In addition to pure tone audiometry (AUX_F) and tympanometry (AUXTYM_F), the NHANES 2009-2010 Audiometry Examination Component included examination data to measure the acoustic reflexes. The acoustic reflex is a protective, automatic reflex contraction of the ear drum in response to a sudden, high-intensity sound stimulus. The acoustic reflex may be of diagnostic value as it is diminished or absent in persons with specific types of hearing loss. Acoustic reflex testing is performed by putting a small probe into the ear that presents a standardized sound stimulus. The resulting changes in the compliance of the ear drum are then measured over a period of 1.5 seconds. If the normal acoustic reflex is diminished or absent, it can be an indication of nerve damage to the middle ear.
NHANES 2009-10 acoustic reflex testing was performed on a full sample of U.S. adolescents ages 12–19 years of age and U.S. adults ages 70+ years. Subjects using hearing aids who were not able to remove them for testing and subjects who had sufficient ear pain at the time of the exam were excluded.
All acoustic reflex tests were performed by a trained examiner on examinees in a dedicated, sound-isolating room in the mobile examination center (MEC). Acoustic reflex testing is performed by putting a small probe into the ear that presents standardized sound stimului at 1000 Hz and 2000 Hz. The resulting changes in the compliance of the ear drum are then measured over a period of 1.5 seconds. Please see the NHANES Audiometry/Tympanometry Procedures Manual for further information on Acoustic Reflex testing.
The instrument used to capture the Acoustic Reflex data was the same Interacoustics Model AD226 audiometer used for pure tone audiometry testing. All acoustic reflex data were unscreened and were entered directly into the computerized NHANES survey database system. Manufacturer’s calibration (traceable to the National Institute of Standards and Technology [NIST]) was performed annually on each audiometer.
The MEC health technicians who performed the acoustic reflex testing were professionally trained by a certified audiologist from the National Institute for Occupational Safety & Health (NIOSH). NIOSH also monitored the performance of each health technician on a regular basis. Field visits to each MEC were conducted by the audiologist at least three times per year. Additionally, NCHS Project Officers visited the MECs approximately twice per year to observe the audiometry examinations and verify that standard testing procedures were being followed. NIOSH consultants provided the MEC health technicians with annual retraining and protocol updates.
All data were captured into the NHANES computerized database system, with acoustic reflex data automatically uploaded. On a continuous basis, a consulting audiologist performed a clinical review of all data for each subject as it was received, checking for quality and consistency.
The acoustic reflex data files (AUXAR_F) represent the raw data as it was collected. They contain a total of 336 variables, 168 representing the right and left ear acoustic reflex curve data at 1000 Hz (the variables AUXRR101 to AUXRR184; and AUXLR101 to AUXLR184, respectively) and 168 variables representing the right and left ear acoustic reflex curve data at 2000 Hz (the variables AUXRR201 to AUXRR284; and AUXLR201 to AUXLR284, respectively).
The data points represent equivalent volume (compliance) data in daPa during the ½ second (500 msec) period of stimulation and in the one second period post-simulation. As with the tympanometry raw data, the responses for each individual ear are contained in a series of 84 equally spaced sequential measurement variables, in this case the intervals between variables representing sequential time units. The average time between each numbered variable is 1500 msec/84 or 17.9 msec.
In each series of variables, the 1st variable (AUXRR101, AUXLR101, AUXRR201 or AUXLR201) represents the start point for testing, and the successive variables in turn represent the entire 1.5 second testing interval. These data can be used to create acoustic reflex graphs at each frequency in each ear.
The acoustic reflex examination for 2009-10 was administered to a full sample of participants in the NHANES Mobile Examination Center (MEC). Therefore, the NHANES MEC examination weights should be used for data analysis. For more information on the use of sample weights in current NHANES data analysis and for combining weighted data across multiple NHANES survey years please refer to the NHANES Analytic Guidelines https://wwwn.cdc.gov/nchs/nhanes/analyticguidelines.aspx) and the on-line NHANES Tutorial (https://www.cdc.gov/nchs/tutorials/) for further details on the use of sample weights and other analytic issues.
Acoustic reflex data analysis is a complex procedure and requires a thorough knowledge of the specialty content area for valid results to be obtained. If an analyst does not have professional experience in this area, it is recommended that audiologic consultation be obtained to help formulate and review the results of the analysis.