Illness perceptions and adherence to therapeutic regimens among patients with hypertension: A structural modeling approach

https://doi.org/10.1016/j.ijnurstu.2010.07.005Get rights and content

Abstract

Background

Patients’ lay views of illness are influential on adherence to therapeutic regimes. However, factors associate with non-adherence are not examined simultaneously.

Objectives

The purpose of the study was to test a hypothetical model of the relationships between illness perception and adherence to prescribed medication and self-management recommendations of hypertensive patients based on theoretical assumptions of the Common-Sense Model.

Design

A cross-sectional, descriptive, correlational design.

Settings

Cardiovascular clinics of three teaching hospitals in central Taiwan.

Participants

Three hundred and fifty-five hypertensive patients.

Methods

Data were collected through face-to-face interviews using structured questionnaires, including the Illness Perception Questionnaire-Revised, the Medication Adherence Inventory, and the Inventory of Adherence to Self-Management. Data were analyzed by structural equation modeling using LISREL.

Results

The findings suggested that the illness identity may directly affect patient adherence to prescribed medications or indirectly affect patient adherence via control of the disease and cause. Control of the disease exhibited direct effects on adherence to prescribed medications and self-management, while the cause of the illness only showed direct effects on adherence to prescribed medications. The relationships were independent of systolic blood pressure, age, the total number of antihypertensive medication, and comorbidity.

Conclusions

The findings of the study extend the utility of the Common-Sense Model, suggesting that adherence to therapeutic regimens may be enhanced by improving a sense of controllability. For patients who experience symptoms related to high blood pressure, barriers to adherence may be reduced by assessing and clarifying the meaning of illness identity and causal attributions.

Introduction

Hypertension is one of the most important preventable causes of death worldwide (World Health Organization, 2003). It is estimated that about a quarter of adults in the world have hypertension (Kearney et al., 2005), and 59% of hypertensive patients have received treatment (Chobanian et al., 2003). Yet, adherence to treatment is around 50–70% (World Health Organization, 2003). DiMatteo (2004) estimated that monetary waste related to non-adherence for patients with hypertension is around US$ 8.4 million per year. In Taiwan, over 60% of elderly hypertensive patients take medication for their blood pressure control, but the control rate is <29% (Chen, 2003). Improving adherence to treatment is one of the most cost-effective strategies for desirable therapeutic outcomes and preventing adverse cardiovascular events.

Many studies have explored issues of non-adherence since the term became popular in the 1970s (Lutfey and Wishner, 1999). However, recent findings of meta-analyses have reported that most interventions are expensive, complex, or labor-intensive, and the effects on improving patient adherence are limited (Haynes et al., 2002, McDonald et al., 2002). Tailoring interventions to address specific barriers to change from the patient's perspective is imperative (Takiya et al., 2004). Nevertheless, in past decades, issues of patient adherence were mostly explored from the perspective of health professionals rather than patients’ lay view (Morris and Schulz, 1992, Vermeire et al., 2001). An individual constructs his/her own views about disease and treatment which can greatly differ from those of health professionals (Steven et al., 2002, Larun and Malterud, 2007). Some studies found that patients may make their own decisions about medication adherence based on their own lay views (Chen et al., 2009, Meyer et al., 1985, Ross et al., 2004). Yet, most studies are descriptive, and a comprehensive understanding of patient adherence behavior is lacking.

Hypertension is one of the most common chronic diseases for which long-term adherence to therapeutic recommendations are required for favorable outcomes. Factors that motivate patients to adhere to long-term therapeutic regimens are not clear. The assumptions of the Common-Sense Model (CSM) reveal that patients taking actions to reduce health risks are guided by their subjective or common-sense perceptions of the health threat (Leventhal et al., 2003). Individuals form this illness perception based on their reactions to external and internal stimuli through two parallel pathways: cognitive and emotional representations. The components of the illness perception are illness identity (symptoms that an individual experiences in his/her illness), cause (causal attribution of the illness), timeline (individual perceptions about the duration of the illness), timeline-cyclical (changeability of the illness), personal control (beliefs about controllability of the illness by the patient), treatment control (beliefs about controllability or curability of the illness by treatment), consequences (impacts of the illness on the patient and his/her daily life), illness coherence (the coherence of usefulness of individual illness representations), and emotional representation (the emotional responses aroused by the illness (Leventhal et al., 2003, Moss-Morris et al., 2002)).

