CHAPTER 1

INTRODUCTION

Background and Significance of the Research Problem

Hypertension is an important public health problem which is a major cause

of death and disability in both developed and developing countries (He & MacGregor,

2007). Kearney et al. (2005) reported that overall 26.4 % of adult population in

different world regions in 2000 had hypertension and the estimated number of adults

with hypertension in 2025 would increase to 60%. In the United States data from the

National Health and Nutrition Examination Survey (NHANES) revealed that the

prevalence of hypertension among U.S. adults was approximately 30% in 2007-2008

(Yoon, Ostchega, & Louis, 2010). In Thailand, the data from the 4th

National Health

Examination Survey (NHES) during 2008-2009 showed that the prevalence of

hypertension was 21.4% (Aekplakorn, 2010). Additionally, the number of Thai

patients who were hospitalized with hypertension has been increasing dramatically

from 2008 to 2010. There were 494,809 patients in 2008 and it increased to 859,583

in 2010 (Bureau of Non Communicable Disease, Department of Disease Control,

Ministry of Public Health, 2013). This data confirms that hypertension is one of

major health problems in Thailand.

The target goal of therapy of hypertension is to control blood pressure to

optimal level (SBP < 140 and DBP < 90 mmHg) in order to prevent severe

complications. The 7th

Report of Joint National Committee (JNC-7) on Prevention,

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Detection, Evaluation, and Treatment of High Blood Pressure proposed the treatment

guideline for hypertension including pharmacology and non-pharmacology

treatments. Hypertensive patients should take medication as prescribed and change

their lifestyles to control blood pressure (Chobanian et al., 2003). Taking

antihypertensive drugs decreases the risk of stroke by 30%, cardiovascular disease by

10-20% and heart failure by 40-50% (Psaty et al., 2003; Roberts & Small, 2002). A

systematic reviews of the experimental designs showed the average systolic blood

pressure decreased of 2.9 mmHg when sodium consumption was restricted to 100

mmol/day in patients with hypertension, 5.2 mmHg when weight was lost and 0.8

mmHg when doing exercise (Ebrahim & Smith, 1998). The combination of two or

more lifestyle modifications achieved more to control blood pressure than one

(Chobanian et al., 2003). For example, the randomized controlled trial study of

effects of combination lifestyles modification on blood pressure showed that

hypertensive patients who adopted a DASH diet and weight management (exercise 3

times per week) had lower systolic and diastolic blood pressure than those who

received only counseling on the DASH diet (Blumenthal et al., 2010). The

effectiveness of an antihypertensive drug and lifestyle modifications are treatments to

attain the goal blood pressure level for persons with hypertension, so they need to

adhere to both medication and adopt healthy lifestyle in order to control their blood

pressure.

Adherence to therapeutic regimens plays a key role to manage

hypertension. The term adherence is viewed as patients having an active role in their

treatment (Cohen, 2009; Shay, 2008). World Health Organization [WHO] (2003)

defined adherence to long term therapy as the extent to which a person’s behavior:

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taking medication, following a diet, and/or executing lifestyle changes, corresponds

with agreed recommendations from the health care providers. Cohen (2009) defined

adherence as persistence in the practice and maintenance of desired health behaviors

and is the result of active participation and agreement and its attributes consist of

alignment of patient behaviors and health recommendations, mastery of a new

behaviors and health knowledge, ongoing collaboration relationship between the

patient and health care providers and their ability to meet the outcome targets. Thus

adherence to therapeutic regimens in persons with hypertension means that persons

with hypertension should agree with and perform recommended behaviors given by

health care providers including taking antihypertensive medications as prescription,

changing healthy lifestyles into their daily activities, collaboration with health care

providers to control their blood pressure and their ability to meet the outcome targets.

