Environmental physiology

SUBJECT: PHYSIOLOGY TOPIC: Environmental Physiology (Human Body and Environment) LECTURER: DR. DEXTER SANTOS DATE: MARCH 2011 This lecture will discuss the reaction of the human body when you go deep sea diving, go to higher altitudes, when you board an aircraft, and when you go to outer space.

At about 33 ft (10m) = 2 atm  You can see that you seem to compress the air into ―half‖ of the container. This makes the molecules of air come closer together.

Again, concepts involved are:    

Deep sea dive In high altitudes Aviation Go to space

So what‘s the translation of this in terms of the human body? Certain parts of your body are filled with air, such as your lungs, sinuses, etc. The gas laws come into play as well.

DEEP SEA DIVING Deep sea diving is all about changes in pressure and the effect of that change in pressure on the human body.  Sea Level Normal atmospheric pressure at sea level

1 atm = 760 mmHg

This is the amount of force exerted by the entire atmosphere at sea level. This all the way from the sea level up to the very outer limits of atmosphere, bordering space. However, it‘s a different story underwater. At just 33 ft (≈10m), you already double the pressure to 2 atm. At a 100 ft, you have 4 atm of pressure already. And at a 100 ft, or 30+ meters, this is actually already the limit of recreational diving.

 Underwater 33 ft (10 m) 66 ft (20 m) 100 ft (≈30 m)

And if you convert that into an inverted container full of air at sea level, you will observe that as you go deeper, you compress the air even more.

2 atm 3 atm 4 atm

LIMIT OF RECREATIONAL DIVING! (Though there are still other divers that go a lot deeper than this)

GAS LAWS 1. BOYLE‘S LAW “At constant temperature, there is inverse relation of pressure and gas volume.”  Therefore, if you increase the pressure, the volume decreases.

Pressure

≈

Volume

2. HENRY‘S LAW “At constant temperature, the amount of gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.” Or in a simpler way, “the mass of a gas which dissolves in a volume of liquid is proportional to the pressure of the gas.” Henry‘s Law and Scuba Diving: At higher pressure our bodies will absorb more gases. At great depths, the amount of nitrogen (and other gases) absorbed into our blood and tissue is greater than the amount absorbed at shallow depths. That is why a diver going to 100' has a greater risk of decompression illness than a diver who dives only 30 feet. Since the shallow diver has absorbed less gas, it is less likely to come out of solution in the body. Taken from: http://www.thescubaguide.com/certification/henryslaw.aspx (emphases by STD)

*see following text for explanation

PHYSIOLOGY: Human Body and Environment

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EFFECTS ON THE BODY (Minor Systems) 1, Air trapped in the ears: (Especially the air trapped in the middle ear!) As you go deeper, that pressure exerted on the tympanic membrane compresses the air inside the middle ear. This must be equalized by opening the Eustachian tube, which you do by swallowing or by pinching the nostrils then exhaling forcefully. This is what divers do. 2. ―Tooth Squeeze‖ For those who had some procedures done on their teeth. For example, a pasta done years ago and right now the seals are no longer in tact, so there is air inside the teeth. This is what we call a tooth squeeze. Once you go underwater, you will feel pain in your teeth. 3. Colds (or Upper Respiratory Tract Infections) There is impaired opening and closing of the Eustachian tube. Thus, you feel pain pressing on your ears because of the pressure. 4. Sinuses These are also air-filled parts of the body. So it‘s a rule for divers that: Don‘t dive if with Upper Respiratory Tract Infections. Because you will just feel pain in all your air-filled spaces (e.g. sinuses, middle ear) and it can also be dangerous underwater. EFFECT ON THE BODY (Major System) The main system in focus here is the Respiratory System. Above sea level (normal state), the normal pressure of Oxygen is 159, and the normal pressure of Nitrogen is around 600. And once this translates to the bloodstream, you have a pO2 of 60, whereas the Nitrogen remains the same because it equilibrates much more readily as compared to oxygen. At the Alveolus Normal pressure of oxygen (pO2)= 159 Normal pressure of nitrogen (pN2)= 601

