Mental Health and Substance Abuse Services Preferences among American Indian People of the Northern Midwest

ABSTRACT
INTRODUCTION
A 2001 supplemental report on mental health to the Surgeon General describes the current United States public health perspective as a “population-based approach (that) is concerned with the health of the entire population, including its link to the physical, psychological, cultural, and social environments in which people live, work, and go to school (Dept of Health and Human Services (DHHS), 2001).” This statement reflects a concept of holistic healing in a time of growing acceptance and utilization of alternative or complimentary health services beyond those available within professional medical systems. Rodenhauser (1994) notes that although psychiatry as a specific medical field shows increasing cultural awareness regarding clinical sensitivity within the academic literature, there has been little to no evidence of cultural factors found within mainstream journals for health administrators. In addition, very little research is available concerning the co-utilization of “alternative” and western medical approaches, let alone an examination of this overlap within specific cultures (Gurley et al., 2001; Rhoades & Rhoades, 2000; but see Novins, Beals, Moore, Spicer, & Manson, 2004). An understanding of these services may be especially important within an American Indian cultural context where traditions often involve complex ceremonies and beliefs that require consideration far beyond that of mainstream religion (Rhoades & Rhoades, 2000).
The purpose of this study is to examine factors that influence the choice between traditional cultural and western mental health and substance use associated care among American Indians from reservations in the northern Midwest. Specifically, we examine preference in terms of perceived effectiveness and actual utilization of traditional vs. Western-based service outlets.
Barriers to Health Services
American Indians and Alaskan Natives have been found to report highest rates (12.9%) of frequent mental distress among all ethnic groups, including Hispanics (10.3%), African Americans (9.7%), Whites (8.3%), and Asian/Pacific Islanders (6.1%) (Centers for Disease Control (CDC), 1998). The 2000–2001 National Household Survey on Drug Abuse found American Indians/Alaskan Natives to be second only to multi-ethnic individuals to have received mental health treatment in the past year. At the same time, American Indian/Alaska Native respondents were second highest among all ethnic groups who had not received mental health care to report perceived unmet service needs (Barker et al., 2004). A similar pattern is found for substance abuse where again, American Indians/Alaskan Natives are second to multi-ethnic persons in terms of prevalence of illicit drug or alcohol dependence (Substance Abuse and Mental Health Services Administration (SAMHSA), 2002).
A majority of Indian people within the United States receive physical and mental healthcare from Indian Health Services (IHS) (Gone, 2004). IHS’s Indian Health Care System served around 1.6 million American Indians/Alaska Natives residing on or near reservations in 2003 (IHS, 2003). Over one-third of service utilization within this system involves mental health and social service related concerns (IHS, 2002). Although Indian Health Services is meant “to raise the physical, mental, social, and spiritual health of American Indiana and Alaska Natives to the highest level” (IHS, 2002), a variety of barriers may impede American Indians’ ability to receive adequate health care. Specific to mental health care delivery, and often overlapping with the characteristics of healthcare in general, Rodenhauser (1994) characterizes barriers into two major groups: (1) those within the current medical system, including under-funding and staffing issues, inconsistent services, insensitivities, fear of litigation and non-compliance with organizational requirements, and staff burnout; and (2) those inherent to American Indian/Alaska Native cultures, such as fear, high rates of accidents/violence, intrinsic conditions (i.e. denial, helplessness and hopelessness), and mistrust of government agencies.
Traditional Help Seeking
Research and anecdotal evidence suggests that many American Indians report health related help-seeking via culturally traditional outlets. For example, Marbella, Harris, Diehr, Ignace, and Ignace (1998) surveyed 150 American Indian adult patients at the Milwaukee Indian Health Center and found that 38% had sought help from a traditional healer in addition to physician-administered care. Furthermore, 86% of those interviewed said that they would consider seeking a traditional healer in the future. In instances where traditional healer’s and physician’s advice differed, patients said they would rely on their healer’s advice 61.4% of the time. In a separate study including respondents from 2 different American Indian tribes, Novins, Beals, Moore, Spicer, and Manson (2004) found traditional healing options to be prevalent and important to both tribes, whether used alone or in combination with biomedical services.
Although traditional beliefs and practices can guide some American Indians through mental and physical illnesses and healing, there is disagreement concerning the degree of connection between traditional and professional medical services at an institutional level. A number of researchers discuss a gap wherein the processes of traditional and mainstream professional healing should be linked (Marbella et al., 1998; Mohatt & Varvin, 1998; Novins, Beals, Sack, & Manson, 2000; Novins, Fleming, Beals, & Manson, 2000). Conversely, others feel that formal funding for traditional practices is difficult and perhaps inappropriate. Payment to a traditional healer by a patient may be compromised in a situation where billing must occur via a third party. Issues surrounding payment are complicated further considering the need to establish credentials for employees of government funded agencies like IHS (Rhoades & Rhoades, 2000). It is also important to consider the heterogeneity of the over 300 different tribal or language groups from which American Indian individuals belong (Beauvais, 1998). Tribal differences extend to various opinions regarding an integration of the two health care systems (Rhoades & Rhoades, 2000; see also Novins et al., 2004).
Despite some documentation on the preference of traditional vs. western medical treatment among American Indians who receive both, we found little empirical evidence that directly tests the factors that affect this choice (but see Gurley et al., 2001; Novins et al., 2004; Robin, Chester, Rasmussen, Jaranson, & Goldman, 1997). In addition, there is a lack of empirical research surrounding American Indian mental health/substance use related services utilization (Manson, 2000), and what work has been done typically focuses on Indian children (i.e. Novins, Harman, Mitchell, & Manson, 1996; Costello, Farmer, Angold, Burns, & Erkanli, 1997; Novins et al., 2000). This research begins to address such gaps in the literature by examining predictors of service preferences among a sample of American Indian adults.
Hypotheses
In a review of the literature, Manson (2000) includes differences related to culture (i.e. acculturation vs. enculturation) as important predictors of formal mental health service utilization. Elsewhere, higher levels of social support (here measured as community support) have been shown to be related to receiving a treatment recommendation for substance use problems (Novins et al., 1996); in turn, being recommended for treatment may increase actual service utilization. In addition, rates of mental health treatment have been found to be higher for adults with a lower perceived health status (Barker et al., 2004).
