What Is mmHg vs. SKU?  Blood Pressure Cuffs vs. KAATSU Air Bands?

What Is mmHg vs. SKU? Blood Pressure Cuffs vs. KAATSU Air Bands?

For who? Baby Boomers, retirees, competitive athletes, post-surgical patients
For what? Athletic performance, functional movement, mobility, flexibility, recovery, rehabilitation

All KAATSU equipment uses the measurement of SKU (Standard KAATSU Unit). For the KAATSU Nano, KAATSU 2.0, KAATSU C3 models, the KAATSU scale ranges from 0 SKU to 400 SKU. On the KAATSU Master 2.0, the KAATSU scale ranges from 0 SKU to 500 SKU.

Many physicians, physical therapists, chiropractors, coaches, physios, athletes and users ask what is the equivalent unit in millimeters of mercury (mmHg) pressure of 1 SKU? It is among the most common questions asked about KAATSU the Original BFR.

The easy answer is 1 SKU = 1 mmHg.

But the correct answer is SKU and mmHg are completely different scales and measure completely different things in the body.

In medicine, pressure is measured in millimetres of mercury. Blood pressure is measured with a sphygmomanometer. Blood pressure is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, blood pressure refers to the pressure in the large arteries.

Blood pressure is usually expressed in terms of the systolic pressure (maximum pressure during one heartbeat) over diastolic pressure (minimum pressure between two heartbeats) in the cardiac cycle. It is measured in millimeters of mercury (mmHg) above the surrounding atmospheric pressure.

Blood pressure, respiratory rate, heart rate, oxygen saturation, and body temperature are used in evaluate a patient’s health. Normal resting blood pressure in an adult is denoted as 120/80 mmHg with 127/79 mmHg as the average for men and 122/77 mmHg as the average for women.

Traditionally, blood pressure was measured non-invasively using a mercury-tube sphygmomanometer [see above].

The photo below shows a standard blood pressure cuff on the right arm and a KAATSU Air Band on the left arm.

SKU as measured by KAATSU equipment is much different.

SKU measures the compression against the air bladder that is located inside the pneumatic KAATSU Air Bands. So, simply compared, blood pressure in mmHg is the pressure of blood against the walls of the blood vessels, but SKU with KAATSU equipment is a measure within an external non-body part (i.e., the air bladder).

mmHg is an internal measure taken at full occlusion of arterial flow. In contrast, SKU is an measure of pressure taken at homeostasis of an external non-body part (i.e., the air bladder).

Those are two completely different measurements. Therefore, in reality, 1 SKU ≠ 1 mmHg and 120 SKU ≠ 120 mmHg when compared side-by-side.

The effects of SKU in a KAATSU Air Band and mmHg in a blood pressure cuff (or tourniquet) on the human body are also vastly different.

Orthopedic surgeons generally practice fixed inflation pressures (typically 250 mmHg for the upper arm and 300 mmHg for thigh) or fixed amount of pressure above systolic arterial pressure (typically +100 mmHg for upper arm and 100–150 mmHg for thigh). At these pressures (e.g., 250 mmHg for the arm), there is full occlusion. That is, arterial blood flow is stopped from the torso to the arm so the surgeon can properly and safely perform surgery. The reason why 250 mmHg creates full occlusion is due to the structure of the blood pressure cuff or tourniquet.

The surgerical tourniquets used are stiff, wide, inflexible and purposefully engineered to occlude – or stop – arterial blood flow from the torso to the arm or leg. So a 250 mmHg pressure on such a tourniquet is what surgeons generally use.

In contrast, a pressure of 250 SKU with KAATSU equipment is the pressure WITHIN the KAATSU air bladder. 250 SKU completely enables arterial blood flow to continue unimpeded into the air or leg. This is easily demonstrated by a pulse oximeter.

So 250 mmHg with a blood pressure cuff ≠ 250 SKU with KAATSU Air Bands. In the former case, blood flow stops temporarily; in the latter case, blood flow continues unimpeded.

Furthermore, the width of standard blood pressure cuffs and the narrow KAATSU Air Bands apply completely different pressures on the veins and arteries of the arms and legs. In the case of a standard blood pressure cuff, the stiff, wide, inflexible material and structure of the cuff effectively cuts off blood flow when inflated. In contrast with the KAATSU Air Bands, the flexible, stretchable and narrow bands enables venous flow and arterial flow to continue gently and repeatable in order to achieve the optimal KAATSU effects.

Many scientific researchers, physicians, coaches, and users interchangeably refer to KAATSU as BFR and BFR as KAATSU.

In fact, KAATSU is the original BFR. KAATSU was the original BFR because the editors of the first peer-review published studies in the 1990’s did not recognize or accept the Japanese word ‘KAATSU’. The scientific and medical community in the 1990’s did not know what ‘KAATSU’ meant or what the protocols were. So the editors required that the word ‘KAATSU’ was substituted by ‘blood flow restriction’ or BFR.

