A new study that looked at the sleep patters of 16 patients in intensive care units found that they are often so busy being tested and medicated that they have little time for sleep.

Disrupted sleep can cause problems with the immune system, infection resistance and wound healing.

The patients studied did get an average of eight hours of sleep, but it was mostly superficial sleep, with very little deep or restorative sleep.

Part of the reason is excessive light and noise in the I.C.U., and a lack of cues to let patients know what time of day it is. In addition, interruptions from medical workers to assess the patient’s condition and give treatments interfere with sleep.