Some studies focusing on patient perspectives reported that patients have their own views of illness, and they self-regulate their treatment behaviors accordingly. Meyer et al. (1985) found that newly diagnosed patients with hypertension were more likely to drop out of treatment if they perceived the disease to be acute or experienced symptoms upon their first clinical visit. Even though some patients may agree that the nature of hypertension is asymptomatic, they will still predict their blood pressure by symptom presentations. Heurtin-Roberts and Reisin (1992) reported that those patients who defined their hypertension as “high-pertension” were less compliant with their treatment and had a lower blood pressure control rate. Enlund et al. (2001) found that patients with three or more problems (such as symptoms and interference with daily routines) were five times more likely to have modified their dosage instructions than those without problems. Similar results were also reported by qualitative studies (Rose et al., 2000).

Based on the theoretical framework of the CSM, Ross et al. (2004) and Patel and Taylor (2002) reported similar predictive effects of adherence behaviors in patients with hypertension. Patients with lower emotional representation, with less perceived personal control, and who were older were more likely to adhere to prescribed medications. Chen et al. (2009) found that significant predictors of adherence to prescribed medications and self-management greatly differ. Variables associated with medication adherence are: treatment control, risk factors, and psychological attribution, while symptoms experienced after a hypertension diagnosis, symptoms for blood pressure prediction, personal control, balance and cultural causal attribution were significantly associated with adherence to self-management. The findings may suggest that patients’ lay views are more influential within the domain of self-management.

Cameron et al. (1993) found that patients use symptoms to create and update representations. Illness is identified by both an abstract label and concrete sensory symptoms. When given a diagnosis (label), a person will look for symptoms to match, and a person experiencing symptoms will seek to label the symptoms (Leventhal et al., 1998). Most patients are usually labeled as being hypertensive after blood pressure screening without experiencing any symptoms. Contrary to the asymptomatic nature of hypertension, in longitudinal (Sigurdsson and Bengtsson, 1983), cross-sectional (Erickson et al., 2004), and population-based studies (Kjellgren et al., 1998) as well as a randomized double-blind clinical trial (Hollenberg et al., 2000), some researchers found that many patients experience symptoms before (Kjellgren et al., 1998) and after (Kyngas and Lahdenpera, 1999, Mena-Martin et al., 2003) a hypertension diagnosis. Some patients may even predict their blood pressure based on their personal inference of somatic cues (Pennebaker and Watson, 1988), even though the inference may largely be inaccurate (Brondolo et al., 1999). Patients may use environmental cues to make sense of the ambiguous symptoms, and seek meaning for the symptoms (Baumann et al., 1989).

Causal attributions of the illness are also at the core of health behaviors (Chang, 2000), and there is a universal need for individuals to conceptualize abstract labels in adapting to health risks (Baumann, 2003). In Taiwanese society, multiple healthcare delivery systems (Western medicine, traditional Chinese medicine, and folk medicine) coexist at the same time. Decisions for health care advice are based on individual symptom perceptions (Chang, 1998), and causal attributions of the illness (Chang, 2000). For example, if a patient perceives the symptom which is resulted from bacteria, he/she will seek help from Western medicine; an imbalance between inner and outer systems may lead one to try Chinese medicine, while bad luck might cause one to seek help from folk medicine. Causal attribution not only implies the possibility of gaining a certain degree of control over an illness, but also affects the experience of symptoms and the illness (Kirmayer et al., 1994). Attention to causal attribution of illness is essential to elicit cultural variations in illness experiences and health behaviors.

