Nitrate in aquifers beneath agricultural systems.

Research from several regions of the world provides spatially anecdotal evidence to hypothesize which hydrologic and agricultural factors contribute to groundwater vulnerability to nitrate contamination. Analysis of nationally consistent measurements from the U.S. Geological Survey's NAWQA program confirms these hypotheses for a substantial range of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and also shallow carbonate aquifers that provide a substantial but smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigated systems can compound this vulnerability by increasing leaching facilitated by additional recharge and additional nutrient applications. The system of corn, soybean, and hogs produced significantly larger concentrations of groundwater nitrate than all other agricultural systems because this system imports the largest amount of N-fertilizer per unit production area. Mean nitrate under dairy, poultry, horticulture, and cattle and grains systems were similar. If trends in the relation between increased fertilizer use and groundwater nitrate in the United States are repeated in other regions of the world, Asia may experience increasing problems because of recent increases in fertilizer use. Groundwater monitoring in Western and Eastern Europe as well as Russia over the next decade may provide data to determine if the trend in increased nitrate contamination can be reversed. If the concentrated livestock trend in the United States is global, it may be accompanied by increasing nitrogen contamination in groundwater. Concentrated livestock provide both point sources in the confinement area and intense non-point sources as fields close to facilities are used for manure disposal. Regions where irrigated cropland is expanding, such as in Asia, may experience the greatest impact of this practice on groundwater nitrate.

Nitrate in aquifers beneath agricultural systems.

Research from several regions of the world provides spatially anecdotal evidence to hypothesize which hydrologic and agricultural factors contribute to groundwater vulnerability to nitrate contamination. Analysis of nationally consistent measurements from the U.S. Geological Survey's NAWOA program confirms these hypotheses for a substantial range of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and shallow carbonate aquifers provide a substantial but smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigated systems can compound this vulnerability by increasing leaching facilitated by additional recharge and additional concentrations of groundwater nitrate than all other agricultural systems, although mean nitrate concentrations in counties with dairy, poultry, cattle and grains, and horticulture systems were similar. If trends in the relation between increased fertilizer use and groundwater nitrate in the United States are repeated in other regions of the world, Asia may experience increasing problems because of recent increases in fertilizer use. Groundwater monitoring in Western and Eastern Europe as well as Russia over the next decade may provide data to determine if the trend in increased nitrate contamination can be reversed. If the concentrated livestock trend in the United States is global, it may be accompanied by increasing nitrogen contamination in groundwater. Concentrated livestock provide both point sources in the confinement area and intense non-point sources as fields close to facilities are used for manure disposal. Regions where irrigated cropland is expanding, such as in Asia, may experience the greatest impact of this practice.

Aircrew fatigue monitoring during sustained flight operations from Souda Bay, Crete, Greece.

BACKGROUND: Operational flight surgeons are often responsible for determining aeromedical readiness of aircrew members whose accumulated flight time exceeds standard limitations. Realizing that operational reports of excessive flight time in aircrew are limited, we used Rayman's 1975 study of fatigue during Cambodian airlift missions as a model to evaluate 42 U.S. Navy EP-3E aircrew members flying reconnaissance missions from Souda Bay, Crete, Greece. Measured parameters focused on information accessible to operational flight surgeons. METHODS: Hoping to identify early indices of fatigue, the aircrews were monitored using anonymous questionnaires, physiologic data (mean arterial pressure, pulse, pulse pressure), and hematologic measurements (CBC, sedimentation rate). RESULTS: As suspected, no physiologic parameter indicated early fatigue. However, some aircrew demonstrated small changes in measured visual phorias as compared to prior evaluations. Anonymous questionnaires and subjective evaluation of crewmembers appeared most valuable in assessing fatigue. CONCLUSION: Incorporating previously reported recommendations for fatigue surveillance, the Souda Bay experience is an example of successful fatigue monitoring in aircrews who accumulate flight time beyond standard restrictions.

The effects of hypertension on the nervous system.

With 60 million Americans meeting criteria for either essential or secondary hypertension, elevated arterial pressures remain a major health problem. While efforts to find etiologies for essential hypertension continue, clinicians battle its effects on organ systems, including the nervous system. Hypertensive changes in the nervous system may be acute, chronic, or both. The intracerebral vasculature is commonly affected. Not infrequently, acute changes including hemorrhage, encephalopathy, and cerebral edema are superimposed on chronic changes of hyaline and fibrinoid arteriolosclerosis. Chronic vascular changes sacrifice vascular lumina. The resulting ischemia is responsible for cystic (lacunar) lesions and subcortical ischemic white matter lesions consistent with Binswanger's disease.

Traumatic pulmonary artery--left atrial fistula: an unusual case of cyanosis in an adult.

Eighteen months after sustaining a stab wound to the left upper chest, a 59-year-old man presented with cyanosis and extertional dyspnea. Arterial desaturation due to a central 22 per cent right-to-left shunt was present. A selective pulmonary arteriogram demonstrated a fistula between the main pulmonary artery and the left atrium. At operation the fistula was closed. A laceration of the pulmonic valve and healed pericarditis were present. Marked symptomatic improvement followed the operation, but a murmur of pulmonic valvular regurgitation persisted. The fistula and laceration of the pulmonic valve were probably traumatic in origin.

Comparison of dobutamine and dopamine in treatment of severe heart failure.

The haemodynamic effects of dobutamine, a new synthetic catecholamine, were studied in 12 patients with severe congestive heart failure and compared with those of dopamine in 10 clinically similar patients. Dobutamine produced a distinct increase in cardiac index, while lowering left ventricular end-diastolic pressure and leaving mean aortic pressure unchanged. Dopamine also significantly improved cardiac index, but at the expense of a greater increase in heart rate than occurred with dobutamine. Dopamine was ineffective in lowering left ventricular end-diastolic pressure, but increased mean aortic pressure. We conclude that dobutamine is an effective, positive inotropic agent in patients with severe congestive heart failure. Because it has comparatively little effect on heart rate and aortic pressure, both major determinants of myocardial oxygen consumption, it may be of special value in patients with the low output syndrome associated with coronary heart disease.