Based on these findings and coupled with the barriers to care discussed earlier, we hypothesize that higher levels of enculturation, experiencing discrimination, and living on a reservation will be positively related to perceived effectiveness or preferences for informal services and negatively related to formal services. In addition, self-reported physical health is hypothesized to be negatively related to preferences of both service types (Barker et al., 2004). We also predict that higher levels of social support will be positively related to use of both informal and formal service outlets. Lastly, we control for the effects of age, gender, education, and employment on service utilization preferences.
METHODS
Sample
These data were collected as part of the “Healing Pathways Project,” a 3-year lagged sequential study currently underway on four American Indian reservations in the Northern Midwest and five Canadian First Nation reserves. Because of national differences in health care systems, the data presented here includes only that from U.S. reservations. The data are from wave one of the study collected on two U.S. reservations from February through October 2002, and wave one on a second pair of U.S. reservations collected from February through October 2003. The reservations share a common cultural tradition and language with minor regional variations in dialects. The sample represents one the most populous Native cultures in the United States and Canada.
The project was designed in partnership with the participating reservations and reserves. Prior to the application funding, the research team was invited to work on these reservations, and tribal resolutions were obtained. As part of this agreement, the researchers promised that participating reservation names would be kept confidential in published reports. An advisory board was appointed by the tribal council at each participating reservation and is responsible for advising on difficult personnel problems, questionnaire development, reading reports for respectful writing, and assuring that published reports protected the identity of the respondents and the culture. Upon advisory board approval of the questionnaires, the study procedures and questionnaires were submitted for review and approved by an Institutional Review Board. All participating staff on the reservations were approved by the advisory board and were either tribal members themselves or non-members who are spouses of tribal members. To ensure quality of data collection, all interviewers underwent special training for conducting pencil-and-paper and computer-assisted personal interviewing for diagnostic measures, including feedback sessions. In addition, all of the interviewers completed a required human subject’s protection training that emphasized the importance of confidentiality and taught procedures to maintain the confidentiality of data.
Each tribe provided lists of families of enrolled children aged 10–12 years who lived on or proximate to (within 50 miles) the reservation or reserve. We attempted to contact all families with a target child within the specified age range. Families were recruited via personal visits from Native interviewers during which they were given an explanation of the project, a gift of wild rice, and an invitation to participate. After agreement to participate and later completion of interviews, each participating family member received $40 for their time. This recruitment procedure resulted in an overall response rate of 79.4%.
Sample Characteristics
The sample for this analysis is made up individuals from the U.S. reservations only and consisted of 865 parents/caretakers (264 males and 601 females) of tribally enrolled children aged 10–12 years. Fathers/male caretakers ranged in age from 21 to 70 years with an average age of 42 years; mothers/female caretakers ranged in age from 17 to 78 years with an average of 39 years.
Measurement
To assess the perceived effectiveness of health service providers, respondents were given a series of questions asking them how effective various service outlets would be if ever there were to have (1) an emotional problem, or (2) a substance abuse problem. The response categories range from not at all effective to extremely effective. Traditional/informal services include family, talking to an elder, sweat lodge, pipe ceremony, offering tobacco, traditional healer, traditional ceremony, and healing circle. Formal services include Indian Health Service (IHS), doctor, psychologist, social worker, counselor, psychiatrist, chemical dependency counselor, and nurse. Respondents were asked to evaluate the perceived effectiveness of formal services both on and off the reservation. For multivariate analysis a mean effectiveness score was computed for three categories of services: (1) traditional, (2) formal on reservation, and (3) formal off reservation, all within each realm of service need (emotional and substance abuse). Each mean score has a range from 1 to 5, with higher scores indicating greater perceived effectiveness.
Enculturation is a latent construct assessed by three basic elements: (1) participation in traditional activities, (2) identification with American Indian culture, and (3) traditional spirituality (see Costello et al., 1997; Whitbeck, McMorris, Hoyt, Stubben, & LaFromboise, 2002). The enculturation scale has high internal consistency (Cronbach’s α = .79), and the standardized version of the scale is used in these analyses.
Perceived discrimination is measured with an 11-item scale designed to tap a range of potential types and sources of discrimination. Respondents were asked to report how often they had experienced specific instances of discrimination. Those items included in the scale were; how often someone said something derogatory or insulting because of your race; how often a store owner, sales clerk or person working at a business has treated you in a disrespectful way because of your race; how often the police have hassled you because of your race; how often you have been ignored or exclude from an activity because of your race; how often someone has yelled a racial slur or racial insult at you; how often someone threatened physical harm because of your race; how often someone suspected you of doing something wrong because of your race; how often you have been treated unfairly because of your race; how often you have encountered whites who didn’t expect you to do well because of your race; how often someone discouraged you from trying to achieve an important goal because of your race; and how often you have been treated unfairly in the courts because of your race. The four response categories range from never to always, with the mean of all 11 items used in these analyses. The scale has a high internal reliability with Cronbach’s α of .90.
Social support is measured with a 17-item scale in which respondents were read statements regarding community and neighborly cohesiveness and conflict. Statements include: this is a close knit community; people around here are willing to help their neighbors; there are adults in this community that children can look up to; there are long standing family grudges in the community; the community is split by politics; the community is split by alcohol or drugs; and so on. Respondents were asked to answer true or false to each statement. Items indicative of community conflict were reverse coded, and then all items were summed so that higher values represent higher community support. Cronbach’s α for this scale is .86.
Health status was assessed by response to the question “In general, how well would you say your health is?” Response categories ranged from excellent (5) to poor (1). Values are coded so that higher scores indicate better health.
Several control variables are included in the present analysis. Gender is a dummy variable coded as male = 0 and female = 1. Education is a five category item ranging from less than high school to an advanced degree. Employment is a dichotomous variable indicating if the respondents are employed full-time. Those with full-time employment are coded as 1. To assess the difference between those enrolled tribal members living on and off the reservation respondents were asked if they currently lived on the reservation at the time of their interview. Those who lived off of the reservation were given a value of 1.
RESULTS
Descriptive Characteristics
The adults who comprised this sample had an average educational level falling between a high school diploma and at least some secondary school experience (mean = 2.4; SD = .87), and more than half (57%) were employed full-time. Very few of the adults lived off of the reservation (12%) at the time of our interviews. The self-reported health status of the adults in our sample averaged between ‘good’ and ‘very good’ (mean = 3.3; SD = 1.0), and the overall level of reported social support in the communities was 8.4 (SD = 4.1). Enculturation is a standardized variable in these analyses (mean = 0; SD = 1), while the mean level of perceived discrimination was 1.5 (SD = .69), indicating that the average response across all of the discrimination questions fell between ‘never’ and ‘a few times.’
