Contrasting nitrate adsorption in Andisols of two coffee plantations in Costa Rica.

Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.) plantations in the Central Valley. Previous work at one site had identified unsaturated zone nitrate retardation relative to a tritium tracer. Differences in nitrate adsorption were assessed in cores to 4 m depth in Andisols at this and one other plantation using differences in KCl- and water-extractable nitrate as an index. Significant adsorption was confirmed at the site of the previous tracer test, but not at the second site. Anion exchange capacity, X-ray diffraction data, extractable Al and Si, and soil pH in NaF corroborated that differences in adsorption characteristics were related to subtle differences in clay mineralogy. Soils at the site with significant nitrate adsorption showed an Al-rich allophane clay content compared with a more weathered, Si-rich allophane and halloysite clay mineral content at the site with negligible adsorption. At the site with significant nitrate adsorption, nitrate occupied less than 10% of the total anion adsorption capacity, suggesting that adsorption may provide long-term potential for mitigation or delay of nitrate leaching. Evaluation of nitrate sorption potential of soil at local and landscape scales would be useful in development of nitrogen management practices to reduce nitrate leaching to ground water.

Ventricular arrhythmia in unrepaired and repaired tetralogy of Fallot. Relation to age, timing of repair, and haemodynamic status.

Ventricular arrhythmias are common after repair of tetralogy of Fallot and are associated with late sudden death. This study examined the relation of ventricular arrhythmia during normal daily activities to the timing of repair, duration of follow up, and postoperative haemodynamic status. Forty eight hour ambulatory electrocardiographic monitoring was performed in 145 patients: 60 (aged 3 months to 46 years) had not yet undergone repair and 85 were followed from four to 22 (mean 14.6) years after repair. Cardiac catheterisation was performed in 47 (55%) one to 22 (mean 8.9) years after repair. Twelve (20%) of the uncorrected group had ventricular arrhythmia. The incidence increased significantly with age from 0% in patients aged less than 8 years to 58% in those aged greater than or equal to 16 years. In the corrected group 44% had ventricular arrhythmia. The incidence of arrhythmia was associated with older age at repair but not with postoperative haemodynamic status, duration of follow up, or era of surgery. It is concluded that ventricular arrhythmia is common in older patients with tetralogy of Fallot before repair and that during long term follow up of patients after repair the incidence of ventricular arrhythmia is influenced by the timing of surgery rather that the duration of postoperative follow up, era of surgery, or the haemodynamic result.

Cardiovascular anomalies in thoracopagus twins and the importance of preoperative cardiac evaluation.

Four pairs of thoracopagus twins have been described. Cardiac catheterisation was performed in all the cases. Angiocardiographic and necropsy findings suggest that the most common abnormality was some form of univentricular heart. The communication between the 2 hearts was at atrial level in 2 cases. Separation was performed in 1 of these cases but only 1 of the twins survived for 14 hours after operation. It is suggested that full cardiac catheterisation with selective angiocardiogram is essential before separation is considered. Identical heart rates were observed in each pair and there was invariably a major communication between the hearts of the twins.

Safe amounts of contrast medium for angiocardiography in neonates and infants.

The results were analysed of 485 (biplane) cineangiocardiograms performed in 200 consecutive cardiac investigations on neonates (under 4 wk) and infants (4 wk to 1 yr). 10 deaths occurred during or within 24 h of cardiac catheterization, all in patients who were profoundly acidemic because of their hemodynamic disturbance. A total dose of Cardio-Conray at any one investigation of 4-5 ml/kg body weight was satisfactory and without undue risk. Single injections of 1.5-2.0 ml/kg body weight were safe whilst providing optimal diagnostic information. The interval between multiple injections did not appear to affect the risk to the patients.