 Knowing deep sea physiology is important because we go underwater for several purposes. One is obviously for recreational purposes you know that people go for scuba diving and then there are military operations which happen underwater and there are also underwater constructions which go on if you are aware that there are internet cables which are running underwater. So understanding deep sea physiology is of considerable significance. So considering that this is the sea level and the weight of the gases which is there above the sea level exerts an atmospheric pressure of 760 millimeter mercury at sea level. As we go deep into the water two things happen. One because of the weight of the water the atmospheric pressure increases. So if somebody is here at this depth say at a depth of 10 meters underwater then there is increase of plus one atmospheric pressure because obviously there will be the pressure of the gases which is there and then there is the pressure of the water. So the total pressure at 10 meters depth underwater will be two atmospheres isn't it because you will add this 760 millimeter mercury which is basically one atmosphere and the pressure at 10 meter depth will hence become two atmospheres. Second thing which happens when we are going underwater is that we are surrounded by water so we cannot breathe the normally underwater we are adapted to breathe in air. So we need some support for breathing. Now because of these effects and especially because of the effect of the high pressure there are various problems which we can face when we are going down into the water. So there are problems which we face when we descend into the water and there are problems which can happen when we ascend up from deep into the surface. So there are problems going into the water descent and there are problems when we ascend onto the surface. So let us see what are these problems? First we will talk about the problems during the descent. So during descent two types of problems occur. One is due to the direct mechanical effect of increase in the pressure. So mechanical effect of increase in the pressure that leads to barrow trauma. We will see in detail little bit. And then second is see as the total pressure is increasing the pressure of individual gases also increases. And this ultimately leads to two types of toxicity that is oxygen toxicity and nitrogen narcosis. So both of these we will see little bit in detail why they are occurring, how to prevent them also. So oxygen toxicity and nitrogen narcosis. First coming to barrow trauma. See as we are descending into water you know that according to Boyle's law which says p1v1 is equal to p2v2 that is pressure of a gas and its volume of a gas when we multiply it is a constant. So when we are descending into water what is happening the surrounding pressure is increasing. So there is compression of gases in our body causing decrease in the volume of gases which are present in various cavities in our body. And where all these gases are present it is present in the sinuses then there is in the middle ear the air is present. Okay you know that middle ear is connected to the pharynx by means of a eustachian tube and the equilibration of pressures in the middle ear with the environment is very very important. So change in pressure outside will definitely affect the middle ear. So yes these are the problems which happen that due to the compression of gases in these cavities there occurs sinus squeeze because the volume of the gas is reducing so the space is going to squeeze. Then similarly in middle ear there will be compression of the gases and equilibration of pressure if it doesn't happen then it will lead to squeezing of the middle ear and when this happens due to the squeezing of the middle ear there will be a pull component on the tympanic membrane and tympanic membrane may rupture also leading to conductive hearing loss. So basically it is very important that there should be equilibration of pressures within the body and that outside the body and this is made possible by means of specially designed diverse suits. So that's how the mechanical effect is prevented. In fact the increase in the external pressure may also lead to the squeezing of the eyes so that you will see hemorrhages in the eyes as well. So one obviously when we are going down first effect which can occur is due to the mechanical effect due to the direct increase in pressure. Second effect is due to increase in the total atmospheric pressure which ultimately lead to increase in the partial pressure of all gases. So you know the Dalton's law, what is Dalton's law? Dalton's law says that the pressure of individual gases is determined by the percentage composition of the gases. So if the percentage composition of the gas which the person is breathing is same as that in atmospheric pressure that means when he's going underwater and taking a cylinder for breathing see he cannot breathe directly in the water so he has to take a cylinder which is connected via pipe and he is breathing through that. Suppose the composition is such that it is consist of 21% oxygen same as that which is present in the air and approximately 80% nitrogen so with this let us write 79% nitrogen. So this composition is same as that of atmospheric air so as the total atmospheric pressure increases what will happen? The percentage composition is same so proportionately the pressure of these oxygen and nitrogen is also going to increase so that is Dalton's law. Then next law is Henry's law which says that the gases dissolve more when their partial pressure is more the dissolution of gases and increases in direct proportion to their partial pressure so these two laws explain oxygen toxicity and nitrogen narcosis simply stating the partial pressure of these gases is increasing and because of this they are dissolving more especially the nitrogen which dissolves more causes nitrogen narcosis so let us see in detail what is this oxygen toxicity and