Among the dependent variables concerning service preferences among respondents, the highest mean scores were found for informal/traditional services for both mental health (mean = 3.06; SD = 1.06) and substance use (mean = 3.09; SD = 1.15) related issues. Next highest were mean preference scores for on-reservation formal services (mental health = 2.51; SD = 1.01; substance use = 2.53; SD = 1.09), followed lastly by mean preference ratings for formal off-reservation care (mental health = 2.32; SD = 1.03; substance use = 2.34; SD = 1.09).
Perceived Effectiveness of Services
Figure 1 illustrates the perceived effectiveness of services that are commonly used for mental health or substance abuse problems. The reported percentage indicates those respondents who felt the services would be very or extremely effective. There is a clear distinction of the perceived effectiveness between informal or traditional services and more formal services. Seventy-one percent of respondents felt that talking to a family member would be very or extremely effective. Nearly 60% felt talking to a tribal elder would be highly effective for dealing with mental health or substance problems. More traditional practices/services such as offering tobacco and praying, seeing a traditional healer, traditional ceremonies, healing circle, sweat lodge, and pipe ceremony all were rated between 30% and 50%. Speaking to a counselor on the reservation was the highest rated professional service with 32.9% of respondents indicating it would be very or extremely effective. Most of the on reservation professional services rated higher than services off the reservation but lower than more traditional services. Those services that were seen as least effective were those professional services located off of the reservation.FIGURE 1Perceived Effectiveness of Services
Use of Informal and Formal Services
Table 1 reports the coefficients from ordinary least squares regression analyses for predictors of respondent perceptions of the effectiveness (i.e. preferences) of informal traditional and formal services for substance abuse and mental health concerns. Because this sample contains some cases where two adult reporters were interviewed within a household, reported coefficients are based on standard errors that have been adjusted to account for the potential bias of nested designs (analyses performed using STATA 7.0). The same sets of variables significantly predict informal service preference for both mental health (MH, Model 1A) and substance use (SU, Model 1B) related problems. For both models, females were more likely to prefer informal services (MH: β = .06, p < .05; SU: β = .05, p < .10), as were the employed (MH: β = .07, p < .05; SU: β = .07, p < .05). For both Model 1A and 1B, higher rates of social support (MH: β = .13, p < .001; SU: β = .13, p < .001), higher enculturation scores (MH: β = .49, p < .001; SU: β = .44, p < .001), and higher reports of perceived discrimination (MH: β = .09, p < .01; SU: β = .11, p < .01) were all positively associated with informal service preferences.TABLE 1OLS Regression Models Predicting Perceived Effectiveness (Preferences) of Mental Health and Substance Use Related ServicesMental HealthSubstance Use1A2A3A1B2B3BInformalFormal (on res.)Formal (off res.)InformalFormal (on res.)Formal (off res.)BβBβBβBβBβBβAge − 0.003 − 0.030.010.05 − 0.002 − 0.020.0010.010.010.07+0.000.003Gender (female = 1)0.150.06*0.130.06+0.040.020.130.05+0.050.002 − 0.03 − 0.01Education0.040.030.140.12**0.210.18***0.040.030.170.13***0.190.15***Employment0.140.07*0.080.04 − 0.01 − 0.010.150.07*0.020.01 − 0.06 − 0.03Live off reservation0.170.050.180.060.280.09*0.070.020.270.08*0.470.14***Physical health status0.010.010.030.030.020.02 − 0.02 − .010.020.010.010.01Social support0.030.13***0.030.13***0.020.08*0.040.13***0.050.17***0.020.09***Enculturation0.520.49*** − 0.05 − 0.05 − 0.05 − 0.050.510.44*** − 0.05 − 0.05 − 0.08-.07*Discrimination0.140.09**0.110.07+ − 0.07 − 0.050.190.11**0.170.1** − 0.09 − 0.06Constant2.371.281.731.101.77R20.290.050.060.250.060.07Adjusted R20.280.040.050.240.050.06+p < .10; *p < .05; **p < .01; ***p < .001 (two-tail test).Sample size across models ranges from n = 803 to n = 822 after listwise deletion.
Moving to predictors of formal service preferences on reservations (Models 2A & 2B), higher levels of social support were a significant predictor in both the MH (β = .13, p < .001) and SU (β = .17, p < .001) models, as were higher rates of perceived discrimination (MH: β = .07, p < .10; SU: β = .10, p < .01) and education (MH: β = .12, p < .01; SU: β = .13, p < .001). Age is significantly associated with formal on-reservation service preferences only for substance use problems (β = .06, p < .10), whereas females are more likely than males to prefer on-reservation formal care in the case of mental health problems (β = .06, p < .10).
Models 3A and 3B illustrate the coefficients for predictors of formal off-reservation service preferences. Both models contain similar findings: higher education (MH: β = .18, p < .001; SU: β = .15, p < .001), living off of reservation lands (MH: β = .09, p < .05; SU: β = .14, p < .001), and higher levels of social support (MH: β = .08, p < .05; SU: β = .09, p < .05) were all positively associated with higher preferences for formal off-reservation services. In addition, Model 3B shows that those who scored higher on levels of traditional enculturation were less likely to perceive formal off-reservation care as effective in terms of substance use related problems (β =  − .07, p < .05).
Across all of the models in Table 1, the independent variables explain proportionately more of the variance for the informal service models than those with formal services as the dependent variable. Adjusted R2 values for these models indicate that the predictors explain 28% and 24% of the variance in informal service preferences for MH and SU problems, respectively. These values for formal reservation-based care are 4% for MH and 5% for SU problems. The models for formal off-reservation care explain 5% of the variance in preferences for MH problems and 6% of the variance for SU problems.
DISCUSSION
The adults in our sample felt that more culturally traditional services (such as family or a traditional healer) would be more effective than either professional services on the reservation, or professional services off the reservation. Off reservation services were perceived to be least effective. These findings support literature that suggests American Indians generally place considerable trust in traditional practices (i.e. Marbella et al., 1998). The finding that mainstream professional services are perceived as less effective than traditional informal services and some of the on-reservation professional services underlies the previous discussion surrounding issues of trust and appropriateness of Western care in relation to American Indian cultures. It is also possible that a crisis-oriented care system may not be suited to adequately deal with mental health and substance abuse needs (Oetting & Beauvais, 1990–1991).
