L25. Lung Volumes and Pressures Flashcards
(20 cards)
Functions of the respiratory system?
Gas exchange
- To provide oxygen (O2) to the body
- To eliminate carbon dioxide (CO2) from the body
- Short-term regulation of the pH of blood
Non-respiratory functions of the respiratory system?
- Defense against microbes
- Phonation (formation of sound)
- Trapping and dissolving of blood clots
- Ventilation of the airways contributes to body heat and water loss
The thorax?
A closed compartment
1. Sealed at the neck (muscles, connective tissue)
2. Separated from the abdomen by the diaphragm
3. Contains lower part of trachea and two lungs
Wall of the thorax:
- Ribs
- Spinal column
- The sternum
- Intercostal muscles
Function:
- Ventilation
- Protection of lungs
Pleura?
Lungs and thorax are lined by pleura
- Each lung is surrounded by a closed pleural sac
- Pleural sac is composed of two layers of membrane:
1. Parietal pleura = lining of the chest wall
2. Visceral pleura = surface of the lung
- Parietal and visceral pleura are separated by pleural space filled with intrapleural fluid
Airway branching?
Trachea –> bronchi –> bronchioles
–> terminal bronchioles –> respiratory bronchioles –> alveolar ducts –> alveolar sacs
- There are approximately 20-23 airway divisions to the level of the alveoli
- Although the base airway diameter decreases with branching, the overall or total cross-sectional diameter increases so that peripheral airway resistance decreases
- Diameter of a branch is related to the number of alveoli
- Longer airways = more branches and alveoli
- Larger diameter = greater airflow
Steps of respiration?
- Ventilation
- Gas exchange
- Transport
- Gas exchange
- Cellular respiration
Mechanics of breathing?
- Lungs have elastic elements that cause an elastic recoil inwards
- The chest wall has its inherent elasticity due to which it tends to recoil outwards
- This leads to a generation of a negative pressure within the pleural space relative to atmospheric pressure called intrapleural pressure Pip (“suction”)
- When chest expands the lungs expand with it
Transpulmonary pressure - Ptp?
Is the pressure difference between the alveoli and the pleural space = “force acting to expand the lungs”
- Pip provides ‘suction’ to keep lungs from collapsing
- Inspiration requires more negative Pip to expand the lungs
Inspiration process?
Active process, affects pressures
1. “Inspiratory” intercostal muscles and diaphragm contracts
2. Thorax expands (increases in volume)
3. Pip (“suction”) changes from -4mmHg to -7mmHg
4. Ptp increases from 4 to 7mmHg –> lungs expand
5. Palv changes from 0 to -1mmHg at mid-inspiration
6. Palv < Patm –> air moves into the lungs
7. At the end of inspiration Palv = 0mmHg
Expiration process?
Passive, affects pressure
- Quiet expiration is a passive process requiring no muscle contraction, just elastic recoil
- Forced expiration requires use of expiratory muscles e.g. expiratory intercostals, abdominal muscles
Expiration process - forced?
- Inspiratory muscles relax
- Thorax shrinks, pulled by the elastic recoil of the lungs
- Pip rises from -7 to -4mmHg
- Palv rises from 0 to +1mmHg at mid expiration
- Palv > Patm –> air flows out of the lungs
- Palv at the end of expiration is 0mmHg
Alveolar dead space?
- Part of the alveolar volume in alveoli which are inadequately perfused with blood is called alveolar dead space
- Gas exchange is reduced
- In healthy people, alveolar dead space is small (~5 ml) but in some lung diseases it can be much larger
Physiological dead space?
= anatomical dead space + alveolar dead space
Minute ventilation - Ve?
Total gas flow into the lungs per minute or minute volume
Ve = tidal volume, Vt (ml/breath) x frequency of breathing, f (breaths/min)
E.g. 6000mL/min = 500mL x 12 breaths/min
Dead space ventilation - Vd?
Vd = dead space x frequency of breathing
= 150mL x 12/min = 1800mL/min
Alveolar ventilation - VA?
VA = (tidal volume - dead space) x frequency of breathing
= (500mL - 150mL) x 12/min
= 4200mL/min
Deep slow breathing?
- Means that breathing rate decreases so deep space ventilation decreased and alveolar ventilation is increased
(Numbers are on slide 32, lecture 1 in respiratory)
Breathing through snorkel?
- Dead space increases
- Tidal volume increases to maintain alveolar ventilation
(Numbers are on slide 33, lecture 1 in respiratory)
Fast and shallow breathing?
- Minute ventilation decreases
- Dead space ventilation increases
- Alveolar ventilation decreases to 0
(Numbers are on slide 34, lecture 1 in respiratory)
Tidal volume - TV or Vt?
Amount of air inhaled or exhaled in one breath during relaxed, quiet breathing
