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Association Between Cardiovascular
Health and Hearing Function: Pure-Tone
and Distortion Product Otoacoustic
Emission Measures
Kathleen M. Hutchinson
Helaine Alessio
Miami University, Oxford, OH
Rachael R. Baiduc
Northwestern University, Evanston, IL
Purpose: A reduction in hearing sensitivity is
often considered to be a normal age-related
change. Recent studies have revisited prior ways
of thinking about sensory changes over time,
uncovering health variables other than age
that play a significant role in sensory changes.
Method: In this cross-sectional study, cardio-
vascular (CV) health, pure-tone thresholds at
1000 to 4000 Hz, and distortion product oto-
acoustic emissions (DPOAEs), with and without
contralateral noise, were measured in 101
participants age 10–78 years.
Results: Persons in the “old”age category
(49–78 years) had worse pure-tone hearing
sensitivity and DPOAEs than persons in the
younger age categories (p< .05), affirming an
age effect. Although hearing decline occurred
in all persons in all CV fitness categories of
every age group, those with low CV fitness in
the old age group had significantly worse pure-
tone hearing at 2000 and 4000 Hz ( p<.05).
Otoacoustic emission measurements were bet-
ter for the old high-fit group but not significantly
influenced by CV fitness level across age groups.
Conclusions: Results of the current study
elucidate the potentially positive impact of
CV health on hearing sensitivity over time.
This finding was particularly robust among
older adults.
Key Words: distortion product otoacoustic
emissions, suppression, cardiovascular fitness,
pure-tone thresholds
Adecline in hearing sensitivity is considered a likely
consequence of age (Gates & Cooper, 1991; Hull,
1989). However, some initial signs of auditory ag-
ing start long before senescence. Early evidence of nerve
degeneration in the cochlea secondary to hair cell degener-
ation was reported by early adolescence nearly 40 years
ago (Johnsson & Hawkins, 1972). Numerous studies have
reported deterioration of hearing levels at 45–50 years of age
and then a notable acceleration above 70 years (Gates &
Cooper, 1991; Robinson & Sutton, 1978; Ross, Fujioka,
Tremblay, & Picton, 2007; Shuknecht, 1955, 1964, 1974).
However, aging is only one of many factors that contribute
to a decline in hearing sensitivity. Hearing ability is also
commonly compromised by otologic and cardiovascular
(CV) disease and exposure to noise.
Previous studies have provided evidence that CV fit-
ness has a protective role in hearing preservation (Alessio,
Hutchinson, Price, Reinart, & Sautman, 2002; Cristell,
Hutchinson, & Alessio, 1998; Hutchinson et al., 2000; Ismail
et al., 1973; Kolkhorst et al., 1998; Manson, Alessio, Cristell,
& Hutchinson, 1994). CV fitness was the main health com-
ponent associated with hearing, with peak oxygen consump-
tion (VO
2
peak) as the basis for comparison. Other health
and fitness determinants—body composition, blood pressure,
and blood lipids—displayed no significant relation to hearing
sensitivity (Hutchinson et al., 2000; Kolkhorst et al., 1998),
whereas muscle strength was inversely related to hearing
sensitivity (Hutchinson et al., 2000). Research in cellular
mechanisms in the cochlea revealed that cells under stress
from noise, ototoxic drugs, and aging generate proteins to
protect surviving cells. Several laboratories have demon-
strated positive protective pharmacological effects of specific
proteins against cochlear damage (Henderson, Bielefeld, Harris,
& Hu, 2006). Antioxidant research has allowed researchers
Research and Technology Paper
American Journal of Audiology •Vol. 19 •26–35 •June 2010 •AAmerican Speech-Language-Hearing Association26
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to better understand the effects of certain nutrients on co-
chlear microcirculation. The results of one randomized
controlled trial demonstrated that participants who supple-
mented their diet with folic acid (an antioxidant that scavenges
free radical molecules) for 3 years evidenced improvement
in low-frequency behavioral thresholds (Durga, Verhoef,
Anteunis, Schouten, & Kok, 2007).
