Carla, a 24-year-old medical student, is an avid diver. She is with some friends
ID: 58805 • Letter: C
Question
Carla, a 24-year-old medical student, is an avid diver. She is with some friends on a diving excursion in the Caribbean. She finds herself alone submerged approximately 55 feet. She notices a rather large barracuda swimming very close to her. Suddenly the barracuda attacks her by biting her left thigh. Though she is an experienced diver and knows full well how to react under a threatening situation, she panics and makes a direct rush for the surface. The barracuda is nowhere near her, but her focus is to jet back to the boat and examine her wound. Her friends pull her aboard, and she starts complaining of joint pain, and a throbbing headache. Her breathing is mildly labored at this point. Her friends to shore, and bring her to the nearest emergency clinic. Regarding respiratory physiology, how might this scenario associate with gases external and internal to the lungs and blood? Specifically define Charles, Dalton's and Henry's laws. Explain how they relate to respiratory physiology. After you have defined the gas laws, can you draw some reasonable conclusion as to how they may be responsible for Carla's dilemma? What might be the cause of her symptoms? Could her symptoms also be a result of how she reacted after being bitten? What would be considered a logical treatment?Explanation / Answer
The barracuda is any of about 20 species of predatory fishes of the family Sphyraenidae (order Perciformes). Barracudas are usually found in warm, tropical regions; some also in more temperate areas. They are swift and powerful, small scaled, slender in form, with two well-separated dorsal fins, a jutting lower jaw, and a large mouth with many sharp large teeth. Size varies from rather small to as large as 4-6 feet (1.2-1.8 meters) in the great barracuda (Sphyraena barracuda) of the Atlantic, Caribbean, and the Pacific.
Barracudas are primarily fish eaters of smaller fishes, such as mullets, anchovies, and grunts. They are good, fighting sporting fishes, and the smaller ones make good eating. In certain seas, however, lately increasingly they may become impregnated with a toxic substance that produces a form of poisoning known as ciguatera.
Barracudas are bold and inquisitive, and fearsome fishes, that may be/are dangerous to humans. The great barracuda is known to have been involved in attacks on swimmers. In Hawai'i, they have been known to inhabit open waters and bay areas in the shadows, under floating objects. To avoid them, don't wear shiny objects. They are attracted to shiny, reflective things that look like dinner. They cause harm with their sharp jagged teeth and strong tearing jaws; slashing and creating jagged tears in your skin. Should you or another be hurt by one get medical treatment.
Stop any bleeding and treat for shock by keeping yourself or the victim calm and warm.
Dalton's law
The total pressure of a mixture or gases is the sum of the partial pressures of each gas in the mixture; it is only true for ideal gases
Dalton’s law of partial pressures states that the total pressure (Pt) of a gas mixture is equal to the sum of the partial pressures of the individual gases in the mixture. If a sphere contains 10 molecules of the gases X, Y and Z, each exerts a pressure proportional to the number of molecules of that gas that the sphere contains.
Dalton’s law may be stated as:
Pt = P1 + P2 + P3…
Atmospheric Air
Atmospheric air is a mixture of several molecular components. Presuming the air is dry (such that water or H20 exerts no pressure), their concentrations are: Nitrogen (N2): 78.08 percent by volume Oxygen (O2): 20.95 percent Carbon dioxide (CO2): 0.03 percent Argon (Ar): 0.93 percent
Some trace components include neon, krypton, xenon, methane and nitrous oxide.
Those partial pressures may be expressed in barometric millimeters of mercury (mm Hg), which are as follows: Nitrogen: 593 mm Hg Oxygen: 159 mm Hg Argon: 7 mm Hg Carbon dioxide: 0.2 mm Hg
In Respiration and In Therapy
Within the lungs, total pressure may be expressed as:
Pt = P(CO2) + P(O2) + P(N2) + P(H20)
While the pressure of C02 is fairly negligible in the atmosphere, its concentrations are far higher within the lungs, as it is a product of respiration.
By increasing the percentage of any gas in air’s mixture, a higher partial pressure of that gas can be achieved, which is the basis of oxygen therapy. Dalton’s law is used in the practices of pulmonary physiology, ventilator care, medical gas administration, arterial blood gas and pulmonary pathophysiology, among other applications.
Henry's law
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Charles's law (also known as the law of volumes) is an experimental gas law which describes how gases tend to expand when heated
During a dive the diver breathes air at the same pressure as the environment. At a depth of 30 m (90 feet) the pressure is 4 bar, whereas at the surface the pressure is 1 bar. Nitrogen is one of the main components of air (78%). When breathing Nitrogen is dissolved in the blood and body tissue. When a diver starts breathing air under pressure, more Nitrogen will dissolve until a new, higher Nitrogen level is established. At this level the partial Nitrogen pressure in the blood and tissue is the same as the partial Nitrogen pressure in the air. When a diver surfaces, the surrounding pressure and the pressure of the air he breathes drop. The surplus of Nitrogen in the blood and tissue has to be removed. Normally when a diver surfaces slowly, the Nitrogen is transported by the blood to the lungs and is expelled during exhaling. However, when there is too much Nitrogen surplus and the diver surfaces to quickly, Nitrogen is forming small bubbles in the blood and in the tissue. These small bubbles tend to stick together forming larger bubbles. These bubbles can block veins, depriving the body parts from the necessary Oxygen. The symptoms the diver feels ranges from itchy skin and fatigue to serious mental problems as numbness, inability to speak and even death
Hypercapnia
Hypercapnia (or hypercarbia) is a situation in which there is excess Carbon Dioxide. Most commonly this problem occurs when the diver fails to breathe slowly and deeply (due to work for example). Because of the enlarged dead air volume associated with diving, the diver inhales great part of the previous exhaled air, containing increasing levels of Carbon Dioxide. Because of this less Carbon dioxide can be expelled by the respiratory system. Elevated levels of Carbon Dioxide lead to headache, confusion and eventually to loss of consciousness. Since it is the Carbon Dioxide level that stimulates the respiratory system, the diver will breathe faster, resulting in even higher Carbon Dioxide levels. This vicious circle is broken if the diver ceases all activity and starts breathing deeply. Hypercapnia is sometimes associated with full-face masks, (semi) closed scuba (rebreather) and skip-breathing. In recreational diving hypercapnia is not very common.
