The rain was coming down in torrents and my shoes were not up to the job. Nevertheless, I pressed forward along the soggy blocks. My 91-year-old patient and I had been together for some 20 years — honestly I’d lost count — so this was the least I could do. Fibrotic lungs and a weak heart set in a 4-foot-5 frame of osteoporotic bones would not seem the stuff of stamina, but until recently, she was still making the grueling 20-hour plane trip back to the Philippines every autumn. She had bounced back from several stays in the I.C.U. even well into her 80s.