To define the prevalence of total coronary occlusion in the hours after transmural myocardial infarction, we used coronary arteriography to study the degree of coronary obstruction in 322 patients admitted within 24 hours of infarction. Total coronary occlusion was observed in 110 of 126 patients (87 per cent) who were evaluated within four hours of the onset of symptoms; this proportion decreased significantly, to 37 of 57 (65 per cent), when patients were studied 12 to 24 hours after the onset of symptoms. Among 59 patients with angiographic features of coronary thrombosis, the thrombus was retrieved by Fogarty catheter in 52 (88 per cent) but was absent in seven (12 per cent false positive). Among an additional 20 patients without angiographic features of thrombosis, a thrombus was discovered in five (25 per cent false negative). Thus, total coronary occlusion is frequent during the early hours of transmural infarction and decreases in frequency during the initial 24 hours, suggesting that coronary spasm or thrombus formation with subsequent recanalization or both may be important in the evolution of infarction.

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Soil bulk density was related to loblolly pine (Pinustaeda L.) seedling establishment and growth during the first 28 weeks after sowing. Seedling heights were lower when bulk densities exceeded 1.3 Mg m−3 on a sandy clay loam and 1.4 Mg m−3 on a loamy sand. Heights were also lower for bulk densities below 1.2 Mg m−3 on the sandy clay loam soil. Seedling depth of rooting, root weight, and shoot weight were reduced at high bulk densities on both a sandy clay loam and a loamy sand. However, root and shoot weights were also reduced when bulk density fell below 1.3 Mg m−3 on the sandy clay loam. Bulk densities for best seedling growth were 1.3 Mg m−3 for the sandy clay loam and 1.4 Mg m−3 for the loamy sand.

No abstract

Initial planting height of loblolly pine (Pinustaeda L.) seedlings from several nurseries and seed sources was related to survival and height growth on "good" and "poor" planting chances in Alabama. A planting chance was classified as poor if 2-year survival was less than 75% and total 2-year height growth was less than 75 cm. Seedling height (measured immediately following planting) was negatively related to survival, and the slope of the regression was four times greater when the planting chance was classified as poor than when it was classified as good. Initial height was also negatively related to 2-year height growth on poor planting chances, with shorter seedlings at planting reaching the same total height as taller ones after two seasons. As a result, initial field height on poor planting chances had little impact on total seedling height after two growing seasons. Therefore, there was no height growth advantage gained by planting seedlings taller than 20 cm when survival was less than 75%. Planting seedlings with heights of 20–34 cm was less of a problem when the planting chance was good. The use of shorter seedlings on planting chances where low survival may be expected may significantly increase loblolly pine seedling survival in the southern United States.