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Cardiovascular Disease Risk Factors in an Amputee Population

Bridget A. Frugoli, MS
W. Kent Guion, MD
Barry A. Joyner, PhD
James L. McMillan, EdD

ABSTRACT

Cardiovascular disease, which remains the number one cause of death in the United States, is particularly prevalent in amputees and in other groups such as men, the elderly, and African Americans. The objective of this study was to identify the underlying risk factors of cardiovascular disease in an amputee population and to determine if those risk factors differ between the vascular and nonvascular amputee groups. In addition, the amputee risk profile was compared with the general population. A survey consisting of previously validated cardiovascular disease risk factor questions was sent to 39 support groups across the United States. From the data of 170 respondents, four highly prevalent risk factors were identified in the amputee profile; these factors included high cholesterol, hypertension, diabetes, and inactivity. The vascular amputees were significantly older than the nonvascular amputees and had an increased occurrence of diabetes (71% versus 13%; p = 0.001), an increased overweight prevalence (71% versus 29%; p = 0.019), and a decreased number of days per week of alcohol consumption (0.64 versus 1.24; p = 0.018). Additionally, it appeared that three risk factors were elevated above the United States population norms for the following categories; these factors included cholesterol, hypertension, and diabetes. The results of this study indicate that special attention should be focused on the modification of risk factors emphasizing high cholesterol, hypertension, diabetes, and inactivity. The high occurrence of reported risk factors could explain the increased rate of death as a result of cardiovascular disease in the amputee population.

Key Words: diabetes, vascular disease, traumatic amputee, modifiable risk factors

Introduction

Cardiovascular disease is a major health problem in the United States. In 1996, 733,361 deaths were attributed to it.¹ However, between 1978 and 1988, death rates from the disease declined by approximately 23%.^2,3 This decline has been attributed to the improved control of cardiovascular disease risk factors, 4 which are classified as either modifiable or nonmodifiable.⁵ Modifiable risk factors include hypertension, elevated blood cholesterol, smoking, and inactivity, whereas nonmodifiable risk factors include gender, age, and heredity.5

Cardiovascular disease, which remains the number one cause of premature death in the United States today, is more prevalent in certain groups, including amputees.⁶ Increased risk factors resulting from underlying diseases predispose vascular amputees to cardiovascular disease, resulting in an increased death rate compared with the general population.⁷ However, nonvascular, lower limb amputees have also been reported to have increased morbidity from cardiovascular disease, with marked increases in the certain risk factors, including inactivity, hyperinsulinemia, and hypertension.8,9,10

As with the general population, it is important to know the underlying risk factors of cardiovascular disease to implement a successful risk reduction program for amputees. Conflicting research exists between the risk factors of cardiovascular disease in the amputee population. Burger and Marincek⁹ reported that, after lower limb amputation, most young, nonvascular amputees participated less frequently in social and physical activities. However, a similar study showed no significant differences in physical activity between nonvascular amputees and a control group.¹⁰ Rose et al.⁸ found an increase in obesity for an amputee sample, whereas Modan et al.¹⁰ reported no significant difference in overweight/obesity between an amputee sample or a control group. Most of the existing literature has investigated vascular or nonvascular amputees only, making it difficult to compare the risks between the groups.

Currently, there is no comprehensive cardiovascular disease risk profile for amputees. The difference in risk factors between amputee groups has also not been clearly documented. Furthermore, a complete risk profile of the amputee population has not been compared with the general population. Therefore, the purpose of this investigation was to identify the underlying risk factors of cardiovascular disease in an amputee population, and to determine if those risk factors differed between the vascular and nonvascular amputee groups. The amputee risk profile was also compared with the general population.

Methods

Participants

The participants in this study were volunteers from Amputee Coalition of America-affiliated support groups. Both upper and lower limb amputees were invited to participate in the study, and age was limited to 18 years of age or older. One hundred seventy-three support groups were contacted, of which 39 groups agreed to participate. All participants gave consent to be a part of the study, and all procedures were approved by the Georgia Southern University Institutional Review Board.

