The results of your spirometric testing are consistent with, but not diagnostic of, restrictive lung disease. Such a pattern is uncommon in persons with the clinical diagnosis of asthma, but not rare. It was found in 8% of 1, 020 adults, aged 20 and older in the NHANES III Study, who self-reported physician-diagnosed asthma any time during their life and only half of these were found to have true restrictive disease, on further testing. There have been reports to suggest that small airway inflammation can result in a restrictive pattern in persons with asthma.
The distinction between true restrictive disease and a restrictive pattern not indicative of true restriction can be made, as suggested, with lung volume determination by plethysmography, not helium dilution. It would be appropriate for you to have this test done, and if true restriction is found to have further evaluation for restrictive disease by CT scan. Clearly, one can have restrictive disease superimposed on asthma.
One could not make the diagnosis of asthma, based on these spirometric values. It would be interesting to perform spirometry during one of your attacks and to review your previous spirometries for evidence of reversible airway obstruction.
The fact that your current spirometry is unchanged from that done 3 years ago is actually very good news. This is an indication that you do not have some form of progressive pulmonary disease.
If your FEV1%FVC is >75% that usually indicates an restrictive disease.
The other results indicate and obstructive disease (asthma, which you say you have).
You could have a mixed or combined disease process.