Physiology of Diving and Aviation PDF

1  Physiology of diving and aviation 2 In deep sea the problem is with HIGH atmospheric pressure In high altitude the problem is with LOW atmospheric pressure 3  I. at the depth As the body descends b...

1  Physiology of diving and aviation 2 In deep sea the problem is with HIGH atmospheric pressure In high altitude the problem is with LOW atmospheric pressure 3  I. at the depth As the body descends beneath the sea, the pressure around the body increases This pressure is the result of 2 forces: The weight of the water column above the body The weight of the atmosphere at the surface 4  A water column exerts a pressure of 1 atm for each 10 m below the surface of the water. Example: a person at 10 m depth is exposed to a pressure of 2 atm. 1 atm weight of air + 1 atm weight of water column 5 6 At depths, high pressure compresses the gases to smaller volumes 7  Boyle’s law High pressure compresses the gases to smaller volumes the volume to which a gas is compressed is inversely proportional to the pressure If the pressure is X2, the volume is 1/2. defined by Robert Boyle 8 Example: If a diver fills his lungs with 6 L of air at sea level and descends to a depth of 10 m (pressure = 2 atm) his lung volume is compressed to 3 L 9 Sea level 10 m 20 m 30 m 40 m 90 m 10 11 While ascending the compressed gas re- expands as the pressure decreases As the diver returns to the surface, the air volume re-expands. If this extra air is not permitted to escape through the nose or mouth during ascending, the lungs will rupture under the force of expanding gases. 12 Problems during Problems during descending ascending due to compression of gases due to re-expansion of gases 13  Special problems during descending Direct effects of pressure during descent Ears - water pressure against the eardrum may cause rupture of the eardrum Sinuses Lungs Lung squizze Eyes Rupture of the vessels in the eyes (due to mask squeeze) mask pressure can be equalized by exhaling through the nose during descent. 14  Special problems during ascending If the diver quicly swims to the surface, surrounding pressure falls rapidly as the diver ascends, the air in the lungs re-expands just as rapidly. Therefore, ascending diver has to keep his/her airway open to exhale the expanding gas; otherwise it is likely to cause pulmonary barotrauma (rupture of the alveoli). 15 Rupture of alveoli alveolar air bubbles (air emboli) are carried to the heart and then to systemic circulation and finally to cerebral circulation. confusion, weakness, dizziness, blurred vision Even with rapid treatment, 16% of air embolism victims die. 16 pneumothorax Following the rupture of the lung (due to overinflation), air escapes into the small, normally airless area between lungs and chest wall. Nitrogen narcosis Oxygen narcosis Decompression sickness 17  Henry’s law At a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas. defined by William Henry 18 When the diver breathes AIR under high pressure for a long time Due to high oxygen and nitrogen pressure in alveolar air Their concentration in blood increases Oxygen and nitrogen partial pressure in tissues also increases 19 Breathing O2 at 4 atm causes seizures and coma Other symptoms Muscle twitchings Dizziness Oxygen toxicity Disturbances of vision Irritability Disorientation 20 Formation of oxygen free radicals Superoxide, hydrogen peroxide Rate of free radical formation > capacity of the antioxidant systems (peroxidases, catalase, SOD) Free radicals oxidize Polyunsaturated fatty acid component of the cell membranes Cellular enzymes damage of the cellular metabolic systems Nervous system is especially susceptible due to high lipid content brain dysfunction 21 Nitrogen dissolves in fat tissues dissolves in the neuronal membranes, changes ionic conductance reduces neuronal excitability (nitrogen narcosis) 22 Decompression sickness When the diver breathes AIR under high pressure for a long time Due to high nitrogen pressure in alveolar air, nitrogen in blood increases Nitrogen partial pressure in tissues also