Instrument

A survey consisting of 18 questions was constructed based on previously used questionnaires (Fig. 1 ). The risk factors chosen included high blood cholesterol, high blood pressure, diabetes, left ventricular hypertrophy, overweight, smoking, inactivity, stress, and alcohol consumption.^1,4,5 Questions adapted from the Framingham Cardiovascular Disease Risk Survey served as the primary instrument and included the risk factors of cholesterol, blood pressure, diabetes, left ventricular hypertrophy, and smoking. The Framingham survey has been validated previously as a measure of cardiovascular risk factors.11

Additional questions pertaining to obesity, physical activity, stress, and alcohol consumption were included to complete the risk factor questionnaire. A previously validated single exercise question from the St. Louis Working Hearts Programs was used to evaluate physical activity level.¹² Questions about stress and alcohol use were included from the Heart Check Cardiovascular Questionnaire.¹³

Subjects were asked to rank their body weight levels in 5-pound increments based on their physician's advice. The researchers considered overweight to be 20 pounds or greater than ideal weight based on participant input. This ranking method was chosen out of concern for body mass index, which does not take into consideration the missing limb.

To test the readability of this questionnaire, a pilot study was conducted through a local orthotics and prosthetic office. Seven randomly chosen individuals were asked to complete the questionnaire and to write feedback on the appropriateness, length, and clarity of the questions. The feedback from this pilot study was considered in completing the construction of the instrument.

Procedures

The leaders of 173 support groups were sent a letter requesting their participation in this study. The letter included a return envelope and a response sheet to which they were asked to respond within 2 weeks. Group leaders who did not respond by 1 week after the requested date were contacted by telephone. Packets including questionnaires, an instruction sheet, and a return envelope were sent to those groups who agreed to participate. The support group leader was responsible for administering the survey and mailing the return envelope back to the researcher. If a participant completed the survey individually, he or she was responsible for mailing the survey back to the researcher.

The respondents were grouped as either vascular or nonvascular amputees. Vascular amputees were those participants who had an amputation because of diabetes, arteriosclerosis, embolism, or vascular disease, whereas nonvascular amputees were those who had an amputation because of trauma, malignant tumor, frostbite, or osteomyelitis. Participants who indicated that they were 20 pounds over ideal weight were classified as overweight.¹ Cholesterol and blood pressure were considered to be risk factors if the participant marked "high" on the questionnaire based on their physician's diagnosis (Fig. 1 ) or if he or she indicated taking a prescription medication to control one of these factors.14

Data Analysis

All statistical analysis was performed using SPSS (Statistical Package for the Social Sciences), Version 8.0 (SPSS, Inc., Chicago, IL). The cardiovascular disease profile of the amputee population was described using sample size, mean, and standard deviation, along with frequency tables to give percentages. Independent t-tests, cross tables, and chi-square tests were performed to analyze differences between amputee subgroups. The National Center for Health Statistics general population percentages for risk factor prevalence in the United States were compared with the total amputee population.¹ Significance was considered at alpha 0.05.

Results

Sample Demographics

The 39 support groups who agreed to participate were mailed 700 questionnaires, of which 24 percent (n = 170) were returned and analyzed. The average age of the respondents was 60.5 ± 13 years, ranging from 32 to 87 years. Of the 170 participants, 121 were men, 47 were women, and two did not report sex. Ninety-four participants (55.3%) were vascular amputees, and 76 were (44.7%) nonvascular amputees. One hundred forty-seven (87%) of the participants were identified as unilateral amputees, with 65 (40%) above-joint and 97 (60%) below-joint amputations. Additionally, 155 (95.7%) of the participants were classified as lower limb amputees. Table 1 details their complete amputation history, including cause and type of amputation, health of the opposite limb, and prosthetic use.

Comparing Vascular and Nonvascular Amputees

In comparing the vascular and nonvascular amputee subgroups, there were several background and cardiovascular disease risk factors that were significantly different. Independent t-tests revealed that vascular amputees were significantly older by an average of 5 years (p = 0.017) and that nonvascular amputees had worn their prosthetic for an average of 10.5 years longer than vascular amputees (p = 0.001). Vascular amputees also had a decreased average number of days of alcohol consumption per week than the nonvascular group (0.64 versus 1.24; p = 0.018).

