How accurate do you think this method of measuring capacity is. I took a 2 gallon jug and filled it with water. then i turned it upside down in a sink full of water. inserted a small air line (from an aquarium pump, my other hobby) I inhaled, packed, then blew into the jug and then reverse packed. I marked the level of the water then emptied the jug and used a measuring cup to fill the jug with water back up to the line. The volume i came up with was the ammount of water poured into the jug to fill it to the line (which is the area that was full of air). about 4.5 liters. i did same with out packing, but i dont remember what i got. at the time i could only pack about 6 times.
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measuring lung capacity question
- Thread starterTNdiver
- Start date
Thread Status: Hello
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I'm no guru on this subject, but my advice would be to repeat the experiment at least three times. If you are getting a lot of variation between those three runs then you may want to do 5 or more runs and take an average.
Otherwise, it seems like a great, simple way to set a baseline to compare any changes in lung volume with. I'm not sure that it would give you an actual lung volume though.
Otherwise, it seems like a great, simple way to set a baseline to compare any changes in lung volume with. I'm not sure that it would give you an actual lung volume though.
I've done similar measurements with a bucket. I put water in in 0.5 increments and drew a "scale" on the side of the bucket with a marker - so you don't have to do the measuring with a cup every time.
Of course it won't be 100% accurate. You have to take into account for exampe the weight of the bucket etc etc. When I do the measure I try to support it very gently so that I don't lift it, but also that the weight is not bearing down on it and let it raise. I then see the point where the waterlevel reaches (how far up does it raise).
If you do it a couple of times and learn to do it the same way ever time - it's within +- 1 litre of my spirometer results.
It's not that useful for approximating your absolute VC, but it can demonsrate pretty well the difference between 2 persons or between normal inhale and packing. My "packing difference" result with the bucket and a spirometer was very close, within a few dl (and even that difference can be in my lungs, not the equipment).
Of course it won't be 100% accurate. You have to take into account for exampe the weight of the bucket etc etc. When I do the measure I try to support it very gently so that I don't lift it, but also that the weight is not bearing down on it and let it raise. I then see the point where the waterlevel reaches (how far up does it raise).
If you do it a couple of times and learn to do it the same way ever time - it's within +- 1 litre of my spirometer results.
It's not that useful for approximating your absolute VC, but it can demonsrate pretty well the difference between 2 persons or between normal inhale and packing. My "packing difference" result with the bucket and a spirometer was very close, within a few dl (and even that difference can be in my lungs, not the equipment).
Find a well sealed plastic bag. Empty it completely. Blow into it. Seal it off with captured air. Place bag in a bucket of water with one of the following characteristics:
1. Partially empty, but enough to sink the bag in. Uniform bucket diameter from top to bottom. Mark the beginning level of the water. Mark the level the water rises. Calculate the volume based on "pi multiplied by square of the bucket radius multiplied by the water change height". You can place predetermined measurements on the bucket.
2. Completely full container, exactly to the brim. Container does not require any uniformity except all around it's surface edges, must be a gutter to direct overflowing water to a single external container. Place the bag in the water-filled container. Water overflows into gutter and drains into external container. Measure water using measuring cup or any other means.
1. Partially empty, but enough to sink the bag in. Uniform bucket diameter from top to bottom. Mark the beginning level of the water. Mark the level the water rises. Calculate the volume based on "pi multiplied by square of the bucket radius multiplied by the water change height". You can place predetermined measurements on the bucket.
2. Completely full container, exactly to the brim. Container does not require any uniformity except all around it's surface edges, must be a gutter to direct overflowing water to a single external container. Place the bag in the water-filled container. Water overflows into gutter and drains into external container. Measure water using measuring cup or any other means.
by forcing the bag under water aren't we incresing the presure and decreasing the volume. Also the water temp can change the air volume or am i being too picky?
thanks for the tips
Fernando
thanks for the tips
Fernando
Marginatus, good point. I had thought about it for the latter example and assumed it to be negligible for the following reasons:
- as the bag exerts pressure on the water surface any significant pressure will cause the water to overflow the container.
- the bag will flatten out before it submerges therefore the volume of water spilled over the edges will be before any significant compression of the air.
For both examples, consider that at a depth of -0.33m (-1.08 feet) a 1 litre volume is decreased by 32mL (0.032 litres). So, if you managed to get the bag completely submerged to 1.08 feet deep, for a 10L lung capacity that would have an error value of 320mL. Chances are you would submerge the bag in between 1 foot and the surface, which means the error is likely to be half.
- as the bag exerts pressure on the water surface any significant pressure will cause the water to overflow the container.
- the bag will flatten out before it submerges therefore the volume of water spilled over the edges will be before any significant compression of the air.
For both examples, consider that at a depth of -0.33m (-1.08 feet) a 1 litre volume is decreased by 32mL (0.032 litres). So, if you managed to get the bag completely submerged to 1.08 feet deep, for a 10L lung capacity that would have an error value of 320mL. Chances are you would submerge the bag in between 1 foot and the surface, which means the error is likely to be half.
You're right the error is minimal. When i was refering pressure i was not thinking of the presure caused by the water colum but in the pressure the we make with our hand against the water surface, compressing the air... but it's still a small error. Sorry for my bad spelling
Fernando
Fernando