Respiratory and Circulatory Systems
The cardiovascular/circulatory system and respiratory system are two systems in the human body that are vital. They continuously provide the body with a flow of nutrients and oxygen and remove waste products. Any breakdown of or interruption to these systems can result in permanent damage to your body, sometimes within minutes. In addition, these two systems are the ones most influenced by the underwater environment.
Every part of the human body constantly needs oxygen. Oxygen is needed for what is called the oxidative metabolism: the oxidation of nutrients in order to supply energy required to live. Every cell in your body needs oxygen. The respiratory system brings oxygen into the body and removes carbon dioxide from the body via the lungs. The cardiovascular system governs the circulation of blood and transport of oxygen and carbon dioxide. It mainly consists of the heart, arteries, veins, and capillaries.
Breathing Stimulation
Carbon dioxide (CO2) is one of the main stimuli triggering your urge to breathe. It’s not required for you to understand what the exact mechanism within your body that controls partial pressures of carbon dioxide and oxygen (O2) is or how the changes in the blood’s acidity affects the urge to breathe. However, as a diver, you should understand the basics of breathing. You can also improve your diving enjoyment by using some of the breathing exercises taught in yoga, martial arts, and meditation.
At rest, the average breathing rate is between 10 to 20 breaths per minute. Under normal conditions, this breathing rate and the depth of your breathing is automatically and unconsciously controlled by respiratory centers deep in the brain.
An increased demand for oxygen by the body as a result of exercise or anxiety proportionally increases the levels of carbon dioxide in the blood, and the breathing rate will increase in relation.
As the carbon dioxide levels reduce (at rest), the breathing rate will return to normal. If oxygen levels are too low but the respiratory centers do not detect overabundance of carbon dioxide, it is possible that breathing is not stimulated. This is what happens in the case of shallow water blackout, mostly breath-hold diving. The important lesson for you in this instance is that lack of oxygen alone will not make a diver breathe.
When diving, the high-oxygen partial-pressure level is more than enough for the body to function. However, as the partial pressure of oxygen drops on ascent, possible symptoms of light-headedness, dizziness, nausea, and headache might occur. In extreme cases, there may be loss of consciousness. The simple solution to this problem is to take three or four normal full breaths before ascent.
Did you know? It’s worth noting that every unit of oxygen metabolized in a diver’s body is converted to almost the same volume of carbon dioxide.
Terminology
The following terms relate to conditions that may occur while diving. The prefix hyper- means “too much.” The prefix hypo- means “too little.”
- Hypercapnia: Too much carbon dioxide
- Oxygen toxicity : Too much oxygen
- Hyperthermia: Too hot
- Hypocapnia: Too little carbon dioxide
- Hypoxia: Too little oxygen
- Hypothermia: Too cold
Hypercapnia
Hypercapnia is a potentially fatal condition for divers that can be caused by an excessive build-up of carbon dioxide in the respiratory and circulatory system. Elevated levels of carbon dioxide lead to headache, confusion, a feeling of breathlessness, and, eventually, loss of consciousness.
Hypercapnia is sometimes associated with full-face masks, rebreathers, and skip-breathing (open circuit). It is not very common in recreational open circuit diving, although it may still occur, especially when skip-breathing or hyperventilating at depth. Therefore, we recommend breathing slowly and deliberately when diving and taking two or three slow, full breaths before ascending and keeping a close watch on your buddy or dive professional.
Shallow Water Blackout
Shallow water blackout can occur when a diver is not using scuba equipment, that is, freediving or snorkeling. It is the opposite of hypercapnia. Excessive hyperventilation (more than five repetitions of deep inhaling and exhaling) before breath-hold diving may lead to shallow water blackout. Three to four normal, full breaths are enough for most people.
When a diver hyperventilates excessively before a breath-hold dive, carbon dioxide levels will become extremely low. Because the carbon dioxide level stimulates breathing (and not low oxygen levels), this stimulus will not be present even when oxygen levels become too low. At depth, the increased oxygen partial pressure in the lungs of the diver allows the respiratory system to receive oxygen. However, when the diver makes an ascent (or goes to shallow depths), the partial oxygen pressure in his or her lungs will drop. As a result, the delivery of sufficient oxygen is interrupted, which will lead to a blackout and possible drowning. If you feel light-headed, nauseated, or the beginnings of a headache, you should stop and rest. Get your breathing back to normal before deciding to continue or to stop and get out of the water.
Effects of Oxygen
Oxygen is required to sustain life and the body requires quite a specific amount of oxygen to function properly. Too much, too little, or more than average amounts of oxygen over a long duration can each cause serious health problems.
In the “Physics” unit, you learned about partial pressure. For the sake of scuba-diving calculations, air is considered to be made up of 21% oxygen and 79% nitrogen at sea level. So, the partial pressure of oxygen at sea level is 0.21. As you descend underwater, the pressure increases, and so do the partial pressures of each gas.
In basic terms. your respiratory and circulatory systems will operate within an oxygen partial-pressure limit of 1.6 bar/ata (maximum) and 0.16 bar/ata (minimum). Going above or below these parameters carries very real risks.
Oxygen toxicity
Hyperoxia/ Oxygen Toxicity – is when the oxygen partial pressure exceeds 1.6 bar/ata (considered the maximum upper limit for recreational diving) or when a diver is exposed to elevated partial pressures of oxygen for a number of minutes exceeding those recommended in the universally used NOAA (National Oceanographic Atmospheric Administration)
This exposure may lead to any number of the following symptoms: (VENTID)
- Visual Disturbances- Tunnel vision
- Ear tinnitus – ring noise in ears
- Nausea
- Twitching of Facial muscle, Tingling sensation
- Irritability, euphoria, restlessness and anxiety
- Dizziness,
- Convulsions and choking under water – death
The symptoms may be sudden or gradual. Generally, open circuit air divers will be unlikely to experience this. Your depth limits and your no decompression limit (NDL) will not allow you to build up a partial pressure of oxygen that could be harmful.
