Dr. Chelsie Rohrscheib, Ph.D.   Millions of Americans are being tested for sleep apnea at home — but the device doing the testing may be guessing. Most home sleep tests on the market don't actually measure breathing directly; instead, they track secondary signals like heart rate and blood oxygen changes, then use algorithms to infer whether a patient stopped breathing.   New peer-reviewed research reveals this indirect approach produces error ranges nearly three times wider than technologies that measure breathing at the source — meaning a patient could be told they're fine when they have a serious condition, or steered...