CHICAGO – Inhaler drugs used by millions of people with emphysema and bronchitis may slightly raise the risk for heart attacks and even death, a study suggests.

The results aren’t conclusive and inhalers provide significant relief for these patients struggling to breathe. But the study authors urged doctors to closely monitor patients who use the inhalers.

Most affected patients have both emphysema and chronic bronchitis. The condition’s formal name, chronic obstructive pulmonary disease, COPD, is the nation’s fourth leading cause of death.

The study’s increased risks were small, and the drugs’ marketer said both medicines are safe. Outside experts called the study compelling but said it has limitations that make it hard to know if the drugs or something else was at fault.

The drugs are tiotropium, sold as Spiriva Handihaler by Boehringer Ingelheim Pharmaceuticals Inc., and ipratropium, available generically and also sold by Boehringer under the brand name Atrovent.

Spiriva, approved in 2004, and the decade-old Atrovent are used once or more daily to relax muscles and open lung airways. They have been used by 8 million patients worldwide.