If a student lying on his back cannot swallow because his neck creates an arch large enough for a Smart Car to drive through, he needs a block, bolster, folded blanket or some combination of the three under his head to avoid hyperextension of the cervical spine. Adding height to the thoracic spine with balls or rollers while the head is unsupported and the neck is hyperextended will affect blood, lymph and electrical flow and may sprain anterior ligaments that normally serve to stabilize cervical vertebrae. The anterior portion of the neck is a crowded house of major arteries, veins, organs and nerves (including the vagus) as well as the trachea. If along with hyperextension, the sternocleidomastoids (“SCM”) are contracted or passively shortened, it has implications for the jugular veins, carotid arteries, and vertebral arteries (that are the main blood supply for the brain stem) – all of which lie behind the SCMs. Additionally, in a body that is upright and at rest, the internal jugular veins are kept almost empty by gravity. These veins fill up when we lie down. So a normally crowded house becomes more like a pressure cooker when the cervical spine pushes into the front of the throat.
With respect to improving lymph function, YTU Therapy Balls are most effective at removing adhesions around the muscles and improving blood flow. Because the lymph system does not have its own pump like the cardiovascular system, the current scientific view is that lymph flow relies on changes in pressure supplied by the surrounding tissue – particularly muscular activity. Massage techniques that change the pressure mechanics around lymph vessels influence lymph flow. But there is a goldilocks effect with respect to lymph circulation: “Any factor that increases the interstitial tissue pressure by 2 mm Hg tends to increase lymph flow in lymphatic vessels. Conversely, if the interstitial tissue pressure is greater than 2 mm Hg above atmospheric pressure, then lymph flow may decrease as a result of compression of the lymphatic vessels …. To achieve a continuous local lymph output, external intermittent compression of the lymphatics is essential from: (i) contraction of muscles; (ii) movement of body parts; (iii) arterial pulsations; and (iv) compression of the tissues by forces outside the body.”
 Disorders of the lymph circulation: their relevance to anaesthesia and intensive care. A. Mallick and A. R. Bodenham, Br J Anaesth 2003; 91: 265–72.