The multivariate analyses supported several of our hypotheses. Among the control variables, females were slightly more likely than males to report higher preference for both (MH & SA) types of informal care, as well as for on-reservation MH care. Though not explicitly hypothesized, these results correspond with previous help-seeking research that has found women more likely than men to view care as an appropriate remedy for psychological issues (Horwitz, 1987). Higher educational levels and employment were generally related to higher effectiveness ratings for services in this study, also corroborating previous research (see, for example, Horwitz, 1999, p. 66).
As expected, those who are more enculturated were more likely to utilize informal traditional services than those who are less enculturated. In addition, in the case of services for substance use disorders, higher levels of enculturation were negatively associated with preferences for formal off-reservation care (Model 3B). Those who lived off the reservation were more likely to use formal services, especially in terms of off-reservation care. Consistent with past research (Novins et al., 1996) and as hypothesized, perceived social support was positively associated with higher perceptions of effective care across all types of services. Our hypothesis that higher rates of perceived discrimination would be associated with preferences for informal or traditional care is supported here. We found similar effects for discrimination and formal on-reservation care. These findings are congruent with Rodenhauser’s (1994) description of the barriers to dominant-culture care in terms of mistrust of government agencies, all stemming from a history of colonization and continued institutional racism experienced by many American Indian peoples (see, for example, Duran & Duran, 1995). Overall, the results of this study highlight a preference for informal or culturally based care, especially among the enculturated.
The differences in the proportions of variance explained across each of the models in Table 1 warrant discussion. These analyses include only one measure of cultural identity: enculturation. As discussed, this measure was significantly associated with ratings of informal service preference, but did little in terms of predicting formal service preferences. It may be that an important predictor of formal services is acculturation, or perhaps even biculturalism. Future work might include such measures to further our understanding of how cultural identity affects service preference and utilization (see Novins et al., 2004).
Limitations
Although we interviewed a broad range of American Indian adults on multiple reservations that are dispersed geographically across two Midwestern states, these results pertain to a single culture and capture variations within this culture. We believe the findings represent the culture well, but they cannot be generalized to other Native cultures. A second caution regarding the sample is that it is made up of parents and caretakers of children aged 10–12 years. This could reflect a selection bias in that parents/caretakers may be more likely to utilize services and to be currently mentally healthy and alcohol and drug free than individuals with no children. Finally, all of our measures are based on self-reports. We did not have access to service utilization rates from local clinics or reports of services use from traditional healers.
Policy Implications
These findings have important policy implications for those who provide health services to American Indian people. Cultural traditions are very much alive on U.S. reservations and are preferred methods of healing for mental health or substance abuse problems. This should be taken into account when designing health services systems either by providing alternative services onsite or through creatively engaging informal traditional services. Simply acknowledging informal service providers by asking the patient if they have seen a traditional healer and then contacting him or her for an opinion would be an important step. Health providers could include key community spiritual leaders and healers on health advisory boards or create health partnerships that would encourage mutual referrals. Perhaps the place to begin would be to respectfully seek the advice of elders on decreasing barriers between the two.
Actual integration of services is already taking place on many reservations, but implementation is not always straight forward (Marabella et al., 1998; Mohatt & Varvin, 1998; Rhoades, & Rhoades, 2000). Issues about selection of traditional healers, and how to reimburse them such as whether they should charge fees for services and coverage for third party payments must be worked out culture by culture. Some view such integration as a potential acculturation risk.
Changing the current short comings in mental health delivery first involves acknowledging that parallel systems exist in some cultures. The impetus for change may have to come from formal services providers who should demonstrate respect for traditional healers, invite their advice, and consult with them if patient’s give permission. Clinicians may need to be proactive in offering their patients this option rather than waiting for the patient to request it. Creating this sensitivity may require specialized training for services providers on American Indian reservations. Grant funding groups may want to consider supporting model programs that bring together the two healing modalities.
Future Research
There is much to be done to increase American Indians’ confidence in health services systems. One avenue for this would be to work more closely with informal traditional services that are trusted. We need control group trials of innovative services models that cross over between formal medical services and traditional approaches to healing to assess the efficacy of combining the approaches. Continued failure to acknowledge the strong preferences for traditional ways is to ignore a valuable health resource.

mental health
substance abuse
american indians
service utilization


Family Planning Services: An Essential Component of Preconception Care

Family planning services are necessary for the widespread adoption of preconception care for two reasons. First, preconception care is more likely if pregnancies are planned, and family planning services encourage pregnancy planning. Second, family planning services usually include counseling, and counseling provides an opportunity to discuss the advantages of preconception care. However, the potential of family planning services to promote preconception care is limited by underutilization of these services and inadequate attention to preconception care during family planning visits. This article suggests ways to reduce these problems.

If all women of reproductive age, or at least those at elevated risk, are to benefit from preconception services, the use of family planning services must be increased and the content of such services expanded. Family planning services are essential for preconception care for at least two reasons. First, in the absence of such services, pregnancies will occur that have not benefited from preconception care. Preconception care during the reproductive years is dependent on women and men planning their pregnancies, not only in respect to their timing but also to health-related factors that would maximize the chances for a healthy pregnancy and a healthy infant. In the absence of such care, offered by family planning services, many pregnancies will not benefit from preconception advice. Second, family planning counseling provides an opportunity for promoting and providing preconception care. At the same time women and their partners are receiving advice about family planning, they can also receive instruction about the range of activities that lead to healthy pregnancies and healthy infants.
Unfortunately, several factors prevent family planning from reaching its maximal potential for preconception care. These include underutilization of family planning services and inadequate attention to preconception counseling during family planning visits.
Underutilization of family planning services
Two types of data point to underutilization of family planning services with implications for decreasing opportunities for preconception care: the percentage of women actually seeking family planning services and the percentage of unintended pregnancies.
Visits for family planning
The 2002 National Survey of Family Growth (NSFG) reported that 41.7% of women 15 to 44 years of age received at least one family planning service from a medical care provider in the 12 months prior to the interview [1]. This percentage is not as alarming as it might appear at first glance, because some of the women who did not seek family planning services already were pregnant, seeking to become pregnant, or infertile because of sterilization or other reasons. Nevertheless, this rather low percentage suggests that some women are not planning their pregnancies either deliberately or because they are experiencing problems obtaining family planning services.