So what happens is that the nitrogen gets dissolved in the bloodstream. (You have nitrogen floating around). But as you go beyond recreational diving, say about 250 ft (≈8.5 atm), then you have more pressures of the gases. Alveolus Normal pressure of oxygen (pO2)= 1400 Normal pressure of nitrogen (pN2)= 4970

Bloodstream pO2= >120 pN2= 4970

When the buffering mechanism of your oxygen also fails (especially beyond 4 atm), you will have dangerously high levels of oxygen and nitrogen in the bloodstream. This will lead to a state called Nitrogen Narcosis.  Nitrogen Narcosis Caused by too much nitrogen dissolved in your blood and it gets dissolved in the fatty substances of neuronal membranes therefore altering the conduction and excitability.  Symptoms of this include: o Drowsiness o Loss of strength o Clumsiness o Loss of consciousness (if you stay there much longer) Nitrogen Narcosis is common in individuals who rapidly descend during diving. Because of this, ROS (Reactive Oxygen Species) are formed, especially in deep waters. As for oxygen, recall that you now also have dangerously high levels of oxygen in the blood too. This leads to the formation of reactive oxygen species (ROS). The hemoglobin can buffer the excess oxygen initially, but if your oxygen levels keep increasing, your hemoglobin will not be able to accommodate this anymore. This will result to oxygen getting dissolved in the blood directly, rather than it being carried by hemoglobin. = Oxygen Toxicity.

(Equivalent in) the Bloodstream pO2= 60 pN2= 601 (just the same as alveolus)

But let‘s say that you had a recreational diving at 100 ft, therefore: At 100 ft: 4 atm, you now have a pO2 of 620 instead of 159 (so approximately 4x that of normal pO2 as well). The level of oxygen in the blood stays the same or at a normal range. However, the nitrogen increases because there is no mechanism for buffering nitrogen in the blood.

PHYSIOLOGY: Human Body and Environment

Quantity of oxygen dissolved in the fluid of the blood and in combination with hemoglobin at very high PO2s.

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 Oxygen Toxicity Due to the formation of reactive oxygen species (aka free radicals) and this oxidizes lipid membranes.  Symptoms include: o Nausea o Muscle twitching o Dizziness o Seizures o Coma The buffering of ROS by enzymes fails above 2 atm of pO2.. You can also have pulmonary edema and atelectasis (collapse of the lungs) due to the direct effect of high oxygen pressure. These rarely happen if you just stay at the level of recreational diving (100 ft). BUT even in recreational diving, you can experience a lot of problems: Case 1. Let‘s say you lingered at a hundred feet down for about a few minutes and your nitrogen gets dissolved in your bloodstream. Suddenly, there is an undercurrent that took you to the surface from 100 ft (4 atm) to suddenly ascend to sea level (1 atm). So what will happen now? The pressure that is exerting on the body (which dissolved the nitrogen in the first place) suddenly decreases. What happens is that you did not allow enough time for the nitrogen in the body to be exhaled, thus forming nitrogen bubbles. This can consequently cause decompression sickness. Decompression Sickness Caused by nitrogen bubbles forming in the blood vessels, so they block the vessels and thus cause tissue ischemia and tissue death. The symptoms can range from very painful joint pains (called ‗the bends‘) and dizziness to unconsciousness and fatal pulmonary edema (called ‗the chokes‘).

The No Decompression Dive Table This shows the depth in meters and the number of minutes that you are allowed to stay in such depth. This just shows how much time you‟re allowed at each depth. This is already quite obsolete! Because gizmos (guide computers) are now being used. Conditions for No Decompression Dives (This means a “very safe” dive.)  Stay within recreational limits  Never hold your breath Continuous breathing is the only way for you to get rid of your excess gases.

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Ascend slowly (1ft/s) Perform safety stops Wherein you stop at prescribed depths (about 5 mins at 5-6 meters) just to eliminate the excess gases.

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Plan your dives (deepest dives first) Buy a dive computer

For very deep dives: (Such as what they use in the navy.)  Use a helium-oxygen mixture because helium equilibrates rapidly and gets expelled much more rapidly compared to nitrogen. Moreover, you receive less oxygen percentage to avoid oxygen toxicity as well.

