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Certain hospital sounds, such as electronic alarms, telephones and conversations, can wake patients up even at relatively low levels, creating an environment that may slow healing, according to a US study.
The report, published in the Annals of Internal Medicine, follows another study earlier this year that discovered hospital noise levels can spike up to 80 decibels (dB), about as loud as a chainsaw.
"It's nerve-wracking enough to be a hospital patient, and there's a lot of racket at night," said Orfeu Buxton, a neuroscientist at Brigham and Women's Hospital and Harvard Medical School in Boston, who led the study.
To measure how loud particular noises have to be to wake people up, Buxton and his colleagues monitored the sleep of 12 healthy people as the researchers pumped sounds into the room where they slept.
Many of the noises were recorded from an actual hospital. They included IV pump alarms, people talking, a plane flying overhead and a laundry cart rolling down the hall.
Throughout the night, the researchers would play the noises one at a time.
Each sound was first played at the level of a whisper and if the person's brain waves didn't show a response, the researchers stepped up the level until the "patient" woke up or the volume reached 70 dB, about the level of people shouting.
The findings showed that alarms and voices were the worst offenders when it came to disturbing sleep, Buxton said.
For instance, during moderately light levels of sleep - where people spend most of the night - an IV pump alarm woke up about 90 per cent of people at 40 dB, the quietest level. Even during deep sleep, more than half of people woke up to the alarm played at the level of a whisper.
Similarly, about three-quarters of participants woke up from the sound of people having a whispered conversation during the lighter stage of sleep, the researchers said.
While people might not remember being aroused by the sounds, they could feel less rested the next day, Buxton said.
Traffic outside, a jet flying overhead, a helicopter taking off and a toilet flushing were much less disruptive.
The researchers also measured how people's heart rates responded to each of the sounds, and they found that arousals caused a slight increase in heart rate.
The result "gives us confidence this is a genuine physiological response in a negative way," said Jeffrey Ellenbogen, chief of sleep medicine at Massachusetts General Hospital, who co-led the study.
All of the patients were healthy and not in the hospital, and Ellenbogen, also from Harvard Medical School, said he would expect to see an even greater disturbance among older and sicker hospitalized patients.
Susan Frampton, the president of Planetree, a group that promotes patient-centered healthcare, said hospitals can lower some disruptive sounds, such as by designing buildings to reduce noise exposure.
"One thing is to close the doors on patient rooms," added Frampton, who was not involved in the study. "You have no idea how many hospitals' staff don't even think of doing that."