Index Pressure Gradient Research Articles

Physiological disease pattern as assessed by PPGI in vessels with FFR and iFR discordance

Abstract Background Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) disagree on the hemodynamic significance of a coronary lesion in≈20% of cases. It is unclear whether the physiological pattern of disease is an influencing factor for this. This study assessed whether the physiological pattern of coronary artery disease (CAD) as assessed by angiography derived pullback pressure gradient index (PPGI) influences discordance between FFR and iFR measurement. Methods and results This study is a centralized off-line analysis by an independent academic core laboratory (CORRIB Core lab) of a prospective cohort of 444 vessels with both pressure wire-instantaneous wave free ratio (PW-iFR) and pressure wire-fractional flow reserve (PW-FFR) measurements. The study population consisted of a patients presenting with chronic coronary syndrome and having at least one epicardial coronary artery lesion with a 40% to 90% diameter stenosis by visual assessment on invasive coronary angiography. Three-hundred and ninety vessels (355 patients; mean age, 68±10 years; 70% men) with combined FFR, iFR, QFR and angiography derived PPGI were included. QFR was calculated using the QAngio XA 3D 2.1 software package (Medis Medical Imaging System BV, Leiden, The Netherlands). PPGI was calculated using the QFR 2.1.38.2 Research Edition software package. Cut points for hemodynamic significance were FFR ≤0.80 and iFR ≤0.89, respectively. Vessels were classified into FFR+/iFR+ (n=103; 26.4%), FFR-/iFR+ (n=27; 6.9%), FFR+/iFR- (n=38; 9.7%), and FFR-/iFR- (n=222; 57%) groups.. Median FFR, iFR, and QFR were 0.84 (0.77-0.90), 0.92 (0.88-0.97), and 0.83 (0.73-0.90) respectively. FFR disagreed with iFR in 16.7% (65 of 390). The Median PPGI was 0.75 (0.67-0.85). Vessels with PPGI ≥0.75 was considered to have predominantly focal disease pattern and vessels with PPGI <0.75 was considered to have predominantly diffuse disease pattern. The physiological pattern of disease was classified according to the angiography derived pullback pressure gradient index (PPGI) as predominantly physiologically focal (n=209; 53.6%) or predominantly physiologically diffuse (n=181; 46.4%). The median PPGI was significantly lower in FFR-/iFR+ vessels as compared to FFR+/iFR- vessels [0.65(0.60-0.69) vs 0.82(0.75-0.85), p<0.001). The physiological pattern of disease was the influencing factor relating to FFR/iFR discordance: predominantly physiologically focal was significantly associated with FFR+/iFR- (76.3% [29 of 38]), and predominantly physiologically diffuse was significantly associated with FFR-/iFR+ (96.3% [26 of 27]; P<0.001 for pattern of disease between FFR+/iFR- and FFR-/iFR+ groups). Conclusions The physiological pattern of coronary artery disease was an important influencing factor for FFR/iFR discordance.

TCT-721 Angiography-Based FFR Derived Pullback Pressure Gradient Index and OCT-Detected Plaque Morphology in Chronic Coronary Syndrome Patients With Intermediate Grade Stenoses

TCT-721 Angiography-Based FFR Derived Pullback Pressure Gradient Index and OCT-Detected Plaque Morphology in Chronic Coronary Syndrome Patients With Intermediate Grade Stenoses

TCT-658 Physiologic Coronary Artery Disease Pattern (Focal or Diffuse) as Assessed by Angiography Pull-Back Pressure Gradient Index (PPGI) in Vessels With Fractional Flow Reserve (FFR) and Instantaneous Wave-Free Ratio (iFR) Discordance

TCT-658 Physiologic Coronary Artery Disease Pattern (Focal or Diffuse) as Assessed by Angiography Pull-Back Pressure Gradient Index (PPGI) in Vessels With Fractional Flow Reserve (FFR) and Instantaneous Wave-Free Ratio (iFR) Discordance

Angiography-derived physiological assessment after percutaneous coronary intervention of chronic total occlusions.

