Resting Energy Expenditure and the GEM Ventilated Hood Indirect Calorimeter
I was woken up at half eight the next morning by the very lovely technician* who did my step test and heart monitor the previous day. She was dragging a large piece of equipment into my room, where it was placed next to my bed; it was time for my resting energy expenditure to be monitored. This has to be done first thing in the morning for maximum accuracy, which is why they kept me in hospital overnight.
There's a tricky balance to be met with regards to this test; on the one hand, you have to be awake for the whole thing, but equally you're not supposed to get out of bed - or even move, as far as possible. For a sleepy creature like me, this makes it pretty hard to stay awake, but fortunately the whole experience was so surreal that I didn't want to let myself drift off.
Firstly, the equipment is switched on, set up, and left to monitor the room for ten minutes. Essentially, your metabolism is monitored by measuring the amount of carbon dioxide you breathe out. These measurements are then used to calculate your respiratory quotient. The technician explained it to me like this: when you're asleep, you usually breathe out a lower level of carbon dioxide, indicating that your body is metabolising your fat stores to produce energy (RQ = <0.7). When you're out and about, you'll be breathing out a higher level of carbon dioxide, indicating that you're metabolising carbohydrates (RQ= >0.7). I have a pituitary tumour which is messing with my hormones so they want to know what the heck my metabolism is actually doing. Or something.
Anyway - in order to make sure that the readings they take of the air you breathe out is accurate, the composition of the air in the room you're in has to be measured before and after the test. So I lay in bed for ten minutes, listening to it whirring happily next to me.
And then the technician returned with the rest of the equipment.
I am genuinely unspeakably ensorrowed by the fact that I didn't get a picture of me in it, but unfortunately it was early in the morning, my brain was still in first gear, and I wasn't actually allowed to move. So you'll have to use your imagination. Essentially, the rest of the equipment (the "ventilated hood") is a large goldfish bowl with a cape hanging off it, a small hole at the top, and a large pipe or two running out of it. Imagine a giant plastic medical jellyfish and you'll be on the right track.
I did find a picture of the machine all bundled up, but it doesn't look as amusing as it did once it was set up:
GEM (Gas Exchange Measurement) ventilated hood indirect calorimeter. Snappy name, right? The GEM Nutrition website describes it as "an open circuit indirect calorimeter designed for nutritionists needing to measure energy balance and substrate turnover. The compact bedside unit measures gas exchange volumes, respiratory quotient and energy expenditure."
So now you know.
This strange contraption was connected up to the machine, and then placed over my head, at which point I understood why the nurses had double-and-triple checked with me whether or not I had claustrophobia the previous day. Then, safely ensconced in my plastic bubble, the cape was draped around me, and after checking that I wasn't freaking out and providing me with a call button, I was left.
I can't actually remember whether it was for twenty minutes or half an hour, but it didn't feel like very long. I could hear my breathing inside the big clear plastic helmet, which made me feel like a very lazy astronaut. Every now and again someone popped their head around the door to make sure I was ok, but it actually felt quite relaxing. The lights were still off in the room and it was all very chilled. I tried to keep my resting energy expenditure normal.
At some point later, I was freed from my goldfish bowl prison, and the GEM calorimeter sat burbling away in the corner for another ten minutes, measuring the room's air again.
The machine comes complete with a program which shows you the results immediately, along with little graphs showing the levels of carbon dioxide you were breathing out vs. the oxygen you were breathing in, etc. This would have been pretty awesome if I had had any clue what the results meant, but sadly they have to play with them further before they can draw any actual conclusions.
My Experience of the GEM Ventilated Hood Indirect Calorimeter:
Hassle: 1/5 (all I had to do was wake up and keep breathing, which I've managed to do every day of my life so far)
Total score: 12/20
*I don't know what her official job title is, so I'm going with "technician" but I could well be extremely wrong; I just know she was neither a doctor nor a nurse.