Physiologic Effects Of Increased Barometric Pressure

Wilhelm Welslau

Gesellschaft für Tauch- und Uberdruckmedizin [German Society for Diving and Hyperbaric Medicine]

Abstract: Increased pressure has no effect on solid parts of the body or fluids, but it does on gas filled cavities. Pressure effects directly on the middle ear and indirectly effects on the inner ear are described, with particular reference to equalizing pressures in the middle ear and the development of alternobaric vertigo. Pressure effects on the sinuses, airways and lungs occur only when ventilation is impaired. To understand pressure effects on ventilation, the influence of gas pressures on gas exchange and the concept of oxygen window are described. Changes in ventilation are shown on the basis of the alveolar gas equation and the breathing responses to decreased and increased oxygen pressure. Reasons for toleration of hypercapnia, changes between laminar and turbulent gas flows at different pressures, and variation of ventilation responses at increased pressure are discussed. In the final section, the toxic effects of nitrogen and other inert gases, together with those of carbon dioxide, are described with reference to air breathing at increased pressure

Keywords: Pressure effect, middle ear, inner ear, Eustachian tube, pressure equalization, Valsalva manoeuvre, vertigo, alternobaric vertigo, sinus, ventilation, breathing volumes, breathing gas, oxygen, carbon dioxide, nitrogen, inert gas, water vapour, oxygen window, alveolar gas equation, respiratory centre, chemoreceptor, Haldane effect, hypercapnia, laminar flow, turbulent flow, gas density, gas viscosity, Reynolds's number, flow rate, breathing resistance, flow volume loop, maximum voluntary ventilation, nitrogen toxicity, nitrogen narcosis, carbon dioxide toxicity

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