The effects of different commercially available radioactive microsphere suspending solutions were studied on the cardiovascular hemodynamics of male, Sprague-Dawley rats. Single left ventricular injections of carbonized radioactive microspheres (15 +/- 5 micron diam) totaling 850,000 spheres, suspended in 10% dextran (mol wt, 73,000) solution with Tween, caused reductions in arterial pressure (control, 101; postinjection, 74 mmHg; P less than 0.001), with no change in heart rate. Identical injections made with isotonic saline solution plus Tween had no effect on either heart rate or arterial pressure. Independent studies were conducted to examine the effects of 1-ml injections of four suspending solutions without microspheres on the cardiovascular hemodynamics of rats. Isotonic saline had no hemodynamic effect, and isotonic saline plus Tween decreased only heart rate. Ten percent dextran soluton with Tween decreased arterial pressure, heart rate, peak left ventricular systolic pressure, and left ventricular end-diastolic pressure. Similar changes occurred when dextran solution without Tween was administered. These data demonstrate that 10% dextran solution used as a microsphere suspending agent induces a severe hypotensive response in rats. Furthermore, injections of up to 850,000 microspheres in isotonic saline solution do not alter arterial pressure in the rat.
Up to 20% of patients who have symptoms suggestive of asthma but a negative MCT can still develop asthma. Declines in sGaw and FEF(25 - 75) in a negative MCT appear to have no clinical significance. A decrease in FEV(1), especially 10% to 20%, is associated with the diagnosis of future asthma.
The FEV(1)/FEV(6) is not as sensitive as the FEV(1)/FVC for diagnosing airways obstruction, but in the presence of a normal FEV(1)/FVC, subjects have greater physiologic abnormalities than when only the FEV(1)/FVC is reduced. The FEV(1)/FEV(6) ratio should not replace the FEV(1)/FVC as the standard for airways obstruction, but there is benefit including this measurement to identify individuals with greater air trapping and diffusion abnormalities.
The two recommended protocols for the diagnosis of asthma are not equivalent and significantly alter the rate of diagnosis of asthma as well as the severity. The differences were seen across all PC20 levels, from those with strongly positive tests (PC20 16.0 mg/mL).
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