Training in heated pool helps to control resistant hypertension

Study shows lasting benefits for systemic arterial pressure reduction.

By Karina Toledo

Agência FAPESP – Physical exercise in heated pools could be a valuable tool for treating patients with persistent hypertension, according to a study conducted at Universidade de São Paulo (USP).

The randomized study investigated 32 volunteers whose arterial pressure remained high despite therapy with three or more types of medication. After 12 weeks, the group that underwent the exercise protocol had not only reached ideal levels of arterial pressure but also showed a reduction in the hormones responsible for vasoconstriction and blood vessel tension.

Specialists note that hypertension is one of the risk factors for several severe illnesses, such as strokes, heart attacks, cardiac insufficiency and kidney disease. It is estimated that this risk is three times greater in treatment resistant cases than in patients with controlled hypertension.

“Resistant hypertension incidence rates in hypertensive populations are high. Between 20% and 50% of patients do not reach their target pressure, even with medication,” explained Guilherme Veiga Guimarães, a researcher at USP’s Medical School and coordinator of the FAPESP-funded study.

According to Guimarães, who coordinates the Heart Institute’s Physical Activity and Health Laboratory (LAtis-Incor), the idea of investigating the effect of exercise in heated pools on persistent hypertension emerged after a previous study conducted on cardiac insufficiency showed several benefits.

“We verified a reduction in cardiac frequency; an increase in the blood volume pumped by the heart per minute; an improvement in cardiac function; and an increase in shear stress [the tension caused by blood flow capable of inducing greater production of nitric oxide, a vasodilatory agent],” he said.

“There was also an increase in atrial natriuretic peptide (a hormone secreted by cardiac muscle cells that is linked to reduction in arterial pressure) and in vasodilators such as cyclic guanosine monophosphate (cGMP), nitrogen dioxide (NO2) and nitrate (NO3). In contrast, there was an inhibition of vasopressin, an antidiuretic hormone that results in greater production of urine by the kidneys and contributes to a drop in blood pressure,” explained the researcher.

When individuals are submersed, added Guimarães, there is suppression of sympathetic nervous activity, which is responsible for increased heartbeat and vasoconstriction. There is also suppression of the renin-angiotensin-aldosterone system, related to vasoconstriction and sodium reabsorption, which favors an increase in arterial pressure.

“We began with the premise that in patients with refractory hypertension, training in heated pools could also cause beneficial neurohormonal, cardiovascular and renal adaptations in the behavior of arterial pressure and the sympathetic nervous system,” said Guimarães.

Vasoconstrictive hormones

The 32 volunteers of both sexes were selected from 125 patients in treatment at USP’s University Hospital. Excluded from the study were people over age 65; carriers of related diseases, such as diabetes or cardiac insufficiency; patients with organ damage (to the heart, kidneys or eyes); patients with orthopedic or dermatological diseases that impeded the use of the swimming pool; and those with persistent hypertension related to another disease, such as kidney failure.

The average age of the selected patients was 55, with a maximum variation of 5 years younger or older. All were medically evaluated prior to the experiment, including a cardiopulmonary stress test; blood sample collection for hormone level measurement; arterial pressure measurements in the doctor’s office; and a method called MAPA (Ambulatory Blood Pressure Monitoring), whereby measurements are conducted every 20 minutes for 24 hours by a monitor attached to the patient’s waist with the objective of registering variations during the sleep-wake cycle.

Half of the volunteers (the control group) did not engage in the 60-minute sessions of physical activity in a heated pool (32°C) three times per week for 12 weeks. However, these volunteers were advised to maintain their routine activities.

“The protocol comprised callisthenic exercises (in which the individual uses the weight of his or her own body as resistance) and walks in the pool. The participants were immersed up to the xiphoid process (equivalent to the entrance of the stomach), promoting a reduction in the vascular tonus and peripheral resistance,” explained Guimarães.

Roughly 772 hours after completing the last exercise session, the volunteers were reevaluated. The control group presented nearly unchanged profiles, as expected, whereas in the exercise group, the ambulatory arterial pressure fell from 165/88 to 129/76 mmHg, which is within the ideal range.

During the stress test, the maximum pressure fell from 198/93 to 175/86 mmHg in the training group. Furthermore, exercise tolerance increased from 9 to 13 minutes on average.

The group’s blood analysis also revealed a significant drop in vasoconstrictive hormones in the training group. Dopamine, for example, rose from 140 µg/ml of blood (µg/ml) to 40 mg/ml. Noradrenaline dropped from 350 µg/ml to 150 µg/ml.

“We performed a reassessment three days after the last exercise session to ensure that the changes were not solely the result of momentary vasodilation caused by the warm water, and we observed that the benefits remained,” explained Guimarães.

According to the researcher, a new reassessment was performed three months after the experiment ended. Although the patients had slightly higher arterial pressure values, rising from 119/71 mmHg to 129/75 mmHg, the values were still within the ideal range.

Part of the study, conducted as a pilot and excluding the control group, was published in the periodical Blood Pressure Monitoring. The complete results will be released in the Journal of Cardiology.

“Now, we are studying patients with real persistent hypertension because in the previous experiment, we included ‘white coat hypertensives,’ or patients who have high blood pressure in emergency rooms but have normal results using MAPA. In this new study, we chose only patients who have uncontrolled arterial pressure in both the emergency room and measured via MAPA,” explained the researcher.