Many athletes intuitively understand how different forms of exercise affect their bodies in unique ways, but they might not understand the reasons why. Researchers from Australia have made a surprising discovery: Simply steeping yourself in a pool of warm water increases blood flow in the brain. “We found that brain blood flow is higher when subjects were immersed in water up to the level of the heart compared to on land — laying the ground work for further investigation of its effects on cerebrovascular health,” said Dr. Howard Carter of University of Western Australia, School of Sport Science, whose new study appears in the American Journal of Physiology.

The team of scientists, led by Carter, hypothesized that water immersion to the level of the right atrium in the heart would increase the delivery of blood within the brain. The right atrium is located on the upper right hand side of the heart and is one of four hollow chambers of the heart. The right atrium receives blood from two large veins: the superior vena cava and the inferior vena cava. The job of both of these veins is to return blood that has provided oxygen to various sites in the body; the returning blood, then, is low in oxygen. The coronary sinus, which is a smaller vein in the wall of the heart, also drains blood into the right atrium.

To investigate their theory of water immersion and its effects on brain activity, the researchers began by enlisting the help of nine, healthy male volunteers. Next, they requested the volunteers stand in an empty tank where they were to remain as still as possible. After a 10-minute period of complete rest, three water pumps began to fill the empty tank with warm water (86 degrees) at a constant rate until it reached the level of the heart’s right atrium.

Then, using a Transcranial Doppler machine, the team of researchers measured cerebral blood flow velocity in each of the volunteers. Ultrasound from the machine recorded the velocity of blood traveling through the cerebral arteries. The researchers also measured changes in arterial carbon dioxide and blood pressure in order to identify the possible cause of change in brain blood flow.

What did the team discover? While the participants were immersed in water, blood flow to their middle cerebral arteries increased by 14 percent while blood flow to their posterior cerebral arteries increased by nine percent.

Carter and his team are now conducting a new six-month study to investigate whether exercise training in water might lead to consistently greater increases in cerebral blood flow compared to exercise on land. They also hope to understand whether water exercises may lead to greater improvements in vascular health and cognitive function. Part of their work should also uncover which exercises are best.  “As with land-based exercise, different types of water-based activities, such as water aerobics and swimming, have slightly different effects on heart function and cerebral blood flow,” said Carter in a press release.


Source: Carter HH, Spence AL, Pugh CJ, Ainslie PN, Naylor LH, Green DJ. Cardiovascular responses to water immersion in humans: Impact on cerebral perfusion. American Journal of Physiology. 2014.