The functional significance of a coronary stenosis can be assessed by measuring the translesional pressure gradient. Thirty-four patients were studied in the setting of percutaneous transluminal coronary angioplasty (PTCA) to evaluate the clinical relevance of the pressure gradient measurements by means of a PTCA balloon catheter. Both before and after PTCA, the mean pressure gradient across the stenosis was measured by means of a newly developed, 0.015-inch pressure-monitoring guidewire, first with only the wire across the stenosis (delta Pw, considered as the actual gradient), and second with the deflated balloon catheter advanced over the wire in the stenosis (delta Pb). Pressure gradients were correlated with quantitative coronary angiography of the stenotic segment. Before PTCA, mean delta Pb was larger than delta Pw (62 +/- 14 vs 30 +/- 20 mm Hg; p < 0.01). After PTCA, delta Pb remained systematically higher than delta Pw (23 +/- 14 vs 3 +/- 5 mm Hg; p < 0.01), despite a significant reduction of percent area stenosis from 84 +/- 9 to 46 +/- 17%, and an increase in minimal obstruction area from 0.98 +/- 0.48 to 3.49 +/- 1.32 mm2. A significant correlation was found between delta Pw and percent area stenosis (r2 = 0.66), with a marked increase after percent area stenosis reached 80%. The correlation between delta Pb and percent area stenosis was weaker (r2 = 0.53), the scatter of the data was larger, and the inflection point of the curve was shifted toward less severe degrees of stenosis severity.(ABSTRACT TRUNCATED AT 250 WORDS)