Pope John Paul’s age and the debilitating effect of Parkinson’s disease are the main factors influencing his health and make him more vulnerable to infections and breathing problems, medical experts said.

The frail 84-year-old Pontiff was said to be in stable condition Wednesday after being rushed to hospital in Rome the previous night with breathing problems following a bout of influenza.

He is expected to remain in hospital for a few more days.

“It is (due) to a combination of his age, his general frailty and the quite severe Parkinson’s that he has,” said Duncan Forsyth, a geriatrician and Parkinson’s expert at Addenbrooke’s Hospital in Cambridge, England.

“Advancing age brings with it increased risk of infection and with any illness, older people take longer to recover and the risks are greater.”

Parkinson’s disease, a neurological illness that affects the control of muscles including those in the throat and chest, compromises the Pope’s health further. Many Parkinson’s patients have difficulty at some point swallowing and breathing.

“It is seen in a sizeable minority of elderly people, particularly those with Parkinson’s disease,” Forsyth said.

The Vatican said the Pope had suffered an acute attack of laryngospasm causing a blockage of air to the lungs.

“It is likely that a bit of phlegm or something of that sort got into his larynx and triggered a closure of the vocal cords. When that happens, especially feeble people may collapse and faint. Then their muscles would open and they would start breathing again,” said Michael Bridger, an ear, nose and throat specialist at Derriford Hospital in Plymouth, southern England.

Bridger treats about six people a year with laryngospasm. He added that it was a symptom, not an illness or a disease. “We don’t actually know exactly what is wrong with him,” he said. “The thing which is threatening for him is the underlying infection for which he has been taken into hospital.”

If the Pope’s larynx has been affected by an infection in his chest then he would have difficulty breathing all the time.

Many elderly people do not have the physical and immunological resources to battle colds, influenza and infections.

“When you are old and enfeebled your muscles don’t work very well, you can’t cough and you are at risk of pneumonia. When old people slide away through pneumonia it is something referred to as ‘the old man’s friend’,” Bridger said.

Once renowned for his physical fitness, the Pope is now unable to walk and has difficulty delivering his speeches.

“He is an extremely frail 84,” said Forsyth.