Discriminant band divides graph int

Discriminant band divides graph into normal and abnormal regions.Results falling on the discriminant band were repeated, and if the result still fell on the discriminant band, the result was considered equivocal.These were divided into two groups, one with normal results at venography(group 1)and the other with abnormal results(group 2).Forty-eight extremities in group 1 had a mean pedal venous pressure of 17.94 cm±5.66(height of saline-solution column).Forty-one extremities in group 2 had a mean pedal venous pressure of 27.5 cm saline±10.67.The range of values for group 1 extremities was 5-34 cm saline, while for group 2 extremities it was 13-57 cm saline.With the Student two-tailed t test, the difference in mean pressure between group 1 and group 2 patients was significant at the P .001 confidence level(7).The frequency histograms for group 1 and group 2 patients are shown in Figure 3.Of the 96 extremities studied veno- graphically, three showed extravasation(3.1%), but without gangrene or skin loss.Among the other complications of venography, there were no severe contrast media reactions, no episodes of renal failure, and three episodes of clinically evident iatrogenic thrombophlebitis.The low sensitivity of impedance plethysmography in detecting calf thrombi has been well described(2,3,6)and can be explained by the fact that a small fresh thrombus in one of the six major calf veins will do little to alter either the venous capacitance or the venous outflow of the extremity.With thrombi in the deep veins of both the calf and the thigh, impedance plethysmography is put to its most rigorous test.Whether such a rigorous test is clinically useful is questionable.Table 1 Correlation of Findings at Venography and Plethysmography in 88 Extremities with Diagnostic Findings at PlethysmographyVenographyNote.—Table excludes eight extremities with equivocal findings at plethysmography.Venous Pressure(cm H2O)% of resultsFrequency histograms for venous pressures recorded in patients with negative(a)and positive(b)venograms.Difference in mean of the two groups was statistically significant at P < .001 confidence level despite the rather broad spread of the abnormal(positive-venogram)group.Generally, small calf thrombi that will yield normal findings at plethysmography are not considered to carry a significant risk of pulmonary embolism, although this contention has not been fully substantiated by a randomized, prospective clinical trial.The more ominous proximal thrombus is, however, capable of causing significant pulmonary emboli, and the sensitivity of impedance plethysmography in its detection or exclusion has ranged from an overall 45% in the studies of Ramchandani et al(6)to as high as 95% in the studies by Hull et al(1-4).Our overall sensitivity results are intermediate between those of Ramchandani et al and Hull et al. Seventy percent of our study group were inpatients as were 65% of the patients studied by Ramchandani, while 75% of the patients studied by Hull et al were outpatients.