Americans are finally making headway in the battle against high blood pressure, one of the biggest contributors to cardiovascular disease. At Kaiser Permanente's big northern California health plan, 80% of more than 600,000 patients diagnosed with hypertension, or high blood pressure, have the condition under control, up from 44% a decade ago. In the Southeast, 70% of nearly a half-million patients whose doctors participate in a South Carolina-based quality-improvement network had reduced their high blood pressure to medically recommended levels. That's compared with 49% in 2000. These achievements, reported last week at a meeting of the American Society for Hypertension, reflect broader gains against the problem nationwide. A major study published last year in the Journal of the American Medical Association that was based on national health surveys found that half of Americans with high blood pressure had it under control in 2008 compared with 31% at the beginning of the last decade and 27% in the early 1990s.