Medical device maker Natus Medical Inc said it bought privately-held Embla Systems LLC for about $16.1 million in cash to expand its sleep diagnostics portfolio.

Denver, Colorado-based Embla makes devices used in diagnosing sleep apnea -- a disorder that causes abnormal breathing conditions during sleep. Embla had an annual revenue of about $30 million for 2010.

Natus said it expects the deal to add 8 cents per share to its 2012 adjusted earnings.

It funded the transaction through available cash.

The deal will also give Natus an opportunity to expand its footprint outside the United States, as about 40 percent of Embla's revenue comes from international markets.

About 100 million people worldwide are suspected to have sleep apnea, and about 80 percent of them remain undiagnosed, Natus said in a statement.

With this acquisition, Natus will now hold the number one position in the worldwide sleep diagnostic market with annual revenue approaching $35 million, Natus Chief Executive Jim Hawkins said.

San Carlos, California-based Natus Medical shares have fallen about 15 percent since July, when the company posted a lower quarterly profit and slashed its full-year outlook.

The shares closed at $9.74 on Thursday on Nasdaq.