Strong international sales helped Aspect Medical Systems Inc. boost revenues 4 percent and pushed the company into the black during the first quarter of 2009.

The Norwood-based brain-monitoring equipment maker posted revenues of $25.3 million for the three-month period ended March 31, compared to $24.4 million for the same period last year.

That pushed the company into the black. Aspect reported net income of $1.9 million, compared to a $235,000 loss during the first quarter of 2009.

Company officials attributed the boost to a 5 percent increase in international sales of sensors, which helped offset relatively flat sales to hospitals in the United States. Aspect said sales increased only incrementally on the domestic front, as hospitals continue to tamp down spending. As a result, the officials said, they are working hard to retain customers and protect existing business.

Aspect also trimmed some debt, which had been a nagging concern at the heart of a nasty proxy challenge earlier this year from at least two of the company’s largest shareholders that forced a delay of the company’s annual meeting. The dispute with First Biomed LLC, which was eventually settled, centered around a significant debt obligation the company incurred in 2007 after selling about $125 million in 2.5 percent convertible notes.

As of the end of the first quarter, there’s about $58 million left on the tab, after Aspect paid off more than $7 million in principal since the start of 2009.

Officials said that sales guidance for the second quarter would be $24 million to $25 million.