Pulmonary Test

[Sharon-T]

  I have posted before and had another test done for MG diagnosis.  I was wondering what normal is on a breathing test.
  I had a test where I blew all of the air out of my lungs and then inhaled through a cylinder like tube with a filter on the end of the tube.  I then exhaled all of the air back through the tube.  I had to do this three times?  What is this test called.  I was told that I failed the test and could only exhale 80% of the volume of air.  
  Questions;  What is normal?  Does this mean that my breathing problems are from weak respiratory muscles?  I feel like I am always in a bear hug, and taking a deep breath is hard most of the time.  Is this a test normally done for MG testing?
  Thank you for your response,
  Sharon T.
===========================================================================
All of the tests done for pulmonary testing involve the manouvers you
mention and several aprameters can be taken form a single test so it is
not clear which one of the many possible parameters gave a score of 80%.
Also it is not clear whether your 80% score was 80% of the average normal
range adjusted for your age,sex,and weight.
In order to give a proper interpretation we really need to know the exact mane of the test performed.
A number of pulmonary test are performed to evaluate MG, the tests we use
here are The NIF, negative inspiratory force and Forced Vital Capacity.
When these tests are adjusted for age and size the normal for that individual
is 100%.
People can get by with values considerable below 100% which is a perfect score and
may be modified by other factors such as smoking of lung disease.
The main value in these tests is not so much to make the diagnosis but as a
repeated test to monitor worsening or improvement in repiratory muscle function
over a period of hours to days in order to determine if respiratory support is
required during a myasthenic crisis.