Scuba Physiology

In this study, we will first learn about the physiological consequences of breathing gases at higher partial pressure than at the surface. To fully understand these effects we must have a firm understanding of these phenomena. The first thing we need to do is identify the substance within the blood that aids in the transport of oxygen and in what component of the blood is this substance contained? To answer this we must know that oxygen is efficiently transported throughout the body because of a substance called hemoglobin, which is contained in the red blood cells. If the blood did not contain this hemoglobin, our blood would have to circulate 15 to 20 times faster to keep up with our bodies demand for oxygen. We also should know that large amounts of carbon dioxide can be carried by our circulatory system back to our lungs for expiration primarily because carbon dioxide can be converted in bicarbonate. For the body to efficiently transport carbon dioxide to the lungs, the carbon dioxide is converted into bicarbonate. Once back in the lungs the bicarbonate is converted back into carbon dioxide and released through respiration. Next, we need to explain how proper diving techniques and equipment can help avoid exhaustion and build up of carbon dioxide. We should breath deeply while scuba diving to compensate for the increased dead-air space resulting from the regulator, the reduced lung volume resulting from compression of the chest and the increased amount of alveolar carbon dioxide. The practice of breathing slowly is important also to minimize resistance caused by turbelence in the airways. Once we understand this we are ready to learn the physiological mechanism by which voluntary hyperventilation enables a diver to extend breath holding time.

Example: When a breath holding diver submerges in cold water, his heart rate will? His heart rate will decrease due to the mammalian diving reflex.

A breath holding diver must move slowly and deliberately through the water in order to reduce the demand for oxygen. The same diver should also take a few rapid, deep breaths before submerging to reduce his alveolar carbon dioxide level. Moving on, we now need to explain the physiological mechanism that cause a "shallow water black out" and why this condition usually occurs on ascent rather than descent. To understand this we must know that the factor controlling our urge to breathe is not primarily the lack of oxygen in our blood but rather the elevated level of carbon dioxide. Hypoxia is the mechanism that causes a shallow water black out and results when the carbon dioxide level cannot accumulate to a level high enough to stimulate breathing before the tissues consume the oxygen. This black out normally occurs on ascent because the partial pressure of the alveolor oxygen rapidly decreases.

Example: If a diver is down to his last breath at 33 ft of depth what will happen when it ascents to the surface? If this diver barely had enough oxygen at depth to remain conscious and functional, he will black out as he ascends to the surface due to the abrupt decrease in the oxygen partial pressure.

We are now ready to explain the physiological mechanism that causes a "carotid sinus reflex" and how this affects the diver. To understand this phenomenon we must understand a few things. The first is we should know that our carotid sinus receptors stimulate the cardioinhibitory center which is located in the brain. This reflex occurs when the heart rate slows down to a point where it is unable to maintain sufficient blood flow to the brain and this is typically caused by an excessively too tight wetsuit or hood that constricts the neck. Once we understand this mechanism we are ready to understand the physiological effect of increased carbon monoxide levels on the diver and how they can be avoided. We should know that carbon dioxide is difficult to detect because it is odorless and tasteless. We should also know that carbon monoxide bonds with hemoglobin 200 times more readily than oxygen and this bond is so strong that it takes 8 - 12 hours for the circulatory system to eliminate it.

Now we need to explain the physiological mechanism of Decompression sickness and list the common factors that can contribute to its occurence. To understand this we should know that our tissues dont absorb and eliminate nitrogen at the same rate due to different densities in our tissues as well as our blood supply differs among tissues. So those tissues receiving more blood supply will have more gas delivered and eliminated. We should also know that DCS occurs to divers upon surfacing because of bubble formation. This phenomenon does not occur until the ambient pressure is reduced upon ascent. As humans we can tolerate some degree of supersaturation. Now we should define the terms "silent bubbles" as it relates to DCS. The term "silent bubbles" refers to bubbles that are so small they do not cause signs and symptoms of DCS. Silent bubbles cannot be detected by the human eye usually but rather by a Doppler Ultrasound Flowmeter which enables scientists to hear the bubbles as they travel through circulation. Next we should understand why oxygen is given to individuals with signs and symptoms of DCS as a first aid measure. Breathing pure oxygen aids the individual with DCS because it increases the pressure gradient between the nitrogen pressure in the tissues and the alveolar nitrogen pressure. Thus resulting in a significant increase in the driving force of the tissue nitrogen, thus aiding in its elimination. We should also explain the cause of nitrogen narcosis, state the approximate depth at which the disorder occurs and list three common sign/ symptoms. Nitrogen narcosis results from disruptions in the transmissions between nerve cells. Narcosis is usually experienced at a depth of 100 feet but differs highly on an individual basis. Three sign/symptoms of narcosis is poor judgement, decreased coordination, and a feeling of false security. Other signs/ symptoms include foolish behavior, anxious or uncomfortable feelings and a general disregard for safety.

Next we should define the term "barotrauma" and explain how it can occur to the lungs, sinuses and ears of the diver during both ascent and descent. The term barotrauma means pressure injury.

Example of a pressure injury would be a round window rupture. This can be caused an excessively forceful valsalva manuever. This is a primary reason why divers are warned to be cautious when clearing their ears under pressure using the valsalva manuever.

We should also know that vertigo refers to dizziness that a diver may experience while diving. To complete this lesson we should review the basic functions of the ear as well as understand the signs/ symptoms of DCS as well as air embolism.

The Ear: Sound vibrations are transferred from the outer to the inner ear via the ossicles. The ossicles are the series of bones that are attached at one end to the tympanic membrane or the outer ear, and are connected to the oval window of the inner ear. The vestibular canals are located in the inner ear and are responsible for balance and the portion of the ear that is most affected by changes in pressure in the middle ear.

Sign/ Symptoms of DCS and air embolism:

DCS: pain in the joints or fatigue
Air embolism: sudden unconsciousness

The most serious form of lung-expansion injury is an air embolism because air bubbles enter the arterial circulation.


We hope you have enjoyed our lesson on Scuba physiology and have benefited from this knowledge. Please return often for our latest blog.

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