Design
This study was a prospective three-arm single-center study of two types of yoga. It was designed as a matched controlled open clinical trial. BP measurement and other tests were carried out at baseline and after 12 weeks of intervention. There were two intervention groups and one control group. We matched the groups based on SBP since BP was the main outcome.
The design of the intervention in group one (yoga class group) has been successfully used previously in an inpatient care study (in Stockholm) of patients who have had myocardial infarction (unpublished data). We wanted to see if we could demonstrate this favorable effect in a primary care setting. The intervention for group two (yoga at home group) was designed in collaboration with the founder of the Institute for Medical Yoga (IMY) in Stockholm, Sweden.
Thus, we wanted to compare a yoga class approach with another, shorter and simpler yoga program (yoga at home) that would require less time and effort for the patient and the health care center.
Patients and recruitment
Adult patients (age 20–80 years) at Svedala Primary Health Care Center in southern Sweden, diagnosed with hypertension, with BP 120–160/80–100 mmHg when last measured at the health care center (e.g. normal, normal high and grade 1 hypertension levels), were eligible for inclusion in the study. We did not want to select patients with extreme BP values, since these would probably be under medical adjustments.
Exclusion criteria were adjustments regarding hypertension treatment within the 4 weeks prior to the start of the study, expected inability to understand instructions about the yoga exercises, physical or mental incapacity to carry out yoga exercises and language difficulties/interpreter needs. Patients with systolic BP (SBP) ≥180 mmHg and/or diastolic BP (DBP) ≥110 mmHg or SBP <120 mmHg at baseline were also excluded. Our consideration regarding these limits was that it seemed unlikely to have any BP lowering effect on patients with SBP <120 mmHg. However, we often see DBP values <80 mmHg in our hypertensive patients. Regarding the upper limit, >180/110 mmHg, we thought it would be unethical to leave medication unchanged for twelve weeks.
Hence, patients with BP values of 120–179/≤109 mmHg at baseline were eligible for enrollment.
As shown in Figure 1, 1027 patients were identified by the electronic chart search (hypertension diagnosis registered between 1 May 2008 and 31 January 2010). A random sample of 814 medical records (computer-generated randomization list) was reviewed regarding inclusion and exclusion criteria. The 406 eligible patients identified were invited by mail to participate in the study. Two weeks later they were contacted by telephone.
In March 2011, the patients who agreed to participate were invited to the health care center for baseline assessments. They were informed about the study and asked to provide written informed consent. BP was measured using automated devices. The participants completed a questionnaire on quality of life (WHOQOL-BREF [13]) and a health status and lifestyle survey designed for this study.
The participants were sorted numerically based on their SBP. They were then assigned, three at a time, to the three different groups in order to avoid large differences in SBP between the groups. This procedure yielded groups that were matched for SBP and it was performed by an independent statistician. There were no statistically significant differences in BP at baseline between the three groups.
The participants were requested not to change their medication during the study, and any change in medication was registered at follow-up.
After 12 weeks of intervention, all participants were assessed again. The patients who had practiced yoga answered questions about their experiences of the yoga.
Interventions
The yoga practiced in the present study is a form of Kundalini yoga developed at the Institute for Medical Yoga (IMY) [14]. Kundalini yoga is relatively easy to perform compared with other forms of yoga and is suitable for all ages and levels of fitness. In most exercises the yoga movement is combined with powerful deep breathing. A typical Kundalini yoga class incorporates the following six elements: 1) tune-in with mantra, 2) warm-up or breathing exercises, 3) physical exercises or postures and breathing exercises, 4) deep relaxation, 5) meditation, and 6) tune-out with mantra.
Intervention group 1 – yoga class with an instructor
Intervention group 1 (28 persons) was divided into three smaller groups, each consisting of 8–12 participants. Each group met once a week for 60 minutes at the health care center to practice yoga with a yoga instructor. The participants were encouraged to practice yoga for 30 minutes every day at home. In order to support their training at home, they received two instruction CDs (each approximately 50 minutes long) and two manuals. They were also given a yoga calendar in which to record when they did yoga.
