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Low-Frequency Hearing Loss May Indicate Cardiovascular Disease
by Pippa Wysong
PHOENIX-Low-frequency hearing loss could be an early indicator that a patient has cerebrovascular disease or is at risk for cardiovascular (CV) disease. These are the key findings in a two-part study investigating whether there is a relationship between audiometric patterns and vascular disease. Findings were presented at this year's Combined Otolaryngology Spring Meeting by David R. Friedland, MD, PhD, Associate Professor of Otolaryngology and Communication Sciences at the Medical College of Wisconsin in Madison.
There are various known risk factors for the development of cardiovascular disease, including diet and lifestyle, family history, and age, as well as conditions such as diabetes, hypertension, and other vascular disease. Of interest to Dr. Friedland and colleagues are the hypertension and vascular aspects of the disease.
Current guidelines look for hypertensive subclinical organ damage to try to predict which individuals may progress on to more clinically significant CV disease, Dr. Friedland said. Several organs are noted in current guidelines (as being associated with risk) but the ear is not one of them. Affected organs that are listed include the heart, brain, arteries, kidneys, and eyes.
However, the inner ear is highly vascularized, especially around the stria vascularis. Previous work in the medical literature has shown that abnormalities of the stria account for low frequency, or a flattened hearing loss sometimes known as strial presbycusis. It has also been shown that there is a relationship between cardiovascular disease and strial loss.
It is possible that a change in vessel health, potentially a sign of vascular disease, could affect hearing, he said. Indeed, the inner ear is so sensitive to blood flow that it is possible that any abnormalities in their condition could be noted earlier here than in other parts of the body that are less sensitive.
In addition, research from the Framingham Study showed an association between low-frequency hearing loss and numerous cardiovascular disease events. Their take on this was to determine whether individuals with cardiovascular disease may be more prone to hearing loss, therefore needing audiometric evaluation. Our take is a little bit of the opposite. Our hypothesis is that strial or low-frequency hearing loss is, in fact, a marker that may predict the presence or potential development of cardiovascular disease, he said.
Studies Analyze Audiograms
A retrospective study was launched in which researchers analyzed audiograms of 1168 patients over a five-year period. They categorized the audiograms according to five distinct audiometric patterns. A total of 186 were normal patterns, 168 were high-sloping, 358 were mid-sloping, 205 were low-sloping patterns, and 251 were strial.
-David R. Friedland, MD, PhD
Researchers then reviewed the medical records of the patients and performed a statistical correlation to cardiovascular disease, risk factors, events, and hearing. The average age of the patients was 67.5 years, and 669 were female.
When cardiovascular risk factors and hearing findings were correlated, it was found that the association between low-frequency hearing loss and specific cardiovascular events is quite high, Dr. Friedland said. Significant correlations were found between low-frequency hearing loss and the presence of myocardial infarction, coronary artery disease, stroke, and peripheral vascular disease. Low-frequency hearing loss was also much more prevalent in patients with hypertension, diabetes, and hyperlipidemia. The question of confirming whether audiometric patterns could predict cardiovascular status led to the second part of the study. Here, a second group of patients was studied.
We recruited individuals from medical clinics who had not had audiograms or who had not come to our clinic for the purpose of evaluating their hearing. They were interviewed and filled out a questionnaire regarding their cardiovascular history, he said. The subjects then underwent audiometric testing. A total of 90 patients were recruited, had an average age of 69 year, and 48 were female.
Developing a Formula
Researchers developed a formula from the initial cohort (which included the risk factors of smoking status, lipid levels, diabetes, hypertension, and age) to see whether cardiovascular status could be predicted as a probability. They then applied this formula to the second cohort of 90 patients and confirmed that the risk factors correlated with the presence of cardiovascular disease. They then added in the details from audiometric tests to see if the correlation with risk for cardiovascular disease was improved-and found that adding in audiometric patterns improved the specificity of the model.
We conclude there is a significant relationship between cardiovascular status and audiometric pattern. There is a particularly strong relationship between cerebrovascular disease and low-frequency hearing loss, Dr. Friedland said.
However, he noted that it is unclear whether this was a local phenomenon meaning a head event, or whether it is an indication of systemic disease. If it is an indication of systemic disease, then the ear and the brain could be two very sensitive markers of this disease. It is still not quite clear whether hearing loss, or one or more risk factors for cardiovascular disease, appears first.
To answer this and other questions, the researchers plan to continue to follow the cohort and do more study. The researchers also plan to apply their risk assessment approach to other independent cohorts of patients, such as those from the Framingham studies, to test its validity. They also plan to do studies that are more longitudinal in nature.
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