Even though many studies explored factors associated with adherence to therapeutic regimens, most of them are descriptive and correlational findings. A comprehensive understanding of relationships among the variables based on a theoretical model is needed (Hagger and Orbell, 2003). There are very few studies analyzing the relationship of illness perceptions with adherence to prescribed medications and self-management at the same time, particularly which describe the roles of illness identity and cause of adherence among patients with hypertension. Symptoms experienced by hypertensive patients may be subjective and not sensitive or specific. Symptom is an important cue activating illness representations (Leventhal et al., 1998), is part of cognitive representation (Leventhal et al., 2003), may be used to appraise the efficacy of the therapeutic regimen (Leventhal et al., 1992), and illness representations may be modified in response to feedback from action behaviors (Meyer et al., 1985, Leventhal et al., 2003). Yet, very few studies validate the role of illness identity in the theoretical framework of CSM. The aim of this study was to test a hypothetical model of adherence to both prescribed medications and self-management behaviors in patients with hypertension in a Taiwanese (ethnic Chinese) social context using the technique of structural equation modeling (SEM).

Based on the CSM and the above literature review, patients’ coping with a health threat is influenced by the illness representation that is shaped by the internal and external stimuli the patient perceives. Illness identity is the symptom related to the illness the patient perceives which serves as an internal somatic stimulus during the coping process (Chang, 1998). Dependent on the acuity and distress prompt of symptom experiences, illness identity may affect patient adherence behavior directly or indirectly via renegotiated with other cognitive or emotional representations (Kirmayer and Sartorius, 2007, Leventhal et al., 2003). The conceptual framework of the hypothesized model is presented in Fig. 1. The framework identifies direct relations among the three factors of illness representations and adherence behavior, while illness identity is an eliciting cue for adherence to prescribed medication and self-management recommendations directly or indirectly through cause, a negative illness representation (negative IR), and control. Four factors including age (Kjellgren et al., 1998, Ross et al., 2004), systolic blood pressure (Kjellgren et al., 1998, Pennebaker and Watson, 1988), the total number of antihypertensive medications (AHMs) (Iskedjian et al., 2002, Schroeder et al., 2004), and comorbidities (Chen et al., 2009, Hagger and Orbell, 2003) were selected as confounding factors. After controlling for confounding factors, the relationships of the hypothetical model remained significant.

Section snippets

Design and setting

A cross-sectional, descriptive, correlational design was used. The study was conducted at cardiovascular clinics of three teaching hospitals in central Taiwan. The study was carried out between 1 September 2006 and 12 December 2007.

Participants

Data were obtained from a purposive sample of 355 hypertensive patients. Inclusion criteria for participation in the study were adult patients with a diagnosis of essential hypertension confirmed by a cardiovascular physician, and having been prescribed an

Characteristics of the sample

The sample of respondents consisted of 214 men (60.3%) and 141 women (39.7%), with a mean age of 65.19 (SD = 12.82) years. The mean duration of hypertension history was 10.45 (SD = 8.74) years, with a mean systolic blood pressure of 138.56 (SD = 15.10) mmHg and a mean diastolic blood pressure of 79.35 (SD = 11.69) mmHg. The majority of the respondents were married (87.3%). About 12.7% of the respondents were uneducated, whereas 35.8% had received an elementary school education, and 51.5% had received

Discussion

The study examines the proposed relationship specified in the CSM, and evaluates the role of illness identity in patient adherence to therapeutic regimens in patients with hypertension. The results of the study found that adding illness identity into the CSM model as an antecedent makes significant improvement in the model fit indices, indicating the feasibility of using the proposed model as an alternative in understanding patient adherence to therapeutic regimen. Illness identity directly and

Conclusions

The findings of this study extend the function of the CSM by identified the role of illness identity in predicting adherence to therapeutic regimens in hypertensive patients. The study identified the disease-specific content of illness identity and culturally specific content of cause, and found that patients’ illness representations may have been influenced by internal stimuli of somatic cues such as symptom experience and likely affected patient adherence accordingly. Variables of illness

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