(Bloomberg) -- Koninklijke Philips NA said the use by customers of unauthorized cleaning products worsened damage to noise-dampening foam inside some ventilators used for treating sleep apnea, hinting that the finding will form part of its defense in looming court cases.

An investigation into faults with some of its sleep apnea machines found that customers’ use of ozone cleaning products “significantly exacerbates” foam degradation, the Amsterdam-based company said late Monday. 

“This is not the time to discuss tactics for how we will do court cases,” Chief Executive Officer Frans van Houten said in a phone interview. “But obviously this information that we publish today show a strong correlation with the use of non-authorized cleaning methods, so that will be helpful information.”

Philips initiated its first recall of potentially faulty devices last June. The company has made cumulative financial provisions of around 885 million euros ($937 million) for the recall and warned it might need to set aside more funds as user lawsuits progress.

Philips shares fell 1.9% by 11:10 a.m. in Amsterdam, bringing the decline this year to 38%. Analysts at UBS said the testing update didn’t provide the “unequivocal” positive news investors were hoping for.

Philips Sinks; UBS Says Breathing Device Update ‘Disappointing’

Consumers have accused Philips in lawsuits of violating the US Federal Food, Drug and Cosmetic Act, which requires that medical devices be safe and effective. They claim the breathing machines were defectively designed by using foam that could degrade if exposed to moisture.

In sleep apnea, breathing stops and starts, which can cause fatigue and longer-term health problems. Philips products designed to improve sleep patterns include its DreamStation CPAP machines and Trilogy ventilators.

Van Houten said Philips’ probe found that only a small percentage of units examined during the testing showed visible signs of foam degradation. The company said that 422 of the 60,847 returned or used devices that were inspected were linked to a reported foam degradation complaint. However, testing found that only 18 of these 422 machines, or 4%, actually showed visible foam degradation.

“What made these people complain about foam degradation when there was no foam degradation in the units they had?” he asked. “All of that is going to be highly relevant in subsequent litigation.”

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