Questions and Answers
What is the formula for calculating minute pulmonary ventilation?
Which factor is primarily responsible for the majority of airway resistance?
How does sympathetic adrenergic innervation affect the airways?
What is the typical tidal volume in a healthy adult at rest?
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Which mediators are known to cause bronchoconstriction?
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What does 'compliance' refer to in the context of pulmonary ventilation?
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Circulating catecholamines act on which receptors to cause bronchodilatation?
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Which of the following best explains the effect of lung movement over the chest wall on pulmonary ventilation?
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What factors contribute to reduced chest compliance?
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What is the primary role of surfactant in the alveoli?
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Which statement accurately describes elasticity in relation to lungs?
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What stimulates the synthesis of surfactant in alveoli?
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Which of the following conditions is likely to decrease surfactant production?
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What is the impact of surfactant on muscle effort during lung expansion?
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What best explains why the lungs do not typically collapse?
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Which component of the lung structure plays the primary role in elastic recoil?
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What is the main effect of serotonin on airway diameter?
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What is intrapulmonary pressure during inspiration?
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What does compliance measure in the lungs?
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Which factor does NOT affect airway diameter?
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What is the typical intrapleural pressure at the end of normal expiration?
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Which of the following conditions would reduce lung compliance?
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During forced expiration, what is the maximum intrapleural pressure that can be reached?
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How much do the lungs expand with an increase of one centimeter of water in transpulmonary pressure?
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Study Notes
Pulmonary Ventilation
- Minute pulmonary ventilation is the total volume of air breathed in and out per minute, calculated as Tidal Volume x Respiratory Rate (e.g., 500 ml x 12 breaths/min = 6 L/min).
- Effective pulmonary ventilation (alveolar ventilation) measures the air volume exchanged between the atmosphere and the alveoli per minute, calculated as (Tidal Volume - Dead Space) x Respiratory Rate (e.g., (500 ml - 150 ml) x 12 = 4.2 L/min).
Factors Affecting Pulmonary Ventilation
- Pulmonary ventilation is influenced by surfactant, compliance, pressures in the thoracic cavity, and resistance of air passages.
Resistance to Air Flow
- Tissue resistance accounts for 20% of total resistance, primarily due to friction from lung movement against the chest wall and pleura.
- Airway resistance comprises 80% of total resistance, largely determined by the radius of the airway; increasing radius decreases resistance exponentially (R α 1/r^4).
Airway Diameter Influences
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Nervous Factors:
- Sympathetic adrenergic stimulation leads to bronchodilation.
- Parasympathetic cholinergic stimulation results in bronchoconstriction and increased mucus secretion.
- Non-adrenergic non-cholinergic (NANC) innervation can result in both bronchodilation (e.g., VIP) and bronchoconstriction (e.g., Substance P).
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Chemical Factors:
- Catecholamines (adrenaline & noradrenaline) stimulate bronchodilation through β2-adrenoreceptors.
- Histamine and serotonin provoke bronchoconstriction, while certain prostaglandins (e.g., PGE2) can induce bronchodilation.
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Irritants:
- Dust, smoke, air pollution, and cold air exacerbate airway constriction.
Thoracic Cavity Pressures
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Intrapulmonary Pressure:
- Pressure within the lung alveoli; during inspiration, it becomes -2 mmHg, while during expiration, it reaches +2 mmHg.
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Intrapleural Pressure:
- Pressure within the pleural cavity; remains negative, measuring -3 mmHg at the end of normal expiration and -6 mmHg at the end of inspiration.
Compliance
- Compliance is the ease of lung inflation, defined as the volume change per unit pressure change (transpulmonary pressure).
- Each 1 cm H2O increase in transpulmonary pressure results in a 200 ml lung expansion.
- The overall compliance of the lung and thorax is 130 ml/cm H2O. Reduced compliance may occur due to pulmonary fibrosis or chest wall deformities.
Elasticity
- Elasticity represents the lung's ability to return to its original shape after expansion.
- Elastic recoil, crucial for expiration, is derived from elastic fibers (elastin & collagen) and surfactant-induced surface tension in alveoli.
Surface Tension and Surfactant
- Surfactant is a phospholipid-protein mixture produced by Type II alveolar cells, reducing alveolar surface tension and preventing alveolar collapse.
- Main surfactant stimulants include alveolar stretch, β-adrenergic stimulation, and cortisol.
- Surfactant decreases muscle effort during lung expansion and possesses antibacterial properties.
Conditions Decreasing Surfactant Production
- Respiratory distress syndrome in infants, cigarette smoking, prolonged heart-lung bypass, and long-term exposure to 100% oxygen can all affect surfactant levels.
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Description
Explore the essentials of pulmonary ventilation, including minute and effective pulmonary ventilation calculations. Discover the various factors affecting ventilation, such as surfactant, compliance, and airway resistance, and their impact on overall respiratory health.
