Measurement of coronary artery stenosis is an invaluable tool in the study of coronary artery disease. Clinical trials and even day-to-day decision making should ideally be based on accurate and reproducible quantitative methods. Quantitative coronary angiography (QCA) using digital angiographic techniques has been shown to fulfill these requirements. Yet many laboratories have abandoned visual analysis in favor of the intermediate quantitative approach involving hand-held calipers. Thus, the purpose of this study was to determine the relation between QCA and the commonly used caliper measurements. Percent stenosis was assessed in 155 lesions using 3 techniques: QCA, caliper measures from a 35-mm cine viewer (cine) and caliper measures from a video display (CRT). Good overall correlation was noted among the 3 different techniques (r greater than or equal to 0.72). Both of the caliper methods underestimated QCA for stenosis greater than or equal to 75% (p less than or equal to 0.001) and overestimated stenosis less than 75% (p less than 0.05). Reproducibility assessed in 52 lesions by independent observers showed QCA to be superior (r = 0.95) to either of the caliper measurements (cine: r = 0.63; CRT: r = 0.73). Therefore, the commonly used caliper method is not an adequate substitute for QCA because overestimation of noncritical stenoses and underestimation of severe stenoses may occur and the measurements have poor reproducibility. These factors definitely preclude its use in rigorous clinical trials. Moreover, since they do not appear to overcome known deficiencies of visual analysis, caliper measurements for day-to-day clinical use must also be seriously questioned.

This study investigates soil N 2 O dynamics in forest soils representing early (3-years) and late ([50 years) post-harvest succession in Atlantic Canada over a 9-month snow-free period in order to develop a better understanding of the role of managed forests as sources and sinks of N 2 O. We couple measurement of surface flux with detailed measurements of subsurface N 2 O concentrations at four mineral soil depths (0, 5, 20 and 35 cm) at 40 plots located within four sites. Median surface fluxes were similar at all sites regardless of the management stage (-5 to ?19 ugN 2 O-N/m 2 /day), with all sites behaving as net sinks and sources of N 2 O over the measurement period. Subsurface mineral soil N 2 O concentrations at early (3-year) post-harvest succession sites, which ranged from median values of 362 ppbv at 0 cm to 1783 ppbv at 35 cm depth, were significantly higher than late post-harvest succession sites where median concentrations ranged from 329 ppbv at 0 cm to 460 ppbv at 35 cm depth. Examination of relationships between subsurface gas storage and surface flux magnitudes, suggested although recently harvested forest soils may be producing N 2 O at a greater rate than mature forest soils, observed patterns are consistent with a strong sink for this gas that prevents its conservative transport through the soil profile, and ultimate emission to the atmosphere through the majority of the measurement period.

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Myocardial ischemia may be produced by limitation of blood flow as in abrupt coronary occlusion, termed supply-type ischemia, or by increasing myocardial oxygen demand in the setting of restricted flow, termed demand-type ischemia. To examine the comparative extent and severity of the dysfunction related to both forms of ischemia, we studied anesthetized, open-chest dogs by means of two-dimensional echocardiography and tracer microspheres. Supply-type ischemia was produced by total occlusion of the LCx (n = 7); demand-type ischemia was induced by infusion of dobutamine after creation of a critical LCx stenosis (n = 6). At the time of the production of ischemia, the group with demand-type ischemia had significant increases in both heart rate (p less than 0.05) and mean arterial pressure (p less than 0.05), whereas the group with supply-type ischemia had a decrease in mean arterial pressure (p less than 0.05). Subendocardial blood flow in the LCx region was severely depressed in supply-type ischemia (0.09 +/- 0.04 ml/min/gm) compared to demand-type ischemia (1.04 +/- 0.07 ml/min/gm; p less than 0.01). Although both groups of animals had an abnormality of left ventricular function during ischemia, as determined by two-dimensional echocardiography, the extent of the dysfunction in the group with supply-type ischemia was greater (146 +/- 12 degrees) compared to the group with demand-type ischemia (99 +/- 9 degrees; p less than 0.01). Similarly, the degree of left ventricular dysfunction in the group with supply-type ischemia was greater than that for the group with demand-type ischemia (p less than 0.05). Thus these data suggest that supply-type ischemia produced by coronary occlusion results in a greater extent and degree of left ventricular functional abnormality than pharmacologically induced demand-type ischemia.