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Truman,

              You are quite right about the real saddle fitting issue is
FORCE. For that reason the Mk I pressure system was called a “Force
Management System”. Now, your focus on tissue physiology is right on the
mark, and we do have some peer review clinical research on mammalian tissue
to better understand the saddle tissue interface.

            Skin and muscle tissue require a constant intermittent flow of
blood to remain healthy.  In strenuous exercise the muscles require
significantly more blood flow to maintain a healthy metabolism. This
exchange of oxygen and waste products occurs in the capillary bed.

          The saddle fitting problems occur when the saddle causes
continuous excessive pressure on the capillaries that exceeds the blood
pressure and structural strength of those vessels and the capillary vessels
collapse. This collapse leads to the deprivation of oxygen and nutrients
brought by fresh blood and the removal of waste products.  CAPILLARY CLOSING
PRESSURE IS THE CRITICAL ISSUE IN PREVENTING SADDLE-RELATED TRAUMA AND
IMPROVING THE PERFORMANCE OF THE HORSE'S MUSCLES UNDER SADDLE.

           The following experiment was made to determine the relationship
of external pressure on blood flow by using a radioactive isotope 133Xe. The
amount of radioactivity was measured as external pressure was applied. One
can observe that as external pressure increases the blood flow reduces. What
is most notable is that pressures as low as .25 P.S.I. or 4 ounces can
reduce flow by as much as 60%.  This is a significant point when related to
saddle fit, especially with a bridging saddle that does significantly
increase pressures.

           Serious saddle fitting problems develop particularly on
"bridging" saddles in a relatively short amount of time because pressures
can easily reach 4 P.S.I or 64 ounces. This excessive pressure not only cuts
off the blood supply but can additionally traumatize the muscle tissue
itself.  In all cases pressure release is followed by reactive hyperemia and
the parts originally starved of arterial blood are instantly flooded with
oxygen. The extent and duration of the blood in flow is proportional to the
needs of the tissues.

            Below is a study performed at University of Georgia on a horse
using a compression bandage. One can observe that the blood flow decreases
significantly with the application of pressure, however, when released the
blood flow increases beyond the original base flow.   This is a clinical
verification of reactive hyperemia and reveals what happens to the tissue
when the saddle is removed i.e. heat bump.

          For a given pressure applied to the surface of the skin
(interface pressure) capillary closure pressure will vary from horse to
horse, as well as location to location on the horse, depending on the amount
of fat, location of adjacent bone, status of the vascular system, systemic
blood pressure and general health of the animal.  As the animal ages its
physiology also changes, compounding this significant Issue.

          A critical discovery in tissue research was that in a given
location, pressure is not even throughout the tissue. Clinical studies have
established that the internal pressure close to bones is three to five times
higher than on the surface This principle is easily demonstrated with a
simple sponge as illustrated above. One can observe that when two different
size areas are pressed towards each other, the smaller area will create
higher pressures. Weight divided by surface area equals interface pressure.

       This is an important issue for horses because the longissimus dorsi
muscle, one of the major muscles used in locomotion, lies adjacent to the
spinal column and is directly affected by saddle pressure. Each vertebrae of
the spinal column has bony prominances with small surfaces that concentrate
points of pressure down the length of the longissimus dorsi muscle.

       It is critically important to understand that muscles are far more
susceptible to the effects of pressure than skin.   The internal damage to
the tissue caused by the surface pressure only becomes obvious at the
surface over an extended time.  Many serious pressure sores first occur
internally adjacent to the bone and then radiate to the surface.

       This fact makes it very difficult to use apparent trauma to the
horse's back as an indicator of saddle fit, because during the time interval
that the horse is not being ridden, the horse begins to heal the internal
trauma. This makes it virtually impossible to develop a cause and effect
relationship between saddle fit using observable external trauma to the
horse as the standard. Therefore, just because we do not see obvious damage
to the skin of the horse does not mean that damage has not occurred
internally.

The most important issue to remember with tissue trauma is that higher
pressures do damage in shorter periods of time, however, even low pressure
for long periods of time can do damage.  This is significant to saddle fit
because the fit of the saddle relates to how much time one can ride before
causing trauma to the horse. Obviously if the saddle fits one can ride the
horse longer without sustaining damage than a saddle the bridges and causes
high pressures.


