Anatomy of Chest Wall and Breathing Mechanics Flashcards
Be able to describe the anatomy of the pleural cavity
The lungs and interior of the thorax is covered by pleural membranes, between which is an extremely thin layer of intrapleural fluid.
Understand the relationship between the parietal and visceral pleura and why this is important for inflation
The lungs are effectively stuck to the ribcage due to the relationship between the pleural membranes.
Elastic recoil of the chest wall tries to pull the chest wall outwards, while the recoil of the lungs creates an inward pull. Thus, the lungs maintain shape.
Be able to describe how the muscles of respiration act to increase and decrease thoracic volume
Inspiration uses the diaphragm, external intercostal, sternocleidomastoid and scalene muscles.
Expiration, when active, uses the internal intercostal and abdominal muscles.
Relate Boyle’s law to the mechanics of breathing, inspiration and expiration
Boyle’s Law states that the pressure exerted by a gas is inversely proportional to its volume, therefore;
Increase in lung volume (inspiration) = decrease in pressure
Decrease in lung volume (expiration = increase in pressure
State the mechanical factors that affect respiratory minute volume
Bulk flow of air = (Patm - Palveoli) / resistance
The major determinant of resistance to air flow is the radii of airways.
Explain why intrapleural pressure is always less than alveolar pressure
Alveolar pressure in negative upon inspiration (-1mmHg) and positive upon expiration (1mmHg). Intrapleural pressure is always negative (-3/-6mmHg). Thus, transpulmonary pressure is always positive.
Define pneumothorax
Air gets into the pleural cavity, causing the lung to collapse due to the sudden rise in intrapleural pressure.
State Dalton’s Law
The total pressure of a gas mixture is the sum of the pressures of the individual gases.
State Charles’ Law
The volume occupied by a gas is directly related to the absolute temperature.
State Henry’s Law
The amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid.
Define intercostal muscles
Muscle groups that sit between the ribs and help to move the chest wall during breathing.
“Pump handle” motion increases anterior-posterior dimension of rib cage.
“Bucket handle” motion increases lateral dimension of rib cage.
Define diaphragm
A thin, muscular partition that separates the thorax and abdomen.
Define accessory muscles of respiration
Muscles that assist but do not play a primary role in breathing i.e. the sternocleidomastoid and scalene muscles in inspiration.
Define mechanics of breathing
Air moves in and out of the lungs in response to changes in pressure.
Define alveolar pressure
The alveolar pressure can be either negative or positive. At the end of an unforced expiration, it is equal to atmospheric pressure.
