Whole blood viscosity and red cell filterability as factors in sensorineural hearing impairment in the elderly

Deficiencies in blood supply can lead to impairments in cochlear function. We have reported significant associations of both measures of whole blood viscosity and derived measures of red cell rigidity with hearing threshold levels in individuals with sensorineural hearing impairments. This paper describes direct measures of red cell filterability in a group balanced across the variables of hearing threshold level and age to facilitate dissociation of the effects of factors correlated with age. After controlling for effects of age, sex and social class, there were strong correlations between whole blood viscosity at high shear rate and hearing threshold levels at 250, 500, and 1,000 and 2,000 Hz. At 4,000 and 8,000 Hz, hearing threshold level was related to red cell filterability. When the data are divided into subgroups by age, the younger age group exhibited a pattern similar to the overall one, but in the older age group the effect of red cell filterability was more apparent, extending down to 1,000 Hz. The data support a strong association between aspects of blood rheology and sensorineural hearing impairment, but in a more complex manner than suggested by previous studies. They imply that there are two processes associated with sensorineural hearing impairment, one of which can be considered as due to bulk rheological properties, while the other appears more related to the properties of individual red cells. The bulk properties are more important at lower frequencies, while the cellular properties are more influential at higher frequencies.