The benefits of adherence to therapeutic regimens among hypertensive

patients have clearly shown in many studies. DiMatteo, Giordani, Lepper, and

Croghan (2002) conducted a meta-analysis study on adherence in hypertensive

patients and found that patients who adhered to antihypertensive medication had a

3.44 times better chance of controlling blood pressure than those who were non-

adherent. Patients who adhered to prescribed medication had a lower level of systolic

blood pressure than those who did not adhere and their diastolic blood pressure also

decreased from 2.7 to 3 mmHg (Morris et al., 2006). Adherence of greater and equal

to 80% to antihypertensive drugs decreased the risk of cardiovascular disease by 22%

compared with the lower adherence group (< 80%) (Kettani et al., 2009). In addition,

the study of Perreault et al. (2009) found that a high adherence level (95%) to

antihypertensive therapy was associated with an additional reduction of chronic heart

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failure. Lower left ventricular mass occurred in the group of hypertensive patients

who adopt a DASH diet and weight management by regular exercise 3 times per week

decreased the risk of cardiovascular disease when compared with those who adopt a

DASH alone (Blumenthal et al., 2010).

The impact of poor adherence to therapeutic regimens are increased of

health care costs and increased length of hospitalization. A study of the impact of

poor adherence to antihypertensive agents on clinical outcomes and hospitalization

costs found that hospitalized patients who had a low adherence to antihypertensive

therapy increased costs by approximately $3,574 per person within a 3 year period

(Dragomir et al., 2010). The average costs in the low adherence group were $1,370

for medical costs, and $3,995 for hospitalization, but the costs decreased to $1,346,

and $2,464, respectively, for the high adherence group. The average length of

hospitalization in the low adherence group was 16 days compared with 10.6 days for

the group with the high adherence. A low level of adherence increased the risk of

hospitalization compared with the high adherence group (Dragomir et al., 2010).

Because of the benefit of adherence to therapeutic regimens (medication and lifestyle

modifications) to decrease blood pressure level, complications and the cost of

treatments, improving adherence to therapeutic regimens needs to be promoted among

persons with hypertension.

Although adherence to therapeutic regimens has shown benefits for

hypertensive patients, the rate of adherence among hypertensive patients was still rate.

In developed countries, only 50% of patients with chronic illness adhered to regimen,

and the adherence rate was higher than developing countries (WHO, 2003). For

example, 43% of Chinese and 51% of Americans having hypertension had high

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medication adherence (WHO, 2003). Kim et al. (2007) reported that approximately

45% of the Korean Americans with high blood pressure were adherent to regimens.

In Thailand, there was no national report to represent the rate of adherence among

persons with hypertension. They were represented in the research. For instance,

Naewbood (2005) who studied factors related to medication adherence among persons

with hypertension reported that 12.8% of persons with hypertension had poor

medication adherence. Moreover, Limcharoen (2006) found that persons with

hypertension had a lower level than cutting point (80%) of adherence to exercise

behaviors (77.9 %) and eating behaviors (77.35).

From the literature review it was found that several factors are associated

with adherence to therapeutic regimens including medication taking and lifestyle

modifications. Factors associated with adherence to therapeutic regimens include age

(Hadi & Rostami-Gooran, 2004; Hassan et al., 2006; Limcharoen, 2006; Naewbood,

2005), gender (Limcharoen, 2006; Naewbood, 2005; Phosena, 2003), income

(Charoenkij, 2000; Naewbood, 2005; Uzun et al., 2009), educational level

(Naewbood, 2005; Saounatsou et al., 2001; Uzun et al., 2009), marital status (Morris

et al., 2006; Tantayothin, 2003), knowledge of hypertension (Kim et al., 2007;

Limcharoen, 2006; Nangyeam, 2007; Uzun et al., 2009), health belief (DiMatteo,

Haskard, & Williams, 2007; Metha, 2001; Nangyeam, 2007), perceived self-efficacy

(Charoenkij, 2000; Charoenkitkarn, 2000; Dongyan, 2000; Roh, 2005), follow-up

interval (Bardel, Wallander, & Svardsudd, 2007; Hadi & Rostami-Gooran, 2004),

number of illness (Hadi & Rostami-Gooran, 2004; Phosena, 2003; Uzun et al., 2009),

duration of therapy (Hadi & Rostami-Gooran, 2004; Nangyeam, 2007; Onchim,

2002), number of pills per day (Fung, Huang, Brand, Newhouse, & Hsu, 2007;