Scant data exploring potential suboptimal physiological results after angiographic successful percutaneous coronary intervention (PCI) of chronic total occlusion (CTO) are available. Sixty cases of successful CTO-PCI were selected for this retrospective analysis. Post-CTO-PCI angiography-based fractional flow reserve was computed using the Murray-based fractional flow reserve (μFR) software. Vessel-specific μFR, residual trans-stent gradient (TSG) and corrected TSGstent were calculated. In physiological suboptimal results (μFR < 0.90), the virtual pullback pressure gradient (PPG) curves were analyzed to localize the main pressure drop-down and characterize the patterns of residual disease. The virtual pullback pressure gradient index (vPPGi) was then calculated to objectively characterize the predominant pattern of residual disease (diffuse vs focal). The physiological result was suboptimal in 28 cases (46.7%). The main pressure drop was localised proximal to the stent in 2 (7.1%), distal in 17 (60.7%) and intra-stent in 9 cases (32.2%). Intra-stent residual disease was diffuse in 7 cases and mixed in 2. Distal residual disease was characterised by a pure focal pattern in 12 cases, diffuse in 2 and mixed in 3. In the predominant diffuse phenotype (vPPGi < 0.65), we found a higher rate of TSG ≥ 0.04 (61.5% vs 20.0%, p = 0.025) and TSGstent ≥ 0.009 (46.2% vs 20.0%, p = 0.017) while in the dominant focal phenotype poor-quality distal vessel was constantly present. In our cohort, post-CTO-PCI suboptimal physiological result was frequent (46.7%). Predominant focal phenotype was constantly associated with poor-quality distal vessel, while in the predominant diffuse phenotype, the rate of TSG ≥ 0.04 and TSGstent ≥ 0.009 were significantly higher.

Geographic disparity of pathophysiological coronary artery disease characteristics: Insights from ASET trials

BackgroundThe geographical disparity in the pathophysiological pattern of coronary artery disease (CAD) among patients undergoing percutaneous coronary intervention (PCI) is unknown. ObjectivesTo elucidate the geographical variance in the pathophysiological characteristics of CAD. MethodsPhysiological indices derived from angiography-based fractional flow reserve pullbacks from patients with chronic coronary syndrome enrolled in the ASET Japan (n = 206) and ASET Brazil (n = 201) studies, which shared the same eligibility criteria, were analysed.The pathophysiological patterns of CAD were characterised using Murray law-based quantitative flow ratio (μQFR)-derived indices acquired from pre-PCI angiograms. The diffuseness of CAD was defined by the μQFR pullback pressure gradient index. ResultsSignificant functional stenoses pre-PCI (μQFR ≤0.80) were more frequent in ASET Japan compared to ASET Brazil (89.9% vs. 67.5%, p < 0.001), as were rates of a post-PCI μQFR <0.91 (22.1% vs. 12.9%, p = 0.013). In the multivariable analysis, pre-procedural μQFR and diffuse disease were independent factors for predicting a post-PCI μQFR <0.91, which contributed to the different rates of post-PCI μQFR ≥0.91 between the studies. Among vessels with a post-PCI μQFR <0.91, a consistent diffuse pattern of CAD pre- and post-PCI occurred in 78.3% and 76.7% of patients in ASET Japan and Brazil, respectively; only 6.3% (Japan) and 10.0% (Brazil) of vessels had a major residual gradient. Independent risk factors for diffuse disease were diabetes mellitus in ASET Japan, and age and male gender in Brazil. ConclusionsThere was geographic disparity in pre-procedural angiography-based pathophysiological characteristics. The combined pre-procedural physiological assessment of vessel μQFR and diffuseness of CAD may potentially identify patients who will benefit most from PCI.

