BP monitors for home use

This study was a cross-sectional survey of adult patients seen in practices within the North Carolina Family Medicine Research Network. The 24 practices in the network were selected to represent the geographic regions and ethnic diversity of the state of North Carolina. Through this practice based research network (PBRN), a cohort of patients was developed for the purpose of facilitating research on health care problems commonly addressed in primary care settings . A complete description of the network's scope and design is presented elsewhere .

For initial enrollment in the PBRN cohort, all patients 18 years and older who presented for a scheduled office visit during a four-week period were approached for participation. Of those, 64% agreed to participate . Subjects who agreed to participate were given a four-page enrollment questionnaire containing standardized questions on self-reported chronic conditions and health habits as well as demographic items. Subjects were asked if they were willing to be contacted for future studies, and 82% granted such permission . The current study surveyed a sample of those individuals who completed the enrollment survey. This study was approved by the Biomedical Institutional Review Board of the University of North Carolina at Chapel Hill School of Medicine.

Sample

In the updated year 2004 to 2005 cohort (n = 2720) of patients enrolled in the PBRN, 1088 patients indicated on their enrollment questionnaire that they had high BP. From these 1088 potential subjects we drew a computer-generated random sample of 700 individuals stratified by race (446 whites and 254 Blacks).

Survey Instrument and Variables

The primary intent of the BP monitoring questionnaire was to examine the use of home blood pressure monitoring (HBPM) by hypertensive patients (results published previously [, ]); therefore our sample size was based on this outcome. We anticipated a 60% response rate, or 420 returned questionnaires, which would allow precision of within 5%, assuming the proportion that used HBPM was 10%. After an initial drafting and revisions of the questionnaire, the final product was guided by a focus group in which clinic nurses and medical assistants were queried regarding their perceptions of patients' performance of out-of-office BP monitoring gleaned from their interactions with patients. The questions were also assessed for clarity and readability during this focus group.

In addition to estimating patients' use of HBPM, we also wanted to explore patients' use of other methods of out-of-office monitoring. Therefore, we also included the partially open-ended question, "Is there a place you go other than your doctor's office to check your blood pressure?" Those who responded "Yes" indicated whether they went to a pharmacy (including those located within a larger retail store), fitness/community center, or other location (with write-in option). Write-in options were re-categorized into one of the designated categories as appropriate, and we created the additional category of "other medical facility" based on several responses. Remaining options were categorized as "other." Respondents could also indicate whether they had a friend or relative check their BP, and respondents could choose more than one option.

For incorporating independent variables of interest, the questionnaire data were linked to the variables already maintained on respondents (e.g., demographics, other health conditions and behaviors). Cardiovascular conditions and health behaviors were based on respondents' previous answers to items on the enrollment questionnaire. For example, the presence of heart disease was based on the respondent's answer to the item: "Please indicate whether or not you have had any of these problems within the past ten years." This was followed by a list of items with the option to indicate "Yes" or "No" for each condition. "Heart disease" was one of the items listed, as was "diabetes" and "stroke or mini-stroke." Smoking status was based on answer (Yes/No) to the question, "Do you smoke at least one cigarette per day?" Age, self-reported health status, and education level were each divided into three categories. Body mass index (BMI) was computed based on self-reported height and weight and divided into three categories.

Survey Administration and Data Management

The survey was mailed with a cover letter and postage-paid return envelope to the 700 potential respondents using the most recent address in the PBRN database. As a small token of appreciation, a $1 bill was attached to the questionnaire. A reminder/thank-you postcard was mailed to all 700 potential respondents one week later. A second questionnaire was mailed to nonrespondents three weeks later. Six weeks after the second mailing, attempts were made to contact remaining non-respondents by telephone. Those contacted were offered completion of the questionnaire via telephone or a third mailing. Upon receipt of completed surveys, the data were double-entered into a Microsoft Access database. Once all survey data were entered, the data were imported into standard statistical software, compared for accuracy, checked for logical errors, and cleaned and compiled.

Analysis

After performing a series of exploratory analyses to insure the integrity of the data, we determined percentages of respondents within categories of the independent variables. We then determined proportion of respondents who reported using monitors stationed in pharmacies (including pharmacies within larger retail stores), fitness/community centers, other medical facilities, and other locations. We determined the proportion who indicated that they had a friend or relative check their BP. We examined bivariate associations of the independent variables with reports of using a pharmacy-stationed monitor and tested for significance using Pearson chi-square. Lastly, we examined the independent effects of these associations by fitting a multivariable logistic regression model. All analyses were performed using Stata 8.1 statistical software (StataCorp, College Station, TX).