Mud volcanoes of trinidad as astrobiological analogs for martian environments.

Eleven onshore mud volcanoes in the southern region of Trinidad have been studied as analog habitats for possible microbial life on Mars. The profiles of the 11 mud volcanoes are presented in terms of their physical, chemical, mineralogical, and soil properties. The mud volcanoes sampled all emitted methane gas consistently at 3% volume. The average pH for the mud volcanic soil was 7.98. The average Cation Exchange Capacity (CEC) was found to be 2.16 kg/mol, and the average Percentage Water Content was 34.5%. Samples from three of the volcanoes, (i) Digity; (ii) Piparo and (iii) Devil's Woodyard were used to culture bacterial colonies under anaerobic conditions indicating possible presence of methanogenic microorganisms. The Trinidad mud volcanoes can serve as analogs for the Martian environment due to similar geological features found extensively on Mars in Acidalia Planitia and the Arabia Terra region.

Oil biodegradation. Water droplets in oil are microhabitats for microbial life.

Anaerobic microbial degradation of hydrocarbons, typically occurring at the oil-water transition zone, influences the quality of oil reservoirs. In Pitch Lake, Trinidad and Tobago--the world's largest asphalt lake--we found that microorganisms are metabolically active in minuscule water droplets (1 to 3 microliters) entrapped in oil. Pyrotag sequencing of individual droplet microbiomes revealed complex methanogenic microbial communities actively degrading the oil into a diverse range of metabolites, as shown by nuclear magnetic resonance and Fourier transform ion cyclotron resonance mass spectrometry. High salinity and water-stable isotopes of the droplets indicate a deep subsurface origin. The 13.5% water content and the large surface area of the droplets represent an underestimated potential for biodegradation of oil away from the oil-water transition zone.

Microbial life in a liquid asphalt desert.

Pitch Lake in Trinidad and Tobago is a natural asphalt reservoir nourished by pitch seepage, a form of petroleum that consists of mostly asphaltines, from the surrounding oil-rich region. During upward seepage, pitch mixes with mud and gases under high pressure, and the lighter portion evaporates or is volatilized, which produces a liquid asphalt residue characterized by low water activity, recalcitrant carbon substrates, and noxious chemical compounds. An active microbial community of archaea and bacteria, many of them novel strains (particularly from the new Tar ARC groups), totaling a biomass of up to 10(7) cells per gram, was found to inhabit the liquid hydrocarbon matrix of Pitch Lake. Geochemical and molecular taxonomic approaches revealed diverse, novel, and deeply branching microbial lineages with the potential to mediate anaerobic hydrocarbon degradation processes in different parts of the asphalt column. In addition, we found markers for archaeal methane metabolism and specific gene sequences affiliated with facultative and obligate anaerobic sulfur- and nitrite-oxidizing bacteria. The microbial diversity at Pitch Lake was found to be unique when compared to microbial communities analyzed at other hydrocarbon-rich environments, which included Rancho Le Brea, a natural asphalt environment in California, USA, and an oil well and a mud volcano in Trinidad and Tobago, among other sites. These results open a window into the microbial ecology and biogeochemistry of recalcitrant hydrocarbon matrices and establish the site as a terrestrial analogue for modeling the biotic potential of hydrocarbon lakes such as those found on Saturn's largest moon Titan.

Outcome of the Norwood procedure in the setting of transposition of the great arteries and functional single left ventricle.