Pullback pressure gradient index: can it predict plaque phenotype?

Pullback pressure gradient index: can it predict plaque phenotype?

Impact of coronary physiological phenotypes on the immediate angiography-derived hemodynamic results of percutaneous coronary intervention

Abstract Background Angiography-based technologies can evaluate the physiological phenotypes of coronary artery disease (CAD) and the functional results of percutaneous coronary intervention (PCI), however, few studies have combined these to assess CAD pre- and post-PCI. Purpose We investigated the impact of physiological phenotypes of CAD on immediate post-PCI angiography-derived functional indices. Methods We analyzed 1004 vessels from three ongoing trials. Pre-PCI physiological phenotypes were characterized according to the angiography-derived pullback pressure gradient index (PPGi) as focal (≥0.66) or diffuse (&amp;lt;0.66). Local disease severity was assessed by instantaneous quantitative flow reserve (QFR) gradient per unit length (dQFR/ds) with a dQFR/ds≥0.025/mm, a "major" gradient. Post-PCI, epicardial and microvasculature functions were assessed using QFR and the index of microcirculatory resistance (angio-IMR), respectively. Results Pre-PCI, 327(35.81%) vessels had a PPGi&amp;lt;0.66, whilst 121 (13.25%) had a dQFR/ds&amp;lt;0.025 (Figure1, panel A). Post-PCI, a QFR&amp;lt;0.91 and IMR≥25 occurred in 247 (24.6%) and 310 (30.9%) vessels, respectively (Figure2, panel B). A post-PCI QFR&amp;lt;0.91 was associated with a lower PPGi (Odds ratio [OR]:1.31[1.17-1.47], p&amp;lt;0.001, Figure 1, panel C) but not a dQFR/ds (OR:0.99[0.96-1.02], p=0.453). A post-PCI IMR&amp;lt;25 was not associated with PPGi or dQFR/ds. Worsening in the IMR post-PCI was significantly associated with lower PPGi (1.31[1.16-1.48], p&amp;lt;0.001, Figure 1, panel D) and higher dQFR/ds (1.08[1.02-1.14], p=0.008, Figure 1, panel E) pre-PCI. Higher PPGi was associated with a higher odds ratio of achieving the optimal result (OR per 0.1 increase 1.25, [1.13-1.38], p&amp;lt;0.001, Figure 1, panel F). Multivariable analysis identified PPGi as an independent predictor of a post-PCI QFR≥0.91 and an optimal outcome (QFR≥0.91 and IMR&amp;lt;25, Figure2). Conclusion the phenotype of CAD pre-PCI can help predict functional outcome post-PCI, and therefore angiography-derived assessment has an important role in determining treatment strategy and outcome.Figure 1Figure 2

Physiological phenotype of coronary artery disease on short-term angina status in patients with CCS after PCI: perspective from PIONEER IV trial