A common explanation of how CV fitness may influence
hearing sensitivity is through the effect on blood circulation,
especially to the organs and muscles of the inner ear, in
particular, the stria vascularis in the cochlea. Metabolism and
blood flow are directly related to the vascular pattern of
the cochlea. Reduction in blood circulation through the inner
ear can also cause reduced hearing sensitivity over time.
Variations in cochlear blood flow may affect the availability
of oxygen and glucose, which is more rapidly metabolized
during sound stimulation (Brant et al., 1996). This hypothesis
is difficult to assess in vivo; therefore, knowledge about
these interactions is based on descriptive and animal studies.
Any decrease in blood flow causes a disruption of the phys-
ical and chemical processes by which metabolic energy is
created in the cochlea (Cruickshanks et al., 1998).
There is evidence that regular exercise may play a role
in hearing conservation via improvements in circulation and
VO
2
peak. Ismail et al. (1973) had participants complete a
20-week-long physical fitness program, which improved
their CV fitness as measured by VO
2
peak, as well as their
baseline pure-tone thresholds (PTTs). A more recent in-
vestigation revealed improved pure-tone and temporary
threshold shifts in healthy, young adults with low-average
fitness levels who improved their VO
2
peak following
8 weeks of twice-weekly aerobic exercise (Cristell et al.,
1998). Hutchinson et al. (2000) and Alessio et al. (2002)
found PTTs to be specifically related to CV fitness, the prem-
ise being that high CV fitness levels are associated with
enhanced circulation within the vascular system. Neverthe-
less, two studies found no consistent pattern between fit-
ness level, exercise, and evoked otoacoustic emission (OAE)
amplitudes (Alessio et al., 2002; Engdhal, 1996).
A growing body of evidence has demonstrated the value
of evoked OAEs in addition to standard PTTs in revealing
the acute effects of noise and ototoxic agents (Engdhal &
Kemp, 1996; Ress et al., 1999). OAE testing has been
shown to reflect alterations in the cochlea and outer hair
cells before a significant hearing loss is present (Arnold,
Lonsbury-Martin, & Martin, 1999; Lonsbury-Martin &
Martin, 1990; Marshall & Lapsley Miller, 2007; Negley,
Katbamna, Crumpton, & Lawson, 2007). OAEs are useful
experimentally for evaluating the status of cochlear func-
tion in experimental models. They have proven valuable in
monitoring the effects of ototoxins and noise on cochlear
function. Furthermore, OAEs also provide a means to assess
the efferent system.
Though a number of studies have investigated the inter-
connection between CV health and hearing sensitivity (Alessio
et al., 2002; Hutchinson et al., 2000), there is no consensus
on the topic. This evidence to date prompts us to examine
more closely the relationship of CV fitness level and hear-
ing. The present study evaluated both pure-tone levels and
distortion product otoacoustic emission (DPOAE) measures
in a representative sample of more than 100 participants
categorized by age and fitness abilities. In this cross-sectional
study, data were gathered from participants who had been
screened for otologic disorders and evidence of noise-induced
hearing loss prior to assessment, thus reducing bias due to
underlying hearing disorders. It is hypothesized that a healthy
CV system attenuates the effects of age on hearing processes,
thus maintaining hearing sensitivity and cochlear function.
Design and Method
Participants
A total of 102 participants were volunteer members from
the central Midwest area, including Ohio and Indiana. All
potential participants reported good general health and hear-
ing ability. None reported smoking. The participants were
screened for middle ear disease with an otoscopic exam
and tympanometry demonstrating Type A tympanograms
(Jerger, Jerger, & Mauldin, 1972). No exclusions were made
for abnormal gradient or pressure. Participants with a uni-
lateral hearing loss or any evidence of noise-induced hearing
loss were excluded. One participant was excluded because
of his report of occupational noise exposure. As Table 1
shows, the participants comprised 67 women and 34 men.
Table 2 shows the mean PTTs across the audiometric fre-
quencies by age.
Procedure
PTTs at 1000, 2000, 3000, and 4000 Hz were obtained
by the standard Hughson-Westlake method using pulsed
tones generated by a diagnostic, clinical audiometer (Grason-
Stadler Model GSI 33) through insert earphones. Participants
were seated in a double-walled sound booth (Industrial
Acoustics Company) suitable for threshold testing (Ameri-
can National Standards Institute [ANSI], 2004). Participants
were then instructed to respond using a push button. Thresh-
old was determined as the softest level obtained two out
of three times on an ascending presentation run. Thresholds
at octave frequencies were obtained at 1000, 2000, 3000,
and 4000 Hz, in order of presentation. One ear of each par-
ticipant was selected randomly for testing.
