NOISE-INDUCED HEARING LOSS—DANIEL TODD, MD
GENERAL -NOISE INJURY IS NOT CORRECTABLE BUT IS PREVENTABLE
NOISE CAN CAUSE THRESHOLD SHIFTS, DECREASED SPEECH DISCRIMINATIONS, AND TINNITUS
INFANTS ARE MOST SUSCEPTIBLE
PRESBYCUSIS -AGE RELATED HEARING LOSS—- THAT CAN BE DISTINGUISHED FROM NOISE INDUCED LOSS BECAUSE THESE LOSSES WILL ACCELERATE WITH TIME
NOSOACUSIS -DISEASE RELATED HEARING LOSS
SOCIOACUSIS -LIFE (WORK) RELATED HEARING LOSS—–TYPE OF NOISE-INDUCED LOSS THAT IS RELATED TO EVERYDAY LIFE EXPOSURE OUT OF THE WORK PLACE; GUNFIRE MOST COMMON AND USUALLY AFFECTS THE LEFT EAR
EPIDEMIOLOGY -NIHL CAUSES SIGN. HANDICAP IN 2% OF MALE POPULATION
-> 30% OF POPULATION EXPOSED TO NOISE > 85 DB
(NITTS)-TEMPORARY THRESHOLD SHIFTS
EXPOSURE TO NOISE FOR SECONDS TO HOURS CAN CAUSE CHANGES IN PURETONE AVERAGES
PATIENT INITIALLY NOTICES “MUFFLED” HEARING POST EXPOSURE
NITTS INCREASE LINEARLY WITH EXPOSURE TIME AND RESOLVE LOGORITHMICALLY WITH TIME
MOST OF IT IS RESOLVED FAST WITHIN18- 24 HOURS OF EXPOSURE–THEN SLOWER RECOVERY CONTINUES OUT TO 2=4 WEEKS—RECOVER IS REALLY A FUNCTION OF TIME AND SILENCE WILL NOT SPEED IT ALONG
MAGNITUDE OF LOSS IS PROPORTIONAL TO THE INTENSITY, LENGTH OF EXPOSURE, PATTERN OF EXPOSURE (CONTINUOUS IS WORSE THAN INTERMITTENT), AND FREQUENCY (> 4000HZ IS MORE DETRIMENTAL)
TEMPORARY THRESHOLD SHIFTS MUST OCCUR BEFORE PERMANENT LOSS WILL OCCUR EXCEPT IN ACOUSTIC TRAUMA
CHANGES ARE USUALLY NOTED ABOVE 4000 HZ WITH STAPEDIAL REFLEX BEING PROTECTIVE TO 2000 HZ —-AFTER 50 MSEC—ONLY PROVIDES 20 DB OF ATTENUATION
(NIPTS)-PERMANENT THRESHOLD SHIFTS——”4 KHZ NOISE NOTCH”
OCCUR AFTER REPEATED TEMPORARY THRESHOLD SHIFTS OR ACOUSTIC TRAUMA
INITIALLY START AS HIGH FREQUENCY LOSSES BUT EVENTUALLY WILL PLATEAU AND START AFFECTING LOWER FREQUENCIES AS WELL
SHIFTS WILL NOT PROGRESS ONCE THE NOISE EXPOSURE IS REMOVED FOR ENVIRONMENT
LOSS WILL USUALLY SLOW OR CEASE WITH TIME
CHANGES NOTED AT THE APICAL OUTER HAIR CELLS USUALLY IN THE 2ND AND THEN 1ST QUADRANT OF THE BASAL TURN OF THE COCHLEA AND ARE RELATED TO THE APICAL STEREOCILIA ATROPHY WHICH EVENTUALLY LEADS TO CELL DEATH——GET A 4 KHZ NOTCH (2ND QUADRANT BASAL TURN CELLS) AND THEN A 4-6 KHZ DIP—-EVENTUALLY LEADS TO A HIGH FREQ SNHL INDISTINGUISHABLE FROM SENSORY PRESBYCUSIS
INNER HAIR CELLS AND THE SUPPORTING CELL NETWORK(PILLAR CELLS, DEITER CELLS, TUNNEL OF CORTI) WILL ALSO BE EVENTUALLY AFFECTEDAND AFFECT THE ABILITY OF THE HAIR CELLS TO REGENERATE
HAIR CELL LOSS WILL EVENTUALLY LEAD TO LOSS OF CENTRAL PATHWAYS (AUDITORY NERVE)
NOISES—DIVIDED INTO TRANSIENT AND CONTINUOUS
TRANSIENT (<0.2SEC—-STAPEDIAL REFLEX OBVIATED)
TYPE A (IMPULSE)—-EXPLOSION—ASINGLE EVENT IN A FREE FIELD ENVIRONMENT
CONSISTS OF A CONDENSATION AND RAREFACTION PHASE
IMPULSIVE (EXPLOSIVE) NOISE MORE DAMAGING THAN IMPACT NOISE
TYPE B (IMPACT)—REVERBERATION AND REFLECTION OF THE INITIAL NOISE AND SUBSEQUENT PRESSURE WAVE OFF ANOTHER OBJECT
RELATED TO A BRIEF EXTREMELY INTENSE NOISE EXPOSURE WHICH IS NOT PRECEDED BY A TEMPORARY THRESHOLD SHIFT
MECHANISM IS PROBABLY RELATED TO MEMBRANE RUPTURE
USUALLY LOSS IS SEVERE
CONTINUOUS (>0.2SEC)
STEADY(MOST PROMINENTLY FROM HIGH FREQ NOISES)
FLUCTUATING(INTERMITTENT)—-IF QUIETER PERIODS OF > 75 DB ARE INTERPOSED
RISKS CRITERIA -< 80 DB – NONE?
