Some physics ATA

[Guest guest]

Freels asked

Dr. ,

How does barometric pressure affect ATA?

If the protocol were 1.5 ATA with a barometric pressure of 30.00,

would the 1.5 ATA need to be changed/adjusted if the barometric

pressure dropped to 28.75?

What if the barometric pressure increased to 31.15?

Is these some sort of formula that can be used to make these

adjustments?

Dear

1ATA is short for one atmosphere absolute, that is the Earth's sea

level air pressure and is standardised in physics as a pressure

which will suppport a column of mercury 760 milimeters high. (about

30 inches) Hence it is called the 'standard atmosphere'. Other

units are pounds per square inch - 1 atmosphere absolute is about

14.7 p.s.i - and kilograms per square centimetre (1 Kg per sq cm) and

Pascals - 1 atmosphere is 1013 hecto Pascals or 101.3 kiloPascals.

The reason for the introduction of the Pascal is to standardise units

in every language of the World - including American in the same way

as Volts and Amperes for electricity. That is named after the

scientists who first described the effect.

So in using a nominal 1.5 ATA for treatment the pressure gauge will

read 0.5 ATA The gauge of course reads zero at the start of

pressurisation However if we start from sea level the pressure varies

with the weather for example barometric pressure AT SEA LEVEL varies

in Scotland from 0.954 to 1.054 ATA. Other than checking a barometer

when beginning treatment there is no way of knowing if the pressure

is 1.5 ATA when the gauge on the chamber reads 0.5 during treatment.

In practice given the large physiological and pathological factors

determining the dose of oxygen reaching the tissues we can ignore

this variation but we need to compensate at altitude.

One inch is equivalent to 25.4 milimetres so a little arithmetic

will allow you to calculate the very small adjustments to compensate

for the barometric changes reported in the USA in inches of mercury.

N.B. It is high time the USA adopted SI units !

So if 30 inches of Hg equals 1 ATA, 1 inch of mercury equals 1

divided by 30 ATA annd therefore 28.75 inches of mercury equals 1

times 28.75 divided by 30. That is 0.95 ATA. For 31.15 inches of

mercury the pressure is 1 times 31.15 divided by 30. That is 1.038

ATA.

Note barometric pressure falls linearly with altitude and on a day

when the pressure is 1 ATA at sea level it will be 0.5 at an altitude

of about 17,500 feet - 15 inches of mercury.

Best wishes

Philip

Wolfson Hyperbaric Medicine Unit

University of Dundee

Ninewells Hospital and Medical School

Dundee DD1 9SY

[Guest guest]

>So if 30 inches of Hg equals 1 ATA, 1 inch of mercury equals 1

>divided by 30 ATA annd therefore 28.75 inches of mercury equals 1

>times 28.75 divided by 30. That is 0.95 ATA. For 31.15 inches of

>mercury the pressure is 1 times 31.15 divided by 30. That is 1.038

>ATA.

>

If HBOT protocol is 1.5 ATA and barometric pressure is 28.75, does that

mean that actual treatment pressure should be 1.55 ATA?

Or if barometric pressure is 31.15, does that mean that mean actual

treatment pressure should be 1.462 ATA to achieve therapy goal of 1.5 ATA?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

" I have sworn upon the altar of God, eternal hostility against every form

of tyranny over the mind of man. " -- Jefferson, probably an early

advocate of Hyperbaric Oxygen Therapy.

----------------------------

Freels

2948 Windfield Circle

Tucker, GA 30084-6714

USA

770/491-6776 (phone and fax)

509/275-1618 (efax, sends fax as email attachment)

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