Pierre Gerard

Effective arterial elastance as an index of pulmonary vascular load.

The aim of this study was to test whether the simple ratio of right ventricular (RV) end-systolic pressure (Pes) to stroke volume (SV), known as the effective arterial elastance (Ea), provides a valid assessment of pulmonary arterial load in case of pulmonary embolism- or endotoxin-induced pulmonary hypertension. Ventricular pressure-volume (PV) data (obtained with conductance catheters) and invasive pulmonary arterial pressure and flow waveforms were simultaneously recorded in two groups of six pure Pietran pigs, submitted either to pulmonary embolism (group A) or endotoxic shock (group B). Measurements were obtained at baseline and each 30 min after injection of autologous blood clots (0.3 g/kg) in the superior vena cava in group A and after endotoxin infusion in group B. Two methods of calculation of pulmonary arterial load were compared. On one hand, Ea provided by using three-element windkessel model (WK) of the pulmonary arterial system [Ea(WK)] was referred to as standard computation. On the other hand, similar to the systemic circulation, Ea was assessed as the ratio of RV Pes to SV [Ea(PV) = Pes/SV]. In both groups, although the correlation between Ea(PV) and Ea(WK) was excellent over a broad range of altered conditions, Ea(PV) systematically overestimated Ea(WK). This offset disappeared when left atrial pressure (Pla) was incorporated into Ea [Ea * (PV) = (Pes - Pla)/SV]. Thus Ea * (PV), defined as the ratio of RV Pes minus Pla to SV, provides a convenient, useful, and simple method to assess the pulmonary arterial load and its impact on the RV function.

Open surgery for abdominal aortic aneurysm or aorto-iliac occlusive disease--clinical and ultrasonographic long-term results.

Abstract Objective: To determine postoperative and long-term outcome and assess the relevance of abdominal ultrasound (US) after surgery for abdominal aortic aneurysm (AAA) or aortoiliac occlusive disease (AIOD). Methods: Records of 1704 consecutive patients having graft implantation from 1988 to 2000, either for AAA (n = 1144) or for AIOD (n = 560), were reviewed. In 2006, follow-up was 9180 patients-years for the AAA group and 5450 patients-years for the AIOD group. Among 1006 alive patients, 377 were invited randomly for US and clinical examination. Results: Hospital death occurred in 99 patients (8.6%) of the AAA group (53% in ruptured and 2% in elective AAA), and in 18 patients of the AIOD group (3.2%). There were 581 late deaths, including eight due to prosthesis infection, one to pseudo-aneurysm rupture, and one to graft thrombosis (0.6% graft-related mortality). Prosthesis thrombosis occurred in 32 patients (26 in AIOD group, p < 0.001), and graft infection in 26 (17 in AAA group, p < 0.01). Pseudo-aneurysms developed in 90 patients (68 in AIOD group, p < 0.001), including eight at the proximal aortic, one at the distal aortic, two at the iliac and 79 at the femoral anastomosis. In the AAA group only, surgery was required for a new thoraco-abdominal and pararenal aneurysm in eight and four patients, respectively, while US evidenced a 26–35 and a 36–50 mm supraanastomotic aortic dilatation in 65 (32%) and in 14 (7%) patients, at a mean follow-up of 10.5 and 9.3 years, respectively. Conclusion: Long-term results are good after open surgery for AAA or AIOD. Prosthesis infection and anastomotic pseudo-aneurysm are the main causes of graft-related mortality and morbidity, respectively. Because of high incidence of asymptomatic supraanastomotic aortic dilatation, all patients with a history of AAA repair should have regular abdominal US.

Hydro-mechanical modelling of the development of preferential gas pathways in claystone

During long-term repository of radioactive waste in argillaceous formation, the gas migration in the host formation and in the engineered barriers is a crucial issue, because it could affect the safety function of the clay barriers. Gas migration tests on Callovo-Oxfordian argillite have been performed by the British Geological Survey. The observations show that gas migration is often accompanied by the development of preferential pathways, which propagate through the sample. Hydro-mechanical numerical modelling of these tests is performed. It appears that a continuum approach to the movement of gas is not sufficient to reproduce the experimental observations. A coupling between deformation of the medium, permeability and air entry pressure is proposed. The numerical results show that such coupling play an important role in a successful simulation of such gas flows.

Gas injection test in the Callovo-Oxfordian claystone : data analysis and numerical modelling

Abstract This paper describes a field-scale experiment on gas transport mechanisms performed at Andras Underground Research Laboratory (URL) in a clay rock. The experimental layout consists of two parallel boreholes that are equipped with multiple packer completions isolating three intervals each, which have been continuously monitoring the pore pressure evolution of the clay rock. Nitrogen gas was injected in the middle test interval of one of the boreholes at increasing rates. The entire gas test comprised six periods of controlled gas injections, each followed by a shut-in pressure recovery phase. The experimental data are presented along with their interpretation by means of numerical modelling of two-phase flow of gas and water using different numerical codes and different geometrical approaches that include axisymmetric, half-space and full 3D models. An iterative modelling process was used to show step-by-step how an accurate description of each component of the experiment system produced a satisfactory reproduction of the experimental data and an improved understanding of the relevant phenomena. For instance, the initial volume of remaining water in the test interval, and the presence of a damaged zone around the boreholes, was important for the models to obtain good agreement with the field data.

Hydro-Mechanical Modelling of the Boom Clay Excavation, Convergence and Contact with Concrete Lining

The Boom Clay is considered as one of the potential host rock formation in Belgium for radioactive waste repository in deep geological layers. Gallery excavations will induce large hydro-mechanical disturbances around disposal system that need to be well understood and characterised. This study discusses particularly the role of interactions between the lining of the galleries and the host formation in the numerical characterisation of excavations in Boom Clay. The excavation and the convergence of the connecting gallery of the HADES underground research facility in Mol is modelled in a hydro-mechanical framework. Zero-thickness interface elements are used to manage numerically the contact between the host rock and the lining. Numerical predictions are compared with strains measurements recorded within the concrete segments of the lining in the underground research laboratory in Mol. The study highlights the impact of the anisotropic behavior of the host rock on the response of the model.

Characterization of gas transport in low-permeability media: two-phase flow analysis of an in-situ experiment

This paper describes a field-scale experiment on gas transport mechanisms performed at the Andra Underground Research Laboratory in a clay rock. The experimental layout consists of two parallel boreholes that are equipped with multiple packer completions delimiting three intervals each and which monitor continuously the pore pressure evolution of the clay rock. Nitrogen gas is injected in the middle test interval of one of the boreholes at increasing constant rates. The experimental data collected so far are presented along with their interpretation by means of 1D and 3D numerical modeling of the boundary value problem. The numerical results show that a predictive model as two-phase flow approach is able to reproduce experimental observations in large scale system, as far as the injection flow rate and the gas pressures remain moderate. Moreover permeability is not modified by gas injection, which indicates that the rock mass is not damaged by the gas pressure increase during the test.