Abstract Background The hemodynamic impact of PCI on major epicardial conductance vessels is the results of a complex interplay between diffuseness and focality of coronary artery atherosclerosis. The pre-procedural identification of these two phenotypes (diffuseness vs. focality) may have important implication on the angina relief after PCI. Purpose The aim of this study was to determine the differential improvement in patient-reported outcomes after PCI in focal and diffuse CAD as defined by the pullback pressure gradient index (PPGi) derived from angiography. Methods The PIONEER IV trial is a prospective, all-comers, multi-center trial, randomizing patients to PCI guided by angiography-derived physiology or usual care, with both arms using the Healing-Targeted Supreme sirolimus-eluting stent. Pre-procedural PPGi derived from angiography was documented. The 7-item Seattle Angina Questionnaire (SAQ-7) was administered at baseline and 30 days after PCI. The median PPG value was used to define focal and diffuse CAD. Residual angina was defined as a SAQ-AF score ≤ 90. Results A total of 203 patients were analyzed, in which 105 patients with focal CAD and 98 diffuse. Focal disease had larger pre-procedure QFR and post-procedure QFR value than patients with diffuse disease (0.71 ± 0.13 vs 0.59 ± 0.19, P &amp;lt; 0.001; 0.96 ± 0.04 vs 0.91 ± 0.08, P &amp;lt; 0.001). The median of PPGi was 0.73 (Figure 1A). In the restricted cubic spline model, the risk of residual angina rises substantially when the pre-procedural PPGi was below 0.74 (Figure 1B). Patients with focal disease who underwent PCI for focal CAD had significantly higher angina frequency score and quality of life score at follow-up than those with diffuse CAD (94.10 ± 11.58 vs 89.80 ± 16.31, P = 0.031; 75.77 ± 26.01 vs 67.17 ± 25.86, P=0.024; Figure 2). After PCI, residual angina was present in 35.0% but was significantly less in those with treated focal CAD (26.7 % vs 43.9 %; P = 0.015; Figure 1C-D). Conclusion Residual angina after PCI was higher in patients with diffuse CAD, whereas patients with focal CAD reported greater improvement in angina and quality of life. Whether pre-procedural physiological phenotyping should alter the therapeutic decision making to perform PCI, and could influence the procedure planning warrants further study.Figure 1Figure 2

Temporary venovenous extracorporeal membrane oxygenation after cardiopulmonary bypass in minimally invasive cardiac surgery via right minithoracotomy.

In minimally invasive cardiac surgery, it can be difficult at times to maintain adequate oxygenation with single-lung ventilation after weaning from cardiopulmonary bypass (CPB), and intermittent double-lung ventilation is required during hemostasis. Venovenous extracorporeal membrane oxygenation (VV-ECMO) after weaning from CPB eliminates the necessity of overinflation of the left lung and intermittent double-lung ventilation and enables secure and fast hemostasis. We investigated the effectiveness and safety of temporary VV-ECMO in MICS. Between May 2018 and March 2021, 149 patients underwent temporary VV-ECMO during minimally invasive cardiac surgery in our institutions. After weaning from CPB, the arterial circuit was reconnected to the right internal jugular venous cannula, the femoral venous cannula was pulled down by 20cm, and VV-ECMO was established using the CPB machine and cannulas. After starting VV-ECMO, we administered protamine and performed hemostasis. Operative data and outcomes were retrospectively reviewed. The mean VV-ECMO time and flow were 26 ± 13minutes and 2.38 ± 0.40L/m2, respectively. There was no thrombus in the CPB circuit, including the oxygenator. The trans-oxygenator pressure gradient index at the end of VV-ECMO significantly correlated with that at the start of VV-ECMO (r=0.88; 95% CI, 0.79-0.94; P=.01). The 30-day mortality rate was 2.0%. The incidences of unilateral pulmonary edema, prolonged ventilation, and re-exploration for bleeding were 2.7%, 5.4%, and 2.0%, respectively. Temporary VV-ECMO is safe and useful to maintain single-lung ventilation without overinflation after weaning from CPB for secure and fast hemostasis in minimally invasive cardiac surgery. No thrombotic event was found during temporary VV-ECMO without heparinization.