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Limcharoen, 2006), number of side effects (Kim et al., 2007; Naewbood, 2005),

social support (DiMatteo, 2004; Naewbood, 2005; Uzun et al., 2009) and provider-

patient communication (Roh, 2005; Schoenthaler et al., 2009; Xu, 2005). In brief, the

factors affecting adherence to therapeutic regimens are intrapersonal factors,

interpersonal factors, condition-related factors, therapy-related factors and health care

system-related factors. Some factors cannot be modified such as demographic

factors, condition-related factors and some factors can not be modified by nursing

roles alone such as therapy-related factors.

Adherence to therapeutic regimens is complex and simultaneously affected

by many factors. Previous models of adherence have been developed to explain this

phenomenon including the Five Dimensions Model of Adherence (WHO, 2003),

Medication Adherence Model (MAM) (Johnson, 2002) and Hill-Levine model

(Fongwa, Evangelista, & Doering, 2006). The Five Dimensions Model of Adherence

focuses on social/economic factors, patient-related factors, condition-related factors,

therapy-related factors and the health system and health care team-related factors

affecting adherence behaviors. The Five Dimension Model of Adherence has

advantages for assessing affecting factors in all aspects. Secondly, Medication

Adherence Model (MAM) was developed by Johnson to explain the process of

medication adherence (Hsu, Mao & Wey, 2010; Johnson, 2002). This model focuses

on the cognitive and behavioral processes which persons with hypertension use to

decide, establish and maintain their medication behaviors to control blood pressure. It

is advantagous to understand how patients create and maintain their adherence

behaviors and it is concerned with the two types of nonadherence behaviors

(intentional and unintentional nonadherence). Lastly, the Hill-Levine model focuses

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on intrapersonal (cognitive and behavior), social factors and access to health care

services. Although it is an advantage to understand adherence phenomenon, some

factors such as access to health care services (presence or absence of health insurance,

regular treating physician and use of emergency department of hypertension-related

care), living arrangement and social isolation are unable to be modified by nursing

roles. Both the Five Dimensions Model of Adherence and the Hill-Levine model

focus on intrapersonal, interpersonal and environmental factors which affect

adherence, whereas the Medication Adherence Model focuses on the cognitive and

behavioral processes of individuals to decide and maintain medication behavior.

Although, the three models of adherence have advantages to explain factors affecting

adherence, they also have limitations. The limitations of the Medication Adherence

Model are focusing only on medication adherence and unable to demonstrate

adherence to lifestyle modifications. The limitations of both the Five Dimensions

Model of Adherence and the Hill-Levine model are that some factors in these models

cannot be modified and some factors cannot be modified by nursing roles.

Because of the importance of adherence in managing hypertension, a full

understanding of adherence to therapeutic regimens and its affected factors in Thai

persons with hypertension is needed in order to develop nursing intervention to

enhance adherence to therapeutic regimens. Nurses have important roles in teaching

and coaching hypertensive patients to adhere to regimens (Ockene, Hayman,

Pasternak, Schron, & Dunbar-Jacob, 2002). Nurses can also encourage hypertensive

patients to maintain healthier lifestyles by providing knowledge and support and

increasing patients’ confidence to perform recommended behaviors. Although, many

studies showed the relationship between sociodemographic factors, such as age,

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marital status and socioeconomic status and adherence to regimen, the American

Heart Association has summarized that sociodemographic factors, socioeconomic

status and personality characteristics have weak and inconsistent effects on adherence

(Borzecki, Oliveria, & Berlowitz, 2005). Some related factors are non-modifiable.