nitrogen narcosis. Oxygen toxicity occurs because of increase in the partial pressure of inspired oxygen and whenever there is increase in the partial pressure of oxygen in inspired air what happens there will be increase in the partial pressure of oxygen in the alveoli and ultimately in the blood so more partial pressure of oxygen will reach to the issues as well and there there will be production of reactive oxygen species which are these reactive oxygen species the common ones include H2O2 hydrogen peroxide and superoxide radical so these form more these reactive oxygen species form more and this ultimately lead to the oxidation of the membrane right so that is the importance of reactive oxygen species they cause the oxidation of the membranes especially where there is increased lipid content okay so that membranes are affected the most and can you tell which of the cells in the body have the maximum lipid content in the membrane yes it is neurons so neurons are affected most when underwater by this oxygen toxicity so what it leads to it leads to disorientation dizziness severe state it can lead to caesars also and ultimately it can lead to coma so you understand that the person is underwater and he is becoming disoriented so will he be able to come up will he be able to save himself no so that is oxygen toxicity we will see how to prevent oxygen toxicity but before that let us discuss about nitrogen narcosis nitrogen narcosis again it occurs due to increase in the partial pressure of the nitrogen and when increased partial pressure of nitrogen happens in blood and then there is more dissolution of this nitrogen in the tissues okay so more nitrogen gets dissolved in tissues again in the membrane and that too because nitrogen has more solubility in lipids okay so membrane has more lipid content so it dissolves in the membrane then it also dissolves in the body fluids and body fat fine it is dissolved there so what again you see because the membranes with the most lipid content is the neurons so the functioning of the neurons is affected and the effect which we see is similar to that of a person who is drunk and the stages in which he is a drunk so at around 120 feet of depth that is around how much meters it will come 33 feet is equal to 10 meters so 120 feet it comes to around 40 meters right so at 10 meters I said that there is rise of one atmospheric pressure so at 40 meters there will be a rise of four atmospheric pressure so that means total the atmospheric pressure at this depth will be five atmosphere so at a depth when the atmospheric pressure is five atmosphere the signs and symptoms which we see are euphoria the person feels exhilarated there is joviality okay and because of this there is loss of sense of judgment as well so that is like the first stage of alcoholism where the person feels euphoria but later as the depth keeps on increasing there are changes so at around 150 to 200 feet there is drowsiness and the muscular incoordination happens so yes imagining that all this happening underwater where there should be proper concentration and muscular coordination should be there then by 200 to 250 feet the person becomes unconscious okay and below that what happens there is almost coma like condition that is known as deep narcosis and it is impossible almost to revive the person so just like the different stages of alcoholism we see the stages of nitrogen narcosis as the person is going into depth and this nitrogen narcosis that's why it's also known as raptures of depth raptures of depth okay so how to prevent now this oxygen toxicity and nitrogen narcosis as we are seeing that main problem is increase in the partial pressure of gases so decrease their partial pressure how to decrease see the total atmospheric pressure is increasing but we have to decrease the partial pressure of the gases so in respiratory system we see that partial pressure of any gas is what is defined by the percentage composition of the gas multiplied by the total atmospheric pressure right so total atmospheric pressure is increasing as we are going into depth what to do decrease its percentage composition so the gas cylinders which these people carry and especially when going into great depths into the ocean then the percentage composition of oxygen should be decreased in fact the cylinders with 95 percent composition helium and five percent of oxygen are used so you see nitrogen is not there so nitrogen narcosis cannot occur and we have decreased the percentage composition of oxygen so the partial pressure of oxygen is going to decrease there will be decreased generation of the free radicals fine so that was about the main problems which occur when we go underwater that is the mechanical effects then there is oxygen toxicity and then there is nitrogen narcosis before proceeding just touching on what is known as a rebreathing of carbon dioxide toxicity so this is toxicity may occur when the person is inhaling from gas cylinders and exhaling carbon dioxide into the gas cylinders and there is no way of reabsorption of this carbon dioxide so this may occur when there is malfunction in the breathing apparatus which the person is carrying so what will happen the person rebreats the carbon dioxide and in that case there will be increase in the partial pressure of carbon dioxide in blood and this is going to stimulate the respiration so that the carbon dioxide can be exhaled out but what will happen the same carbon dioxide will be inhaled again isn't it because there is malfunction so this increase in partial pressure of carbon dioxide is tolerated up to partial pressure of carbon dioxide of 80 millimeter mercury in blood when it reaches this level then there occurs carbon dioxide narcosis you know that the normal partial pressure of carbon dioxide in arterial blood is 40 millimeter mercury so when it almost doubles there occurs carbon dioxide narcosis that is there is direct cns depression and ultimately which leads to unconsciousness moving