Accretion of aerodynamically large pebbles

ABSTRACT Due to their aerodynamical coupling with gas, pebbles in protoplanetary discs can drift over large distances to support planet growth in the inner disc. In the past decade, this pebble accretion has been studied extensively for aerodynamically small pebbles (Stokes number St &amp;lt; 1). However, accretion can also operate in the St &amp;gt; 1 mode, e.g. when planetesimals collisionally fragment to smaller bodies or when the primordial gas disc disperses. This work aims to extend the study of pebble accretion to these aerodynamically loosely coupled particles. We integrate the pebble’s equation of motion, accounting for gas drag, stellar and planetary gravity, in the mid-plane of a laminar disc. The accretion probability (ϵ) is calculated as function of Stokes number, disc pressure gradient index, planet mass, and eccentricity. We find that for Stokes number above unity ϵ(St) first rises, due to lower drift and aided by a large atmospheric capture radius, until it reaches a plateau where the efficiency approaches 100 per cent. At high St, the plateau region terminates as particles become trapped in resonance. These results are well described by a semi-analytical ‘kick-and-drift’ model and we also provide fully analytical prescriptions for ϵ. We apply our model to the accretion of ${\sim }30\, \mu \mathrm{m}$ dust particles in a dispersing protoplanetary and secondary (CO-rich) debris disc. It shows that such physically small particles are mainly accreted as aerodynamically large Stokes number pebbles during the debris disc phase. Earth-mass planets may obtain ∼25 per cent of their heavy elements through this late accretion phase.

Corrected pressure gradient index on the pulmonary artery valve in patients with pulmonary embolism

Corrected pressure gradient index on the pulmonary artery valve in patients with pulmonary embolism

Angiographic quantitative flow ratio in acute coronary syndrome: beyond a tool to define ischemia-causing stenosis-a literature review.

Numerous studies have demonstrated the safety and effectiveness of physiology-guided coronary revascularization in chronic coronary syndrome, resulting in a high level of guideline recommendation for these patients. However, the application of coronary physiology in acute coronary syndrome (ACS), especially in the acute phase of myocardial infarction, remains challenging. Over the last decade, the number of novel physiological indices derived from the computation of angiography have been developed as alternatives to pressure wire-based fractional flow reserve. Among these angiography-based indices, the quantitative flow ratio (QFR) is undoubtedly the one with the largest amount of data cumulated so far. In this article, we aim to review the related studies that describe efforts to investigate the diagnostic role of QFR and discuss perspectives for its current and future applications in the setting of the ACS. A literature search was performed on the electronic databases, including PubMed, Google Scholar and Web of Science covering publications in English up to May 2022. An emerging body of evidence has validated the diagnostic accuracy of angiography-derived QFR for the assessment of functional severity of coronary stenosis in both acute and chronic coronary syndromes. In parallel, multiple technologies, i.e., QFR-based pullback pressure gradient index, angiography-derived index of microcirculatory resistance and intravascular imaging-based morphofunctional evaluation methods, have been proposed, allowing operators to easily obtained physiological data of micro and macro-circulation, together with atherosclerotic lesion characteristics in catheterization laboratories. More recently, promising results supporting the clinical value of QFR in guiding revascularization and predicting outcomes for ACS patients have been published. Angiography-based QFR bears the potential of a wider adoption of coronary physiology assessment in the ACS setting due to its quicker and less-invasive nature. However, the current evidence mainly derived from retrospective studies or post-hoc analyses of prospective trials. Future studies are needed to further explore the benefits of QFR-guided revascularization on outcomes in ACS.

Extreme cold wave in early November 2021 in China and the influences from the meridional pressure gradient over East Asia

In early November 2021, China experienced its second strongest cold wave event during 1981–2021. Although the Siberian high is considered the main factor influencing cold wave events in East Asia, it was not extremely strong from 4 to November 9, 2021. The spatial distribution of the correlation coefficients between the sea level pressure and the daily temperature anomalies shows a monopole pattern, with a notable negative centre in the southern part of the Siberian high monitoring domain. However, the correlation between the sea level pressure and temperature drop presents a typical dipole pattern, with a distinct negative centre in the northern monitoring domain and a positive centre in southern East Asia. During the November 2021 super cold wave process, the sea level pressure anomalies display a dipole pattern with a higher centre in the north and a lower centre in the south owing to the northward shift of the Intertropical Convergence Zone. The meridional pressure gradient index clearly reveals the non-negligible effect of subtropical low-pressure on this super cold wave process, indicating its possibly essential supplementary role in enhancing this process. The above findings provide a new understanding of its mechanism and long-range forecasts.