Annual calibration of audiometric equipment was per-
formed according to ANSI (2004) guidelines. A listening
check was performed daily on audiometric equipment.
DPOAEs were recorded using an Otometrics Madsen
Capella 503 Cochlear Emissions Analyzer coupled to an
IBM personal computer with RS232 cables to present the
primary tones and record DPOAEs. Participants were seated
quietly and instructed to keep movement to a minimum.
Table 1. Sex and age with standard deviations.
Sex nAge (years) ± SD
Women 67 34.88 ± 18.9
Men 34 31.68 ± 15.3
Total 101
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The DPOAEs were recorded with the input/output (I /O)
function at an audiometric frequency of 4000 Hz by insert-
ing an adult ear probe into the test ear of each participant.
Good reliability has been found for DPOAE measurement
at 4000 Hz; DPOAEs in the midfrequency range are sen-
sitive to changes caused by aging and noise factors. The
I /O function of the 2f1-f 2 DPOAE (f1 = 3649 Hz) was
recorded. Briefly, I/O curves were obtained at 4000 Hz using
equilevel stimuli between 70 and 55 dB SPL in 5-dB incre-
ment steps. Because the growth of the distortion product
(DP) varies by primary tone level differences (Kummer,
Janssen, & Arnold, 1998), the growth of the DPs was mea-
sured at equal levels. A limitation of this DPOAE instrument
is its inability to vary tone levels continuously instead of
in discrete steps. A measurement was considered valid if the
signal-to-noise ratio was +3 dB SPL or better (Cilento, Norton,
& Gates, 2003). Response amplitude at the four intensity
levels was assessed both with and without contralateral white
noise.
To assess efferent suppression, the DPOAE was recorded
in both the presence and absence of contralateral suppression
supplied by white noise (bandwidth of 1600 to 8000 Hz) pre-
sented continuously at 84.1 dB SPL by a Beltone 2000 audio-
meter using an insert earphone in the opposite meatus. Prior
to stimulation, the “check probe fit”procedure was performed
to ensure accurate fit of the DPOAE probe as well.
The amplitude of the DPOAE responses in relation to
the noise floor was noted for each of the eight test conditions;
those with a +3-dB SPL signal-to-noise ratio were accepted
as valid DPOAEs. The proportions of valid DPOAEs at
55 dB SPL without and with contralateral noise were .96
and .95, respectively; the proportions of valid DPOAEs at
70 dB SPL in the same two conditions were .97 and .98, re-
spectively. The DPOAE data collected at 60 and 65 dB SPL
were not included in this report because they paralleled
the findings at 55 and 70 dB SPL; additional analyses of re-
peated measures at all SPLs might reduce the power to detect
differences without additional contribution to the experi-
mental questions.
VO
2
peak was determined using either a maximal or
a submaximal graded exercise test protocol on a Monark
Bicycle ergometer. Participants began by pedaling at
50 revolutions/min against a 1-kg resistance for 2 min.
Thereafter, resistance was increased 0.5 kg every 2 min.
Heart rate response, blood pressure, and respiratory gases
were monitored continuously throughout the test. Oxygen
uptake was measured by the open-circuit method using a
low-resistance, two-way breathing valve. Respiratory gases
were analyzed for CO
2
and O
2
concentrations on Ametek gas
analyzers. Modified regulations that required a physician to
be present when administering maximum graded exercise
tests to participants age 35 years and older forced a switch
to use of submaximal exercise tests for most of the partic-
ipants in this study (American College of Sports Medicine,
2000). The VO
2
peak was calculated using a standard Young
Men’s Christian Association (YMCA) submaximal graded
exercise test (Sanders & Duncan, 2006). No test had to be
terminated due to participant report of angina or any other
abnormal exercise response.
Statistical Analyses
Analyses were done with SPSS Version 16.0. The data
were first summarized and examined for outliers and con-
sistency. Multivariate analyses of variance (MANOVAs)
were done for four age categories and three fitness levels
using PTTs and DPOAE amplitudes as dependent variables.