on to the problems of ascent which occur when we are coming up from the deep sea and this condition many of you might be aware is known as cases disease or also known as decompression sickness so what is happening that we have seen that when the person is going deep into the water lot of gases are getting dissolved in the various tissues because of their increased partial pressure now when the person comes up these gases which have dissolved their solubility is going to decrease right because the partial pressure is slowly going to decrease as the person ascends up so the solubility of the gases is also going to decrease so these gases are now going to be released into the blood right so gases are coming into the blood and from blood they are going into the respiratory system where they will be exhaled out fine but you see there is a limit at which this respiratory system can work there is a particular rate at which it can work isn't it so if the gases which are dissolved they are released very very fast into the blood all the gases will not be able to be exhaled out in fact they will form bubbles in the blood vessels and these bubbles will go and lodge in the various blood vessels simple terms the rate at which these bubbles are forming our body is not able to match that rate and is not able to exhale the gases out as fast as it is needed so these bubbles where they go and lodge they go and lodge into the blood vessels of different tissues for example in respiratory system they can block the blood vessels and this leads to cuff dyspnea and popularly it is known as chokes okay then it affects the joints where it causes joint pains so that is known as bends then it can even affect the blood vessels in the central nervous system in the spinal cord so when the spinal cord is affected it leads to paralysis okay so that is commonly known as diverse paralysis then where else where else it can affect it can go and affect the cerebral blood vessels so cerebral blood vessels when it will be affected it will cause a stroke there may be visual disturbance speech disturbances the person may become disoriented then it affects the cardiovascular system so it will cause chest pain arrhythmia so depending on which blood vessels are blocked we will have various signs and symptoms and which gas do you think is responsible for this is it oxygen nitrogen yes it is nitrogen because nitrogen is the one which is going and dissolving into the lipids maximum that is the maximum composition of the gas which the person is inhaling okay so now tell me how this can be prevented yes first is that same mixture which we spoke about breathing the 95 percent helium and 5 percent oxygen mixture because this helium as opposed to nitrogen it is less lipid soluble less lipid soluble understanding so that much dissolution in the lipids is not going to happen also whatever dissolves it is less toxic as well so that nitrogen narcosis which we are talking helium narcosis doesn't occur so they are also it is preventing so the problems of descent also it prevents and also it prevents the problem of ascent how it prevents the problems of ascent because it diffuses faster than nitrogen and it is easy to eliminate okay so add the respiratory membrane the diffusion is much faster compared to that of the nitrogen easily diffuses into the alveoli and easily can be exhaled out so that is one second method of prevention is that the person should ascend slowly ascend slowly in fact there is a full scheme with these divers there is a full scheme that how the person should ascend up that means after coming up say suppose few meters he has to stay at that meter for particular time so that the bubbles which are formed they can be exhaled out so these are known as mandatory stops which the person should take so that the formed bubbles are exhaled out but remember this is precautionary but it doesn't guarantee that the person will not suffer from decompression sickness but always this protocol should be followed so suppose despite following the protocol or if the person has not followed the protocol he ascends up and he suffers from decompression sickness then what should be done what is the treatment treatment is known as recompression okay so there are chambers where the person is asked to go and in these chambers we increase the pressure to same as that of what the person was exposed to so again the gases which have formed bubbles now again will go and dissolve into the tissues so what we are doing we are pausing the recompression and then slowly slowly we mimic the ascent that is slowly slowly we decrease the pressure so that the bubbles which are forming they can be exhaled out so basically this method mimics that of the slow ascent right and the chamber is known as decompression chamber because we are recompressing and then we are slowly slowly causing the decompression okay so that is all about the cases disease now before we finish I just want to touch on one more problem which can occur during the ascent and that is again due to the change in the pressure so what happens that this is the alveoli and when the person is ascending again due to poise law what will happen that the pressure is going to decrease now so the volume of gases is going to increase so the volume of gases which is most affected is that in the alveoli and this can lead to alveolar rupture you see alveoli are going to expand because this volume is increasing and they can expand only up to a certain limit only after that they will rupture and this will cause the release of the gases which will enter into the blood as bubbles and this will lead to arterial gas embolism and again it can block the cerebral blood vessels the cardiovascular blood vessels and lead to various problems so what are the problems of ascent we discussed we discussed about case and disease that is a decompression sickness and also arterial embolism so that was all about deep 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