Scientists at the Weizmann Institute, along with colleagues at the Loewenstein Rehabilitation Hospital, have developed a "sniff test" that can accurately predict whether or not unconscious brain-injured patients are likely to regain consciousness, the institute said in a statement on Thursday.
The study found that 100% of unconscious patients with brain injuries who responded to the smells regained consciousness during the four-year study period, even those that were classified as being in a "vegetative state."
"In some cases, the result of the sniff test was the first sign that these patients were about to recover consciousness – and this reaction was observed days, weeks and even months prior to any other signs," says Dr. Arzi, who led the research.
"Diagnosing the level of consciousness of a patient who has suffered a severe head injury is a major clinical challenge. The sniff test we have developed may provide a simple tool to tackle this challenge," Arzi said.
Patients' responses were measured through a small, yet still measurable, change in the airflow of their nasal breathing when reacting to certain smells.
The researchers briefly placed jars containing various odors under the patients' noses, including a pleasant scent of shampoo, an unpleasant smell of rotten fish, or no odor at all.
At the same time, the scientists precisely measured the volume of air inhaled through the nose in response to the odors.
Each jar was presented to the patient ten times in random order during the testing session, and each patient participated in several such sessions.
In healthy humans, the sniff-response which the study is based on can occur unconsciously in both wakefulness and sleep. For example, an unpleasant odor will lead to shorter and shallower sniffs.
According to the researchers, the inexpensive test will aid doctors in more accurately diagnosing the degrees of individual brain injuries and customizing their treatment plans accordingly.
The current "gold standard" used for diagnostics, the Come Recovery Scale, can lead to patients with brain injuries being diagnosed incorrectly in up to 40% of cases.
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"Misdiagnosis can be critical as it can influence the decision of whether to disconnect patients from life support machines," says Arzi.
"In regard to treatment, if it is judged that a patient is completely unconscious and doesn't feel anything, physicians may not prescribe them painkillers that they might need," she added.
Consciousness levels are currently measured based on testing patients' responses to sound, light and pain. The high rate of error requires the tests to be performed at least five times, and even then, still leads to inaccuracies.
"In a well-known study, a patient diagnosed as being in a 'vegetative state' following a car accident was scanned in an MRI machine. While in the scanner, the researchers asked the patient to imagine that she was playing tennis and observed that her brain activity was similar to the brain activity of healthy people when they also imaged playing a tennis game. Suddenly, they realized: 'hold on a minute, she's there. She hears us and is responding to our requests. She simply has no way of communicating'," says Arzi
Researchers at the institute said the tests accuracy levels highlighted the "primal role of the sense of smell in human brain organization," saying that the fact that it is the most ancient part of the brain led to it's responses being easier to accurately gauge.