The U.S. Food and Drug Administration is reminding patients who use the popular 600-series MiniMed insulin pumps made by Medtronic that the devices contain an issue that could cause their buttons to get stuck while flying or other situations when air pressure changes quickly.

The FDA on Wednesday issued alerts for more than 189,000 MiniMed insulin pumps worldwide. Such pumps are used by diabetic patients who need a steady infusion of the drug insulin to break down the glucose in their blood, in addition to periodic doses (or "boluses") of insulin related to meals, exercise and other factors.

The alerts issued Wednesday are classified by the FDA as a class 2 recall, which is a medium-severity action used when a problem caused by a medical product would be temporary, or when the probability of serious adverse consequences related to the problem is considered remote.

Medtronic has issued an urgent safety notification to patients, which the FDA calls a "recall." However, FDA and Medtronic are not requesting any devices be returned to the manufacturer. The FDA uses the term "recall" to include situations where no product need be returned.

The recalls apply to Mini­Med 670G, 640G, 630G, and 620G models, which have physical keypad buttons that can temporarily become "unresponsive" when atmospheric pressure goes up or down quickly around the pump, typically during takeoff and landing.

"If this happens, in most cases you may not even notice because the pump will resolve this on its own," Medtronic has told patients in a letter.

The problem has long been known. Medtronic first notified patients about the problem in 2017. An FDA spokeswoman said by e-mail that agency officials were looking into why the recall notices were posted by the FDA on Wednesday.

Medtronic's diabetes group spokeswoman Pamela Reese confirmed Wednesday that the issue still exists in the pumps.

"We are investigating different hardware solutions … for this rare situation in a long-term manner," she said. "Since this original notification, we made changes to the instructions for use for customers who have purchased these systems after this notification happened so they can be aware."

In most cases, Medtronic said the issue will resolve when the atmospheric pressure normalizes. A pump user can resolve the issue immediately by taking off the battery cap and then putting it back on again.

Medtronic's letter to customers said that if a pump user notices that the keypad buttons are difficult to press down or stuck in the down position, the device is designed to continue pumping basal insulin.

"You may not be able to program a bolus or suspend delivery as the buttons temporarily will not press down, but this will resolve on its own, usually within 30 minutes," the letter said.