A joint investigation by ProPublica and NPR looked at how CPAP data is collected by Medicare and private insurance companies to determine coverage for patients with sleep apnea.

Medicare, the government insurance program for seniors and the disabled, began requiring CPAP “compliance” after a boom in demand. Between 2001 and 2009, Medicare payments for individual sleep studies almost quadrupled to $235 million. Many of those studies led to a CPAP prescription. Under Medicare rules, patients must use the CPAP for four hours a night for at least 70 percent of the nights in any 30-day period within three months of getting the device. Medicare requires doctors to document the adherence and effectiveness of the therapy.

Sleep apnea experts deemed Medicare’s requirements arbitrary. But private insurers soon adopted similar rules, verifying usage with data from patients’ machines — with or without their knowledge.

Kristine Grow, spokeswoman for the trade association America’s Health Insurance Plans, says monitoring CPAP use is important because if patients aren’t using the machines, a less expensive therapy might be a smarter option. Monitoring patients also helps insurance companies advise doctors about the best treatment for patients, she says.