Shares for San Diego-based medical device maker ResMed Inc. plummeted 12 percent following news that its quarterly earnings were lower than expected.

The company had a 5 percent increase in sales to $357.7 million in the first quarter — about $15 million short of Wall Street expectations, as analysts across the board projected a 17 percent increase in sales over the like quarter in 2012.

Shares closed at $49.55 on Oct. 25 — down $6.76, or 12 percent, from the previous day of trading.

CEO Mick Farrell cited recent rounds of competitive bidding as the reason its sleep apnea devices didn’t sell as well — other companies are gaining traction in the marketplace.

Deutsche Bank analyst David Low, for instance, downgraded ResMed stock, writing that the company “seems to have suffered greater market share pressure than expected.”

The company opened the year at $42.48 per share.

— Meghana Keshavan