questions
By then, however, Sam was signed up for oxygen deliveries every week from Castles in the Air(a company based in Castle Rock, of course), and he never canceled the service. Why would he? Like his hypertension medicine, the oxygen was covered by what he referred to as THE MEDICAL. Sam didn’t really understand THE MEDICAL, but he understood that the oxygen cost him nothing out of pocket. He also discovered that huffing pure oxygen had a way of cheering a body up.

Question 1: Does “Sam was signed up for oxygen deliveries”mean that “Somebody signed Sam up for oxygen deliveries”? In this case “sign up” means “subscribe”?

Question 2: What’s the meaning of “THE MEDICAL”? MEDICAL INSURANCE?

Question

questions
By then, however, Sam was signed up for oxygen deliveries every week from Castles in the Air(a company based in Castle Rock, of course), and he never canceled the service. Why would he? Like his hypertension medicine, the oxygen was covered by what he referred to as THE MEDICAL. Sam didn’t really understand THE MEDICAL, but he understood that the oxygen cost him nothing out of pocket. He also discovered that huffing pure oxygen had a way of cheering a body up.

Question 1: Does “Sam was signed up for oxygen deliveries”mean that “Somebody signed Sam up for oxygen deliveries”? In this case “sign up” means “subscribe”?

Question 2: What’s the meaning of “THE MEDICAL”? MEDICAL INSURANCE?

Answer

1. Yes. Maybe "arranged for" or "set up" is better than "subscribed." 
The somebody could be Sam or someone else.

2. Yes. Medical insurance.

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