Participants were divided into four age categories containing
22 to 27 participants for analysis purposes: youth = 10 to
19 years; young adult = 20 to 27 years; middle-aged adult =
28 to 48 years; old adult = 49 to 78 years. Dividing participants
into four groups for initial analysis enabled large enough
samples (n=22–26) to avoid single participants overwhelming
an average across-aged adult responses. The old age par-
ticipants were lowest in number (n= 22) and spanned the
widest age range. The VO
2
peak was also analyzed as a
categorical variable to represent an individual’s CV fitness
level (high, medium, or low). In other words, the VO
2
peak
parameters indicated whether an individual’s fitness level
acted as a buffer for age-related hearing decrement. Low-fit
individuals had an aerobic capacity equal to the least fit 20%
of the population for that age group and sex (Sanders &
Duncan, 2006). Moderately fit participants had an average
aerobic capacity equal to 20%–59% of the population for that
age group and sex. The high-fit group had an aerobic capac-
ity equal to the most fit 60%–100% of the population for
each age group and sex.
It has been shown that the individuals in the highest
fitness level should show less of an age-related impact on
pure-tone and DPOAE amplitude test results than those
individuals in the lowest fitness level (Alessio et al., 2002).
A value of p< .05 was set as the level of statistical sig-
nificance for all tests reported here. Because significant
Table 2. Mean pure-tone thresholds by frequency and age groups with standard deviations.
Age classification n
1000 Hz 2000 Hz 3000 Hz 4000 Hz
M SD M SD M SD M SD
Youth 26 3.65 4.80 2.31 6.81 3.65 6.09 3.85 6.05
Young adult 27 3.89 5.43 2.22 5.93 4.63 8.42 4.63 7.32
Middle-aged adult 26 10.38 9.04* 8.08 8.49* 12.12 8.38* 17.12 10.50*
Old adult 22 11.82 7.95* 10.23 9.1* 14.09 10.3* 15.00 12.53*
*p< .05.
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interactions were present, separate MANOVAs were done for
age and fitness variables.
Amplitude measurements obtained at 55 dB and 70 dB SPL
and PTTs for the same ear were compared by participants’
CV fitness level by age group. Previous research has detailed
no effect of sex on DPOAE results (Sheppard, Brown, &
Russell, 1996); therefore, no separate sex analyses were done.
Results
Participant Information
Table 1 illustrates the demographic characteristics of
the participants. Audiometric and DPOAE test results for
67 women and 34 men were analyzed. The mean age of the
women was 34.88 years (SD = 18.9; range = 10–78), and
the mean age of the men was 31.68 years (SD = 15.3; range =
10–56). The sex age difference was not significant, F(1, 100) =
0.73, p> .05.
Table 2 illustrates the means of the PTTs by age group;
pure-tone levels increased with age, with more variability
in the middle and old age groups. Ninety-four percent of
the participants had normal PTTs (i.e., ≤25 dB HL) at all
audiometric frequencies. Examination of Table 2 shows
mean thresholds at 1000, 2000, 3000, and 4000 Hz were
worse for the middle and old age groups compared with the
two younger age categories.
Table 3 shows the mean DPOAE amplitudes both with-
out and with contralateral noise at two intensity levels. The
DPOAE amplitudes show a similar pattern to PTTs, with
values worsening with increasing age among the middle and
old age groups at both intensity levels. Table 3 also illustrates
better DPOAE thresholds at 70 dB SPL without noise in
comparison to two mean thresholds at 55 dB SPL (with and
without contralateral noise).
Suppressive effects did not increase with emissions evoked
at lower levels. In fact, some ears exhibited an enhance-
ment of amplitudes with contralateral noise. However, mean
DPOAE magnitude did not change as systematically with
age compared to the PTTs with age; much more variability
was found at both intensity levels and age classifications.
Test–retest changes have been found in the magnitude of
DPOAEs with multiple measurements (Kim, Frisina, &
Frisina, 2002).