Some modifiable factors are unable to be changed by nursing roles. Moreover,

several studies indicated that some factors such as social support (Khuwatsamrit,

2006; William & Bond, 2002), provider-patient communication (Roh, 2005; Xu,

2005), and knowledge of hypertension (Xu, 2005) had both direct and indirect effects

on adherence to therapeutic regimens among persons with hypertension.

Although, many studies show influencing factors on adherence to

therapeutic regimens, most of these studies focused only on medication adherence

among hypertensive patients (Hadi & Rostami-Gooran, 2004; Karaeren et al., 2009;

Kim et al., 2007; Naewbood, 2005; Phosena, 2003; Ross, Walker, & MacLeod, 2004;

Saounatsou et al., 2001). There are few studies which demonstrated the relationship

between related factors and each of lifestyle modifications such as nutritional

behavior (Charoenkij, 2000; Metha, 2001; Nangyeam, 2007), exercise behavior

(Charoenkitkarn, 2000; Tantayothin, 2003; Trivedi, Ayotte, Edelman, & Bosworth,

2008) and stress management (Riounin, 2007) but there is no study which indicated

the relationship between related factors and all lifestyle modifications. Few studies

focus on adherence to both medication and lifestyle modifications among

hypertensive patients (Limcharoen, 2006; Roh, 2005; Uzun et al., 2009). To date, the

factors that affected adherence to therapeutic regimens including medication and

lifestyle modifications among Thai persons with hypertension were not clearly known

and there is still a gap in the knowledge. In Thailand, there are two studies of

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adherence to therapeutic regimens among persons with hypertension. One study

investigated factors related to medication adherence among persons with hypertension

(Naewbood, 2005). It focused only on medication adherence and the findings showed

that knowledge of hypertension and medication use, and educational level could

predict medication adherence at 19.7% (Naewbood, 2005). Another one has assessed

factors related to adherence to treatment both medication and lifestyle modifications

among essential hypertensive patients (Limcharoen, 2006). The results indicated that

there was a positive significant relationship between knowledge of hypertension and

medication adherence and adherence to lifestyle modifications (Limcharoen, 2006).

Moreover, a survey of existing non-experimental nursing research among patients

with hypertension in Thailand conducted during 1978-2005 found that only a few

researches have determined factors affecting treatment compliance (Khamhown,

2007). Also the previous models have the limitations that some factors are unable to

be modified by nursing roles.

Thus, the model of adherence to therapeutic regimens, including

medication and lifestyle modifications among Thai persons with hypertension, need to

be developed to fill a gap in the knowledge. The present study will develop a new

model of adherence based on empirical evidences which indicate direct and indirect

effects of factors on adherence to therapeutic regimens among persons with

hypertension. Therefore, to select factors affecting adherence to therapeutic regimens

to explain the model of adherence is based on empirical evidences which obviously

indicate direct and indirect effects of the selected factors on adherence to therapeutic

regimens and the selected factors can be managed by nursing roles. The studies of

modifiable factors influencing adherence to therapeutic regimens in persons with

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hypertension and other chronic illness show that the significant modifiable factors are

social support, provider-patient communication, knowledge of hypertension, health

belief and perceived self-efficacy.

Social support is perceived and provided support from other people

including emotional, instrumental, informational and appraisal support. Social support

was associated with adherence; patients who perceived high social support were more

adherent than those who perceived low social support (Naewbood, 2005). DiMatteo

(2004) found that social support had a correlation with patients’ adherence to medical

treatment in various chronic diseases including hypertension. Patients who received

support had a higher adherence than those who did not. Several empirical studies on

social support found that social support and adherence were mediated by perceived

self-efficacy (Khuwatsamrit, 2006; William & Bond, 2002). Also, social support was

significantly directly related to knowledge among hypertensive patients (Roh, 2005).

Thus, social support may have a direct effect on adherence to therapeutic regimens,

knowledge of hypertension and perceived self-efficacy. Also, social support may

indirectly affect adherence to therapeutic regimens through knowledge of

hypertension and perceived self-efficacy.

