Hello, I'm Dr. Deb.
I recently came online and see that your question about Hugo hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
I can understand your concern for Hugo which, unfortunately, I share. When any dog, especially an older one, develops exercise intolerance (which means they get tired very quickly and may show respiratory issues), then I'm going to be worried. I'd want to know what's going on in the chest cavity in general and more specifically what's going on with the heart in these patients.
Cardiovascular disease is typically the most common cause of the symptoms you're seeing with secondary respiratory issues although there are other possibilities as well such as fluid in the chest or even a mass, unfortunately.
In some cases, abnormalities will be detected on a thorough physical exam (a murmur might be heard, for example, when the heart is ausculted) although they aren't in every case. Whether they are or not, we'll often suggest additional diagnostic procedures such an x-ray or ultrasound.
I would dearly love to tell you that he's just slowing down because of his age (which may be to true to a certain extent) but what you're describing would not be considered part of the normal aging process. It would be prudent to have him evaluated by your vet, if at all possible.
I hope this helps although, again, my profuse apologies for the delayed reply. Deb