Although there are now a handful of outcome studies published each month on the power of the pool, there is certainly not a tsunami of irrefutable evidence showing the unequivocal superiority of aquatic therapy. The patient populations in most aquatic studies are just too small and this affects sizes needed to show statistical significance. That’s the bad news.
The good? Misery loves company and we have a lot of it. Most physical medicine and rehabilitation does not have the weight of irrefutable evidence on its side. Do not allow yourself to believe that in the absence of solid evidence, we are required to sit down, have a good cry, and wait for evidence about the benefit of aquatic therapy to spring from the earth.
The very act of attempting to convert to an evidence-based practice lays down a light through the void, providing a narrow, now-visible path upon which to tread in the future. It prevents us from wasting our time.
So, in that spirit, let’s continue on in our question to understand what benefits aquatics brings to the therapeutic table. To see a fine crop of earlier discussions about the benefit of pool therapy, read also Aquatic Physiotherapy: What Does it Bring to the Therapeutic Table? and Improving a Patient’s Strength and Range of Motion with Aquatic Therapy.
Let’s think about this as researchers do. We believe that placing a patient in vertical immersion in water will result in a haemo-dynamic shift from an area with greater pressure (e.g. the legs) to an area of lesser pressure (e.g. the abdomen and thoracic cavity).
This shift can reduce oedema, lymphoedema, effusion and soft tissue and joint swelling, in both lower and upper extremities.
Pascal’s Law states that:
‘Fluid pressure is exerted equally on all surfaces of an immersed body at rest at a given depth.’ – Pascal (1623 – 1662)
Hydrostatic pressure acts on people while they stand in water, even in the absence of exercise. What does that pressure do? We know that while pressure is symmetric at any given depth, pressure increases as the depth increases, and this difference creates a shift in fluid from the legs upward.
The resulting pressure gradient can be used to create a therapeutic effect similar to the effect sought when wearing compressive garments, such as Jobst stockings or compression boots.
There are several ways to think about it.
There isn’t a massive amount of pressure change within the first 5’ of depth of water. You can not even feel the pressure in your ears until you get closer to 8-9’ down. So, how does this small amount of pressure do anything useful? And exactly how much pressure does the typical patient experience when standing chest deep in water?
To calculate how much more pressure there is underwater than on the surface, take any depth and divide it by 34’.
As an example, look at a 6’ tall man standing in water, immersed to his neck. At 2’ under the surface you will find his abdomen. This region will experience approximately 45 mm more pressure than will his neck.
At 3’ under the surface, you’ll find his pelvis. This region will experience even greater pressure, almost 70 mm.
At 4’ under the surface, the man’s legs are experiencing almost 90 mm of pressure — approximately the same pressure as a normal “at rest” arterial system.
Consider that the pressure in the venous and lymphatic systems is much lower than that found in the arterial system, as low as 1-20mm mercury. Because the external hydrostatic pressure exceeds the internal venous pressure, fluid moves from the area of greater pressure to the area of lesser pressure. The end result is a shift in haemodynamic flow from distal to proximal, or from legs to the chest and abdomen.
It becomes evident that immersion alone creates a dramatic haemodynamic shift from the lower extremities to the trunk. The therapist can compound this effect by tapping into another natural tool in the fight against lower extremity fluid excess — muscle pump — during immersion by exercising.
One researcher stands out “head and shoulders” for exploring issues of oedema control for patients with lymphoedema. As early as 2004, Tidhar examined the application of aquatic lymphatic therapy for the upper extremities. At the time, conventional wisdom stated that immersion would not have any significant affect on the upper extremity due to the lack of pressure gradient experienced with lower limb immersion. Tidhar’s team studied the affect of aqua lymphatic therapy in women post-mastectomy with axillary node dissection and found a significant reduction in oedema with a technique they called Aquatic Lymphatic Drainage.
Tidhar’s 2007 publication “Aqua lymphatic therapy in managing lower extremity lymphoedema” again addresses whether it was possible to make a significant impact on oedema with immersion – this time in the lower extremity.
By 2010, Tidhar was back again. This time he pondered whether Aqua Lymphatic Therapy (ALT) was a safe method for lymphoedema control and whether there are differences in adherence, limb volume, and quality of life between women who perform only self-management treatment and women who participate as well in aquatics. A significant immediate and insignificant long-term effect on limb volume was noted with aquatics.
Other researchers followed and soon the discussion shifted. It was now accepted that immersion could reduce upper extremity oedema, something that took a long time to recognize.
Researchers decided to ask more practical questions. For instance, is it possible to create a specially designed aquatic exercise program especially for oedema management? You should copy the one that already exists.
Researchers tested out the value of their program when they placed 16 patients with chronic lower limb oedema into a program comprised of 5 sessions of physical exercises designed for oedema control. One week after the end of the protocol, the average reduction in lower limb volume was 303.13 ± 69.72 ml and 334.38 ± 62.50 ml in the right and left legs, respectively. Ankle range of motion and feeling of heaviness significantly improved.
These results are a delight to observe.
Such a protocol offers hope for individuals with chronic oedema who have – for so long – been unable to find any treatment with a lasting effect.
And the pool once again shows its power to overcome the limitations we live with on land.