Prognostic Implications of Quantitative Flow Ratio-Derived Physiological 2-Dimensional Residual Disease Patterns After Stenting.

Post-percutaneous coronary intervention (PCI) residual disease is associated with clinical outcomes. Nevertheless, the prognostic value of residual disease patterns remains unknown. This study aimed to evaluate clinical implications of 2-dimensional residual disease patterns after PCI. One thousand six hundred seven vessels that underwent successful PCI were included. Two-dimensional residual disease patterns were determined by visual assessment or the quantitative flow ratio (QFR)-derived pull back pressure gradient index (with a cutoff value of 0.78 to define predominant focal versus diffuse disease) and instantaneous QFR gradient per unit length (with a cutoff value of≥0.005/mm to define a major gradient). The clinical outcome was the 2-year vessel-oriented composite outcome (VOCO). Residual disease patterns were classified into 4 groups: predominant focal without and with a major gradient (group 1 [n=1,058] and group 2 [n=63], respectively) and predominant diffuse without and with a major gradient (group 3 [n=318] and group 4 [n=168], respectively). At 2 years, VOCO was lowest in group 1 (1.4% vs 5.4% in group 2 vs 4.8% in group 3 vs 8.5% in group 4, all P< 0.05), whereas there was no prognostic value for classifications by visual assessment. Physiological residual disease patterns were independently associated with VOCO and showed increased prognostic value when introduced to a model with clinical risk factors only (C index: 0.77 vs. 0.68, P = 0.008; net reclassification improvement: 0.65, P< 0.001; integrated discrimination improvement: 0.020, P< 0.001). Objective analysis of post-PCI QFR pull backs using the concept of 2-dimensional residual disease patterns is feasible and superior to visual assessments. The residual disease patterns were independently associated with VOCO at 2 years.

Physiological Distribution and Local Severity of Coronary Artery Disease andOutcomes After Percutaneous Coronary Intervention.

The aim of this study was to evaluate prognostic implications of physiological 2-dimensional disease patterns on the basis of distribution and local severity of coronary atherosclerosis determined by quantitative flow ratio (QFR) virtual pull back. The beneficial effect of percutaneous coronary intervention (PCI) is determined by physiological distribution and local severity of coronary atherosclerosis. The study population included 341 patients who underwent angiographically successful PCI and post-PCI fractional flow reserve (FFR) measurement. Using pre-PCI virtual pull backs of QFR, physiological distribution was determined by pull back pressure gradient index, with a cutoff value of 0.78 to define predominant focal versus diffuse disease. Physiological local severity was assessed by instantaneous QFR gradient per unit length, with a cutoff value of≥0.025/mm to define a major gradient. Suboptimal post-PCI physiological results were defined as both post-PCI FFR≤0.85 and percentage FFR increase≤15%. Clinical outcome was assessed by target vessel failure (TVF) at 2 years. QFR pull back pressure gradient index was correlated with post-PCI FFR (R=0.423; P< 0.001), and instantaneous QFR gradient per unit length was correlated with percentage FFR increase (R=0.370; P< 0.001). Using the 2 QFR-derived indexes, disease patterns were classified into 4 categories: predominant focal disease with and without major gradient (group 1 [n=150] and group 2 [n=21], respectively) and predominant diffuse disease with and without major gradient (group 3 [n=115] and group 4 [n=55], respectively). Proportions of suboptimal post-PCI physiological results were significantly different according to the 4 disease patterns (18.7%, 23.8%, 22.6%, and 56.4% from group 1 to group 4, respectively; P< 0.001). Cumulative incidence of TVF after PCI was significantly higher in patients with predominant diffuse disease (8.1% in group 3 and 9.9% in group 4 vs 1.4% in group 1 and 0.0% in group 2; overall P=0.024). Both physiological distribution and local severity of coronary atherosclerosis could be characterized without pressure-wire pull backs, which determined post-PCI physiological results. After successful PCI, TVF risk was determined mainly by the physiological distribution of coronary atherosclerosis. (Automated Algorithm Detecting Physiologic Major Stenosis and Its Relationship With Post-PCI Clinical Outcomes [Algorithm-PCI], NCT04304677; Influence of FFR on the Clinical Outcome After Percutaneous Coronary Intervention [PERSPECTIVE], NCT01873560).

