Roundworm migration and lungworms can both be hard to detect,so sometimes we just deworm with wide sprectum dewormer to see it helps. Heartworms are a problem in our area and we do see some cats coughing due to this parasite. We have not seen this in more than one cat in a household, yet, that I can remember, though. I have a hard time being certain that asthma is present based on X-rays. If your vet is not sure of the diagnosis haveing a radiologist examine the films can be helpful.
Cortisones are the most consistently effective medications for asthma.
There is more and more interest among vets in using the inhalers to deliver cortisones since there is less systemic problem with corticosteroids delivered through inhalers. This might allow effective treatment of the asthma with very little risk of complications such as diabetes or liver damage. It looks like he is choking and disappears after a few moments. I am very worried. The most common causes of coughing in cats are probably asthma, chronic bronchitis and heartworm disease.