The key definitions used in the BFR and KAATSU community include the following:

Restriction (noun): something that restricts, an act of restricting, the condition of being restricted from the Merriam-Webster online dictionary

Occlusion (noun): the act of occluding (or close up or block off or obstruct) from the Merriam-Webster online dictionary

Patent: open, unobstructed, affording free passage from MedicineNet

KAATSU (or 加圧 in Japanese): translated as additional pressure in English.

Blood Flow Restriction (or BFR): a training strategy that involves the use of blood pressure cuffs, tourniquets or occlusion wraps placed proximally around a limb that maintains some arterial inflow while occluding venous return during exercise or rehabilitation. KAATSU was original defined as such.

The Doppler ultrasound images above [300 SKU in the upper photo and 200 SKU in the lower photo] show the arm’s artery and vein of a male using KAATSU Air Bands at different pressures. The ultrasound shows that the blood flow from the torso to the arm (arterial flow in the artery) and the blood flow back from the arm to the torso (venous flow in the vein) remain open and not occluded or restricted.

How is the pressure in BFR and KAATSU determined by BFR users and KAATSU Specialists?

BFR is commonly started by occluding the brachial systolic blood pressure in the arms or the femoral systolic blood pressure in the legs [known as ‘Limb Occlusion Pressure’ or LOP]. Once this pressure is measured in mmHg, then the BFR bands are set at a certain percentage of that pressure measured in mmHG [50-80%]. In other words, BFR starts by occluding the arterial flow from the torso to the limbs – and then proceeding with exercise or rehabilitation at a lower pressure.

Some BFR advocates, with inexpensive equipment, recommend using the Borg Scale; a simple self-determination of the perceived exertion on a scale of 1 to 10. The ideal tightness for these BFR (or Occlusion) bands is reportedly 7 on the Borg Scale; but, if there is numbness, the BFR advocates recommend loosening the pressure.

In contrast, KAATSU starts at homeostasis or the stable state of equilibrium in the body with complete patent (i.e., open) arteries and veins. From this point, the “KAATSU Cycle” is used to very gradually and precisely increase the pressure until an “optimal pressure” for each person and each limb is reached (note: the pressure on each limb can be different if there is an injury or significant difference in limb strength, range of motion, or girth).

That is, BFR starts at the point of occlusion where there is no arterial blood flow to the limbs – but KAATSU starts at the point of homeostasis where there is complete and open arterial blood flow to the limbs.

Even when the KAATSU Air Bands have significant air pressure inside them, there is no occlusion of arterial or venous flow [see photos above and read here]. The KAATSU Air Bands are specifically designed to allow this condition to occur even at the highest KAATSU pressure possible.

Decades of testing with different materials, elasticities, and widths enabled the KAATSU inventor, Dr. Sato, to develop this innovative design. KAATSU protocols were researched at the University of Tokyo Hospital under the supervision of experienced cardiologists including Doctors Nakajima and Morita.

Also importantly, the structure and composition of the KAATSU Air bands are different than other BFR and Occlusion Bands on the market today.

Most importantly, when the KAATSU Air Bands are inflated, they take on a parabolic shape. This enables a very mild effect on the veins and arteries of the arms and legs. That is the veins and arteries are NOT compressed as they are with standard blood pressure effects. They are only minimally compressed so arterial flow continues unimpeded. This is the reason why there is no occlusion and the effect is an engorgement of blood in the limbs with KAATSU.

BFR or Occlusion bands are engineered to cut off or restrict blood flow – similar to blood pressure cuffs. Their structure and materials are purposefully designed to achieve this objective. The width of the bands apply a pressure that is effective in reducing or restricting arterial flow.

In contrast, the KAATSU Air Bands are specifically engineered to maintain arterial flow, and only slightly modify the venous flow. The width and the center axis of the inflated KAATSU Air Bands are significantly different than BFR or Occlusion Bands or modified tourniquets or cuffs. This means that the pressure transmission region of the KAATSU Air Bands – especially within the limb on the arteries and veins, is significantly less than the larger, wider BFR bands.

Larger pressure transmission region and effects of BFR bands.

Smaller, narrower pressure transmission region of KAATSU Air Bands.

When the optimal pressure in reached with the KAATSU Air Bands, the KAATSU users see a pinkness or a beefy redness in their limbs as the blood fills the capillary vascular space. When the limbs are moved in this state, there is alternating distension and emptying of the venous/capillary vascular space.

The KAATSU Air Bands gradually apply pressure to the veins. This modifies the venous outflow in the limbs. As the pressure increases during the KAATSU Cycle mode, this modification of the venous outflow eventually modifies the arterial inflow. As exercise or movement continues with the KAATSU Air Bands on, the blood flow into the limbs must soon match the (venous) blood flow out of the limbs. Given about 80% of the body’s blood is in the venous system, there is some capacitance for holding extra blood in the limb, and when that capacity is reached, the blood flow in must match the blood flow out of the limb.