Arctic Sea Ice Area Export Through the Fram Strait Estimated From Satellite-Based Data:1988–2012

By combing ice motion and concentration fields, we obtain the estimates of ice area flux passing the Fram Strait over a 25-year period (1988–2012). Mean monthly area flux exhibits a prominent cycle with the peak in March $\rm{(78 \times 10}^{3}\,\text{km}^{2}\text{/month)}$ and the trough in August $\rm{(5 \times 10}^{3}\,\text{km}^{2}/\text{month)}$ . Mean net annual ice area flux $\rm{(644.1 \times 10}^{3}\,\text{km}^{2}\,\text{km}^{2}\rm{)}$ is primarily/slightly attributable to winter (October–May)/summer (June–September) outflow of $\rm{598.7\times 10}^{3}\,\text{km}^{2}$ $\rm{(or\; 93.0\%)/ 45.4 \times 10}^{3}\,\text{km}^{2} (\rm{or} 7\%)$ . However, these quantities need to be considered with great prudence since comparisons with preceding studies indicate distinct difference may exist between calculated Fram Strait sea ice outflow based on varied ice motion datasets. In particular, major bias emerged during winter rather than summer. Trends are also affected due to this bias. Despite the clear disparity in magnitude, we found a good agreement with preceding estimates in terms of temporal variability. The linkage between ice area flux via the Fram Strait and various atmospheric circulation indices, such as the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), a west-east dipole anomaly pattern (DA), as well as a seesaw structure between Beaufort and Barents Sea (BBO), was examined. Results show that atmospheric circulation patterns linked to the DA and BBO possess a relatively stronger influence on Fram Strait ice export over the 25-year period. By contrast, the AO- and NAO-related atmospheric circulation pattern exhibit weaker connections with ice outflow through the strait. In addition, correlation analysis further justify the robust connection with a cross-strait surface level pressure gradient index. Depending on months, it is suggested that a manifold of aforementioned atmospheric indices may jointly or alone impose a significant influence on sea ice export through the Fram Strait.

Projection and Analysis of Extreme Wave Climate

Abstract The nonhomogeneous Poisson process is used to model extreme values of the 40-yr ECMWF Re-Analysis (ERA-40) significant wave height. The parameters of the model are expressed as functions of the seasonal mean sea level pressure anomaly and seasonal squared sea level pressure gradient index. Using projections of the sea level pressure under three different forcing scenarios by the Canadian coupled climate model, projections of the parameters of the nonhomogeneous Poisson process are made, trends in these projections are determined, return-value estimates of significant wave height up to the end of the twenty-first century are projected, and their uncertainties are assessed. The uncertainty of estimates associated with the nonhomogeneous Poisson process estimates is studied and compared with the homologous estimates obtained using a nonstationary generalized extreme value model.

Winter surface pressure anomalies over Eurasia and Indian summer monsoon

In this study, the spatial relationships between the monthly mean sea level pressure (MSLP) anomalies and Indian summer monsoon rainfall (ISMR) have been examined using the gridded MSLP data (GMSLP2) for 46 years (1949–1994). Winter MSLP anomalies over NW Europe (south Europe) are negatively (positively) correlated with ISMR. During the strong (deficient) monsoon years, there is enhanced (weakened) poleward pressure gradient over Eurasia. The Europe pressure gradient index, which is an indicator of the winter poleward pressure gradient, is significantly and positively correlated with ISMR. This relationship also suggests a link between the North Atlantic Oscillation and ISMR on inter‐annual time scale. The winter pressure gradient over Eurasia has physical linkage with Indian summer monsoon rainfall, through winter snow cover anomalies and springtime mid latitude activities like upper tropospheric blocking highs and stationary wave anomalies.