Hypocapnia - shallow water blackout
Hypocapnia is a situation in which the Carbon Dioxide level is to low. It occurs during excessive hyperventilation (deep in- and exhaling). Hyperventilation can be voluntary or unintentionally. Symptom of hyperventilation is light-headedness and, in case of unintentional hyperventilation, can lead to loss of consciousness.
Hypocapnia during breath hold diving may lead to shallow water black out. When a diver hyperventilates excessively before a breath hold dive, Carbon Dioxide levels will become extremely low. Since it is this level which stimulates breathing (and not low Oxygen levels) this stimulus will not be present, even when Oxygen levels become to low. At depths the increased Oxygen partial pressure in the lungs of the diver allows the respiratory system to get some Oxygen from the air. However, when the diver surfaces (goes to shallow depths), the partial Oxygen pressure in his lungs will drop. The lungs no longer get Oxygen from the air, leading to blacking out due to hypoxia.
Oxygen Toxicity
Breathing Oxygen at high partial pressures makes Oxygen toxic. In atmospheric air at sea level the partial pressure of Oxygen is 0.21 bar. There are two types of Oxygen toxicity:
Central Nervous System (CNS) Oxygen Toxicity
Exposure to partial pressures above 1.4-1.6 bar result in unacceptable risk for this type of toxicity to occur. It results in trembling, nausea, lip-twitching, convulsions and unconsciousness. Breathing air, a diver is exposed to a partial pressure of 1.4 bar at a depth of 57 meters. So in recreational diving this type of toxicity is not common.
Pulmonary Oxygen toxicity
This type of toxicity occurs when a diver is exposed to partial pressures of 0.5-1.4 bar for a long period of time. At a depth of 15 meter the partial pressure is 0.5 bar. Toxicity problems are to be expected after exposures of more than 90 hours. At a depth of 40 meter the partial pressure is 1 bar. Problems are to be expected after a 12 hour exposure. So in recreational diving this toxicity is highly unexpected to occur. Using Oxygen enriched air (Nitrox) makes this toxicity possible, though still not very likely. Symptoms are burning in the chest and an irritating cough. When continuing the exposure, effects get worse.
Carbon Monoxide poisoning
Most often Carbon Monoxide poisoning happens outside the realm of diving. However, a contaminated air supply may cause this problem. Carbon Monoxide (CO) is a tasteless and odorless gas, which usually originates from incomplete burning of fuel due to lack of sufficient Oxygen. Exhaust gas from engines contains Carbon monoxide. When breathing in, Carbon Monoxide binds to the hemoglobin in the blood, forming carboxyhemoglobin. Because Carbon monoxide binds much easier to hemoglobin than Oxygen and does not unbind as easily, the Carbon Monoxide sticks to the hemoglobin, making it useless for the transport of Oxygen. Continuing breathing Carbon Monoxide result in decreasing amount of active hemoglobin, resulting in hypoxia. Carbon Monoxide bound to hemoglobin (carboxyhemoglobin) is far more red than Oxygen bound hemoglobin. Hence Carbon Monoxide poisoning may color the lips and nail-beds of the victim red. However, during diving this may remain unobserved due to equipment and (red) color absorption at depth.
Carbon Monoxide poisoning during diving is more complicated: at depth more Oxygen is dissolved (due to higher partial Oxygen pressure) in the blood than at the surface. This dissolved Oxygen helps meeting the tissue Oxygen requirement, even if part of the hemoglobin is locked out by the Carbon Monoxide binding. When the Carbon Monoxide poisoning symptoms (headache, confusion, narrow vision) occur the diver ascends. Due to decreasing dissolved Oxygen levels in the blood the diver might black out from hypoxia at shallow depths.
Carotid-Sinus reflex
Blood pressure is monitored by receptors called the carotid-sinus receptors, which are located in the carotid arteries. The carotid arteries branch up from each side of the neck, leading to the brain. If blood pressure is high, the carotid-sinus receptors signal the cardioinhibitory center in the brain, which slow down the heart rate and causes vasodilatation (widening of the blood vessels). Low blood pressure stops the signaling of the cardioinhibitory center and heart rate goes up again.
Problems may occur if a divers suit or other equipment is to tight around the neck. The resulting pressure may incorrectly be interpreted by the carotid-sinus receptors as high blood pressure, resulting in a stimulation of the cardioinhibitory centers and a lowering heart rate. Less blood flows to the brain. Since the pressure persists, less blood keeps flowing to the brain. Symptoms are discomfort, light-headedness and eventually loss of consciousness.
Prevention
A diver can take a lot of precautions to prevent accidents to happen such as:
MEDICATION
In case of a diving accident the best one can do is assure respiration and circulation of the victim and provide Oxygen to the victim. Providing Oxygen is essential despite of the cause of the accident: