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Thorax - Coggle Diagram
Thorax
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Revision
Ventilation
- The mechanical process by which air is inhaled and exhaled through the lungs and airways
- Average respiratory rate is approximately 10-18 bpm at rest • Ventilation: “quiet” vs. “forced”
- Quiet ventilation: during relatively sedentary activities that have low metabolic demands
- Forced ventilation: during strenuous activities that require rapid and voluminous exchange of air • E.g. exercise or presence of respiratory diseases
Definitions
- Dead space (VD): Volume of air that doesn't undergo gas exchange
- Tidal volume (TV; VT ): Volume of air entering lungs at each resting breath (or exiting lungs on passive expiration)
- Inspiratory reserve volume (IRV): Extra air entering lungs with maximal inspiration (on top of TV)
- Expiratory reserve volume (ERV): Extra air expelled from lungs with maximum expiration (after passive expiration)
- Residual volume (RV): Volume of air left in lungs after maximum expiration
- Vital capacity (VC): Total amount of air exhaled after maximal inhalation
- Functional reserve capacity (FRC) = ERV + RV
Ventilation Volumes can change
- E.g. exercise vs rest
- Chest wall dimensions
- Lungs conditions
Boyle's Law
- It describes the inverse relationship between the volume and absolute pressure of a perfect gas at constant temperature.
- PV = K or 𝑉=𝐾/𝑃
- P represent pressure
- V represent volume
- K represent the coefficient
- At room’s temperature, the deviation is negligible for oxygen, nitrogen and of little practical importance for carbon dioxide or nitrous oxide.
- Volume and pressure is inversely proportional, given constant pressure
Mechanics of Inspiration
- Increase volume, reduce alveolar pressure, air drawn into lungs
- Intrathoracic volume is increased by contraction of the muscles that attached to the ribs and sternum
- Increases intrathoracic volume
- Reduces the alveolar pressure
- Negative pressure draws air into the lungs
- Primary muscle in use include:
- Diaphragm
- Scalenes
- Intercostales
- Intercostales externi
- Intercostale interni
Mechanics of Expiration
- Reducing intrathoracic volume increases the alveolar pressure
- Driving air from the alveoli out of the lung, and into the atmosphere
- Healthy individual:
- Quiet expiration is a passive pressure that does not depend on muscle activation
- By elastic recoil of lungs, thorax and connective tissues of stretched inspiratory muscles
- Forced expiration
- During deeper or rapid breathing
- Requires active force by expiratory muscle, e.g. abdominals
- Actions such as: coughing, blowing out a candle
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