Pregnancy planning
It is undoubtedly true that some women do not wish to plan the timing of their pregnancies. In many cases, these are married women who have religious objections to family planning. In Women of Crisis, one woman states “you don't think of life that way – of having children that way. You don't sit down and say you can afford to have a certain number of boys and girls; you have your children and try to do the best you can to be a good parent” [2]. This attitude is probably not widely held, rather most women and their partners have some preferences in terms of the timing of births. This may be expressed in terms of age, marital status, or attainment of some educational, career, or economic goal. Despite this, a large percentage of pregnancies are unintended, including those that were experienced earlier than wanted (mistimed) or those that were not wanted at the time they occurred or at any future time (unwanted).
According to the 2002 NSFG, 30.8% of all women 15 to 44 years of age had experienced an unintended birth at some time in their lives and, in the five years before the survey, 20.8% had had a mistimed birth and 14.1% an unwanted birth [3]. Using data from the 1982, 1988, and 1985 NSFGs, as well as abortion data, Henshaw estimated that in 1994, 49.2% of all pregnancies were unintended [4]. Employing a different set of questions to assess wantedness, the Pregnancy Risk Assessment Monitoring System (PRAMS) noted that in 1999 the percentage of unintended pregnancies resulting in live birth ranged from 33.7% to 52% across the 17 reporting states [5].
Although the relationship between use of a family planning method and pregnancy planning is sometimes tenuous - an analysis of the 1995 NSFG found that 30.9% of the women who stated that their pregnancies had resulted from a contraceptive failure nevertheless classified the pregnancy as intended [6]. These data suggest that if preconception care were to be practiced widely, a larger percentage of women will need to seek family planning services to avoid unplanned pregnancies.
Reasons for underutilization
Many reasons have been suggested for the underutilization of family planning services, including cost, availability, and limited contraceptive methods [7, 8].
Financial issues
The possible patient payment sources for family planning services include private health insurance, Medicaid, or out-of-pocket payments. The March 2005 Current Population Survey found 24.5% of women 18 to 20 years of age, 30.6% of those 21 to 24, 21.8% of those 25 to 34, and 17.1% of those 35 to 44 to be uninsured [9]. If these uninsured women want to receive family planning services, they must rely on their own funds or seek care from facilities that provide services free of charge or on a sliding fee scale. These include publicly supported facilities such as health department family planning clinics, community health centers and public hospitals, and facilities that combine public and private funding sources, such as Planned Parenthood centers, women's clinics, school-based health centers, and not-for-profit hospitals. Public funds for family planning services in such facilities come primarily from Medicaid and Title X (the family planning act). These funds are inadequate to meet the need. For women whose eligibility is due to a pregnancy, eligibility for all medical services, including family planning, ends 60 days postpartum, except in states with a waiver to extend the period. Title X tries to fill in the gaps in coverage but it is chronically underfunded. Even for those with employer-based health insurance, coverage for family planning services is not universal. In 2003, 93% of health plans offered an annual ob/gyn visit, 88% covered oral contraceptives; 87%, sterilization; and 72%, all five reversible contraceptives. HMOs were more likely to offer contraceptives and sterilization than conventional plans, PPOs or POSs [10].
Availability
Family planning facilities need to be easily available both physically and psychologically. This means that they should be located where they can be reached easily by private or public transportation, be open days and hours that are convenient for potential users, offer the full range of contraceptive methods, provide educational materials in the languages of their patients, and employ personnel who can speak the language of the users and whose attitudes and behaviors are warm, friendly, and culturally sensitive. A recent four-state survey found that distance to a publicly financed family planning facility was not associated with teen or unintended pregnancies, suggesting that geographic availability is no longer a problem for family planning facilities [11], although it still is for abortion services [12]. The same study found major differences in terms of the other availability factors, such as limited hours, few contraceptive choices, and lack of translators [13]. Such problems may be partially responsible for inadequate contraceptive use.
Limited contraceptive methods
Although the number of family planning methods has increased in the past few decades, many women and men have difficulty finding one with which they are comfortable. The 2002 NSFG gave respondents a list of 19 family planning methods from which to choose. Among women 15–44 years of age, 61.9% currently were using a contraceptive method: the pill-18.9%; female sterilization-16.7% and the condom-11.1%. About 4% were using the least effective methods, including periodic abstinence and withdrawal. Among women who had intercourse in the three months before the interview and who were not sterile, pregnant, postpartum, or seeking pregnancy, 7.4% were not using a contraceptive - an increase from the 5.2% in the 1995 NSFG. (Of those at risk for an unintended pregnancy, 89.3% were currently using a method.) [1]. It is important to recognize that contraceptive use data are based on self-reports and provide no indication of how consistently or correctly the methods are being used. Failure rates are high possibly because of inconsistent or improper use. In one study of the 1995 NSFG, 9% of women experienced a contraceptive failure within one year of starting to use a reversible method of contraception: 7% of those on the pill, 9% of those relying on a male condom, and 19% of those practicing withdrawal [14].
After female or male sterilization, hormonal methods are considered the most reliable form of contraception, but many women remain concerned about their safety. The side effects of many hormonal methods, especially Depo-Provera, discourage many women from their use [7, 8]. Further, the need to take a pill daily even in the absence of frequent intercourse creates problems for many women. Finally, the absence of a male contraceptive other than sterilization and the condom is a major barrier to effective and ongoing contraception.
The availability of one effective family planning method, emergency contraception (meant as back-up protection, not as a primary method), is currently limited by the refusal of the federal Food and Drug Administration to allow it to be sold over the counter and by the refusal of some pharmacists to fill prescriptions for this medication.
Inadequate attention to preconception counseling
Research is just beginning on the availability of preconception care overall although certain conditions, such as folic acid supplementation and counseling of diabetic women, have been studied extensively. The little existing evidence suggests that preconception care is not routinely integrated into family planning services, whether provided by obstetricians or family medicine specialists in private practice or HMOs, or by personnel in family planning facilities [15, 16]. Under such circumstances, the potential of this service delivery system for improving pregnancy and infant health through preconception care is not yet being realized.
Approaches to increasing utilization
Several evaluations indicate that the utilization of family planning services can be increased. California's Family Planning, Access, Care, and Treatment Program (Family Pact) provided contraceptive services to low income, medically indigent women increased use and reduced the numbers of unintended pregnancies [17]. State family planning waivers that expand Medicaid coverage for women beyond the 60 day postpartum limit have had a similar impact [18, 19]. Programs such as these should be expanded to more states, but they address only financial barriers. Attention should also be paid to other access-related problems, such as hours and days that facilities are open and language problems. Additional outreach also needs to be directed to low literacy and immigrant populations [20].