Values of the VO
2
peak measurements ranged from
17.2 to 78.6 ml/kg /min, with a mean of 37.6 (SD = 11.4;
see Table 4). Because the three fitness categories were de-
termined by participant age and sex, both classification
values are listed. Although absolute mean levels appear
consistent across age classifications, analysis of variance
(ANOVA) follow-up test results show that the values for the
youth group classification were significantly better than the
old age group, F(3, 100) = 3.78, p<.05.
MANOVA Results
Considering age as a categorical variable, a MANOVA
model tested using the age category as a factor and PTTs
measured at 1000 to 4000 Hz as dependent variables. Figure 1
illustrates better hearing levels across frequencies in the two
younger groups compared with the old group, in which the
pure tones were worse, F(3, 100) = 13.14, p< .05. Dunnett’s
post hoc tests point to a significant drop-off in pure-tone
hearing sensitivity in the middle-aged group and continued
in the old age group at 1000, 2000, 3000, and 4000 Hz (see
Table 2).
A MANOVA using fitness level as a factor (i.e., VO
2
peak) and pure-tone responses as dependent variables in-
dicated significantly better thresholds for the high- versus
low-fit participants at 1000 Hz, F(2, 100) = 2.01, p< .05.
Although hearing decline occurred in persons in all CV
fitness categories of all age groups, a MANOVA performed
using both age and fitness level as factors showed that
those with low CV fitness in the old age group had sig-
nificantly worse pure-tone hearing at 2000 Hz, F(6, 100) =
2.30, p< .05, and 4000 Hz, F(6, 100) = 4.56, p< .05. The old
Table 3. Mean distortion product otoacoustic emission amplitudes (dB SPL) by intensity and age groups with standard deviations.
Age classification n
55 dB 70 dB 55 dB suppressed 70 dB suppressed
M SD M SD M SD M SD
Youth 26 4.77 7.68 15.2 8.29 5.82 7.84 17.33 5.55
Young adult 27 0.078 7.16 11.72 8.54 0.004 7.85 13.23 6.17
Middle-aged adult 26 –7.283 9.74 0.185 10.3 –7.88 8.95 9.22 5.82
Old adult 22 –12.110 10.79 –0.108 12.6 –11.55 10.51 4.64 12.80
Table 4. Mean oxygen consumption values by age group and
gender with standard deviations.
Age classification n
VO
2
peak
MSD
Youth
Female 16 40.24 9.77
Male 10 43.49 14.81
Young adult
Female 20 39.10 10.52
Male 7 42.00 5.83
Middle-aged adult
Female 14 32.34 8.76
Male 12 41.36 11.92
Old adult
Female 17 30.09 11.03
Male 5 36.51 12.87
Total 101
Female 67 35.67 10.82
Male 34 41.40 11.77
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high-fitness level’s hearing values were consistently better
than the mean thresholds of the low-fitness levels in the same
age group.
The two-factor ANOVA model was repeated to assess
the factors of CV fitness and fitness level on DPOAE am-
plitudes at 4000 Hz at two intensity levels, with and without
contralateral noise. Figure 2 illustrates the mean DPOAE
thresholds categorized by age and fitness categories. The
DPOAE thresholds at 55 dB and 70 dB SPL were signifi-
cantly better in the youth and young groups in comparison to
the two elder age groups, F(3, 100) = 9.26, p< .05. Similarly,
the DPOAE level with contralateral noise at 55 dB SPL
was also significantly better in the youth group (10–19 years)
compared with the middle-age and old age groups, F(3, 100) =
8.11, p< .05. There was no statistical separation of the fit-
ness level factor on DPOAE amplitude in any test condition
across age groups ( p> .05).
Multivariate regressions of PTT and DPOAE amplitude
on age were done at each frequency for each fitness level.
Linear regression estimated the coefficients of the linear
equation involving the two continuous independent variables,
VO
2
peak and age, that best predicted PTTs and DPOAE
amplitudes. For each value of the independent variables,
the distribution of the PT and DPOAE variables was normal.
The mean rates of change and the slope coefficient (b) with
age and fitness are displayed in Table 5. As expected, the
slopes of the pure-tone–age functions increased with increas-
ing frequency. That is, pure-tone levels increase with increas-
ing age, representing age-associated hearing loss. These
differences were significant (p< .05) for all comparisons by
frequency and age. The pvalue of each predictor measures
the unique effect of age and fitness on the variance of the
PTTs after the effects of each of the other predictors on PTTs
have been accounted for. Therefore, the pvalue of VO
2
peak
(range =.00–.23) measures the amount of unique variance
it explained for the PTT after accounting for the effects of age.