Physiologically, exercise becomes unsustainable when light and easy exercises or movement (e.g., KAATSU Walking or unweighted KAATSU limb movements) are conducted with this impeded circulation. The pO2 and pH gradually (or quickly, depending on the KAATSU intensity) drop to critical levels with even mild exercise. Additionally, higher levels of lactate are generated during KAATSU (compared to non-KAATSU exercise). ATP levels drop as the ADP and Pi levels rise, and ATP dependant electrolyte pumps (e.g. Ca++) cannot maintain proper electrolyte gradients. In this state, there are a significant amount of metabolite and hormonal changes and increases that are subsequently realized.

The fact that KAATSU Air Bands do not approach occlusion pressure , nor result in Blood Flow Restriction, was identified by Professor Alyssa Weatherholt of the University of Southern Indiana, Professor William VanWye of Western Kentucky University, and Johnny Owens of Owens Recovery Science (the exclusive distributor of the Delfi Portable Tourniquet System for Blood Flow Restriction equipment). They presented a study called Pressure Needed to Achieve Complete Arterial Occlusion: A Comparison of Two Devices Used for Blood Flow Restriction Training [see above].

The researchers concluded the wider cuff of the Delfi Portable Tourniquet System for Blood Flow Restriction is able to restrict arterial blood flow at significantly lower pressures compared to the narrow cuffs [KAATSU Air Bands] using the KAATSU Master. The key finding of this study is as follows:

“We were unable to achieve complete arterial occlusion in any participant with the KAATSU cuff.”

The KAATSU equipment is designed and is specifically manufactured to avoid arterial occlusion in the limbs. This fact is precisely why KAATSU was originally defined by Dr. Yoshiaki Sato, the KAATSU inventor, and leading Japanese cardiologists at the University of Tokyo Hospital as a Blood Flow Moderation (BFM) device. KAATSU equipment is specifically not a Blood Flow Restriction (BFR) device.

While the vernacular nuance between BFM and BFR may be overlooked by many (venous flow modification versus arterial flow restriction), the modification of venous flow is critical to understanding the safety and goal of KAATSU, as certified KAATSU Specialists understand.

There is no part of the KAATSU protocols which tries to achieve arterial occlusion. This is why KAATSU is not occlusion training, tourniquet training, or O-training,” explains Steven Munatones. “This is why KAATSU equipment does not use blood pressure cuffs or surgical tourniquets that are specifically designed to occlude, or manufactured to restrict arterial flow. Rather, the stretchable KAATSU Air Bands are designed with flexible, elastic air bladders that inflate inwards, towards the limb, at very moderate pressures to minimally modify venous flow.

This pressure is gentle on the body and uniform, because the limb is evenly and safely compressed by a bed of air. This principle and practical engineered solution leads to blood pooling in the limb – not arterial occlusion. This fact was independently determined by researchers and the leading Delfi proponent of BFR.”

Furthermore, the patented KAATSU Cycle allows normal arterial and venous flow every 20 seconds which means it is safe, effective and gentle for people of all ages (including up to 104 years – see here).

In summary:

  1. The purpose of KAATSU equipment and its protocols is a reduction in venous flow via blood flow moderation, a term first coined in the 1990s by Dr. Sato and Doctors Nakajima and Morita, cardiologists at the University of Tokyo Hospital.
  2. The pneumatically controlled KAATSU Air Bands are designed to achieve a reduction in venous flow, and is a very different approach from BFR and widely-promoted use of blood pressure cuffs that are specifically designed to achieve limb occlusion.
  3. When the KAATSU equipment is used, its users agree to follow the specific protocols as defined by its inventor, Dr. Sato. Specifically, KAATSU protocols and equipment are designed not to occlude.
  4. The stretchable, pneumatically controlled KAATSU Air Bands are not (blood pressure) cuffs. A cuff is a term that refers to devices specifically engineered for limb occlusion.
  5. KAATSU Specialists understand the importance of users to know both their Base SKU pressure and their Optimal SKU pressure while using in the KAATSU Cycle and KAATSU Training modes. To refer to KAATSU pressure without reference to both Base SKU and Optimal SKU pressures is misleading.

There is another paper written by Jeremy P. Loenneke, Christopher Fahs, Lindy Rossow, Robert Thiebaud, Kevin T. Mattocks, Takashi Abe, and Michael G. Bemben (Blood flow restriction pressure recommendations: a tale of two cuffs) that addresses this subject from another perspective.

Fourth, proper and safe KAATSU extensively (or exclusively in most cases) utilizes the patented KAATSU Cycle mode. In the KAATSU Cycle mode, there is only 20-30 seconds of pressure applied at a time. The pressure is regularly and intermittently released (turned off) – and, most importantly, the pressure starts off gently and only gradually increases to the user’s optimal pressure levels. This enables the vascular system to become more elastic during the session, enabling a greater vascular capacity to handle higher pressure and increased blood circulation.