Provider-patient communication is one aspect of a relationship which

induces trust, satisfaction, and confidence for patients to perform the required

behaviors (Vermerire, Hearnshaw, Royen, & Denekens, 2001). Exchanging

information between patients and health care providers is one purpose of

communication and improves patients’ knowledge and perceived self-efficacy to

perform the required behaviors. Patients, who perceived collaborative communication

from their providers, had higher adherence than those who perceived non-

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collaborative communication with providers (Schoenthaler et al., 2009). Also,

provider-patient communication had a direct positive effect on perceived self-efficacy

and an indirect positive effect on adherence to therapeutic regimens among

hypertensive patients (Roh, 2005). In the diabetes study of Xu (2005) it was found

that provider-patient communication had a positive direct effect on perceived self-

efficacy and knowledge and had a positive indirect effect on self-management in type

2 diabetes. Thus, provider-patient communication may have a direct positive effect

on adherence to therapeutic regimens, perceived self-efficacy and knowledge of

hypertension among hypertensive patients and have an indirect positive effect on

adherence to therapeutic regimens through perceived self-efficacy and knowledge of

hypertension.

Knowledge of hypertension is the cognitive process which establishes

patients’ understandings of their illness and treatment plan for controlling their illness.

In addition, it also affects the patients’ decision to adhere to therapeutic regimens.

Knowledge is associated with adherence to therapeutic regimens when knowledge of

hypertension increases, adherence to therapeutic regimens also increases (Limcharoen,

2006; Naewbood, 2005; Nangyaem, 2007; Uzun et al., 2009). Moreover, Xu (2005)

who studied Chinese with type 2 diabetes found that knowledge was positively

associated with perceived self-efficacy and had a positive indirect effect on self-

management. Hence, knowledge of hypertension may have a direct effect on

adherence to therapeutic regimens and an indirect positive effect on adherence

through perceived self-efficacy.

Health belief is a modifiable factor which influences adherence to

therapeutic regimens. Health belief refers to individual’s subjective probability

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decision concerning hypertension and its treatment. Patients who perceived the risk

of complications, perceived the severity of those complications, perceived the

usefulness of performing adherence and perceived fewer barriers to performing

adherence were more adherent to therapeutic regimens (Metha, 2001; Nangyaem,

2007; Riounin, 2007; Tantayothin, 2003). In conclusion, health belief may positively

affect adherence to therapeutic regimens among hypertensive patients.

Lastly, perceived self-efficacy is the patients’ perception of their own

ability to perform adherence behaviors. Most studies indicated that perceived self-

efficacy was a powerful factor influencing adherence to therapeutic regimens among

hypertensive patients (Dongyan, 2000; Kressin et al., 2007; Onchim, 2002;

Tantayothin, 2003). Patients, who had high perceived self-efficacy, are likely to

perform the required behaviors. Additionally, perceived self-efficacy is the mediating

factor between adherence to therapeutic regimens and social support and provider-

patient communication. Many studies indicated perceived self-efficacy as a

mediating factor. Perceived self-efficacy was a mediator between provider-patient

communication and adherence to therapeutic regimens among hypertensive patients

(Roh, 2005). Also, the finding in type 2 diabetes found that perceived self-efficacy

was a mediator between self-management and social support, provider-patient

communication and knowledge (Xu, 2005). The result in the study of patients with

coronary artery disease showed that perceived self-efficacy was a mediator between

adherence to self-care requirements and knowledge and social support (Khuwatsamrit,

2006). In summary, perceived self-efficacy may have a positive direct effect on

adherence to therapeutic regimens among hypertensive patients and may serve as a

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mediator between adherence to therapeutic regimens and knowledge of hypertension,

social support and provider-patient communication.

