OP
mtdivegirl
Contributor
The skill of clearing a mask was mastered after having my question about it answered...no matter how you look at it a physical ability has nothing to do with mental capacity.
lung expansion???
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landlocked
Contributor
You go girl! Not that she seems to need any help but,...... sorry WreckWriter mtdivegirl is a student and as such is allowed to ask purely academic questions and to argue points. It is in the job description. That is how you do well in school. If I were going to take the responses here to go argue with some academic folks, I too would want to fully explore it. Therefore, the arogance award goes to.... (drum roll please)....... Anyway, ya'all get the point. Mask clearing? Honestly, that was low!:nono:
The Iceni
Medical Moderator
Mtdivingal.
You have every right to ask your questions and I feel some of the responses you have received reflect more badly on the posters than on you. I hope I am not included in that group but you have not answered my question about free divers. I posed the question in the hope that, by working out what happens to them, you could see why - underwater - lung volume and chest volume are not necessarily the same.
In my original post, and I apologise to Dr Deco for once more stealing his thunder, I stated that the diaphragm could only change the intrathoracic pressure +- 0.03 bar around that at the oropharynx and this is why you cannot snorkel below about a foot.
Clearly obstetric patients, when bearing down, when you cough or when you sneeze the intrathoracic pressure is raised considerably by the use of the muscles of the chest wall, the abdomen and the diaphragm working together AGAINST A CLOSED GLOTTIS. The reason you cannot snorkel at depth is because these muscles cannot act against ambient pressure to REDUCE the intrathoracic pressure by more than that amount:-
A deep snorkeller can beath out but he cannot breath in!
All varieties of the Valsalva manoeuvre produce an active increase of intrathoracic pressure because the glottis is closed. It only takes very little efort to close the glottis and it acts as a self-sealing flap valve.
I would also like to think this is true but I am not absolutely sure that every unconcious diver would necessarily have an open glottis. This may be particularly the case if he is in the tonic phase of a CNS toxic reaction. . . .
On the other hand an uncoucious diver has only one chance of survival, and that is if he is brought to the surface pretty damn quickly.
You have every right to ask your questions and I feel some of the responses you have received reflect more badly on the posters than on you. I hope I am not included in that group but you have not answered my question about free divers. I posed the question in the hope that, by working out what happens to them, you could see why - underwater - lung volume and chest volume are not necessarily the same.
In my original post, and I apologise to Dr Deco for once more stealing his thunder, I stated that the diaphragm could only change the intrathoracic pressure +- 0.03 bar around that at the oropharynx and this is why you cannot snorkel below about a foot.
Clearly obstetric patients, when bearing down, when you cough or when you sneeze the intrathoracic pressure is raised considerably by the use of the muscles of the chest wall, the abdomen and the diaphragm working together AGAINST A CLOSED GLOTTIS. The reason you cannot snorkel at depth is because these muscles cannot act against ambient pressure to REDUCE the intrathoracic pressure by more than that amount:-
A deep snorkeller can beath out but he cannot breath in!
All varieties of the Valsalva manoeuvre produce an active increase of intrathoracic pressure because the glottis is closed. It only takes very little efort to close the glottis and it acts as a self-sealing flap valve.
I would also like to think this is true but I am not absolutely sure that every unconcious diver would necessarily have an open glottis. This may be particularly the case if he is in the tonic phase of a CNS toxic reaction. . . .
On the other hand an uncoucious diver has only one chance of survival, and that is if he is brought to the surface pretty damn quickly.
No offense meant here
but you still seem to doubt what every post here is trying to get across to you, why not use your own body to see if YOU can hold your breath during assent.
May I suggest you have on hand a helicopter, and a booking at your local chamber......
Cheers
Chris
but you still seem to doubt what every post here is trying to get across to you, why not use your own body to see if YOU can hold your breath during assent.
May I suggest you have on hand a helicopter, and a booking at your local chamber......
Cheers
Chris
OP
mtdivegirl
Contributor
Dr. Thomas,
Thanks again for the info. I could not have answered your question posed about free diving because as stated before I really don't have the much knowledge on the subject (hence the question in the first place).
If you cannot snorkel below about a foot how is it that a hooka can work at depth? (please...no one assume this means I am doubting anything the doctor has said..i am just asking the next question that came to my mind...)
As for Sydney's commentary...you are just lumped in with the rest of the group who offered little or no information of substance. If you read you will see that I never once questioned the accuracy of anything anyone purported to be the truth all I did was follow my sense of logic to ask the next question that came to mind. You will also see that after working your skills as a literate human being, I said a number of times that I was not proposing this as an expirement or that I wished to try it myself.
Thanks again for the info. I could not have answered your question posed about free diving because as stated before I really don't have the much knowledge on the subject (hence the question in the first place).
If you cannot snorkel below about a foot how is it that a hooka can work at depth? (please...no one assume this means I am doubting anything the doctor has said..i am just asking the next question that came to my mind...)
