Changes in functional walking distance and health-related quality of life after gastric bypass surgery

Physical Therapy, August, 2008 by James Tompkins, Pamela R. Bosch, Rochelle Chenowith, Judy L. Tiede, James M. Swain

Obesity prevalence is rapidly rising to epidemic proportions in the United States, resulting in a corresponding increase in health care costs. (1-3) Estimates from the World Health Organization indicate that more than one billion adults are overweight and that 300 million of them are clinically obese. The sequelae of obesity may include hypertension, cardiovascular complications, type 2 diabetes mellitus, respiratory complications, liver and gallbladder diseases, osteoarthritis, cancer, integumentary complications, decreased health-related quality of life (HR-QOL), and an increased risk of premature death. (2,4-6)

Gastric bypass surgery (GBS) is an accepted and effective means of managing morbid obesity, not only for weight loss but also for reducing or eliminating associated comorbid conditions (7,8) These benefits may result in improved HR-QOL, enhanced functional abilities, and improved cardiorespiratory fitness.

Although changes in HR-QOL and a reduction in comorbid conditions related to obesity have been documented after weight-loss surgery, (2,9,10) one question that has not been addressed is the early postoperative effect of GBS on physical function as measured by over-ground walking at self-selected speeds. The 6-minute walk test (6MWT) is widely used by physical therapists as a measure of functional exercise tolerance. (11-18) There are currently no normative values for functional walking distances for patients with obesity. Therefore, we were interested in whether 6MWT distances varied for patients before and after GBS. In addition, we wanted to examine the relationship between functional walking distances and patients' perceptions of HR-QOL before and after GBS.

Specifically, we hypothesized that: (1) patients with obesity would walk a shorter distance in a 6MWT compared with normative data; (2) the distance walked during the 6MWT would increase significantly at 3 months and at 6 months after GBS compared with before GBS; (3) the patients' rating of perceived exertion (RPE) at the end of the 6MWT would decrease significantly at 3 and 6 months after GBS compared with before GBS; and (4) the perceptions of patients about HR-QOL, as assessed with the 36-Item Short-Form Health Survey (SF-36), would improve significantly at 3 and 6 months after GBS compared with before GBS.

Method

Subjects

Prospective subjects with a minimum body mass index (BMI) of 35 were recruited as volunteers from a group of patients scheduled for GBS at a local hospital that specializes in this type of procedure. Exclusion criteria included inability or unwillingness to return to the clinic at 3- and 6-month intervals after GBS, uncontrolled medical conditions, inability to walk, and pregnancy. Before data collection, all subjects signed an informed consent form that was approved by both the hospital's and the university's institutional review boards.

Twenty-eight women and 2 men, ranging in age from 31 to 58 years ([bar.X] [+ or -] SD=44 [+ or -] 6.3 years) and with a mean [+ or -] SD BMI of 45.5 [+ or -] 6.9, agreed to participate in the study. Of these 30 subjects, 25 completed all components of the investigation. Four subjects were excluded from the 6MWT and SF-36 analyses because they did not participate in both follow-up sessions, and a fifth subject was lost to follow-up.

Each subject participated in 3 testing sessions. The first session occurred on the day before surgery (pre-GBS) after the preoperative appointment with the bariatric surgeon, the second session took place after a 3-month postoperative follow-up appointment with the surgeon (3 months after GBS), and the final session took place 6 months after GBS.

Measures

Before each testing session, the surgical nurse measured the subjects' height and weight for the BMI calculation. The subjects then completed the SF-36 and participated in a 6MWT.

BMI. The BMI is the most common method of estimating an individual's body composition, and it is calculated by dividing body weight in kilograms by height in meters squared (kg/[m.sup.2]). (15,19) Regardless of sex, adults with a BMI of 25.0 to 29.9 are considered overweight, those with a BMI of 30.0 to 39.9 are considered obese, and those with a BMI of 40.0 or higher are considered morbidly obese. (6,19) All weights were measured on an SR555, Stand-on Scale System (1,000 lb capacity), * whereas the initial heights were measured using a wall-mounted Seca 222 stadiometer. ([dagger])

SF-36. The SF-36 has been used to describe the health status and physical ability of people with numerous impairments who are receiving physical therapy. (13) This questionnaire is a generic measure of HR-QOL, with high content and external validity. Reliability values (Pearson r) range from .89 to .94 for the Physical Component Summary (PCS) and from .84 to .91 for the Mental Component Summary (MCS). (20) The questionnaire contains 36 questions grouped into 8 scales, and these scales are further clustered into the PCS and MCS components. The PCS includes scales to measure physical functioning, role limitations due to physical health problems (role-physical), bodily pain, and general health. The MCS includes scales to measure vitality, social functioning, role limitations due to personal or emotional problems (role- emotional), and mental health. Validity studies suggest an advantage of the PCS and the MCS over individual scales when interpreting health outcomes. (20) At each testing session of our study, subjects were given the SF-36 before doing the 6MWT. Test scores were normalized according to the instructions provided in the SF-36 user manual. (20)