The role of the modifiable factors influencing adherence to therapeutic

regimens among Thai persons with hypertension is not clearly known and less

studied. Therefore, this study will fill this gap in the knowledge by developing the

model of adherence to therapeutic regimens in order to enhance the understanding of

the direct and indirect effects of modifiable factors on adherence to therapeutic

regimens among Thai persons with hypertension. Once this information is obtained,

the model of adherence will be essential to nursing knowledge for assessing the

factors affecting adherence to therapeutic regimens and developing effective nursing

intervention to improve and promote adherence to therapeutic regimens in Thai

persons with hypertension.

Research Objectives

The general objective of this study is to test a model of adherence to

therapeutic regimens among persons with hypertension.

The specific objectives of this study are:

1. To examine the relationships between social support, provider-patient

communication, knowledge of hypertension, health belief, perceived self-efficacy and

adherence to therapeutic regimens among persons with hypertension.

2. To identify factors directly and indirectly affecting adherence to

therapeutic regimens among persons with hypertension.

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Research Questions

The research questions for this study are as follows:

1. What relationships are there between social support, patient-provider

communication, knowledge of hypertension, health belief, perceived self-efficacy

and adherence to therapeutic regimens among persons with hypertension?

2. What factors have direct and indirect effects on adherence to

therapeutic regimens among persons with hypertension?

Scope of the Study

This was adescriptive, cross-sectional, predictive correlation design was

used to identify predictors and test a causal model of adherence to therapeutic

regimens in persons with hypertension who attened hypertension clinic in one of the

community hospitals in Lampang province, Thailand. Data were collected from May

to July 2012.

Definition of Terms

Adherence to therapeutic regimens. It is defined as the extent of

agreement and performance of persons with hypertension about the recommended

behaviors provided by health care providers including antihypertensive medication

taking, dietary modifications, weight control, avoiding risk factors, physical activity,

stress management and follow-up visits. The attributes of agreement consist of

alignment of patients’ behaviors and recommendations, mastery of new behaviors,

15

ongoing collaboration with health care providers on the treatment plan and their

perceived ability to meet optimal blood pressure. It was measured by the

Hypertensive Adherence to Therapeutic Regimens Scale which was modified from

the Hypertensive Adherence Scale (Limcharoen, 2006).

Provider-patient communication. It is defined as the level of patients’

perception of health care provider’s behaviors about general clarity during their

talking, explanation of hypertension medication and lifestyle modifications and

carefully listening to and responding to patient problems and concerns about

hypertension management. The Provider-patient Communication Scale modified by

Xu (2005) was modified to measure the provider-patient communication in this study.

Knowledge of hypertension. It is defined as the level of understanding

regarding hypertension, including etiology, signs and symptoms, complications,

medication and behavioral modification to control blood pressure (dietary, physical

exercise, weight control, avoiding risk factors, stress management and follow-up

visit). The Knowledge of Hypertension Scale modified from the Hypertension

Knowledge Scale developed by Limcharoen (2006) was used to measure the

knowledge of hypertension in this study.

Social support. It is defined as the level of emotional, instrumental,

information and appraisal support perceived by hypertensive patients in order to

maintain an adherence to therapeutic regimens. The Hypertensive Social Support

Scale developed by Pongudom (2006) was modified to measure social support in this

study.

Health belief. It is defined as the level of the perception of hypertensive

patients including perceived susceptibility to the hypertensive complications,

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perceived severity of the hypertensive complications, perceived benefits of

performing disease control behaviors and perceived barriers to performing disease

control behaviors. The Health Belief for Hypertensive Patient Scale developed by

Riounin (2007) was modified to measure health belief in this study.

Perceived self-efficacy. It is defined as the level of the confidence a person

with hypertension has that he/she can be successful in the activities recommended by

the health care providers. These activities include taking of antihypertensive

medication, dietary modifications, weight control, physical exercise, avoiding risk

factors, stress management and follow-up visits in order to control their own blood

pressure. The Hypertensive Self-efficacy Scale developed by Kairoj (1999) following

of Bandura’s self-efficacy theory, was modified to measure perceived self-efficacy.

Persons with hypertension. They are defined as persons who have been

diagnosed with essential hypertension and take at least one antihypertensive

medication.