Approaches to improving content
Moos [15] reviewed many of the activities that will be essential if preconception care is to be integrated into health care generally. The American College of Obstetrics and Gynecology recently published a Committee Opinion, “The Important of Preconception Care in the Continuum of Women's Heath Care” [21]. Here the focus is on adding preconception counseling to visits for family planning. The recent publication by the Centers for Disease Control and Prevention of ``Recommendations to Improve Preconception Health and Health Care - United States'' [22] should also lead to more and better preconception counseling.
In all likelihood, it may be most difficult to change patterns of family planning practice among physicians in private practice. In contrast, those in HMOs have the potential for exposure to more education about the need for such counseling. The establishment of standards for family planning services by the Health Plan Employer Data and Information Set (HEDIS) might also accelerate change. However, standard setting and financial and other incentives may be most effective when used with community health centers and health department and other publicly-funded sites of family planning services - as the women who use seek family planning at these sites may be those most in need of preconception care. Because such sites are funded by federal, state, and local governments, these units can insist that preconception care be integrated into their family planning services.
Conclusions
Progress towards preconception care for all women will only be possible if a larger percentage of women and men plan their pregnancies. At present, although visits for contraceptive advice and methods provide an excellent opportunity for counseling about ways to achieve healthy pregnancies and healthy infants through preconception care, this potential is not being achieved. Increased use of family planning and increased attention to preconception care within family planning services may require that additional resources be devoted to public and professional education and to service delivery standards and financing.

family planning
preconception care
pregnancy
access
intendedness


Changes in CMDP and DPOAE during acute increased inner ear pressure in the guinea pig

During and after an increase of inner ear pressure, induced by injection of artificial perilymph, the 2f1 − f2 and f2 − f1 distortion products (DPs) in cochlear microphonics (CM) and otoacoustic emissions (OAE) were recorded in the guinea pig. An inner pressure increase of ∼600 Pa gave only small changes in CMDP and DPOAE. Along with a decrease in f1 amplitude, a small decrease in amplitude of the 2f1 − f2 and a small increase in the f2 − f1 were measured in CM. This matches a shift from a symmetrical position of the operating point for hair cell transduction, leading to an increase in even-order distortion and a decrease in odd-order distortion. Similar, a decrease in 2f1 − f2 DPOAE was expected. This might be the case at the generation sites but this effect was then more than compensated for by a better middle ear transfer, accounting for the increase of 0.4 dB of the 2f1 − f2 DPOAE amplitude. In conclusion, changes of overall inner ear fluid pressure have minor effects on cochlear function. This is a relevant finding for further understanding of diseases with changed inner ear fluid volumes, as Ménière’s.
Introduction
The cochlea is a non-linear mechano-electrical transducer that transforms sound pressure waves into electrical information, the so-called mechanoelectric transduction (MET). The reverse electromechanical transduction is performed by the outer hair cell (OHC) which mechanically influences the vibration of the cochlear partition [7]. When the cochlea is stimulated by two tones, distortion products (DPs) can be measured in cochlear microphonic potentials (CMDP) and in the external auditory meatus as otoacoustic emissions (DPOAE). Both microphonic and acoustic DPs are considered to be reflections of OHC electromotility in the cochlea. Obviously, it is of interest to find a relation between these two functional modalities of the cochlea and the OHC in particular.
In this study the most prominent DPs, the 2f1 − f2 and f2 − f1, have been observed while increasing inner ear pressure. This was done by rapid injection of artificial perilymph into the scala tympani of the guinea pig’s cochlea. Measurement of specific DPs may describe changes in gain and operating point of the non-linear cochlear amplifier. Furthermore, transfer characteristics of forward and backward transmission may be clarified by using CMDP and DPOAE [17]. These data could help gaining insight into pathophysiological mechanisms involved in pathologically increased inner ear pressures.
When pressure variation is in the normal physiological range, this does not influence cochlear function as measured by compound action potentials in the guinea pig [2]. In humans, during activities like coughing or sneezing, perilymphatic pressure may undergo substantial fluctuations up to 10 mmHg (1.4 kPa).
An increased pathologic inner ear pressure may be the result of an increased intracranial pressure since the perilymphatic space is linked to the subarachnoid space via the cochlear aqueduct. Human OAE have been proven to be very sensitive to modifications of intracranial pressure [10]. Another clinical example of increased inner ear pressure or volume with an accompanying change of cochlear function is the endolymphatic hydrops in patients with Ménière’s disease.
In a previous study [11], we measured solely the 2f1 − f2 DPOAE’s in response to microinjection of artificial perilymph into the cochlea. Large changes of ∼500 Pa in overall inner ear pressure gave only a small mean change of 0.7 dB in 2f1 − f2 DPOAE amplitude. The magnitude of change could (partly) be explained by a change in oval window stiffness. In this study, the same experimental setup was used, with the addition of the simultaneous recording of the 2f1 − f2 and f2 − f1 CMDP. We attempt to establish a better understanding of increased inner ear pressure effects on DPs in both CM potentials and OAE’s.
Materials and methods
Experiments were performed in eight guinea pigs (Harlan Laboratories, The Netherlands; body weight 350–450 g) with a positive Preyer reflex. Animal care and use were in accordance with the principles of the declaration of Helsinki and approved by the animal experiment committee (protocol number 3047/3103).
General anesthesia was induced by intramuscular administration of ketamine/xylazine (60/3.5 mg/kg). Maintenance doses of the anesthetic were administered every hour. Muscle relaxation was obtained with succinylcholine (2.5 mg/kg). The animals were artificially ventilated through a tracheostoma (Columbus Instruments, model 7950). Body temperature was maintained at 38°C with a heating blanket. Heart rate was monitored by skin electrodes placed on both sides of the thorax. The animal’s head was kept in a stationary position by means of a steel bolt fixed to the skull with dental cement. Following a retroauricular incision, the bulla and external auditory canal were exposed. Subsequently, the bulla was opened equalizing middle ear pressure to normal air pressure [17]. By opening of the bulla, the round window was exposed. Through the round window membrane, the tip of a double-barreled micropipette was inserted into scala tympani. The double-barreled micropipettes were drawn from borosilicate glass (1.5/0.84 mm diameter per barrel) and the tips were beveled (Narishige EG-40). The total tip diameter was around 60 μm, which is a compromise between a low enough flow resistance for fluid injection and tip smallness. One barrel of the pipette was used to measure inner ear pressure (WPI 900A micropressure system). Through the other barrel, artificial perilymph [9] was injected with a constant flow rate by applying a controllable pneumatic pressure to the barrel end. The injected volume was measured as the displacement of the fluid meniscus in the pipette, for which the inner diameter is precisely known (0.84 mm). The fluid injection rate was calculated as the total injected volume divided by the total injection time.