**Some divers long ago, before the advent of high-tech diving gear, get the bends to the point of being paralyzed because the joints get destroyed by the tissue ischemia. The dissolved nitrogen in the body needs to be excreted! But how? 1. Breathe. Just breathe it out. 2. Give it enough time. This is also why there is a “No fly” time, wherein you cannot board an aircraft for 24 hours after the dive because low pressure in the atmosphere (even if that‟s a pressurized chamber) can trigger more nitrogen bubbles to form. Treatment: Inhaling 100% oxygen Go to a decompression chamber

PHYSIOLOGY: Human Body and Environment

Decompression Chamber. Divers spend much time in the chamber after a dive to prevent abrupt changes in pressure and to prevent accumulation of Nitrogen Bubbles.

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This is usually most useful or applicable in rescue or emergency situations wherein one has to ascend rapidly and safety stops cannot be observed anymore. Once the diver is inside the decompression chamber, they once again increase the pressure or mimic the pressure beneath the water, and slowly decrease the pressure as time goes by. This procedure somewhat „mimics‟ the gradual ascend that you should have done in the first place. Again, this eliminates the chances of nitrogen bubbles forming. (It must be remembered that rapid ascents must be avoided as much as possible so as to prevent nitrogen bubbles from occurring.) Carbon Dioxide The pCO2 in the alveoli remains constant (at 40mmHg)  Standard dive equipment: So you have the mask + breathing apparatus. But what actually happens when you exhale is that you exhale the carbon dioxide so that it will not accumulate. However, there are masks such as this:

Possible at 600 feet with rebreathing apparatus o Continually exhale to prevent lung overexpansion  If you don‘t exhale, your lungs will burst! Because when in the submarine, your lungs are actually holding about 5 to 6x more air than if you were at sea level (due to the pressure present in the sub). So if you suddenly escape from that, you have about 6x more air than normal in your lungs! If you don‘t exhale it, your lungs will burst by the time you get up. (Events such as pneumothorax may occur). Inside the submarine: o Danger of radiation o Danger of accumulation of gases:  Carbon Monoxide  Freon o

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HYPERBARIC OXYGEN THERAPY High oxygen pressure is not all bad news. We actually use this to treat certain diseases such as gas gangrene, which involves anaerobic organisms. Anaerobic, meaning they thrive on low oxygen environment. Therefore, when you give high doses of oxygen, they die.  

The primeval dive equipment that is attached to a hose to the surface. This has a closed-circuit setup and this can have a danger of CO2 accumulation. Even modern dive equipment such as the rebreathing apparatus can pose a risk.

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What is the rebreathing apparatus for? There are some divers who do not like bubbles when they dive (e.g. photographers, water videographers); they do not want their exhaled bubbles to get in the way of their craft. So they wear these rebreathers. They recycle the air, wear smaller tanks so that they‘re more mobile. This can also pose a risk for carbon dioxide accumulation. Again, Special masks, rebreather masks, 1st generation dive helmets: Dangerous accumulation of CO2 (80 mmHg)

CO2 accumulation can result to Respiratory Acidosis o Signs: Lethargy, narcosis, anesthesia, and eventually respiratory depression SUBMARINES  Escaping from submerged submarines (such as those seen in old James Bond films) o Possible at 300 feet without assistance

PHYSIOLOGY: Human Body and Environment

Administered in pO2 of 2-3 atm Medically used in treatment of: o Gas gangrene o Decompression sickness o Carbon monoxide poisoning o Osteomyelitis o Myocardial infarction

HIGH ALTITUDE PHYSIOLOGY This is like the opposite of ‗underwater‘. This time, you go very high up, such as in the mountains. Again, this is all about pressure.  Air pressure changes  Physiologic effects of low air pressure on the body  Diseases that can arise from low air pressure environment If underwater the problem was high pressure, ―up‖ there, the problem is low pressure.  At sea level,760 mmHg (pO2 = 159 mmHg) By 10,000 ft, 523 mmHg (pO2 = 110 mmHg) At 30,000 ft, 226 mmHg (pO2 = 47 mmHg) At 30, 000 ft, which is about the height of Everest, you only get just a little less of a third of what you should normally breathe when you‟re at sea level. This is usually where the problem arises for low oxygen tension. ALTITUDE AND ARTERIAL OXYGEN As we go higher, the amount of oxygen in the blood dramatically decreases. This is why mountain climbers wear rebreather masks and oxygen tanks – so that even at 30,