increases If the diver remains at the depth for several hours, nitrogen remains dissolved in the body (mainly in fat tissues) 23 If the diver then suddenly comes back to surface Nitrogen bubbles develop in body fluids block the blood vessels leading to tissue ischemia and tissue death Symptoms depend on the number + size of bubbles 24 Major symptoms: Pain in joints and muscles of the legs and arms (in 85-90% of people) Nervous system symptoms (5-10% ) Dizziness, paralysis, unconsciousness Chokes (2%) Shortness of breath 25 Treatment of decompression sickness pressurized tank to lower the pressure gradually to normal atmospheric level 26 27 Quechua women in the town of Ollantaytambo, Peru. 28 29 30 OXYGEN PRESSURE pO2 ❑ Oxygen molecules dissolved in plasma (i.e., not bound to hemoglobin) are free to impinge on the measuring oxygen electrode. This "impingement" of free O2 molecules is reflected as the partial pressure of oxygen. ❑ Number of O2 molecules dissolved in plasma determines, along with other factors, how many molecules will bind to hemoglobin ❑ Once bound the oxygen molecules no longer exert any pressure (bound oxygen molecules are no longer free to impinge on the measuring electrode). ❑ PaO2 cannot tell us "how much" oxygen is in the blood; for that you need to know how much oxygen is also bound to hemoglobin, information given by the SaO2 and hemoglobin content. 31 OXYGEN SATURATION: SaO2 ❑ The percentage of all the available heme binding sites saturated with oxygen is the hemoglobin oxygen saturation OXYGEN CONTENT: CaO2 CaO2 = Hb (gm/dl) x 1.34 ml O2 /gm Hb x SaO2 + PaO2 x (.003 ml O2/mm Hg/dl). 32 ❑ The human body can adapt to high altitude through both immediate and long-term acclimatization. ❑ At high altitude, in the short term, the lack of oxygen is sensed by the carotid bodies, which causes an increase in the breathing depth and rate (hyperpnea). ❑ However, hyperpnea also causes the adverse effect of respiratory alkalosis, inhibiting the respiratory center from enhancing the respiratory rate as much as would be required. 33  Chemoreceptor The decrease in PaO2 hypobaric hypoxia stimulation hyperventilation resulting in Bicarbonate diuresis resulting water loss, increased PaO2 from respiratory alkalosis and decreased PaCO2. partly masks the decreased PaCO2 in the alveoli ventilatory reaction produces respiratory alkalosis to hypoxia Circulating levels of catecholamines increase, creating an increased heart rate, blood pressure and venous tone34 35 36 37 38 39 ∙ At higher elevations such as in the Andes and Himalayas, the reduced loading of hemoglobin with oxygen is readily apparent, and sustained physical activity is difficult. 40 41 42 43 44 45 46 47 48 ❑ Diamox, acetazolamide is a sulfonamide carbonic anhydrase inhibitor that enhances renal excretion of bicarbonate, producing a mild acidosis. ❑ Carbonic anhydrase is an enzyme catalyses H2CO3 H2O + CO2 lowering blood pH ❑ In kidneys this enzyme allows reabsorption of bicarbonate, sodium and chloride. Inhibiting enzyme these ions are excreted blood becomes acidic ❑ Ventilation increases in response to acidosis, mimicking the process of acclimatization. 49 50 51  Pathophysiology of Pulmonary Edema HVR: Hipoksik ventilatuar yanıt HPV: Hipoksik pulmoner vazokonstriksiyon 52 HAPE: Yüksek irtifa pulmoner ödemi 53 54 55 56 57 58 59 60 61 62 ∙ The intensity of this force is said to be + 1 G because it is equal to the pull of gravity. If the force with which he presses against the seat becomes five times his normal weight during pull-out from a dive, the force acting upon the seat is + 5 G. 63 ∙ If the airplane goes through an outside loop so that the man is held down by his seat belt, negative G is applied to his body; and if the force with which he is thrown against his belt is equal to the weight of his body, the negative force is —1G. 64 65 66 ∙ As the pressure in the vessels of the lower part of the body increases, the vessels passively dilate, and a major proportion of the blood from the upper part of the body is translocated into these lower vessels. 67 68 69 70