PTTs systematically increased, indicating compromised
hearing, with decreasing fitness levels.
In Table 5, the rate of change (b) with age in the DPOAE
amplitudes is shown at the two intensity levels; the slopes
varied only slightly by intensity, and values also deteriorated
with age. The slopes of the DPOAE–age functions were
statistically significant ( p< .05). The pvalue of VO
2
peak
(p= .03) illustrates the significant positive impact of fitness
Figure 1. Mean pure-tone (PT) threshold at 1000, 2000, 3000, and 4000 Hz (±SD) by fitness level and age classification. The population
was separated into 4 age groups with similar numbers of people in each group.
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level on DPOAE amplitude at 55 dB SPL accounting for the
effects of age.
Table 5 also displays the slope coefficient (b) for the effect
of age and fitness on DPOAE at the two intensity levels
when amplitude values were adjusted for hearing threshold
level at 4000 Hz; the decline in DPOAE amplitude was
attributable to the worsening auditory thresholds. Patterns
of DPOAE amplitudes measured with contralateral noise
were similar to results found in Table 5. The unique variance
of fitness level did not significantly account for DPOAE
Figure 2. Mean distortion product otoacoustic emission (DPOAE) thresholds by age and
intensity level (±SD).
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amplitudes after accounting for the effects of the PTT at
4000 Hz. Multivariate regression findings were consistent
with the MANOVA results.
Discussion
Of the various age, genetic, environmental, and lifestyle
interactions that affect hearing sensitivity, there is one var-
iable, CV fitness, that is potentially modifiable. The main
result reported in this article was a significant positive impact
of fitness level on PTTs among old adults. Previous stud-
ies have reported benefits to PTTs in young adults who
participated in regular exercise. However, there has not
been a systematic study of hearing sensitivity using both
pure-tone and DPOAE in young and old persons of differ-
ing CV fitness levels. This information may contribute to
understanding the role of CV fitness in protecting and pre-
serving hearing at different ages. Clinicians may benefit from
gathering a more detailed CV history from their patients,
including presence of hypertension, blood pressure, hyper-
lipidemia, and physical activity each week.
In our cross-sectional design, mean pure-tone hearing
level was most sensitive in the younger age groups. Figure 1
illustrates better hearing levels in the younger groups com-
pared with the old group (age 49–78 years). Hearing levels
for the 10–27-year-old participants primarily ranged be-
tween –5 and 15 dB HL, whereas the participants age 28
and older ranged between 0 and 40 dB HL across fitness
categories. Variability within categories is more evident in
the mid- and low-fit levels, showing more dramatic changes
between the teen years and early 20s versus middle to old age
groups. The PTT range of the high-fit category indicated a
narrower range of hearing levels and more consistent, sen-
sitive levels.
Nevertheless, the cross-sectional “snap shots”(see Figure 1)
indicate that pure-tone hearing sensitivity is not consistently
associated with better CV health at all frequencies. Hear-
ing levels were similar in teens and 20-year-olds within all
fitness levels; an increase in pure-tone hearing sensitivity,
indicating worse hearing, was observed in the middle and old
age range. For the study participants, however, mean PTTs
at 2000 and 4000 Hz were significantly better within the
high-fit compared with the low-fit old adult group.
Earlier reports have observed significant associations be-
tween CV fitness and hearing sensitivity (Alessio & Hutchinson,
1991; Cristell et al., 1998; Hutchinson et al., 2000; Manson
et al., 1994). Other laboratories have reported similar re-
sults using criteria such as VO
2
peak, blood pressure, and
percentage body fat to distinguish persons with low and
high CV health (Axelsson & Lindgren, 1985; Ismail et al.,
1973). Alessio et al. (2002) illustrated better hearing thresh-
olds among high CV health fitness participants compared
to the low and medium fitness level groups only at the older
ages (i.e., over 55 years). Age 50 appeared to be a separa-
tion point, after which fitness level and age were related in
a statistically significant direction, with high fitness being
positively related to better hearing levels (Alessio et al.,
2002). In the current study, primary changes were most prom-
inent for individuals over 60, especially at 4000 Hz or above.