The pulmonary vein Doppler flow velocity waveform: feature analysis by comparison of in vivo pressures and flows with those in a computerized fetal physiological model

Doppler flow velocity waveforms (FVW) in fetal veins that discharge into the atria show fluctuations related to atrial events. Pulmonary veins are of particular interest because both ends (atrial and collecting venule) are within the intrathoracic pressure environment reducing fetal breathing artifacts. Indices, such as pulsatility index for veins (PIV), have been suggested to classify FVWs and relate them to fetal well being. We wished to examine the relationship between function and FVW in circumstances which cannot ethically be examined in vivo, by studying the mechanisms which produced altered 'flows' in a detailed fetal computer model. We then related these findings to current flow indices. A computer model of the feto-placental unit, responding to changes in organ oxygenation and regional flow is briefly described. In vivo intracardiac pressures and FVWs obtained from other studies were used to extend detail in the model until matching 'pressures' and 'flows' resulted. The effects of flow redistribution in the hypoxic fetus on pulmonary vein 'Doppler' flow velocity waveforms were then studied. Flow reversal in pulmonary veins during atrial contraction indicates hypoxia, but change of shape of the FVW envelope reflects the changes in the pressure waveform of the left atrium. Of the major veins the pulmonary vein Doppler FVW gave the truest representation of atrial pressure response to both intracardiac and systemic vascular status. Although current indices indicate general fetal condition, more specific indices are needed if pulmonary venous flow is to be used as an end-point. A pulmonary vein pressure gradient index is suggested.

Relation between progressive decreases in regional coronary perfusion and contractile abnormalities

To determine the quantitative relation between partial coronary obstruction and its resultant effects on local contraction, the left anterior descending coronary artery was partially obstructed (while the decrease in both distal pressure and flow were observed) and local tension and len gth were mea sured in 10 open chest dogs. A pressure gradie nt in dex ([AO-COR] /AO) across the obstruction was derived, where AO = mean aortic pressure and COR = mean distal coronary pressure, and was correlated with change in flow ( control flow = 95.3 ± 3.8 ml/100 g). Contractile function of ischemic and nonischemic zones was measured using both Walton-Brodie strain and mercury-in-Silastic segment length gauges. Small pressure gradients (index 0.27 ± 0.03 [mean ± standard error of the mean]) and decreases in distal flow (to 74.2 ± 1.6 ml/100 g) caused no change in tension or length. Further reduction in distal pressure (gradient index 0.52 ± 0.04) and flow (to 50.0 ± 0.8 ml/100 g) produced a decrease in tension to 87.3 ± 3.6 percent of control level ( P < 0.005) and an increase in length to 129.1 ± 4.6 percent ( P < 0.01). The upstroke of the tension curve during the ejection phase persisted despite the decrease in total tension. Additional reduction of pressure (gradient index 0.71 ± 0.03) and flow (27.7 ± 1.3 ml/100 g) caused a marked decrease in tension to 55.5 ± 11.9 percent of control level ( P < 0.01) and an increase in length to 182.0 ± 14.1 percent ( P < 0.001). The tension curve demonstrated loss of ejection tension with a negative slope inscribed during the ejection phase. Total occlusion resulted in no additional decrease in distal pressure and, although flow decreased to 5.0 ± 1.2 ml/100 g, no further change in tension (56.8 ± 9.3 percent) or length (183.3 ± 8.9 percent) occurred. Thus, an acute reduction in coronary pressure and flow of 50 percent or more results in regional contraction abnormalities that are further accentuated as the pressure and flow are reduced by 75 percent or more. Maximal abnormalities produced by total occlusion are similar to those produced by a reduction in flow of 75 percent or more.