Spirometry measures the volume and rate of air flow in your larger airways and your results are within the range of predicted "
normalNormal saline flush values".
Peak flows should be compared, not to predicted
normalNormal saline flush values, but to your personal best peak flow, that is your peak flow when your asthma is optimally controlled. You could, as suggested by your doctor, have small airway obstruction with air-trapping and a
transientTransient ischemic attack
Transient ischemic attack (tia) increase in lung volume; this could increase your work of breathing but without much change in the spirometric values. An alternative explanation would be that, when your asthma is very well controlled, your spirometric values would be better than those listed and this is consistent with the small reduction in peak flow.
It would be appropriate for you and your doctor to step-up your asthma therapy for a few days to see if your symptoms and your spirometric values improve.