Formation of stromatolite lamina at the interface of oxygenic-anoxygenic photosynthesis.

In modern stromatolites, mineralization results from a complex interplay between microbial metabolisms, the organic matrix, and environmental parameters. Here, we combined biogeochemical, mineralogical, and microscopic analyses with measurements of metabolic activity to characterize the mineralization processes and products in an emergent (<18 months) hypersaline microbial mat. While the nucleation of Mg silicates is ubiquitous in the mat, the initial formation of a Ca-Mg carbonate lamina depends on (i) the creation of a high-pH interface combined with a major change in properties of the exopolymeric substances at the interface of the oxygenic and anoxygenic photoautotrophic layers and (ii) the synergy between two major players of sulfur cycle, purple sulfur bacteria, and sulfate-reducing bacteria. The repetition of this process over time combined with upward growth of the mat is a possible pathway leading to the formation of a stromatolite.

Goretex patch aortoplasty for coarctation in children: nuclear magnetic resonance assessment at 7 years.

From 1979 to 1990, 56 children ranging between 4 days and 16 years of age (mean 73 +/- 51 months) underwent Goretex patch aortoplasty for coarctation of the aorta. The mean weight at operation was 20.2 +/- 3.5 kg (range 3.3-42 kg). Forty-two patients had primary repair, and the remaining 14 had reoperation for recoarctation. The aorta was opened through a standard left thoracotomy, the posterior fibrous ridge was partially excised when it was prominent, and a large patch from a Goretex tube was sutured into place. The postoperative complications were as follows: paradoxical hypertension in 14 cases, massive haemorrhage due to aortic wall rupture in a diabetic child, and intestinal bleeding in 1 case. There were no early deaths and only 1 case of late death, which was not related to coarctation repair (mortality rate 1.8%). The average follow-up was 48 +/- 26 months. Continuous wave-Doppler examination at rest showed no arm-leg systolic gradient in 52 cases and a gradient of about 15 mmHg in 4 cases. Graded exercise testing showed only 1 case with an arm-leg gradient higher than 35 mmHg. Nuclear magnetic resonance (NMR) imaging, performed on 26 patients at a mean of 7 years from operation, showed excellent morphology and size of the aortoplasty. No cases of recoarctation or late aneurysm formation were found. We conclude that Goretex patch aortoplasty can be performed effectively and safely in children. Nuclear magnetic resonance provides high resolution imaging of the coarctation repair site.

Clinical evaluation of oxidative stress and myocardial reperfusion injury in pediatric cardiac surgery.

BACKGROUND: To evaluate oxidative stress and myocardial damage after aortic crossclamping release (ACCR) during cardio pulmonary bypass (CPB) in children two parameters were investigated: total glutathione (GSH) and its oxidoreductive reactions (GSH/GSSG) as expression of oxidative stress, and plasmatic turnover of myocardial taurine (TAU) as expression of cell damage. METHODS: The study was divided in two periods: 1) first period: analysis of oxidative stress and myocardial damage in 18 children. 2) Second period: evaluation of myocardial cell protection by controlled anterograde low oxygen warm reperfusion (ALOWR) before declamping. Twenty-one children were divided in two groups: not receiving (Group 1, 9 patients) and receiving (Group 2, 12 patients) ALOWR. RESULTS: In the first period GSH values increased significantly after onset of mechanical ventilation (MV) in vein, after CPB start in artery and after ACCR in coronary sinus. Moreover TAU turnover in aortic and coronary sinus blood increased significantly after ACCR. In the second period, Group 2 showed a lower oxidative stress after ACCR, while no differences were observed in TAU turnover. CONCLUSIONS: 1) Assessment of TAU and GSH levels can be considered a good method to clinically evaluate myocardial injury during cardiac surgery. 2) MV and CPB can induce oxidative stress before aortic clamping and can decrease the physiologic scavengers. Therefore, to prevent that depletion, the strategy of these techniques must be adapted to the patient and to his cardiac disease. 3) Intramyocardial TAU turnover is not significantly modified by the reperfusion technique. 4) ALOWR can reduce myocardial oxidative stress and can improve heart recovery after the cardioplegic arrest.