Figure 2 illustrates the decrease of DPOAE amplitude
across the age groups by fitness categories. Results show
highest amplitudes for all younger participants at both the
55- and 70-dB SPL stimulus levels. CV fitness, as an isolated
variable, resulted in stabilization of amplitudes as the par-
ticipants increased in age over 49 years at both intensity
levels. This demonstrated a protective effect of CV fitness on
hearing; participant age and 4000-Hz PTT appeared to drive
the decrease in levels. Similarly, DPOAE amplitudes with
contralateral noise did not exhibit sensitivity to CV health
status. In some ears, a small enhancement of DPOAEs
created by contralateral stimulation was observed. Similar
findings have previouslybeen reported (Grazyna, Smurzynski,
Morawski, Namyslowski, & Probst, 2002). With lower and
higher levels of fitness, the clinical performance of DPOAEs
did not separate groups for early identification for suscep-
tibility to hearing loss. The DPOAE results are consistent
with Hutchinson et al.’s (2000) findings; no association was
found between fitness and muscle strength measures and
DPOAE measures. Cilento et al. (2003) examined the effects
of age and PTT shift and also found much variability in
DPOAE findings.
Measurement of DPOAEs exhibits properties of sup-
pression, tuning, and vulnerability closely paralleling the
properties of hearing. Gains in CV fitness result in changes
in underlying physiological mechanisms such as cerebral
structure and both cerebral and cochlear blood flow (Colcombe
& Kramer, 2003; Torre, Cruickshanks, Klein, Klein, &
Nondahl, 2005). CV improvements have led to improved
visuospatial and executive control processes. Corticofugal
activity has been shown to influence efferent suppression
of OAEs (Perrot et al., 2006). Ipsilateral sound stimulation
suppresses the contralateral sound-evoked excitation of
almost half of inferior colliculus neurons (Faingold, Gehlbach,
& Caspary, 1989; Rose, Gross, Geisler, & Hind, 1966). If
cortical function is a beneficial consequence of CV fitness
training, then subcortical modulation of the evoked OAEs
measured from the contralateral ear could also be influenced.
The present DPOAE suppression results exhibited much
variability and were not sensitive to differences in the func-
tion of the efferent system between fitness levels.
Current results support the statistical inferential associa-
tion between CV fitness and pure-tone hearing ability pres-
ervation across a 68-year time period. Moderate and high
CV fitness levels have protected against temporary hearing
loss caused by noise (Hutchinson et al., 2000; Manson et al.,
1994). Current concepts in auditory physiology include
an active mechanism that serves to counteract the effects
of trauma and stress (Campbell et al., 2003; Henderson,
Table 5. Slope (bcoefficients) and significance ( pvalues) at
55 and 70 dB SPL accounting for pure-tone hearing threshold at
4 kHz.
Value 55 dB SPL 70 dB SPL
b(pvalue) Age –.215* –.218*
VO
2
peak .092 .093
4 kHz –.455* –.417*
*p< .05.
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Subramaniam, & Boettcher, 1993; Patuzzi, 1992). The
observations that hair cells contain specific proteins that
undergo changes in expression with slight edema suggest
that active elements exist to protect tissue from damage.
Suchproteinsmayalsoplaykeyrolesinprotectingthe
hair cell from metabolic and aging changes, as has been
suggested as the function of stress-induced proteins (Campbell
et al., 2003; Lindquist, 1986). Other studies have also raised
the possibility that stress proteins could protect the auditory
periphery from damage due to noise, ototoxic drugs, or trauma
(Patuzzi, 1992).
A limitation of this study is that it was a cross-sectional
analysis of the relation between fitness and hearing func-
tion. Directionality associations cannot be inferred from this
investigation, as cochlear and brainstem function preceded
fitness level achievement or the measured fitness level pre-
ceded auditory function. Another limitation of this study
was self-reported history of lifestyle factors (i.e., smoking,
noise exposure, medication use, activity, and alcohol). Some
participants may have misrepresented their health history
during the questionnaire interview. Misinformation may
bias the association either in favor or away from the null
hypothesis. An evaluation of the pure-tone levels and DPOAE
levels of participants in a 5-year follow-up study may help
clarify whether cochlear hearing function is influenced by
CV health. Despite the adequate sample size, comparison of
these results with otherCVanalysesof age-related hearing loss
will be an important next step to confirm the long-term effects
of health on cochlear function.
