Respiratory System: Inspiration and Intrapleural Pressure

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Questions and Answers

What is the direction of the transpulmonary pressure during inspiration?

Decreases

Becomes more negative

Remains constant

Increases (correct)

What is the main function of the pleural fluid?

To facilitate diaphragmatic contraction

To expand the lungs

To provide cohesion between the chest cavity and the lungs (correct)

To generate negative pressure

What happens to the intrapleural pressure during chest cavity expansion?

It becomes more positive

It becomes zero

It remains constant

It becomes more negative (correct)

What is the value of the intrapleural pressure at rest?

-5 cm H2O Signup and view all the answers

What happens to the lungs when the thorax returns to its original volume?

They recoil inward Signup and view all the answers

What is the formula to calculate the transmural pressure?

Pinside - Poutside Signup and view all the answers

What is the function of intrapleural pressure during inspiration?

To prevent the lung from collapsing inwards Signup and view all the answers

Which muscles are recruited during inspiration?

Diaphragm and external intercostals Signup and view all the answers

What allows the chest to expand in three dimensions?

Rib movements Signup and view all the answers

What happens to alveolar pressure when air flows into the lungs?

It becomes lower than barometric pressure Signup and view all the answers

What is the effect of high transpulmonary pressure on breathing?

It increases the work of breathing Signup and view all the answers

What is the result of inspiratory muscle contraction?

Increase in thoracic cavity dimensions and decrease in intrapleural and airway pressure Signup and view all the answers

What is the relationship between transpulmonary pressure and intrapleural and alveolar pressure?

It is the difference between intrapleural and alveolar pressure Signup and view all the answers

What is the role of trans chest wall pressure in the respiratory system?

It opposes the outward elastic recoil of the chest wall Signup and view all the answers

What happens to the intrapleural pressure when the diaphragm and accessory muscles contract?

It falls, becoming more negative Signup and view all the answers

What is the relationship between transpulmonary pressure and alveolar expansion?

An increase in transpulmonary pressure causes alveolar expansion Signup and view all the answers

What is the direction of air flow when alveolar pressure is less than atmospheric pressure?

Air flows into the lungs Signup and view all the answers

What happens to the lung after a chest wall puncture?

The lung collapses due to inwardly directed elastic recoil Signup and view all the answers

What is the relationship between functional residual capacity and expiration?

FRC is the volume of the lung at the end of a normal expiration Signup and view all the answers

What is the effect of forced expiration on intrapleural pressure?

Intrapleural pressure becomes positive Signup and view all the answers

What is the balance of forces at FRC?

Inward recoil of the lungs is balanced by the outward recoil of the chest wall Signup and view all the answers

What is the direction of air flow during inspiration?

Air flows into the lungs Signup and view all the answers

What is the primary reason for the chest wall expanding to its resting state?

Outwardly directed elastic recoil of the chest wall Signup and view all the answers

What is the average tidal volume for a 70 kg young man at rest?

500 mL Signup and view all the answers

What is the equation to calculate minute ventilation?

Breathing rate x tidal volume Signup and view all the answers

What is the physiological dead space in a healthy individual?

150 mL Signup and view all the answers

What is the total lung capacity for a 70 kg young man?

7300 mL Signup and view all the answers

What is the function of the anatomic dead space?

Airway volume with no gas exchange Signup and view all the answers

What is the inspiratory capacity for a 70 kg young man?

3800 mL Signup and view all the answers

What is the functional residual capacity for a 70 kg young man?

3500 mL Signup and view all the answers

What is the formula to calculate Alveolar Ventilation?

Minute Ventilation - Dead Space Ventilation Signup and view all the answers

What is the volume of air that remains in the conducting zone from the previous breath?

150 ml Signup and view all the answers

What is the frequency of breathing if the tidal volume is 500 ml and the minute ventilation is 7500 ml/min?

15/min Signup and view all the answers

What are the two main sources of resistance that the respiratory muscles must work against to breathe in?

Elastic resistance of the lung and airway resistance Signup and view all the answers

What is the result of an increase in elastic resistance of the lung and/or airway resistance?

Increased work of breathing Signup and view all the answers

What is the total ventilation if the tidal volume is 500 ml and the frequency of breathing is 15/min?

7500 ml/min Signup and view all the answers

What is the volume of alveolar gas?

3000 ml Signup and view all the answers

What is the formula to calculate Physiologic VD?

Anatomic VD + Alveolar VD Signup and view all the answers

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:
1. Elastic resistance of the lung
2. 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.