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Respiratory Physiology

Respiratory Physiology. Pulmonary Ventilation . A.K.A. “ Breathing ” Consists of two phases: Inspiration : period of time when air flows into the lungs Expiration : period of time when gases exit the lungs Multiple mechanic factors work together to promote these gas flows. Inspiration.

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Respiratory Physiology

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  1. Respiratory Physiology

  2. Pulmonary Ventilation • A.K.A. “Breathing” • Consists of two phases: • Inspiration: period of time when air flows into the lungs • Expiration: period of time when gases exit the lungs • Multiple mechanic factors work together to promote these gas flows

  3. Inspiration • Diaphragm and intercostals muscles contract • Diaphragm moves inferiorly and flattens during contraction, causing height of thoracic cavity to increase • Intercostals contraction lifts the ribcage and thrusts sternum forward, increasing anterioposterior and lateral dimensions (circumference) • Lungs adhere tightly to the thorax walls (due to surface tension of fluid between pleural membranes), they are stretched to the new, larger size of the thorax. • As intrapulmonary volume increases, gases with in the lungs spread out to fill the larger space. • Resulting decrease in the gas pressure in the lungs produces a partial vacuum (pressure less than atmospheric pressure), which sucks the air into the lungs.

  4. Expiration • Passive process that depends mostly on natural elasticity of the lungs than on muscle contraction. • As inspiratory muscles relax and resume normal resting length, rib cage descends and lungs recoil. • As the thoracic and pulmonary volume to decrease, gases inside the lungs are forced closer together and intrapulmonary pressure rises to above atmospheric pressure. • This causes gases to flow out to equalize pressure inside and outside of the lungs. • Normally this is a passive process, but if passageways are narrowed due to spasms of bronchioles (asthma) or clogged with mucus/fluid (bronchitis/pneumonia), it becomes an active process, using intercostal muscles to help depress rib cage and abdominal muscles to help squeeze air out of lungs.

  5. Pulmonary Ventilation • Mechanical process that depends on volume changes in the thoracic cavity • Important physics rule to remember for breathing mechanics: • Volume changes lead to pressure changes • Pressure changes lead to flow of gases to equalize pressure • Boyle’s Law: (when temp constant) P1V1 = P2V2 • P = pressure in mm Hg • V = volume in cubic mm

  6. Events of Inspiration

  7. Steps of Expiration

  8. Respiratory Adjustments: Exercise • Ventilation can increase 10-20x during exercise • Breathing becomes deeper and more vigorous (“Hyperpnea”), but respiratory rate may not be significantly changed. • Any respiratory changes meet metablolic demands so O2/CO2 levels in the blood are not altered. • Change in breathing is prompted by rising CO2 and declining O2, which causes drop in blood pH.

  9. Respiratory Adjustments: High Altitude • At elevation above 8000ft, air density and oxygen pressure are lower, which may cause symptoms of “acute mountain sickness” (AMS) • Respiratory and hematopoietic adjustments occur called “acclimiatization”. • Chemoreceptors become more responsive to increases in CO2/decreases in O2, resulting in increased ventilation. • Within a few days, respiratory volume stabilizes at a level 2-3 L/min higher than at sea level.

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