The yoga classes comprised various yoga movements and positions, breathing techniques and meditation. The exercises were adapted for those who had trouble sitting on a yoga mat or had other difficulties in carrying out the exercises. The yoga was taught in a room, specially arranged for the purpose, with yoga mats, pillows, blankets and chairs. The entrance was separated from the health care center.
Intervention group 2 – yoga at home
The participants in intervention group 2 (28 persons) were each given a doctor’s appointment (20 minutes) during which they received instructions for two yoga exercises, which they were encouraged to perform at home for a combined total of 15 minutes a day. The doctor was a study physician who was not a trained yoga instructor but was familiar with the yoga exercises and had received basic teacher instruction. The participants received one instruction CD (approximately 20 minutes long), a short manual and a yoga calendar.
The two yoga exercises were: 1) “Left nostril breathing” – deep breaths in and out through the left nostril while sitting or lying down, with the right nostril closed off by the right thumb or an earplug (about 11 minutes); and 2) “Spinal flex” – movement that alternates between flexing the spine forwards (arching) and relaxing the spine back in time with deep breaths while sitting in a chair (about 4 minutes).
In summary, the yoga class group had a more extensive yoga program, with several different exercises (including left nostril breathing and spinal flex). The educational material was provided by IMY [11].
Group 3 – control
No changes were made for the participants in the control group (27 persons) (treatment as usual: treatment with the medication they were already taking and annual medical examination by the general practitioner).
Outcome
The main outcome was BP at the end of the program and change in BP. The secondary outcome was self-rated quality of life.
Measurements
Clinical data
BP measurement was standardized in a sitting position, right arm, two readings (three readings when the first and second readings differed by >5 mmHg) [15], and was carried out by nurses using a validated BP monitor (Omron i-C10). BP was measured after 5–10 minutes of rest. Blood samples were collected at baseline for assessment of the following metabolic biomarkers: HbA1c, fasting plasma glucose and total cholesterol.
Self-reported data
On their yoga calendars, the participants marked with a cross the dates they completed the yoga training. At follow-up, the patients submitted their yoga calendars. The information in the calendars was not controlled or questioned. As described above, the patients were encouraged to practice yoga once a day.
All patients who attended follow-up appointments were included in the analyses (as observed cases, OC). We also made calculations through which patients who did not perform yoga for at least 9/12 weeks or who changed their medication were excluded (per protocol set, PPS). This criterion (9/12 weeks) was set up together with the IMY founder, and it was not known to the patients.
The WHOQOL-BREF is a shorter version of the WHOQOL-100, containing 26 items which measure the following four domains: physical health, psychological health, social relationships and environment. There are also two items that are analyzed separately: overall perception of quality of life and overall perception of health.
The health status and lifestyle survey was designed for this study and is not validated. The survey contained questions regarding comorbidity for diabetes and CVD, smoking and drinking habits and physical activity.
Statistical analysis
Assuming a mean treatment difference in SBP of 5 mmHg between the yoga at home and control groups, a standard deviation of 6 mmHg and a drop-out rate of 30%, 33 patients per group would have 80% power to detect a statistically significant difference at the 5% level using a two-sided test. The assumption about differences in SBP is based on a Swedish literature review [2].
The differences in mean change from baseline between the two yoga groups and the control group were investigated using a linear regression model with baseline BP as a continuous variable and treatment group as a categorical variable (ANCOVA). A corresponding model was used for quality of life (single items and domains). We studied the residuals to ensure that the normality assumption was not violated in a way that could affect the interpretation of the estimates. All tests were two-sided.
We further investigated whether other baseline characteristics (age, sex and BMI) could influence the outcome using the same linear regression model as above and including the baseline characteristic of interest. However, the study was not sufficiently powered to do subgroup analyses or to detect statistically significant differences for other covariates.
Version 9.2 of the SAS System for Windows was used in the statistical analyses.
Ethical aspects
The study conforms to the principles outlined in the Declaration of Helsinki and was approved by the Regional Ethical Review Board in Lund, Sweden (2010/728). The study was registered at ClinicalTrials.gov (NCT01302535).