[Circulation support in left thoracotomy for descending thoracic aorta diseases in pediatric patients]. / L'assistenza circolatoria in toracotomia sinistra nella patologia dell'aorta toracica discendente nel paziente pediatrico.

BACKGROUND: Complications of surgery of the descending thoracic aorta could include neurological problems such as paraparesis and paraplegia. Intestinal ischemia and acute renal failure could occur, too. During the cross-clamping time, the perfusion of the distal aorta by means of extracorporeal circulatory assistance can be useful to protect the spinal cord and the splanchnic organs and to reduce the incidence of these untoward events. The aim of this study was to verify the efficacy and suitability of this type of circulatory assistance in a pediatric age group. METHODS: From January 1996 to March 2000, in the Pediatric Cardiac Surgery Department of the Gaslini Institute (Genoa, Italy), 6 patients (mean age 39 months, mean weight 14.4 kg) were treated using extracorporeal circulatory assistance through the left thoracotomy. Indications for surgery included the removal of a migrated device previously inserted in order to close a patent ductus arteriosus in 1 patient, recurrent coarctation in 2 patients, and native coarctation with a poor collateral circulation in 3 patients. RESULTS: The early and late mortality rates as well as the morbidity rates (both neurological and splanchnic) were nil. CONCLUSIONS: Extracorporeal circulatory assistance can be helpful in pediatric patients and it can prevent neurological and renal injuries in cases of a) coarctation of the aorta with a poor collateral circulation and low distal pressure (< 40 mmHg during aortic occlusion); b) recoarctation with complex anatomy; c) other pathologies requiring prolonged descending thoracic aorta cross-clamping.

[Closure of patent ductus arteriosus in thoracoscopy: analysis of the experience in the Gaslini Institute of Genoa]. / Chiusura del dotto arterioso persistente in toracoscopia: analisi dell'esperienza dell'istituto Gaslini di Genova.

In 1993, Laborde et al described a new surgical approach for closure of the patent ductus arteriosus (PDA), using a videoassisted technique. For the first time, videosurgery was utilized in pediatric cardiovascular surgery. The advantages of this new method are that it is minimally invasive (thoracotomy is replaced by three small holes), it reduces postoperative pain, recovery is more rapid with a shorter hospital stay and convalescence, and last but not least, it offers better aesthetic results. Between July 1994 and June 1996, we utilized the videoassisted thoracoscopic technique described by Laborde in 23 patients with PDA (age: 8 m-12 yrs, mean 45.2 m +/- 37.8; weight: 5.3-32 kg, mean 23 kg +/- 10.3). In two patients, we converted the procedure to standard thoracotomy due to anatomic problems. Echo-doppler evaluation, performed in the operating room shortly after the procedure, confirmed the complete closure of the PDA in all patients. There was neither morbidity nor mortality. The average hospital stay was four days. At a mean follow-up interval of 7.2 months (range 1-13 months), all patients showed excellent cosmetic results. We conclude that thoracoscopic closure of PDA is a valuable therapeutic option that can be used as an alternative to open-chest surgery and interventional cardiology.

Activation of the intracellular glutathione system by oxydative stress during cardiopulmonary bypass and myocardial perfusion.

The glutathione (GSH) system is the main defence of tissues against free radicals and red blood cells (RBC) are the most efficient sites for GSH redox cycle activation. Total GSH was assayed during cardiopulmonary bypass (CPB) in RBC and serum from the coronary sinus, peripheral arteries and veins in 18 children corrected of their cardiac defect. Our conclusions are: (1) RBC-GSH redox cycle is activated during heart ischaemia and reperfusion; (2) the activation of intracellular GSH system is preponderant compared with the extracellular one; (3) variations in intraerythrocytic total GSH during heart ischaemia and perfusion are detectable in peripheral veins and arteries, which can be the convenient sites for monitoring changes in the GSH cycle; and (4) increased total GSH levels are present in RBC before aortic crossclamping: at the beginning of mechanical ventilation in veins and, when CPB is started, also in arteries.