The voices of people who have decided to commit suicide are higher pitched than those who are merely depressed, a United States study has found.
Intending suicides in the study also used a narrower range of frequencies when pronouncing vowels.
The researchers, a psychiatrist and a biomedical engineer from Vanderbilt University in Nashville, Tennessee, said the changes appeared to be caused by ``stress-induced physiological changes" changes in muscle tone and the moisture and elasticity of the vocal cords.
``In suicidal patients, the voice becomes slightly hollow and empty, you get this change in quality," electronics engineer Dr Mitchell Wilkes told New Scientist.
``They call it the voice from the grave."
The study began after a Yale University psychiatrist, Dr Stephen Silverman, noticed he could sense from a patient's voice whether he or she was likely to attempt suicide.
Dr Wilkes said they were now investigating whether their findings could be developed into an early warning system to alert mental health workers which patients were seriously suicidal.
``The goal is to have a diagnostic device for emergency rooms, or that could be linked up to help lines," he said.
But Australian psychiatrists said even if such a development was possible, it was unlikely to be useful with individual cases of severe depression or mania leading to suicide.
``You might have hundreds of people whose voices sounded odd ... The dilemma is that none of the predictors of suicide have any clinical relevance with individual people," said Professor Bob Goldney, from the Adelaide Clinic.
``My first reaction is one of scepticism. But the reality is suicide is such an enigma that anything that gives us more information is worth following up."
Professor Gordon Parker, head of psychiatry at the University of NSW, said the study was not reflected in his clinical experience.
People who were most likely to kill themselves were usually biologically depressed, in which case they spoke in slow monotones, or manic, where their voice might be husky because they had been talking a lot and quickly.
``And when people decide to kill themselves, they often will settle and appear more calm," he said. People who had survived serious suicide attempts later recounted, `` `I became very calm and tranquil and knew exactly what I'd do"', he said.