Questions and Answers
What is the direction of the transpulmonary pressure during inspiration?
What is the main function of the pleural fluid?
What happens to the intrapleural pressure during chest cavity expansion?
What is the value of the intrapleural pressure at rest?
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What happens to the lungs when the thorax returns to its original volume?
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What is the formula to calculate the transmural pressure?
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What is the function of intrapleural pressure during inspiration?
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Which muscles are recruited during inspiration?
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What allows the chest to expand in three dimensions?
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What happens to alveolar pressure when air flows into the lungs?
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What is the effect of high transpulmonary pressure on breathing?
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What is the result of inspiratory muscle contraction?
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What is the relationship between transpulmonary pressure and intrapleural and alveolar pressure?
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What is the role of trans chest wall pressure in the respiratory system?
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What happens to the intrapleural pressure when the diaphragm and accessory muscles contract?
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What is the relationship between transpulmonary pressure and alveolar expansion?
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What is the direction of air flow when alveolar pressure is less than atmospheric pressure?
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What happens to the lung after a chest wall puncture?
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What is the relationship between functional residual capacity and expiration?
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What is the effect of forced expiration on intrapleural pressure?
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What is the balance of forces at FRC?
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What is the direction of air flow during inspiration?
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What is the primary reason for the chest wall expanding to its resting state?
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What is the average tidal volume for a 70 kg young man at rest?
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What is the equation to calculate minute ventilation?
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What is the physiological dead space in a healthy individual?
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What is the total lung capacity for a 70 kg young man?
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What is the function of the anatomic dead space?
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What is the inspiratory capacity for a 70 kg young man?
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What is the functional residual capacity for a 70 kg young man?
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What is the formula to calculate Alveolar Ventilation?
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What is the volume of air that remains in the conducting zone from the previous breath?
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What is the frequency of breathing if the tidal volume is 500 ml and the minute ventilation is 7500 ml/min?
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What are the two main sources of resistance that the respiratory muscles must work against to breathe in?
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What is the result of an increase in elastic resistance of the lung and/or airway resistance?
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What is the total ventilation if the tidal volume is 500 ml and the frequency of breathing is 15/min?
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What is the volume of alveolar gas?
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What is the formula to calculate Physiologic VD?
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Study Notes
Inspiration
- External inspiration: more forceful contraction of diaphragm and intercostals, recruitment of accessory muscles
- Expansion of the chest cavity causes expansion of the lungs (not the other way around)
- Ribs movements allow the chest to expand in three dimensions
- Intrapleural pressure usually slightly negative (around -0.5 KPa or -5 cm H2O at rest)
Intrapleural Pressure and Transmural Pressures
- Pleural membranes and fluid provide cohesion between chest cavity and lung surface
- Intrapleural pressure (Ppl) falls during inspiration
- Transpulmonary pressure (PL) rises, causing expansion of the lungs
- Lungs are forced to stretch during inspiration, but recoil inward when the thorax returns to its original volume
Transmural Pressures
- Calculated as the pressure differential of the inside compartment minus the outside compartment
- Transpulmonary pressure (PL) is the "distending pressure" that inflates the lung
- Palv = alveolar pressure, PPl = intrapleural pressure, PB = barometric pressure, Pw = trans chest wall, Prs = trans total system
The Inspiratory Process
- Involves changes in intrapleural pressure (PPl), alveolar pressure (PAlv), and transpulmonary pressure (PL)
- PPl becomes more negative during inspiration, opposing inward elastic recoil of the lung
- Alveolar pressure (PAlv) falls, allowing air to flow into the lungs
- Transpulmonary pressure (PL) rises, making the alveoli expand
Expiration
- Respiratory muscles relax, and the process is reversed
- PPl becomes more positive, forcing more air out
Pneumothorax
- Normally, at FRC, inward recoil of the lungs is balanced by outward recoil of the chest wall
- After chest wall puncture, air is sucked into the pleural space, causing the lung to collapse due to inwardly directed elastic recoil
- Chest wall expands to its resting state due to outwardly directed elastic recoil
Lung Volumes and Capacities
- Total lung capacity (TLC)
- Functional residual capacity (FRC)
- Residual volume (RV)
- Average values for a 70 kg young man:
- Tidal volume (VT): 500 mL
- Vital capacity (VC): 5500 mL
- Inspiratory reserve volume (IRV): 3300 mL
- Expiratory reserve volume (ERV): 1700 mL
- Inspiratory capacity (IC): 3800 mL
- Functional residual capacity (FRC): 3500 mL
- Residual volume (RV): 1800 mL
Minute Ventilation
- Total ventilation per minute
- Measured in L/min
- Calculated as breathing rate (R) x tidal volume (VT)
- Typically at rest: R = 15 breaths/min, VT = 500 mL, VE = 7.5 L/min
Dead Space
- Anatomic dead space: airway volume with no gas exchange, typically 150 mL
- Physiologic dead space: anatomic dead space plus areas where gas exchange is dysfunctional
- Physiologic dead space = anatomic dead space + alveolar dead space
Dead Space and Alveolar Ventilation
- Alveolar ventilation (V) = minute ventilation (VE) - dead space ventilation (VD)
Lung Mechanics – The Work of Breathing
- To breathe in, the respiratory muscles must work to overcome two main sources of resistance:
- Elastic resistance of the lung
- Airway resistance (to airflow)
- In many common lung diseases, there is an increase in one or both of these resistances, increasing the work of breathing and giving rise to symptoms such as dyspnoea (breathlessness)
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Description
Learn about the mechanics of breathing, including the role of diaphragm and intercostal muscles, chest cavity expansion, and intrapleural pressure in the respiratory system.