OBJECTIVE: To assess the surgical results of the Norwood procedure and subsequent clinical outcome in the setting of transposition of the great arteries (TGA) with a dominant morphologic left ventricle. METHODS: Among 486 patients who underwent the Norwood procedure from 1988 to 2007 at our institution, there were 37 patients with TGA and left ventricular dependant circulation with the following associated lesions: double inlet left ventricle (DILV) (n=24), tricuspid atresia (n=9), ventricular septal defect (VSD) with hypoplastic right ventricle (RV) (n=4). Outcomes for all three-staged procedure were compared with the overall Norwood group. RESULTS: Early mortality was 21.6% (8/37) compared to 26.7% (120/449) in the overall Norwood group (p=ns). There was only one subsequent death giving a 5- and 10-year actuarial survival of 72.8+/-7.4% compared to 55.3+/-2.6% and 52+/-2.9% at 5 and 10 years for the overall series (p=0.06). Median follow-up was 4.7 (0.7-10.2) years. Eighteen patients underwent stage III completion at 3.9+/-1.5 years from the second stage with no mortality. Preoperative mean pulmonary artery (PA) pressure and transpulmonary gradient were respectively 11.6+/-3.4 and 5.2+/-3.3 mmHg. All patients had good left ventricle (LV) function at time of stage III. All patients except one are currently in NYHA I. One patient (with DILV) had congenital heart block and required a pacemaker. There was no postoperative heart block. The systemic outflow was unobstructed in all patients and no patient required any additional intracardiac procedure. CONCLUSIONS: The Norwood procedure provides good palliation in this subgroup of patients and avoids the need for subsequent intracardiac operations, maintaining unobstructed systemic outflow tract and avoiding the risk of postoperative heart block.

Use of tissue microdialysis to investigate hyperlactataemia following paediatric cardiac surgery.

We investigated tissue lactate, pyruvate and lactate:pyruvate (LP) ratio post cardiac surgery and the relationship of cardiac index and oxygen delivery to late onset hyperlactataemia in ICU. It involved a prospective study of 10 children, mean age 4.9 (0.4) years, post-Fontan operation admitted with normo-lactataemia. Tissue lactate, pyruvate and LP ratio were monitored postoperatively every 30 min for 12 h via subcutaneous microdialysis in the abdominal wall. Cardiac index was measured by PiCCO at 0, 4, 8 and 12 h. Blood and subcutaneous tissue lactate were strongly correlated (r=0.87; P=0.001). Mean (S.D.) blood lactate rose from 2.23 (0.49) to 3.73 (1.16) mmol l(-1) in the first 5 h after ICU admission (P=0.008), only one child remaining normal. Microdialysis revealed lactate rising from 3.8 (0.83) to 5.3 (1.6) (P=0.011), with a parallel pyruvate rise. LP ratio remained below 20, indicating no tissue oxygen debt. Cardiac index increased from 2.83 (0.63) to 3.77 (1.34) l min(-1) m(-2) over the same period (P=0.05), with a corresponding increase in oxygen delivery from 4556 (1094) to 6076 (2322) ml min(-1) (P=0.04). Tissue microdialysis provides near-continuous measurement of tissue lactate and pyruvate, post cardiac surgery. Blood lactate rise post-Fontan is mirrored by tissue lactate and pyruvate concentrations, and not associated with a low or falling cardiac index or with tissue oxygen debt.

Creation of aorto-pulmonary window with pulmonary artery band is not good palliation for hypoplastic left heart syndrome.

OBJECTIVE: A small sub-group of patients with hypoplastic left heart syndrome (HLHS) have normal-sized ascending aorta and arch. An alternative to the Norwood I procedure in these patients is the creation of an aorto-pulmonary (AP) window with a distal pulmonary artery band (PAB). We reviewed our experience with this technique and compared outcomes to the Norwood procedure for HLHS. METHODS: All patients treated for HLHS in a single institution between 1992 and 2005 were analysed. This identified 13 patients treated with AP window and PAB compared to 333 patients undergoing stage I Norwood procedure. An unrestrictive AP window was created and the main PA was banded. Patient records and echocardiograms were analysed. Median follow-up was 10 (IQR 0-655) days and 100% complete. RESULTS: There were seven early deaths (54%) in the AP window group and two conversions to Norwood circulation. This was a significantly worse outcome than for the Norwood procedure over the same period, which had an early mortality of 29% (p=0.03). Kaplan-Meier actuarial analysis demonstrated a continued survival benefit of the Norwood group at 6 months (p=0.0005). Deaths were due to either low cardiac output syndrome (n=4) or sudden unheralded arrest (n=3). This occurred despite aortic cross-clamp and circulatory arrest times being significantly lower in the AP window group compared to the Norwood group (35+/-27 vs 55+/-16 min, p<0.01 and 16+/-29 vs 55+/-20 min, p<0.01, respectively). No differences in arterial saturations or systolic blood pressure existed between the groups, but diastolic blood pressure was significantly lower in the AP window group at 27+/-10 mmHg compared to 42+/-8 mmHg in the Norwood group (p=0.01) with evidence of flow reversal in the descending aorta. Differences in diastolic blood pressure between groups were abolished after conversion to stage II. CONCLUSIONS: Despite favourable anatomy and shorter ischaemic times, the AP window/PAB technique has a poor outcome compared to the Norwood procedure for HLHS. Low diastolic blood pressure with reversal of descending aortic flow in diastole was a feature of the AP window/PAB circulation. We recommend the Norwood procedure for these sub-types. This may have implications for newer 'hybrid' procedures for HLHS which create a similar palliative circulation.

