What is a decreased ae of the lung base? What is its medical significance?

Abbreviations. And acronyms can cause confusion and I generally avoid them. As such, I don't know what ae means. If you can determine the full meaning of the finding and resubmit your question it may be answerable.
Egophony. I think that what you are asking about is a physical examination technique to detect lung consolidation. I am most familiar with people talking about listening to the lungs with a stethoscope and asking the patient to say "eeeeee". If it sounds like "eeee", the lung is healthy. If it sounds like "aayy", there is consolidation (pneumonia.).