echocardiography: a novel method for left ventricular stroke work estimation

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Institute for Surgical Research, Oslo University Hospital. Introduction Left ventricular pressure-volume analysis is a powerful method to quantify left ventricular function. A major limitation of its clinical utility, however, is the need for invasive pressure and volume measurements. We hypothesized that accurate non-invasive left ventricular (LV) stroke work analysis is feasible by combining continuous 3-dimensional (3D) echocardiographic LV volume measurements with non-invasive LV pressure curve estimation. Purpose To investigate if LV stroke work can be estimated non-invasively by combining 3D echocardiographic volume measurements with non-invasive pressure curve estimation. Methods In 21 open-chest anesthetized canines, piezoelectric crystals were placed in the LV subendocardium for volume measurements and a micromanometer catheter was placed in the LV cavity for pressure measurements. Echocardiography was performed directly on the heart to acquire 3D LV volumes and timings of mitral and aortic valve events. The estimated LV pressure curve was obtained by adjusting the cardiac phases of an LV reference pressure curve to these valve events and adjusting its amplitude to measured peak LV pressure. Stroke work was calculated as the area under the pressure-volume curve from mitral valve closure to mitral valve opening. Non-invasively estimated and invasively measured stroke work were compared. Recordings were done during baseline, aortic constriction, dobutamine infusion and after induction of left bundle branch block by ablation. Results Panel A in the Figure illustrates non-invasive (left) and invasive (right) pressure-volume loops from a representative experiment. Baseline and the different interventions are colour-coded allowing visual comparison of the similar non-invasive and invasive stroke work. Panel B shows the pooled data from all experiments. There was a strong correlation (r=0.98, p&amp;lt;0.0001) and good agreement between the non-invasive and invasive stroke work. Furthermore, the non-invasive method captured similar changes in stroke work during interventions as compared to the invasive method (Panel C). Conclusions Non-invasive pressure-volume analysis by combining 3D echocardiography and estimated pressure for stroke work evaluation, is feasible and accurate.

Identifying Plant Physiological and Climatic Drivers in the Woody Shrub Prosopis strombulifera: Effects of Spring Traits on Flower Sprouting and Fruit Production

Prosopis strombulifera is a widely distributed woody species distributed along arid ecosystems in America. The interannual evolution of ecophysiological parameters and their effects on fruit production and flower sprouting in Prosopis strombulifera were studied for three years in a natural population distributed in the Atacama Desert. Xylem water column tension, pressure–volume curves, specific leaf area (SLA), and chlorophyll fluorescence parameters were assessed. Flower sprouting was assessed in different weeks using tagged flowers. To assess fruit production, four small containers were placed under twenty-five individuals, allowing the estimation of total annual production and individual production. We found considerable variability between years and between individuals. Positive relationships were found between plant water parameters, SLA, and chlorophyll variables measured in spring at flower sprouting and during fruit production. A negative correlation was found between the mean of the minimum temperatures in spring and flower sprouting. These results suggest that spring ecophysiological parameters strongly affect the reproductive status of P. strombulifera. The results also reflect the potential of this species to adapt to a hyperarid climate by preserving a high relative water content before flower sprouting.

MATERNAL LEFT VENTRICULAR ADAPTATION IN TWIN PREGNANCY

Objective: During pregnancy, a maternal left ventricular (LV) remodeling occurs to face significant hemodynamic changes. Although twin pregnancy can require greater modifications than in singleton, limited data are currently available. The aim of the study was to longitudinally investigate maternal changes of LV function and compliance in twin pregnancy. Design and method: 35 uncomplicated twin pregnancy women underwent transthoracic echocardiography at first (T1, 10-15 weeks) and third trimester (T3, 30-35 weeks) of gestation. Left atrial (LA) and LV dimensions, LV volumes, systolic and diastolic function were measured, LV mass was calculated. Speckle-tracking imaging was used to evaluate global longitudinal strain (GLS). Non-invasive pressure-volume curves (PV loops) were reconstructed using a dedicated software. Results: Maternal LA and LV dimensions, LV volumes and mass increased from T1 to T3. Ejection fraction and GLS showed no changes between visits. Assessment of diastolic function (at pulsed wave Doppler and tissue Doppler) showed no changes in E/A ratio, while E/e’ ratio was higher at T3. At PV loops analysis, ventricular-arterial coupling (VAC) was stable due to the reduction of both LV end-systolic elastance (Ees) and arterial elastance (Ea). An increase in stroke work was observed. The increase in LV end-diastolic volumes from T1 to T3 with no changes in LV end-diastolic filling pressure suggested enhanced LV cavity compliance (rightward shift of the end-diastolic pressure-volume relationship, EDPVR). Conclusions: Maternal heart in uncomplicated twin pregnancy adapts to the increased hemodynamic load with an increase in stroke work and enhancement of LV volumes without altering ventricular filling pressure.

Hydraulic differences between flowers and leaves are driven primarily by pressure-volume traits and water loss.

Flowers are critical for successful reproduction and have been a major axis of diversification among angiosperms. As the frequency and severity of droughts are increasing globally, maintaining water balance of flowers is crucial for food security and other ecosystem services that rely on flowering. Yet remarkably little is known about the hydraulic strategies of flowers. We characterized hydraulic strategies of leaves and flowers of ten species by combining anatomical observations using light and scanning electron microscopy with measurements of hydraulic physiology (minimum diffusive conductance (g min) and pressure-volume (PV) curves parameters). We predicted that flowers would exhibit higher g min and higher hydraulic capacitance than leaves, which would be associated with differences in intervessel pit traits because of their different hydraulic strategies. We found that, compared to leaves, flowers exhibited: 1) higher g min, which was associated with higher hydraulic capacitance (C T); 2) lower variation in intervessel pit traits and differences in pit membrane area and pit aperture shape; and 3) independent coordination between intervessel pit traits and other anatomical and physiological traits; 4) independent evolution of most traits in flowers and leaves, resulting in 5) large differences in the regions of multivariate trait space occupied by flowers and leaves. Furthermore, across organs intervessel pit trait variation was orthogonal to variation in other anatomical and physiological traits, suggesting that pit traits represent an independent axis of variation that have as yet been unquantified in flowers. These results suggest that flowers, employ a drought-avoidant strategy of maintaining high capacitance that compensates for their higher g min to prevent excessive declines in water potentials. This drought-avoidant strategy may have relaxed selection on intervessel pit traits and allowed them to vary independently from other anatomical and physiological traits. Furthermore, the independent evolution of floral and foliar anatomical and physiological traits highlights their modular development despite being borne from the same apical meristem.

A New Dynamic Slow-Flow Esophageal Balloon Pressure-Volume Curve Calibration Method to Assess Transpulmonary Pressure Monitoring.

A New Dynamic Slow-Flow Esophageal Balloon Pressure-Volume Curve Calibration Method to Assess Transpulmonary Pressure Monitoring.

Bedside Assessment of Lung Recruitability: Making Sense of the Recruitment-to-Inflation Ratio.

Determination of optimum PEEP levels remains an elusive goal. One factor is the recruitability of the lung, yet this is another difficult determination. Recently, a simple bedside technique, called the recruitment-to-inflation ratio, has been described and validated by comparison to the dual pressure-volume curve method. We describe the prior research and concepts of lung mechanics leading up to this metric and develop some background mathematics that help clinicians understand its meaning.