-> 80 DB – INCREASED RISKS ESPECIALLY WITH HIGHER FREQUENCY NOISE
ADDITIVE RISK FACTORS=HTN, CAD, HYPERLIPIDEMIA, BLUE EYES, OTOTOXIC MEDS, AND MALE SEX
LOOP DIURETICS NOT A RISK FACTOR
*CHILDREN ESPECIALLY AND ADULTS CAN GET NITTS—PTS FROM THEIR HEARING AIDS—- IF CONSERNED GET AN AUDIO—-REST EAR FOR 2 WEEKS AND THEN REPEAT AUDIO—CAN ALTERNATE EARS–MUST DOCUMENT THIS!!
AUDIOGRAM–USUALLY SEE A NOTCH AT 4000 HZ (2ND QUADRANT CELLS) WHICH WILL EVENTUALLY BE LOST WITH TIME IF EXPOSURE CONTINUES—GET A 4-6 KHZ NOTCH AND THEN FADE INTO A HIGH FREQ SNHL WHICH IS INDISTINGUISHABLE FROM SENSORY PRESBYCUSIS
RARE TO SEE GREATER THAN A 15 DB ASYMMETRY BUT IS POSSIBLE WITH GUNFIRE EXPOSURE—-OR IN TRUCK DRIVERS
NL TONE DECAY
COMPENSATION—HEARING LOSS MUST BE WORSE THAN 26 DB AT 500, 1000, AND 2000HZ (THIS IS DBA—A WEIGHTED SOUND PRESSURE METER WEIGHTED TOWARD THE SPEECH FRREQUENCIES
MONAURAL HEARING IMPAIRMENT(USUALLY LEFT) = 1.5 X (PTA-25)
HEARING HANDICAP = (5 X MI OF BEST EAR + MI OF WORST EAR)/6
CONSERVATION -CONSERVATION MEASUREMENTS REQUIRED IF PATIENT EXPOSED TO 90 BD FOR > 8 HOURS; FOR EACH 5 DB INCREASE THE TIME EXPOSURE IS CUT IN HALF (95 DB – 4 HOURS)
90—8, 95—-4, 100—-2, 105—-1, 110—30MIN, 115—15MIN, 120—7.5MIN
PROGRAMS-NOISE MEASUREMENTS IN THE WORK PLACE
IF ABNL – NOISE CONTROL MEASUREMENTS IMPLEMENTED TO ENVIRONMENT
IF UNABLE TO REACH ACCEPTABLE LEVEL – PTS NEED ROUTINE AUDIO AND IF > 10 DB THRESHOLD SHIFT NOTED OR > 90 DB EXPOSURE CONTINUED NEED INDIVIDUAL HEARING PROTECTION
BEST FREQ TO MONITOR IS 3-6 KHZ
BEST TREATMENT IS TO ELIMINATE THE NOISE—-NOT PRACTICLE
EAR PROTECTION IS THE NEXT BEST OPTION——EAR MUFFS IN COMBO WITH EAR PLUGS IS BEST
EAR MUFF TYPE HEARING PROTECTION ATTENUATE SOUND IN LOW FREQ (1000HZ) BEST AS THEY COVER THE AURICLE
HEARING PROTECTION WILL NOT LOWER YOUR SDS!!!—OFTEN PATIENTS THINK THAT THEY WILL NOT BE ABLE TO UNDERSTAND SPEECH OR WARNINGS IN A BUSY ENVIRONMENT—-THIS IS NOT THE CASE (PARACUSIS VON WILLISI)