Innominate venous aneurysm presenting as a rapidly expanding mediastinal mass.

Thoracic venous aneurysms are extremely rare conditions. Only 14 innominate venous aneurysms have been reported in the literature. We report a case of a 13-year-old girl who presented with a mediastinal mass on chest roentgenogram, which was performed because the patient was postoperatively tachypneic after a routine appendectomy. Further investigations revealed a large left innominate venous aneurysm that was growing rapidly. The patient underwent aneurysmectomy and reconstruction of the innominate vein. The patient's postoperative course was uneventful, and her respiratory symptoms resolved.

Factors influencing early and late outcome following the Fontan procedure in the current era. The 'Two Commandments'?

OBJECTIVE: This study was undertaken to identify the factors affecting early and late outcome following the Fontan procedure in the current era. We have examined whether conventional selection criteria, the 'Ten Commandments', are still applicable in the current era. MATERIALS AND METHODS: Between January 1988 and July 2004, 406 patients underwent a modified Fontan procedure at a median age of 4.7 years (IQR, 3.8-7.1 years). The single functional ventricle was of left (n=241, 59%) or right ventricular morphology (n=163, 40%). The modified Fontan procedure was performed using an atriopulmonary connection (n=162, 40%) or total cavopulmonary connection (TCPC) involving a lateral atrial tunnel (n=50, 12%) or extracardiac conduit (n=194, 48%). They were fenestrated in 216 patients (53%). RESULTS: The early mortality was 4.4% (n=18) and four other patients required takedown of the Fontan circulation. On multivariable analysis, early outcome was adversely influenced by two factors (p<0.05): preoperative impaired ventricular function and elevated pulmonary artery pressures. Two risk models were constructed for early outcome based on preoperative and predictable operative variables (Model 1) and all preoperative and operative data (Model 2). Both models were calibrated across all deciles (p=0.83, p=0.25) and discriminated well. The area under the ROC curve was 0.85 and 0.89, respectively. There were 21 late deaths, 1 patient required late takedown of the Fontan circulation and 3 required orthotopic cardiac transplantation. Actuarial survival was 90+/-2%, 86+/-2% and 82+/-3% at 5, 10 and 15 years, respectively. Multivariable analysis identified that outcome was influenced by preoperatively impaired ventricular function, elevated preoperative pulmonary artery pressures and an earlier year of operation. The freedom from reintervention was 83+/-4%, 76+/-4% and 74+/-8% at 5, 10 and 15 years, respectively. Additional risk factors for reintervention were right atrial isomerism and preoperative small pulmonary artery size. CONCLUSIONS: Late outcome of the Fontan circulation is encouraging. Ventricular morphology, surgical technique and fenestration do not appear to influence early or late outcome. Preoperatively impaired ventricular function and elevated pulmonary artery pressures have an adverse influence on both early and late outcome. Reintervention is common, with small preoperative pulmonary artery size being an additional risk factor.