| George 2004-11-06, 2:08 am |
| A possible cause for valve incompetence.
The idea is that during valsalva maneuver, which many of us are
performing some times even unconsciously some more often than others
and some more intensely than others, the intra abdominal pressure
(IAP) may increase to values up to 340 mm/Hg.
"To my knowledge, it has not been demonstrated that sneezing or
coughing leads to a higher IAP than a valsalva maneuver. Instead, the
highest IAP values have been found during valsalva maneuvers (Harman
et al. 1988: 277 mm Hg; McGill and Sharratt 1990: 340 mm Hg). A
valsalva maneuver is the voluntary pressurization of the abdominal
cavity, with a closed glottis (to keep the intrathoracic pressure
high, and therefore to support the diaphragm), and a contraction of
all muscles contributing to IAP: diaphragm, transversus abdominis,
partly the obliques, and the pelvic floor musculature. So why should a
valsalva maneuver ("sustained"??) has a different effect than
sneezing/coughing?"
from
http://isb.ri.ccf.org/biomch-l/arch...9-04/00036.html
The interesting thing is that according to some articles on the net,
arterial blood pressure may increase to similar values.
"The Valsalva maneuver or holding the breath while performing an
exercise can increase blood pressure to extremely high and dangerous
levels. Blood pressures of nearly 400/350 have been recorded during
such actions. Existing aneurisms can burst, blood vessels in the eye
can rupture and even retinas can tear (Valsalva Retinopathy). This is
a common and dangerous practice. It is also the job of the trainer or
spotter to recognize when the breath is being held and bring it to the
exerciser's attention immediately."
from
http://www.siliconcentral.info/sc309.htm
(last paragraph)
That would also explain why intra cranial pressure durring sneezing
increases to values up to 50 mm/Hg.
"Intracranial pressure is not a constant value but is variable. It can
increases sharply with coughing and sneezing, up to 50 or 60 mm/Hg to
settle down to normal values in a short time."
from
http://www.health.adelaide.edu.au/p...o/pressure.html
Using simple logic, one can assume that the venous pressure may
increase to similar values (340 mm/Hg), since simple hydraulics tell
us that the extra arterial pressure during valsalva is created by the
same intra abdominal pressure squeezing both the central arteries and
veins, and that would be the reason that valves will fail along the
veins starting with the ones close to abdomen/thorax and not
surrounded by muscles (saphenous, jugular, etc.)
I am wandering if anyone has ever dynamically measured the venous
pressure before the jugular valve during valsalva and in general.
No need to mention in this hypothesis what happens to someone if has
jugular valve incompetence and sneezes. (It may be possible that
dynamic increase of the blood pressure in the vein to occur at such
values that will temporarily close the failing valve.)
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