Accumulating evidence has pointed to a large number
of physiological, psychological, and sociological risk factors
that are either directly or indirectly related to late-onset
hearing loss (Gates & Cooper, 1991). Although different
mechanisms underlie these various types of stressors, com-
monalities exist including free radical formation and alter-
ations in the body’s antioxidant activity (Wang, Puel, &
Bobbin, 2007). The current state of knowledge regarding the
interaction of risk factors for hearing loss is still limited.
Genetics, nutrition, and pharmacological factors have been
shown to play a role in the susceptibility to hearing loss
(Campbell & Rybak, 2007; Gates, Schmid, Kujawa, Nam,
&D’Agostino, 2000; Wang et al., 2007). It is generally
accepted that antioxidative mechanisms in the vasculature
protect the auditory system from excessive free radical
formation. An imbalance favoring free radicals over anti-
oxidant activity results in oxidative stress and may result in a
suppressed ability to repair cellular function (Cruickshanks
et al., 1998). Antioxidant levels can be increased from nu-
tritional supplementation as well as with regular exercise. A
large number of exercise studies, both acute and chronic
(Alessio & Blasi, 1997), indicate a protective role of regular
exercise in boosting antioxidants, especially during exer-
tion or stress, when free radicals are elevated. In this way,
physical activity positively affects cellular mechanisms
related to oxidative stress.
In summary, although hearing sensitivity and age were
negatively related, considerable variability existed among
hearing levels for the old adult cohorts as well as within the
different fitness categories. High CV fitness was associated
with the best PTTs in the old adult participants, suggesting
that high CV fitness protected and preserved hearing in
high-fit persons regardless of other factors. In the teens and
20s, persons with moderate and low CV fitness displayed
good hearing between –5 and 15 dB HL, experienced worse
hearing as they became older, and demonstrated high var-
iability in hearing threshold levels. The DPOAE thresholds
appeared at higher amplitudes among the younger partici-
pants and stabilized among the most fit participants as they
aged.
Most certainly, the dedicated and steady accumulation
of scientific knowledge about the processes that protect hear-
ing decrement lay the basis for developing successful clinical
applications for incorporation of remediation approaches.
The ways regular physical activity affect health and longev-
ity have, in the past, focused on improved CV health and
cancer prevention. Another explanation is that physically
active individuals may be better equipped to handle acute
oxidative stress associated with disease or other metabolic
stressors (Colcombe & Kramer, 2003). While a general mea-
sure of physical fitness using maximum oxygen consumption
may be less sensitive to subclinical circulation patterns, the
current study points to the beneficial influence of CV health
on hearing function, especially as one ages.
Conclusions
Multiple pathophysiological factors participate in wors-
ening auditory sensitivity. Three conclusions can be drawn
from the present cross-sectional study:
1. Hearing sensitivity is at its peak in the teens and 20s,
regardless of fitness level. PTTs decline over time;
however, compared to the low CV fit persons, the high
CV fit persons have more sensitive thresholds after 50 years
of age.
2. After age 49, persons with low CV fitness had worse
hearing levels than persons with high CV fitness from
1000 to 4000 Hz.
3. The DPOAE amplitudes were stronger among the
younger age cohorts and were observed to stabilize
among the old age participants with high-fitness level.
Acknowledgments
The authors acknowledge support from Miami University’s
Undergraduate Summer Scholars program and the College of Arts
and Science Dean’s Scholar program.
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Received April 9, 2009
Revision received July 3, 2009
Accepted December 21, 2009
DOI: 10.1044/1059-0889(2009/09-0009)
Contact author: Kathleen M. Hutchinson, Department of Speech
Pathology and Audiology, Miami University, 2 Bachelor Hall,
Oxford, OH 45056. E-mail: hutchik@muohio.edu.
Hutchinson et al.: Cardiovascular Health and Hearing 35
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