Factors Influencing Pulmonary Ventilation

1. Respiratory Passageway Resistance
1. upper respiratory passageways - relatively large, very little resistance to airflow (unless obstruction such as from food lodging or cancer)
2. lower respiratory passageways - from medium-sized bronchioles on down, can alter diameter based on autonomic stimulation
• a. parasympathetic - causes bronchioconstriction
• b. sympathetic - inhibits bronchioconstriction
• epinephrine - used to treat life-threatening bronchioconstriction such as during asthma and anaphylactic shock (carried by people susceptible to sudden constriction)
2. Lung Compliance & Elasticity
1. Lung Compliance - the ease with which lungs can be expanded by muscle contraction of thorax
• fibrosis - decreases compliance
• blocked bronchi - decreases compliance
• surface tension - alveoli difficult to expand
• thorax inflexibility - decreases compliance
2. Lung Elasticity - the ease with which lungs can contract to their normal resting size (exhalation)
• emphysema - decreases elasticity
3. Alveolar Surface Tension - liquid on surface of alveoli causes them to collapse to smallest size
• surfactant - lipoproteins that reduces surface tension on alveoli, allowing them to expand more easily
• infant respiratory distress syndrome - premature babies that do not yet produce enough surfactant; must be ventilated for respiration

Category: Physiology Notes