As for Sydney's commentary...you are just lumped in with the rest of the group who offered little or no information of substance. If you read you will see that I never once questioned the accuracy of anything anyone purported to be the truth all I did was follow my sense of logic to ask the next question that came to mind. You will also see that after working your skills as a literate human being, I said a number of times that I was not proposing this as an expirement or that I wished to try it myself.
tchil01
Guest
mtdivegirl
I think this question illustrates why everyone is frustrated with you. I do understand that you are new to the sport and as such have a lot of questions. However, people on here are giving you advice as well as answering your questions. However, you seem to be not only questioning their advice and answers, but also not doing any work yourself or not using common sense to answer the questions. You questioned why a Hookah would work but deep snorkeling would not. If you looked at a Hookah you would see that it is a compressor on a float providing a diver with pressurized air. In deep snorkeling there is no such mechanical help for the diver and his or her lungs are required to overcome the pressure difference.
One a side note, I have two kids both fairly young. When they were very young they would ask the inevitable questions such as why is the sky blue or the grass green. I would give them the proper answer, tailored to their age but in a lot of cases they would just keep asking why, why, why As they got older they would ask other questions and I would explain the answer and help them look up additional information. The why why whys stopped. Now they find out the answers themselves and come to me with what they have learned. If they dont understand something, they ask the question and we figure it out. If it is something they should know I have them think about it or research it before asking why why why And sometimes the answer is just the answer. No asking why why why will make it any different.
Ty
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Perhaps you're right Land. In any case I have nothing more to contribute to this discussion so I will take my arrogance elsewhere
Tom
The Iceni
Medical Moderator
Right!
1) Free divers hyperventilate to excrete CO2 so they can breath- hold for longer and they take a maximal deep breath before descending.
2) They do not take any more air into their lungs as they descend.
3) Boyle's law tells us that all the gas in the lungs will be compressed to a smaller volume. At 30 mtres or 4 bar the air spaces will be a quarter of the full, surface, total lung capacity of about 6 litres in a fit young male adult and will therefore be compressed to 1.5 litres - a diffference of 4.5 litres.
4) If the chest wall and diaphragm did not move at all, as nature abhors a vaccuum an equal volume of blood from venous return fills the pulmonary capillaries - there will be a net transfer of 4.5 litres of blood from the peripheral circulation into the pulmonary circulation, which the body can cope with.
5) On ascent this blood returns to the periphery.
On the other hand. . .
If a diver takes a lung-full of air at 30 mtres and then ascends without breathing out Boyle' law tells us that the 6 litres (TLC) of air will expand to 4 x 6 = 24 litres at the surface. If the pulmonary bed normally contains 3 litres of blood which can be evacuated under pressure this means even when ALL blood has been evacuated from the chest there will be an additional 21 litres of gas confined within the chest wall as the diver surfaces.
Although the lungs will attempt to passively expand and the diaphragm to be forced down, this will be reflexly resisted and the linings of the airways will continue to expand against the pressure drop and they cannot expand to more than three times their maximum natural size without tearing.
I hope that explains it!
1) Free divers hyperventilate to excrete CO2 so they can breath- hold for longer and they take a maximal deep breath before descending.
2) They do not take any more air into their lungs as they descend.
3) Boyle's law tells us that all the gas in the lungs will be compressed to a smaller volume. At 30 mtres or 4 bar the air spaces will be a quarter of the full, surface, total lung capacity of about 6 litres in a fit young male adult and will therefore be compressed to 1.5 litres - a diffference of 4.5 litres.
4) If the chest wall and diaphragm did not move at all, as nature abhors a vaccuum an equal volume of blood from venous return fills the pulmonary capillaries - there will be a net transfer of 4.5 litres of blood from the peripheral circulation into the pulmonary circulation, which the body can cope with.
5) On ascent this blood returns to the periphery.
On the other hand. . .
If a diver takes a lung-full of air at 30 mtres and then ascends without breathing out Boyle' law tells us that the 6 litres (TLC) of air will expand to 4 x 6 = 24 litres at the surface. If the pulmonary bed normally contains 3 litres of blood which can be evacuated under pressure this means even when ALL blood has been evacuated from the chest there will be an additional 21 litres of gas confined within the chest wall as the diver surfaces.
Although the lungs will attempt to passively expand and the diaphragm to be forced down, this will be reflexly resisted and the linings of the airways will continue to expand against the pressure drop and they cannot expand to more than three times their maximum natural size without tearing.
I hope that explains it!
In order to breath off a snorkle the diaphragm must be able to overcome the pressure of the surrounding water to gain air from the surface. As has been said earlier a depth of about a foot is the best the average diaphragm can do. On a hookah the air is still compressed and you essentially have a "power boost to the air". Its being fed to you.
Simply put an answer to your other question...
The tracheal muscles that hold your air way closed are stronger than the pressure of the air trying to escape your lungs. The conscious effort to keep these muscles contracted can close off the air way long enough to result in lung over expansion.
TwoBit
Simply put an answer to your other question...
The tracheal muscles that hold your air way closed are stronger than the pressure of the air trying to escape your lungs. The conscious effort to keep these muscles contracted can close off the air way long enough to result in lung over expansion.
TwoBit
Dr Deco
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Dear Dr T.:
Thanks---
Thank you for your comments. It often happens that I am quite busy, and it is helpful when someone is willing to pen an answer to these missives. Additionally, I do not have an in-depth knowledge of pulmonary mechanics
Dr Deco :doctor:
Thanks---
Thank you for your comments. It often happens that I am quite busy, and it is helpful when someone is willing to pen an answer to these missives. Additionally, I do not have an in-depth knowledge of pulmonary mechanics
Dr Deco :doctor:
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