Always use Dive computer and add the mix, check the depth and PaO2 as 1.4
You can stay safe by not exceeding these limits. The maximum recreational depth limit is 40 meters/130 feet for divers who have the appropriate training and experience.
It is, however, possible with nitrox-certified divers who are trained to use higher concentrations of oxygen in their breathing gas to approach closer to the limits where oxygen toxicity is a tangible problem. Specialized training is required for nitrox diving.
IMPORTANT: The oxygen partial pressure limit of 1.4, for recreational dive,
Overexertion
You can experience overexertion by swimming against a current for long distances or carrying excessive weight. You may feel tired, short of breath, and weak. You may also have a tendency for your muscles to cramp and for you to feel panicky. What should you do?
Stop, breathe, and think about the situation.
To counteract the results of overexertion, work out a rational approach and implement it. For example, overexertion at the surface requires you to establish buoyancy, rest, catch your breath, signal for help, and move slowly to the boat or shore. If overexertion occurs underwater, stop, breathe, and think. And do not neglect to signal that you have a problem to your buddy or dive professional.
Overheating and Hypothermia
In an ideal world, it would be wonderful to be neither hot nor cold underwater. To achieve this, wear exposure protection suitable to the conditions you’ll be diving in. If you don’t wear appropriate exposure protection, you could suffer from overheating (hyperthermia) and/or cold (hypothermia). Just 2° Celsius/3.5º Fahrenheit above or below the standard body temperature can lead to either of these conditions.
Water will conduct heat away from your body 20 times faster than air. So, what feels like a mild temperature out of the water can be an effective cold temperature in the water. Further, even with exposure protection, the length of submersion will eventually cool you down to the extent it becomes uncomfortable. As soon as this happens, get out the water and warm up!
Overheating can also be a problem, especially before diving. Your exposure suit should be put on after getting your dive gear ready, just before the actual dive, and taken off right after exiting the water because a suit limits the normal emission of heat in the air. Remember, if you are not feeling comfortable for the environmental conditions that you are in, notify your buddy/divemaster/instructor, and take appropriate action to either cool down or, in the case of cold, warm up.
Remember…
Exposure protection is one of the most important considerations in diving. Make sure you get good advice from your dive center, and choose an exposure suit that is best for the environment you are diving in.
Effects of Over heating:
Heat Exhaustion :
Although your body can cool itself in relatively hot conditions, your exposure suit can interfere with its ability to do so. Perspiration provides a principle means to dissipate heat, but wetsuit or dry suits prevent evaporation by cooling.
avoid exercising or exertion in hot climate
prepare your gear first and then wear the wet suit
have a shower to cool you down, which will keep you cool
avoid direct exposure to sunlight, seek shady area
A diver suffering from heat exhaustion has,
weak and rapid breathing
weak and rapid pulse
heavy sweating.
if a diver with heat exhaustion remains hot or continues to heat, the physiological control mechanisms will eventually fail, and result in heat stroke.
Heat stroke:
diver pulse is strong and rapid
Sweating ceases
skin is hot and flushed
at this point the core temperature rises because body’s cooling mechanism have failed. Without medical attention, heat stroke can caused brain and organ damage, and even death is possible.
Heat stroke is an emergency medical condition
Treatment:
remove the exposure suit, cool him
shade and cool place
misting, sponging and fanning
call EMS and shift to medical facility for aggressive aid.
Hypothermia:
Diving in cold environments need to have proper exposure suits,
Diving in cold environments causes shivering and if you ignore and continue diving, as you continue to lose heat, your core temperature will drop, leading to hypothermia. Uncontrollable shivering and impaired coordination indicates mild hypothermia and a reduction in core temp as low as 34 deg Celsius.
As hypothermia advances, uncontrollable shivering and vasoconstriction ceases. This marks the onset of severe hypothermia, indicating that he body’s heating regulation has failed, just as in heat stroke, but in the opposite direction. When this happens, a diver will suddenly feel comfortable as warm blood rushes to the skin. This is dangerous condition, because although the diver no longer feels cold, the body now loses heat at an uncontrolled rate and the core temperature drops rapidly.
Decline in core temperature casuses
Slow in mental process, Drowsy,Uncoordinated and forgetful,
If hypothermia continues unchecked – diver loses consciousness followed by coma and death
Treatment:
End the dive if mild hypothermia
Seek warmth and shelter
Remove wet clothes, cover with blankets, drink warm non alcoholic beverages
Severe hypothermia: above procedures, monitoring for breathing and circulation,
Call EMS.
Provide CPR if needed,
Effects of Nitrogen
Nitrogen represents almost 79% of standard breathing air and has specific properties that can lead to two important dive maladies: nitrogen narcosis and decompression sickness. This topic is covered in elaborate way in other page.
Barotrauma
Body air spaces, such as the lungs, ears, and sinuses, can suffer barotrauma (pressure injury) when descending or ascending. During descent or ascent, the hydrostatic pressure changes, and trouble occurs if the diver fails to equalize the air space. During descent, a barotrauma is called a squeeze. During ascent, a barotrauma is called a reverse block, reverse squeeze, or expansion injury.
