36 Questions
What is the primary purpose of the respiratory system?
To provide oxygen and remove carbon dioxide
Which of the following pressures is responsible for expanding the lungs during inhalation?
Intra-pleural pressure
What is the term for the movement of air in and out of the lungs?
Ventilation
Which of the following is NOT a function of the respiratory muscles?
Regulating body temperature
What is the term for the exchange of oxygen and carbon dioxide between alveolar air and blood in lung capillaries?
Diffusion
What is the effect of 'dead space' on alveolar ventilation?
It decreases the efficiency of gas exchange
What is the term for the pressure that inflates the lung?
Transpulmonary pressure
During inspiration, intrapleural pressure is:
Negative
What is the effect of inspiratory muscles contraction on intrapleural pressure?
Intrapleural pressure decreases
When does air flow into the lungs?
When PAlv is lower than PB
What is the result of high transpulmonary pressure?
Increased work of breathing
What opposes the inward elastic recoil of the lung?
Negative intrapleural pressure
What is the primary function of the diaphragm during inspiration?
Forceful contraction to increase chest cavity volume
What happens to the intrapleural pressure (Ppl) as the chest cavity expands?
It falls slightly
What is the primary purpose of the pleural fluid and membranes?
To provide cohesion between the lungs and chest cavity
What happens to the lungs during inspiration?
They expand to increase volume
What is the transmural pressure calculated as?
The pressure inside the compartment minus the pressure outside
What is the usual value of intrapleural pressure (Ppl) at rest?
-0.5 KPa (-5 cm H2O)
What happens to the transpulmonary pressure (PL) as the chest cavity expands?
It increases
What is the purpose of recruiting accessory muscles during inspiration?
To increase the force of contraction
What is the ratio of anatomical dead space to tidal volume in this example?
1:5
What is the total ventilation in this example?
7500 ml/min
What is the alveolar ventilation in this example?
5250 ml/min
What are the two main sources of resistance that the respiratory muscles must work to overcome?
Elastic resistance and airway resistance
What is the result of an increase in elastic resistance and airway resistance in lung diseases?
Increased work of breathing
What is the volume of alveolar gas in this example?
3000 ml
What is the frequency of breathing in this example?
15/min
What is the primary mechanism by which the chest wall expands to its resting state?
Outwardly directed elastic recoil of the chest wall
What is the pulmonary blood flow in this example?
5000 ml/min
What is the approximate total lung capacity for a 70 kg young male?
7300 mL
What is the formula for calculating minute ventilation?
Breathing rate (R) x tidal volume (VT)
What is the approximate value of residual volume for a 70 kg young male?
1800 mL
What is the term for the volume of air that does not participate in gas exchange?
Dead space
What is the approximate value of anatomic dead space in a healthy individual?
150 mL
What is the term for the sum of the tidal volume and the inspiratory reserve volume?
Inspiratory capacity
What is the value of minute ventilation at rest, given a breathing rate of 15 breaths/min and a tidal volume of 500 mL?
7500 mL/min
Study Notes
Respiratory System Overview
- The respiratory system provides oxygen (O2) and removes carbon dioxide (CO2) through the process of respiration.
Steps in Respiration
- Ventilation: movement of air in and out of the lungs by bulk flow
- Exchange of O2 and CO2 between alveolar air and blood in lung capillaries by diffusion
- Transport of O2 and CO2 through pulmonary and systemic circulation by bulk flow
- Exchange of O2 and CO2 between blood in capillaries and respiring tissues by diffusion
Respiratory Muscles
- Diaphragm: contracts during inspiration, relaxes during expiration
- Intercostals: external and internal intercostal muscles contract during inspiration, relax during expiration
- Accessory muscles: recruited during forced inspiration
Lung Mechanics
- Expansion of the chest cavity causes expansion of the lungs due to the pleural membranes and fluid between them
- Intrapleural pressure (Ppl) is usually slightly negative, falling during inspiration and rising during expiration
- Transpulmonary pressure (PL) rises during inspiration, causing expansion of the lungs
Transmural Pressures
- Calculated as the pressure differential of the inside compartment minus the outside compartment
- PAlv: alveolar pressure
- PPl: intrapleural pressure
- PB: barometric pressure
- PL: transpulmonary pressure (the "distending pressure" that inflates the lung)
- Pw: trans chest wall pressure
- Prs: trans total system pressure
Inspiratory Process
- Intrapleural pressure (PPl) becomes negative during inspiration
- Alveolar pressure (PAlv) becomes lower than PB during inspiration
- Transpulmonary pressure (PL) increases during inspiration
- Inspiratory muscles contract, increasing the dimensions of the thoracic cavity and reducing intrapleural and airway pressure
Lung Volumes and Capacities
- Total lung capacity (TLC)
- Functional residual capacity (FRC)
- Residual volume (RV)
- Tidal volume (VT)
- Inspiratory reserve volume (IRV)
- Expiratory reserve volume (ERV)
- Inspiratory capacity (IC)
Average Volumes and Capacities
- Average values for a 70 kg young man
- Female values are lower on average
Minute Ventilation
- Total ventilation per minute (VE)
- Measured in L/min
- Calculated by breathing rate (R) x tidal volume (VT)
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
- Dead space ventilation (VD) = anatomic dead space + alveolar dead space
Dead Space and Alveolar Ventilation
- Alveolar ventilation (V) = minute ventilation (V) - dead space ventilation (VD)
- Calculated by (500 x 15) - (150 x 15) = 5250 ml/min
Summary of Volumes and Flows
- Total ventilation: 7500 ml/min
- Anatomic dead space: 150 ml
- Alveolar ventilation: 5250 ml/min
- Alveolar gas volume: 3000 ml
- Pulmonary capillary blood volume: 70 ml
- Pulmonary blood flow: 5000 ml/min
Lung Mechanics - Work of Breathing
- Two main sources of resistance: elastic resistance of the lung and airway resistance
- Increased resistance in lung diseases increases the work of breathing and leads to symptoms like dyspnea (breathlessness)
Learn about the respiratory system, lung mechanics, and how pressure differences generate airflow in the chest cavity. Explore the relationship between pressure changes and volume changes.
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