Forward fold, plank, upward facing dog, downward facing dog, a sequence we flow through time and time again in a typical vinyasa or ashtanga practice. Instructors often reference this as a way of building heat and some encourage it if you’ve got fire to burn. While this vinyasa sequence no doubt helps to build heat or increase the calories burned during the practice, there’s more to it than that.
The transition from standing to forward fold, then from upward facing dog to downward facing dog shifts blood volume back and forth between the upper (forward fold or downward dog) and lower segments (upward dog) of the body. This is significant because there are pressure sensors (baroreceptors) in the upper body (aorta and carotid arteries) that are constantly regulating blood pressure. When blood volume shifts upward, these sensors are activated and when blood volume is shifted downward or toward the lower body, they're deactivated.
Both activated and deactivated pressure sensors signal the brain to alter nervous system function. When we stand suddenly for instance, blood travels away from these sensors toward the legs. The result of this is an increase sympathetic or “fight or flight” nervous system activation. This releases adrenaline which causes heart rate and blood pressure to increase. When we get into a position that drives blood toward the upper body like downward facing dog, these sensors signal the brain which then responds by increasing parasympathetic activation. This results in a decrease in heart rate and blood pressure though both still remain elevated in the pose because we're also simultaneously contracting our muscles.
Moving through the vinyasa flow sequence is an exercise in moving blood toward and away from these pressure sensors and causing short term changes in the nervous system output. Intermittent bouts of activating and deactivating these pressure sensors has been used therapeutically with implantable devices that electrically stimulate these sensor sites. These devices are used to decrease blood pressure and improve hypertension severity. The connection is that activating and deactivating these pressure sensors makes them more sensitive to changes in pressure resulting in a long term benefit of improving their capacity to maintain blood pressure within a normal, healthy range.
Since having a device implanted into the arteries isn't practical, a recent study found a way of activating and deactivating these pressure sensors by simply having participants lie down and go through 2 weeks of daily “head up, head down tilt” or raising and lowering of the upper body combined with slow breathing. These exercises were done passively while participants lay down on pillows which inflated and deflated. After two weeks of simply raising and lowering their heads, there were significant reductions in blood pressure.
Studies have shown that yoga lowers blood pressure in people with hypertension but researchers haven’t quite pinpointed why. It could be due to reductions in mental stress with yoga as this has also been demonstrated to improve blood pressure, but I believe there are other physiological mechanisms involved and this recent study has shed some light on the topic. Research participants also practiced slow breathing during the head up, head down tilt exercises and that has benefits of its own. We'll discuss that in the next blog.