During the experiment the DPOAE’s were continuously measured using an Etymotic ER-10C DPOAE probe system. The two primary frequencies were set at 6 kHz (f1) and 7.4 kHz (f2), meaning a f2/f1-ratio of 1.23. The low-level intensities were set at, respectively, 65 dB SPL (L1) and 55 dB SPL (L2). Full details of the measuring equipment are described elsewhere [11, 12].
Cochlear microphonic potentials were recorded with two differential Ni–Cr electrodes with a diameter of 50 μm. One electrode was placed in scala tympani through the bony wall of the basal turn of the cochlea. The other was placed in scala vestibuli next to the oval window. The signals were routed via an amplifier to a spectrum analyzer and two lock-in amplifiers (SRS, model SR830 DSP). The lock-in amplifiers displayed the amplitude of the 2f1 − f2 and f2 − f1 CMDP which were referenced to an electronic 2f1 − f2 and f2 − f1-DP derived from the original primaries.
A measurement contained a sequence of ten microinjections of artificial perilymph of 10 s each with pauses of 40 s. The rate of microinjection was 50 nl/s. The repetitive microinjection was controlled with a precision electronic timer (Stanford DG535). During an experiment, National Instruments LabVIEW® was used for recording of the following output signals: amplitude and phase of the 2f1 − f2 DPOAE, 2f1 − f2 CMDP, f2 − f1 CMDP, f1 CM, and inner ear pressure. Calculations and fits to relevant portions of the obtained recordings were made off-line with an appropriate software package.
Results
Successful repeated sequences of injection with a rate of 50 nl/s (n = 10) were performed in all guinea pigs (n = 8). The mean steady state inner ear pressure measured prior to injection of artificial perilymph was 205 Pa.
To determine the rise and fall times of the curves from the measured signals, proper fits were obtained with a simple exponential function: In some cases (Figs. 1c, 2c, 4c) the curves needed an extra term in the formula for a proper fit: According to Wit et al. [13] time constants τ were calculated from the fits.
Fig. 1a Averaged changes (n = 8) in inner ear pressure (Pa) during and after injection of 0.5 μl of artificial perilymph into scala tympani. The gray area depicts the injection period. Standard error bars are shown at t = 5, 15, and 40 s. b The shape of the mean inner ear pressure curve at the start of injection (time axis corresponds with Fig. 1a). The recording (filled circles) is fitted (broken line) with an exponential function, yielding a time constant τ. c The same is done for inner ear pressure recovery directly after injectionFig. 2a Averaged changes (n = 8) in f1 CM amplitude (μV) during and after injection of 0.5 μl of artificial perilymph into scala tympani. The gray area depicts the injection period. Standard error bars are shown at t = 5, 15, and 40 s. b The shape of the mean f1 CM amplitude curve at the start of injection (time axis corresponds with Fig. 2a). The recording (filled circles) is fitted (broken line) with an exponential function, yielding a time constant τ. c The same is done for f1 CM amplitude recovery directly after injection
In Fig. 1a, the averaged recorded inner ear pressure during and after injection of 0.5 μl of artificial perilymph is shown. At the start of injection the mean pressure increased to an ∼600 Pa higher level within seconds. At the end of injection, the pressure immediately decreased, returning to its initial value within seconds. This pattern was consistently observed in all individual experiments. The time constant for increase and subsequent decrease of inner ear pressure were 1.25 and 1.16 s, respectively (Fig. 1b, c).
The averaged f1 signal in the CM (Fig. 2a) showed a mirrored behavior in respect to the inner ear pressure. Directly after the start of injection, the f1 CM decreased by 30 μV. The corresponding time constant was 1.17 s (Fig. 2b), which is very close to the time constant for pressure increase. Conversely, at the end of injection the f1 amplitude returned to its initial value with τ = 3.49 s (Fig. 2c), which is slow with respect to the corresponding τ for pressure.
The averaged DPOAE 2f1 − f2-amplitude showed a similar typical course as the inner ear pressure (Fig. 3a). Almost directly after the start of injection the 2f1 − f2-amplitude increased to reach a maximum of 0.4 dB above its original value at the end of the injection period. When the injection was instantaneously terminated, the amplitude dropped and returned to slightly above its onset level. There was a small observable time lag with respect to the pressure curve. The time constant for increase and subsequent decrease of the 2f1 − f2-amplitude were 1.52 and 3.43 s, respectively (Fig. 3b,c).
Fig. 3a Averaged changes (n = 8) in 2f1 − f2 DPOAE amplitude (dB SPL) during and after injection of 0.5 μl of artificial perilymph into scala tympani. The gray area depicts the injection period. Standard error bars are shown at t = 5, 15, and 40 s. b The shape of the mean 2f1 − f2 DPOAE amplitude (μPa) curve at the start of injection (time axis corresponds with Fig. 3a). The recording (filled circles) is fitted (broken line) with an exponential function, yielding a time constant τ. c The same is done for 2f1 − f2 DPOAE amplitude recovery directly after injection
In Fig. 4a, the typical temporary decrease for the averaged 2f1 − f2 CMDP amplitude relative to the f1 CM is shown. The time constant for decrease in amplitude at the onset of injection was 1.12 s (Fig. 4b), which corresponds with τ for pressure. The recovery is somewhat slower (2.28 s, Fig. 4c), but still faster than the time constant for 2f1 − f2 DPOAE recovery.
Fig. 4a Averaged changes (n = 8) in 2f1 − f2 CMDP relative to f1 CM amplitude during and after injection of 0.5 μl of artificial perilymph into scala tympani. The gray area depicts the injection period. Standard error bars are shown at t = 5, 15, and 40 s. b The shape of the mean 2f1 − f2 CMDP (relative to f1 CM) amplitude curve at the start of injection (time axis corresponds with Fig. 4a). The recording (filled circles) is fitted (broken line) with an exponential function, yielding a time constant τ. c The same is done for 2f1 − f2 CMDP (relative to f1 CM) amplitude recovery directly after injection
Finally, in Fig. 5, the averaged results of the f2 − f1 CMDP amplitude relative to f1 CM depict an increase during injection of artificial perilymph. When the injection was terminated, the f2 − f1 CMDP amplitude returned to the pre-injection level. Unfortunately, due to a low signal-to-noise ratio for the f2 − f1 CMDP, the obtained curve could not be fitted properly and no time constants could be derived.
