The results point to ways hospitals can focus on mitigating the most disruptive noises, researchers said.

"We don't necessarily just have to make (the hospital) quieter," said Dr. Jeremy Ackerman from Emory University School of Medicine in Atlanta, a member of the international Healthcare Acoustics Research Team.

"We need to be particularly careful to avoid designing into systems and into the architecture very disruptive sounds."

Nighttime noises are one of the chief complaints among patients who are surveyed about their time in the hospital.

In addition, "we have a general sense that loud sounds, interruptive sounds all create an environment that is likely to slow healing," said Ackerman, who was not involved in the study.

"It's nerve-wracking enough to be a hospitalized 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.

Previous research has found hospital noise levels can spike up to 80 decibels (dB), about as loud as a chainsaw (see Reuters Health report of January 10, 2012).

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.

Most 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. If the person's brain waves didn't show a response to the sound, 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 when it comes to disturbing sleep, "Alarms and voices are clearly the worst offenders," Buxton told Reuters Health.

For instance, during moderately light levels of sleep -- where people spend most of the night -- an IV pump alarm woke up about 90 percent 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 reported in Annals of Internal Medicine.

Buxton said although people might not remember being aroused by the sounds, they could feel less rested the next day.

Traffic outside, a jet flying overhead, a helicopter taking off and a toilet flushing were much less disruptive.

During the lighter stage of sleep, for instance, less than 20 percent of people woke up to a helicopter taking off when played at the lowest level and 80 percent were aroused by the same sound played at the volume of people shouting.

The researchers also measured how people's heart rates responded to each of the sounds, and they found arousals caused a slight increase in heart rate.

The result "gives us confidence this is a genuine physiological response (to hospital noises) in a negative way," said Dr. Jeffrey Ellenbogen, chief of sleep medicine at Massachusetts General Hospital, who co-led the study.

All of the patients in his study were healthy and not in the hospital, and Ellenbogen, also from Harvard Medical School, told Reuters Health 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 there are ways hospitals can reduce some disruptive sounds.

"One thing is to close the doors on patient rooms. You have no idea how many hospitals' staff don't even think of doing that," said Frampton, who was not involved in the study.

There are also ways to design buildings so patients are exposed to fewer loud noises.

Frampton said sound reduction is important because patients' psychological and physical health can suffer from having their sleep disturbed.

The study could not tell whether disruptions in sleep or increases in heart rate would affect people's health, and Ellenbogen said future studies will try to reduce sounds in a hospital to see how that affects patients' recovery.

SOURCE: bit.ly/atTzv0 Annals of Internal Medicine, online June 11, 2012.

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