Lung in extreme environments

Lung in extreme environments - Lung in extreme environments...

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Lung in extreme environments Dr. Karan Madan Senior resident Deptt. Of Pulmonary Medicine
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Introduction Lung - First barrier between the body and its surrounding atmosphere. arious activities expose humans to different environments in which Various activities expose humans to different environments in which the stresses are beyond our physiologic capabilities. Extreme environments & the lung Underwater High altitude pace Space Extreme cold
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History of Diving – Apnoea diving SCUBA osteau agnan Costeau & Gagnan 1943 French navy
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Lung physiology in diving Diving - Exposure to higher than normal ambient pressure. Compression, isobaric, and decompression phases. One atmosphere - 760 mm Hg or 101.3 kPa. One bar corresponds to a pressure of 750 mm Hg, 100 kPa, or 10 msw (Metres of sea water). Depth of 30 msw - pressure of 4 bars 00 sw - ressure equivalent of 11 bars. 100 msw pressure equivalent of 11 bars. 4 bars / 30 msw, the fractional concentration of oxygen is still 0.21 but the partial pressure is 84 kPa.
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Hyperoxia - > 50 kPa , reduction in VC dependent on pressure and exposure time. Unit pulmonary toxic dose (UPTD) - toxic effect equivalent to the exposure to oxygen at 101 kPa for 1 minute. ymptoms of onproductive oughing and a trosternal urning Symptoms of nonproductive coughing and a retrosternal burning sensation before a reduction in VC takes place. The recovery of VC reductions as large as 20%–30% is usually complete within 1 or 2 weeks. Toxic effects of oxygen are mediated by reactive oxygen species, and inflammatory changes in the lung parenchyma are induced.
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Gas density and respiratory mechanical loading Density increases proportionately with pressure. Airway resistance is proportional to density with turbulent flow characteristics a imal e pirator flo rate is in ersel proportional to the sq are Maximal expiratory flow rate is inversely proportional to the square root gas density. When breathing air at a pressure of 4 bars, gas density is 4 times normal and maximum voluntary volume (MVV) and FEV1 are duced by 50% of normal reduced by 50% of normal. To reduce the internal resistance of breathing gas mixtures, helium is usually used instead of air when diving deeper he helium and oxygen mixture breathed in deep experimental The helium and oxygen mixture breathed in deep experimental dives to pressures (500–700 msw) has a fractional concentration of oxygen of less than 2%, with the rest being helium and, sometimes, some nitrogen.
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Respiratory heat and water loss Gas mixtures used for diving are dry so as to prevent icing in the gas supply lines. pecific heat capacity for helium is five times greater than for Specific heat capacity for helium is five times greater than for nitrogen but density is only 0.18 g/L for helium and 1.25 g/L for nitrogen. Therefore, respiratory heat loss when diving with air remains higher compared with diving with helium-oxygen mixtures, gp g yg , because it is the product of density and specific heat capacity that determines heat loss.
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This note was uploaded on 12/03/2011 for the course MEDICINE 350 taught by Professor Dr.aslam during the Winter '07 term at Medical College.

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Lung in extreme environments - Lung in extreme environments...

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