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000 ft, they can have a very good oxygen saturation in their blood. Increase in height

Decrease in oxygen in the blood

chemoreceptor neurons. Once this happens, you will have full respiratory stimulation. (So you‘ll breathe deeper, you can breathe much faster, you‘ll recruit more alveoli, and in total increase your pulmonary ventilation). Recap:

EFFECTS OF LOW ARTERIAL OXYGEN TENSION  At 12,000 ft:  Drowsiness, headaches  Mental and muscle fatigue  18,000 feet  Seizures and muscle twitching  23,000 feet (wherein you have only about 60% O2 saturation)  Coma and death

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Other symptoms: Poor judgment, poor memory, and poor mental proficiency Why do a lot of people live in the mountains? Acclimatization The process of physiologically adapting to the low oxygen environment. So as you go up, you have an increase in pulmonary ventilation. This means you breathe much deeper and you recruit more alveoli. To some point, you also increase your respiratory rate, and increase RBC counts. There is also an increase in the vascularity of your tissues.

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Increase in RBCs and Hemoglobin Levels o Develop this if you have hypoxia for weeks; Haematocrit and hemoglobin increases Increase in oxygen diffusing capacity o Increase in pulmonary capillaries o Increase in pulmonary arterial blood pressure

So what is the mechanism behind your increase in hemoglobin/ RBCs?

When you have more blood vessels in your tissues, you increase the capability of that organ to extract oxygen from the low oxygen environment. Increase in Pulmonary Ventilation:  Takes about 5 days for lungs to adapt. For example, on the 1st day you have about 1.6x the normal amount of ventilation (breathing rate, etc). The low pO2 is then actually sensed by the receptors, therefore increasing ventilation. BUT if you increase ventilation, remember that you also consequently blow off carbon dioxide. This low carbon dioxide environment inhibits your oxygen sensors so that your ventilation gets subdued. However, if you stay longer and you keep blowing off your carbon dioxide, your bicarbonate production also decreases. This decrease in bicarbonate is also sensed around the central

PHYSIOLOGY: Human Body and Environment

Hormone responsible is your erythropoietin. The main trigger for its release is hypoxia or low oxygen. This is sensed by the kidneys  release erythropoietin stimulate stem cells  eventually end up with more RBCs.

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Hypoxia is also a trigger for angiogenesis. You have increased extraction and utilization of oxygen from the blood. And when there is an increase in hypoxia, you release the HIF (hypoxia inducible factor) which is a transcription factor. Eventually you will produce more VEGF (vascular epithelial growth factor). The VEGF is the ligand for the angiogenesis or new blood vessel formation. And at normal oxygen levels, that transcription factor is bound to the VHL protein so that it is not available for transcription.

o o

Increased quantity of mitochondria and cellular oxidative enzymes Increased extraction and utilization of oxygen from the blood

In the short term, the haematocrit does not rise agad, and it is your heart that compensates for that. It contracts more forcefully to meet the demands of the tissues and the organs. Increase respiratory rate Increase diffusing capacity in lungs Increase vascularity of peripheral tissues Increase ability to extract oxygen o

Tissue and cellular changes: o Increase in capillarity

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MOUNTAIN SICKNESS: Acute: Acute cerebral edema from vasodilation of cerebral arterial blood vessels  Symptoms: disorientation, coma, death Acute pulmonary edema Chronic Mountain Sickness: Increase in red cell mass and this consequently increases blood viscosity Pulmonary Artery Vasoconstriction Induced by hypoxia also An increase in this will result to increased right ventricular afterload Both lead to HEART FAILURE. Since ang lapot na ng blood and ang taas ng pressure na kailangan niya i-overcome just to pump the blood, mapapagod si heart = FAILURE