Chi-squared tests revealed that vascular amputees had an increased percentage of diabetes-related amputations (69.1% versus 0%; p = 0.0001) and that nonvascular amputees had a significantly higher rating of the health of opposite limb (p = 0.002). The cardiovascular disease risk factors that differed between these two groups included an increase in the presence of diabetes mellitus (71% versus 13%; p = 0.001) and a higher number of overweight persons (71% versus 29%; p = 0.019).

Table 2 illustrates the differences in risk factors between the general population and amputee population. Cholesterol, hypertension, smoking and overweight factors are divided to match appropriate age and gender classification. The risk factor profile (Table 3 ) for the sample, includes the actual number of reported responses, valid percent of population, and sample size.

Discussion

Sample Description

Although the majority of amputee demographics are very similar to previous studies, one difference is the lower percentage of vascular participants in this study. Other studies^6,17,18 have reported 80% to 93% of their samples as having vascular-related amputations, compared with the 55.3% in this present investigation. The reason for this difference is unclear, because there was no specific selection process used to enroll participants in this study other than that already described. The lower percentage of vascular amputees may be reflective of the members in the particular support groups solicited for this study.

Comparison with Previously Published Amputee Studies

Cardiovascular risk factors were compiled using frequencies of the given risk factors. The "high" ranking of cholesterol occurred in 38.9% of the sample. In recent studies,^8,10 hyperlipidemia was also found in 37.6% to 47% of amputee population. In contrast, Solonen et al.¹⁹ found that there was no increase in total cholesterol compared with a control group, a discrepancy that may have occurred because the Solonen study looked at only young traumatic amputees.

Hypertension was reported in 42.3% of the current study population, a finding comparable with the Modan et al.¹⁰ and Rose et al. 8 observations of 43.6% and 47.4%, respectively. Additionally, 43% of the sample in the present study reported having diabetes mellitus, with approximately 77% of those individuals classified as type 2. The overall percentage of participants with diabetes fell into the 31.7% to 50% range of previous studies.10,17,20

Smoking habits were also investigated by the Modan study,10 which found that 21.8% of their amputee subject population smoked at the time of the study, a percentage that is very similar to the present study's finding of 23%. This percentage is also reflected in other reports,^7,8 which did not find a significant increase in smoking habits of their amputee samples.

This current study found that 58% of the participants were not regularly physically active. Modan et al1 reported no difference in physical activity level compared with a control group. However, Burger and Marincek⁹ and Narang et al.²¹ reported that amputees have a decrease in daily and physical activities from preamputation to postamputation. Although an amputee may demonstrate such a decreased physical activity level, the postamputation percentage is comparable with that of the general population.

Unfortunately, there were four variables that could not be compared with previous research because of a paucity of previously reported information. These variables included left ventricular hypertrophy, overweight, stress, and alcohol consumption. The results of this study suggest some interesting trends. Only two subjects in this study (1.2%) reported left ventricular hypertrophy, and twenty-six members of the sample (15.4%) did not even know if they had this condition. No previous reports investigated the occurrence of left ventricular hypertrophy in amputees.

Although no direct comparisons can be made with previous research, it is important to illustrate the differences that exist in the research on the overweight and obese. This study used a body weight rating and found that 22.9% of the sample was classified as greater than 20 pounds overweight. Rose et al.⁸ used hydrostatic weighing in hypertensive amputees and reported an average of 37.2% body fat, a percentage that is considered obese by national standards.²² However, Modan et al.¹⁰ inspected overweight/obesity three ways, including body mass index (BMI), waist/hip ratio, and a one-site, skin-fold measure at the subscapular area, and found no difference between the amputee sample and the control group.

In previous studies, it has been implied that increased stress in the amputee population is linked to an increase in cardiovascular disease.^10,23 The majority of the present sample (79.5%) had self-reported, moderate-to-low stress level ratings. Smith et al.²⁴ used the SF36 Health Status Questionnaire and found no significant difference in mental health or emotional problems, including stress factors between amputees and a control group. From the present study, it does not appear that stress would be a major determining factor in the increasing risk of cardiovascular disease in the amputee population.

Hrubec and Ryder7 reported an increased relative risk in an amputee sample compared with a control for alcoholic cirrhosis (1.9) and pancreatitis (3.8), both of which are alcohol-related processes. However, the amount of alcohol consumed was not indicated in the Hrubec study. Two questions regarding alcohol consumption were included in the present research survey to identify the amount of alcohol consumption and the tendency of binge drinking. The findings show that the average number of days the respondent consumed alcohol was 1 day per week and that 78% of those persons had only 1 to 2 drinks per occasion. This type of drinking would be considered moderate;²⁵ therefore, it does not appear that alcohol consumption in this sample would be a major contributor to cardiovascular disease.

Comparing Vascular and Nonvascular Amputees

The average age for vascular amputees was significantly higher than the nonvascular amputee age, and the average number of years of prosthetic use was 4.25 years in vascular participants and 14.88 years in nonvascular participants, a finding that was also significant (p = 0.001). This trend may be attributed to the age of the subject at the time of amputation. A large majority of our traumatic subjects served in combat, and their amputation occurred at a young age. Conversely, the risk of amputation in vascular patients increases with age.²⁸

As expected, the cause of amputation was also significantly different between vascular and nonvascular groups. More vascular amputees have diabetes, a condition that is often the underlying disease process leading to amputation in this group. It has been established that 80 to 90% of amputees have peripheral vascular disease and that diabetes greatly contributes to peripheral vascular disease.¹⁸

The only two cardiovascular disease risk factor categories that differed between the groups were diabetes and overweight. There was a higher frequency of diabetes mellitus in the vascular group. The vascular group also had a significantly higher percentage (p = 0.019) of overweight subjects, which may also have contributed to the prevalence of type 2 diabetes in that group.²⁸

The differences that have been identified between vascular and nonvascular amputees are important. Vascular amputees are significantly older, more likely to have diabetes, and are more likely to be overweight. This information illustrates significantly that vascular amputees are at a potentially higher risk for cardiovascular disease.

Comparing Amputees with the General Population

Cardiovascular disease is the number one cause of death in the general population of the United States, as it is within the amputee population,^1,6,11 and it has been reported as more prevalent in vascular and nonvascular amputees compared with control groups, with prevalence rates as high as 75% in some studies.^8,26 Mortality rates from cardiovascular disease have also been reported as being significantly higher in amputees.^6,7,10 To better understand why the disease is more prevalent in amputees, the individual risk factors were compared with current national norms in the United States based on appropriate classifications. These risk factors included cholesterol, hypertension, smoking, overweight, and inactivity.

Cholesterol

In this study, it appeared that men had higher percentages of elevated cholesterol, with vascular male amputees having about a 15% higher occurrence of high blood cholesterol than nonvascular male amputees (Table 2 ). Female amputees did not show this same increase of hyperlipidemia, which may have been because of the small number of female respondents. High blood cholesterol remains an important, well-established major risk factor for cardiovascular disease.3

Hypertension

High blood pressure is another major contributor to cardiovascular disease. Elevated hypertension is also associated with increased age; on average, there is a 20 mm Hg systolic and a 10 mm Hg diastolic incremental increase in blood pressure from age 30 to 65.31 Hypertension appeared elevated in the total amputee sample, 42.7% in amputees versus 23.0% in the general population. There are several theories as to why hypertension may increase. Once thought is that this occurs because of increased insulin and/or mechanical limb irritation, both of which cause a rise in blood pressure.^37,38 Further research on these topics is warranted to better understand the relationship.