Fig. 5Averaged changes (n = 8) in f2 − f1 CMDP relative to f1 CM amplitude during and after injection of 0.5 μl of artificial perilymph into scala tympani. The gray area depicts the injection period
Discussion
The most striking result of this study is the minimal change in amplitude of the DPs in both OAE and CM during an acute increase of inner ear pressure. Besides, amplitudes changed to normal when inner ear pressure returned to its initial level. These results indicate a dynamically stable inner ear which is able to cope with a pressure increase of 600 Pa with only minimal and reversible cochlear function loss. According to Böhmer [2] this level of pressure increase would still be in the physiological range of the guinea pig ear varying between −100 and +700 Pa.
The inner ear is an elastic structure completely encompassed by bone, in which pressure changes depend on the compliance of the membranous structures [14]. In normal ears, hydrostatic pressure in the perilymph equals pressure in the endolymph, and pressure changes applied to one compartment are immediately transmitted to the other through the elastic walls. The perilymph is in a dynamic equilibrium with the cerebrospinal fluid via the cochlear aqueduct. An excess of perilymph will escape through the cochlear aqueduct restoring inner ear fluid level.
When increasing inner ear pressure, a cochlear disturbance with functional loss is expected. The observed decrease in CM f1 amplitude thus seems obvious. An increased cerebrospinal fluid pressure also suppresses the CM [16]. The increase in 2f1 − f2 DPOAE is counterintuitive, but in accordance with a previous publication in which we demonstrated the same change in cochlear function as measured by 2f1 − f2 DPOAE’s [11]. According to Büki et al. [3] a change in stiffness of the oval window might slightly improve middle ear transfer and thus explain the small increase in DPOAE amplitude. In contrast to the 2f1 − f2 DPOAE, the 2f1 − f2 CMDP showed a decrease in amplitude during injection. Unfortunately, in literature very little can be found about the relation between DPOAE and CMDP. Still, it were Kemp and Brown [6] who found close parallels in the behavior of the 2f1 − f2 DPOAE and CMDP during and after anoxia in the guinea pig. Group latencies and third-tone suppression were found to be very similar, linking both signals to have a common origin.
The DPOAE and CMDP are generated in response to the same acoustic stimuli. The acoustic primaries are transferred through the external and middle ear to eventually reach the sensory epithelia in the cochlea. The cochlea as a non-linear mechano-electrical transducer transforms sound pressure waves into electrical information. This forward transduction process is called the MET. The CM potential is a direct result of this process and is thought to be mainly produced by OHCs. On the other hand, there is also a reverse electromechanical transduction in which the OHC mechanically influences the vibration of the cochlear partition [7]. Sound is transmitted back to the external ear where the acoustic DPOAE can be measured; the backward transmission.
The rise and fall times of the DPs in response to changes in inner ear pressure were derived from the fitted curves (Figs. 2, 3, 4). As both CMDP and DPOAE were measured, this yielded information on forward and backward transmission. As anticipated, the time constants for the CMDP were smaller than the time constants for the DPOAE. Indeed, the latter would travel back and forth the middle ear which understandably costs more time. However, the difference has not the form of a simple longer delay. The explanation for this observation remains tentative. The averaged differences were 0.4 and 1.15 s for the 2f1 − f2 DP during increase and decrease of inner ear pressure, respectively.
At pressure increase all measured signals almost directly followed the change in inner ear pressure. Time constants varied from 1.17 to 1.52 s with respect to 1.25 s for the inner ear pressure curve. However, with pressure decrease there was a delay of 1–2 s for all measured signals. Measured differences cannot be accounted for by delay in measuring equipment, for this was <0.18 s. Assumed that the overall stiffness of the stapes-oval window-system governs the behavior of the DPOAE 2f1 − f2 amplitude, it is expected that it would follow stiffness changes directly and not 2 s later, as observed. It is conceivable that a delayed change in the endocochlear potential (EP) could be the cause of difference in τ values. However, in experiments by Salt and DeMott [9] the EP followed a temporary pressure change with a delay of <0.1 s. So, the mechanisms for the observed delays in inner ear pressure recovery remain to be elucidated.
Two-tone distortions are generated during non-linear mechanical amplification in the cochlea. Generation of the 2f1 − f2 depends on asymmetric component of a non-linear transfer function whereas the f2 − f1 depends on symmetric components. A change of the operating point is reflected in the level of the f2 − f1 distortion. In the gerbil low-frequency tones of 5 Hz were used to bias the position of the cochlear partition by Frank and Kossl [4, 5].
By low-frequency modulation of the 2f1 − f2 DPOAE, Bian et al. [1] described the forward MET by a sigmoid-shaped function, which related the displacement of the basilar membrane to the response of the hair cells.
By injecting artificial perilymph into scala tympani of the cochlea, the basilar membrane is temporarily displaced. Thus, by this displacement toward scala media, the operating state of the cochlear amplifier is also influenced. We measured a small decrease in the amplitude of the 2f1 − f2 distortion in CM (with respect to the amplitude of f1 in CM) and a small increase in the f2 − f1 in CM. Using the model by Bian et al. [1] this leads to the conclusion that the operating point for hair cell transduction is somewhat shifted from a symmetric position. This shift leads to an increase in even-order distortion and a decrease in odd-order distortion. Along these lines of reasoning we would also expect the 2f1 − f2 DPOAE to decrease. This might be the case at the generation sites [15], but this effect is then more than compensated for by an improved middle ear transfer.
Anyhow, the observed changes are small. Changes of overall inner ear fluid pressure have minor effects on cochlear function. It may be that creating an artificial endolymphatic hydrops, by injecting artificial endolymph into scala media instead of scala tympani, has a larger effect. This is currently tested in further research, which will hopefully give insight into diseases with pathologically changed inner ear fluid volumes, as in Ménière’s disease.

cmdp
dpoae
inner ear pressure
guinea pig
injection
perilymph
2f1 − f2
f2 − f1