Laurence Reynolds was 28 when a doctor stood at the foot of his military hospital bed in Karachi and wondered aloud if they had a suitable coffin for him.

The medical officer expecting the worst for the young Kiwi wartime doctor, who was near death with heart toxicity from the high doses of drugs treating his amoebic hepatitis, didn't know who he was dealing with.

"He told himself he wasn't going anywhere", Reynolds' son Roger said this week, after his father died of heart failure on May 17 aged 107.

Family say the centenarian, born on April 1 1915, three weeks before the first Kiwi boot landed on Gallipoli's shores in the infamously ill-fated World War I battle, was New Zealand's oldest man at the time of his death.

The Department of Internal Affairs wasn't able to confirm, but according to the Gerontology Wiki website Reynolds became the oldest living man in New Zealand after 108-year-old Cantabrian Bill Mitchell died in November.

The website doesn't list who is now the country's oldest living man, but 110-year-old Auckland-based Joan Brennan, born in the United Kingdom on March 10 1912, is thought to be our oldest living woman.

The longest-lived male in New Zealand was UK-born Arthur Bates, who died in Hawke's Bay aged 110 years and 86 days in 1992. The longest-lived woman was Florence Finch, also UK-born, who died aged 113 years and 109 days in 2007.

With no New Zealand equivalent initially available, Aucklander Laurence Reynolds joined the Royal Army Medical Corps when World War II began while he was working in London. Photo / Supplied

His father's response to his early brush with death, and a near-drowning soon after, was characteristic of the later coronary care pioneer's "dogged determination to live", said Roger Reynolds, also a doctor.

"He always chose to live, and to live fully. Even in his final days, [one night] he hoisted himself up to a sitting position and I heard him call out, 'I think I need a pacemaker'."

Tackling health problems without fear was another characteristic of their father, said Alison Dyson, the youngest of his four children.

It's a no-no now, but as a practising doctor Reynolds sometimes treated his own conditions, such as high blood pressure, and saw illness as something to be dealt with, rather than dwelt on.

Among his most important work was establishing the first coronary care unit in New Zealand, where important medical trials were undertaken, and setting up the first cardiac rehabilitation unit.

The move came after an epidemic of coronary issues in the 1950s, when decades of the popularity of smoking began to take its toll, on men in particular.

A self-funded 1961 tour of cardiac units in North America and Europe strengthened Reynolds' resolve for a coronary care unit and he wrote to the Auckland Health Board.

The resulting unit opened at Greenlane Hospital six years later.

Laurence Reynolds, centre, with his wife Claire Reynolds, second left, and children, from left, Stephanie Markson, Linda Skala, Alison Dyson and Roger Reynolds. Photo / Supplied

He also pushed for heart attack patients to be out of bed within a week and when able - albeit limited and monitored - exercising, Roger Reynolds said.

"[Before then] it was thought the best way to treat them was to put them to bed for six weeks. They weren't even allowed to feed themselves.

"It was a disaster. They got weak, they got clots in their legs… Dad saw this and advocated for the early mobilisation of heart attack patients."

Sometimes that involved walking with patients in nearby Cornwall Park, sharing the enjoyment of living an active life, which included walking every day until he was 106.

His father would cite an active life and his 75-year marriage to their mum Claire - who died aged 95 in January - when asked the secret to his longevity, Roger Reynolds said.

"First and foremost, he attributed it to his relationship with our mum."

Retiring aged 75 in 1990 after a 24-year career at Greenlane and then 12 years in private practice didn't bring an end to his curiosity, with travel, movies and reading enjoyed until late in life.

Cosmology, string theory and the multiverse were among favourite areas of interest, and he would talk to his grandchildren about modern concerns such as climate change and the environment, Dyson said.

"He wasn't stuck to ideas [even though] he'd grown up in a certain age."

Both his parents lived their lives "looking forward and without regret", although they had many years to reminisce on, Roger Reynolds said.

After graduating in 1938 from Otago Medical School, where fees were £22 (about $2500 in 2022) a term, Reynolds became a ship's doctor to fund his passage to the United Kingdom.

Post-graduate study and stints in London hospitals, including the National Heart Hospital, followed but when World War II began in September 1939 Reynolds immediately enlisted in the Royal Army Medical Corps.

One of Reynolds' - whose full name was Juda Laurence Reynolds - first acts was to refuse a commanding officer's warning not to list his Jewish faith.

If captured, the inclusion of his faith on official documents could've meant being shot, but his father wasn't deterred, Roger Reynolds said.

"That was the strength of his faith."

After time with a field ambulance unit and the Signals headquarters, the young doctor found himself on a ship bound for faraway military hospital posts, including in rural Sudan, Baghdad and remote areas of British-ruled India, now part of Pakistan.

During his service he rose to the rank of Major, and held acting rank of Lieutenant-Colonel for a time.

Laurence Reynolds, right, on Baghdad's Tigris River in about 1943. The Kiwi doctor was posted to the 31st British General Hospital in Baghdad while in the British Army Medical Corps. Photo / Supplied

By the time he returned to New Zealand in 1946, marrying their mum two weeks later, it was with stories of a hospital built from date palms, the lavish banquet one grateful sheikh - and father - put on after Reynolds successfully treated his teenage son, and army engineers building a wooden iron lung from scratch in 24 hours to save the life of a polio-stricken comrade.

The stories were there to be enjoyed, but the real gift of his dad's wartime experience was the exposure it gave him to a world of health and medicine he'd not have seen had he remained in New Zealand.

"What he came back with was a huge experience of treating a wide range of medical conditions, and doing so with the very limited drugs available at the time."