          Tissues do not need a constant flow of blood, but tissues do need
a CONSTANT INTERMITTENT FLOW OF BLOOD.  This is the reason a healthy
individual does not get bedsores. By tossing and turning in our sleep we
provide our tissues a constant intermittent flow of blood.
It is also important to understand that tissue damage is variable from very
slight damage to extremely debilitating damage. As an example, human
bedsores are graded in Stages I, II, III, IV, from a slightly red skin to an
open sore.  The following is a simple scale of increasing severity of trauma
caused by an ill-fitting saddle:

v Decline in performance
v Discomfort - indicated by attitude change in the horse
v Inhibited Gait - noted by the horse being a little "off"
v Lameness - secondary lameness due to pain or excessive pressure
v Swelling - slight swelling under the saddle panels
v Bruising - significant inflammation indicating capillary damage
v White hair - due to damaged follicles
v Hair loss - obvious trauma to the skin and internal muscles
v Ulcerous condition - an open, oozing wound with swelling

WHAT DO WE "REALLY" KNOW ABOUT PHYSIOLOGY?

         The clinical research on a variety of mammals has established the
following factors to give us a better understanding of the issues relating
to saddle fit.

v Tissue damage is a function of pressure over time.
v Pressure is not distributed evenly throughout tissue.
v Pressure on the surface of the skin increases 3 - 5 X close to bones.
v Muscle is more susceptible to pressure damage than skin.
v Low pressure for long periods of time is more damaging
             than high pressure for short periods of time.

SO WHAT IS GOAL HERE?

IN PRACTICE THE GOAL IS TO ACHIEVE THE MOST EVEN PRESSURE THROUGHOUT THE
SADDLE CONTACT AREA WITH A RIDER MOUNTED AND TO REMOVE THE SADDLE EVERY FEW
HOURS FOR A SHORT PERIOD OF TIME TO PERMIT BLOOD TO FLOW TO THE TISSUES.

OH, MY ACHING BACK

           "Quantifying the degree and precise site of pain in animals
always has been difficult. This is complicated further because the major
clinical sign in many horses with a back problem is impair performance
rather than pain. On the other hand, many horses appear to perform
satisfactorily despite some low-grade back pain. To add to the confusion,
some horses are naturally sensitive and resent being palpated along the
back, which might be wrongly interpreted as a sign of pain."

After decades of equine back research, Dr. Leo Jeffcott, BvetMEd, MA, PhD,
DVSc, FRCVS, Dean of Cambridge University Veterinary Clinic, notes that

    1. Some horses can perform badly without suffering from a back problem
    2. Some horses can perform adequately despite having a back problem
    3. Spontaneous recovery for many types of back problems is quite common

Robert Ferrand
Saddle Researcher

 Husain, Tafazzul, An Experimental Study of Sore Pressure Effects on
Tissues, with Reference to the Bed Sore Problem.,  J. Path. Bact, Vol LXVI,
1953, pg. 354
 Allen, Doug, Blood Flow Restriction caused by bandaging and equine in vivo
study conducted at the University of Georgia, March 1996, Kimberly-Clark
Clinical Study-Flexus 3
 Chow, William, et al, Effects and Characteristics of Cushion Covering
Membranes Kenedi, R.M. and Cowden, J.M.  Bedsore  Biomechanics,  University
Park Press, London, 1975, pg. 96-97
 Husain, Tafazzul, An Experimental Study of Sore Pressure Effects on
Tissues, with Reference to the Bed Sore Problem., J. Path. Bact, Vol LXVI,
1953, pg. 356
 Le, Khanh M., et al, An In-Depth Look at Pressure Sores Using Monolithic
Silicon Pressure Sensors Microvascular Research, Vol 17, 1979, PG 753
 Husain, Tafazzul, An Experimental Study of Sore Pressure Effects on
Tissues, with Reference to the Bed Sore Problem., J. Path. Bact, Vol LXVI,
1953, pg. 356
 Guyton, Arthur C., Acute Control of Local Blood Flow, Textbook of Medical
Physiology, 1986, pg. 349
 Kosiak, Michael, Etiology and Pathology of Ischemic Ulcers, Arch. of
Physical Medicine and Rehabilitation, 1959, pg. 62
 Le, Khanh M., et al, An In-Depth Look at Pressure Sores Using Monolithic
Silicon Pressure Sensors Microvascular Research, Vol 17, 1979, PG 748
 Le, Khanh M., et al, An In-Depth Look at Pressure Sores Using Monolithic
Silicon Pressure Sensors Microvascular Research, Vol 17, 1979, PG 748
 Husain, Tafazzul, An Experimental Study of Sore Pressure Effects on
Tissues, with Reference to the Bed Sore Problem., J. Path. Bact, Vol LXVI,
1953, pg. 355 & Groth, K.E. 1942, Acta Chir Scand.,lxxxvii,suppl 76
 Husain, Tafazzul, An Experimental Study of Sore Pressure Effects on
Tissues, with Reference to the Bed Sore Problem., J. Path. Bact, Vol LXVI,
1953, pg. 356 & Groth, K.E. 1942, Acta Chir Scand.,lxxxvii,suppl 76
 Jeffcott, Leo, The Equine Back, the Essential Horse, May 1998, Pg.1
 Jeffcott, Leo, The Equine Back, the Essential Horse, May 1998, Pg.10

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