Blood Lactate as a Biomarker of Vocal Function: Validating a Novel Vocal Muscle Strength Task in Older Adults with Presbyphonia

Northwestern University At Chicago, Evanston IL

Investigators

Abstract

Voice disorders affect 12-35% of the population over 60 years of age, causing significant health, psychosocial, and occupational consequences. The cause of age-related changes in voice quality, known as presbyphonia, is multifactorial including muscle atrophy and reduced muscle strength capacity. Voice therapy is the first line of recommended treatment for presbyphonia, yet two-thirds of older patients do not show improvement with voice therapy. To date, there are no objective physiological measures of vocal muscle strength to evaluate the effectiveness of voice therapy in older adults. Here, we propose establishing the first outcome measure to assess vocal muscle strength capacity. Physiologically, anaerobic systems generate the energy needed for muscle strength, with blood lactate (La-) as a byproduct. Blood La- is routinely used pre- and post- exercise to evaluate changes in limb anaerobic muscle strength. Preliminary studies have found that an adapted 60-second laryngeal diadochokinetic task (LDDK) resulted in a significant increase in blood La-, demonstrating that this vocal task requires demand of anaerobic energy systems. Given that direct study of human vocal musculature in vivo is impractical, we hypothesize that measuring blood La- is a novel and practical approach to assessing vocal muscle strength capacity. This proposal will establish validity, the extent an outcome tool captures what it is intended to measure, of a vocal demand task outcome measure of vocal muscle strength. We will recruit healthy voice participants and patients over 60 years with presbyphonia from the Northwestern Memorial Hospital Voice Clinic. In healthy voice participants, to establish construct validity, Aim 1(a) will identify the point within a 2-minute window of completing three vocally demanding tasks (LDDK, Loud Sustained Phonation, Loud Oral Reading) that elicits the largest increase in blood La- from resting levels to establish the most anaerobically demanding task (construct validity). Aim 1(b) will compare vocal demand-induced changes in blood La- with age. We hypothesize that LDDK will result in the largest increase in blood La- concentration and the rate of blood La- increase will be smaller for older adults compared to younger adults for LDDK. To establish criterion validity, Aim 2 will determine the association between vocal muscle strength capacity and limb muscle strength capacity in patients over 60 years of age with presbyphonia, to establish if there is a correlation between our hypothesized LDDK measure of vocal muscle strength with an already established measure of limb muscle strength (criterion validity). We hypothesize that diminished LDDK function correlates with reduced limb muscle strength in older adults with presbyphonia. This innovative proposal will establish the first known quantitative vocal muscle strength task, from a physiological perspective, —an outcome measure that addresses goal 1 of NIDCD’s Theme 5. The findings from this proposal will provide an essential foundation for a subsequent R01 that will apply the novel biomarker and vocal demand task outcome measure to evaluate the anaerobic vocal muscle strength changes that occur during various voice therapy programs designed for treating the aging voice.