Diabetes Mellitus

Diabetes is present in 8.2% of the general population (20 to 60 years of age),28 compared with 17.9% of nonvascular amputees and 58.9% of vascular amputees. In the 60 years and older group, diabetes affects 18.4% of the general population,28 12.1% of nonvascular amputees, and 81.5% of vascular amputees. Persons with diabetes are 15 times more likely to have an amputation of the lower limb than nondiabetic individuals.³² Not surprisingly, the frequency of diabetes is drastically different for vascular amputees than for nonvascular amputees in this study (Table 2 ). There has been a 39% increase in the occurrence of diabetes in the general population over the past 14 years.²² From this data, it is apparent that nonvascular amputees under 60 are at an increased risk of cardiovascular disease because of an increased incidence of diabetes.

Smoking

Overall, smoking habits in the general population of United States dropped from 43.4% in 1965 to 24.7% in 1997.³³ Smoking habits in the amputee sample appear similar to those in the general population. It should be highlighted that, even though the overall percentage of smokers in this study is comparable and may appear to be low compared with the general population, smoking is a strong modifiable predictor of cardiovascular disease and should not be ignored.

Overweight

There is evidence that weight loss in overweight and obese individuals reduces the risk for cardiovascular disease and diabetes.³⁴ The prevalence of overweight individuals has increased substantially in the United States population during the past 10 years. In 1997, 54% of adults in the United States were reported to be overweight.³⁴ The results of the present study were inconsistent with this finding and appeared to be lower in the amputee population (22.9% of amputees versus 43.7% of the general population). This inconsistency may be explained partially by the method used for calculating increased body mass, which varied from previous studies.

Inactivity

In the present study, 55.4% of the amputee sample reported that they were not regularly active (Table 2 ). This finding is similar to current trends seen in American adults, more than 60% of whom don't engage in the recommended amount of physical activity.³⁵ Regular physical activity has many important, positive effects on the musculoskeletal, cardiovascular, respiratory, and endocrine systems. Other positive results of physical activity are decreased hypertension, lower blood cholesterol, control of diabetes, and reduction in obesity.30,36

Summary/Profile

The complete cardiovascular profile for this amputee sample can be found in Table 3 . This profile is similar to the general population, but with three distinct differences. There was a higher prevalence of hyperlipidemia in the male amputee sample, a higher occurrence of hypertension in the total amputee sample, and a higher occurrence of diabetes in nonvascular amputees under the age of 65 years.

Limitations

The results of the present study could have been influenced by several factors. The use of support groups members may have confounded the results, making this sample be substantially different from the amputee population as a whole. Only about 24% of the questionnaires were returned, which may not accurately represent the total population of amputees. Furthermore, we found the proportion of vascular to nonvascular amputees to be inconsistent with previous literature, which limited comparison to previous studies, and 11 of the female respondents did not specify their age, which limited comparisons of sample size for individual risk factors. A final source of concern was the measurement of overweight/obesity. A question on this risk factor was included to complete the cardiovascular profile and to allow a comparison to other amputee samples to be made. However, the validity of this question is debatable; the specified range of weight classification may have been too narrow to differentiate between overweight and obesity.

Conclusion

No published, comprehensive cardiovascular risk profile for American amputees currently exists. The sample in this study had a similar risk factor profile to the general population; however, the amputee population had a higher prevalence of high cholesterol, hypertension, and diabetes. Within the amputee population, there were several differences. The vascular amputees were significantly older and had a higher occurrence of diabetes and excess body weight than the nonvascular amputees.

Cardiovascular disease can be successfully controlled and prevented by intervening with regard to known risk factors.³⁵ There are several organizations that focus on addressing these risk factors, such as the American Heart Association, the American Association of Cardiovascular and Pulmonary Rehabilitation, and the American Diabetes Association, just to name a few. Based upon the findings of this investigation and others, the potential benefits of a cardiovascular disease prevention program in an amputee population are strongly suggested. The results of this study indicate that the amputee population should focus attention on the three main risk factors of high blood cholesterol, hypertension, and diabetes.

Acknowledgements

This study was supported in part by a grant from the Georgia Southern University Office of Research and Sponsored Programs Graduate Student Funds and the Department of Health and Kinesiology. The authors would like to express their gratitude to both the Amputee Coalition of America and the American Amputee Foundation for their cooperation in this project.

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