According to a post-mortem examination, she died of high-altitude pulmonary oedema (HAPE), resulting in cardiorespiratory arrest, Senior Constable Keith Stevens told the court.
HAPE is a form of fluid accumulation in the lungs which can occur in otherwise healthy people at high altitudes and is life-threatening. It is also known as acute mountain sickness, or AMS.
At the inquest this morning, trip organiser and marketer John Dobbs said he had noted the trip itinerary - which he did not personally plan - spent more time than usual at high altitudes and crossing high passes than previous treks had.
"This combination placed participants at higher possible risks and for longer."
He raised concerns with trip leader Joe Nawalaniec but said "Joe was confident".
"I relented and permitted the trip to go ahead as planned."
The club hired trekking company Hayan Himalaya as expert guides for the trip, having used the company in the past and had an "excellent" experience with them.
Dobbs said if dangers or health issues were to arise during a trek, the guide company was in charge of making decisions around how to respond to those issues.
He noted the trip leader was an unpaid volunteer position, while the guide was an expert, fully paid position.
Edward Cox, lawyer for Nye's husband Robert Joiner, asked Dobbs what consideration was given to what would happen if someone developed HAPE on the trek.
Dobbs said he did not specifically consider that, but knew it was a "critical move" to reduce altitude if someone was suffering from the condition.
Cox questioned whether Dobbs had applied his knowledge of the condition to the trek route.
"Did you look at the route of the second trek, note the high passes that would need to be walked over, and how between some of them there appeared to be no option for going down without having to ascend again first?"
Dobbs said he didn't "personally dissect the route".
Witness Debbie Hogan was on the trek, and described watching Nye's health deteriorate throughout the tramp.
She said she raised concerns about Nye's health with Nawalaniec multiple times, but he assured her Nye was simply not fit enough for the trip and had previously been a smoker.
Hogan noted there had been some issues during the tramps the group did where they ascended higher and faster than they should have for an acclimatisation tramp.
On the day Nye died, her lungs were making a "crinkly" sound when she breathed, and she couldn't walk to the toilet tent at the campsite without stopping and sitting in a chair every 20m.
"Joe came up and I said Jan was very sick and needed to get off the mountain immediately," she said.
She asked if there was more oxygen for Nye, but when the guides pulled out an oxygen cylinder they discovered it had not been closed properly and all the oxygen had leaked out.
"Our only hope was to get Jan down to a lower altitude as soon as possible."
Nye was put on a horse for the descent, but eventually fell unconscious.
Members of the group performed CPR for about five or six hours, but could not save her. Two army helicopters arrived from a nearby village to evacuate her, but did not have medical equipment on board.
Nawanalaniec said he disputed Hogan's evidence, and that he never said Jan was "fine" on earlier tramp days.
He labelled Hogan's comments as "fiction".
He repeatedly asked Hogan why she hadn't done more or told Nye she needed to leave the tramp earlier. Hogan said it was not in her authority to do so, but that she had raised concerns about Nye's health on multiple occasions.
The inquest is expected to take three days.
