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Physiology 3120
Tom Stavraky

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Respiratory Fick’s Law of diffusion Vgas = (c ΔP A)/T diffusion constant is proportional to the gas solubility and inversely proportional to the square root of its molecular weight Partial Pressue – total pressure times the fractional concentration. In the lungs must subtract 47 mmHg because of water saturation. -BGB is 0.5 um thick. But surface area is 50-100 square meters. 300 million alveoli. - 23 generations of airways. 1-16 trachea  terminal bronchiole is conducting zone, 17-23  respiratory bronchiole to alveolar sac is transitional and respiratory zone. - Intrapleural space has negative pressure Major Inspiratory muscles: diaphragm (innervated by phrenic nerves) and external intercostals. Major expiratory muscles: muscles of the abdominal wall, internal intercostals. Pulmonary compliance = difference in volume / difference in pressure - Lung is most compliant between 10-20 cm H2O. 1/3 of the lungs pressure is caused by the elastic forces and 2/3 is the surface tension. Laplace’s law 2Υ ΔP = r - Tidal Volume – Volume of air inhaled with each breath - Vital Capacity – Volume of air that can be forcibly exhaled after a maximal inspiration - Residual Volume – volume of air remaining in the lungs after a maximal expiration - Functional Residual Capacity – volume of air remaining in the lungs at the end of a normal expiration - Inspiratory Reserve Volume – volume of air that can be forcibly inhaled following a normal inspiration - Expiratory Reserve Volume – volume of air that can be forcible exhaled following a normal expiration - Total Lung Capacity – volume of air in the lungs at the end of a maximal inspiration - Minute Volume or Pulmonary Volume – Volume of air inhaled per minute, tidal volume x frequency of respiration - Forced Expiratory Volume – fraction of vital capacity expired in one second. Normally it is about 80%. In restrictive diseases, the vital capacity is lowered so the FEV is normal (pulmonary fibrosis), but in obstructive diseases (asthma) FEV is reduced much more. - Maximal Voluntary Ventilation – Volume of air that can be moved into and out of the lung in one minute by voluntary effort. - TLC, RV and FRV cannot be measured Helium Dilution method C1V1 = C2(V1+V2) V2 = FRC Alveolar Ventilation = pulmonary ventilation – Dead Space Anatomical Dead Space – 150 ml, air in conductive zone Physiological total dead space – total amount of air that does not participate in gas exchange. Normal subjects would have similar anatomical and physiological dead spaces. Bohr equation for dead space VD (PaCO2− PeCO2) = VD = deadspace VT = tidal volume VT PaCO2 Alveolar Ventilation = (tidal volume – dead space) x respiration rate (breathing through a tube will create a larger tidal volume and less exhaled PCO2 more inhaled CO2) O2 – highest in inspired gas  expired  alveolar  arteries  veins CO2 – Veins  alveolar gas, arteries  expired gas  inspired gas H20 – higher inside N2 – higher outside VO2 (l/min) = [(tidal volume x bpm) x %O2 inhaled] – [(tidal volume x bpm) x %O2 exhaled)] VO2 max – 30-40 ml/min/kg. Affected by CV, musculoskeletal and respiratory Henry’s Law Concentration of a dissolved gas = pressure * solubility - O2’s not very soluble - O2 transport on hemoglobin is the major form of transport Oxyg
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