Respiratory Cycle Lecture 3 Flashcards
What are the basic respiratory mechanics
Flow = Pressure / Resistance
Air flows from high to low pressure
Barometric pressure PB= pressure outside lungs
Alveolar pressure PA = pressure inside lungs
At rest there are no external influences on the respiratory system. PA=PB
At inspiration there is an increase in volume of lungs, causing alveolar pressure to fall. Generates pressure gradient which causes air to flow into lungs. PA<pb></pb>
<p>At expiration the lung volume decreases and increases alveloar pressure, so air flow out/ PA>PB</p>
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What are the muscles of respiration?
External and internal intercostal muscles - supplied by T1-T11 nerves, stimulation allows ribs to expand outwards increasing thorax dimensions (decreasing pressure)
Diaphragm - lower ribs, contracts and flattens when you breath in (increases size of thoaric cavity which drops alveolar pressure). To breath out, muslce is relaxed
Acessory muscles are used during really big breathing (scalene and sternocleidomastoid). Scalene lifts first 2 ribs. Sternocleidomastoid lifts out the sternum.
External and internal oblique, rectus and transverse abdominus help to squeeze stomach which reduces size of thoaric cavity
At rest expiration is passive due to elastic recoil which stops diaphragm contracting, returning to dome shaped position making thoaric cavity smaller.
Nerve activity assocaited with breathing -
Diaphragm is stimulated by phrenic nerve
During inspiration, lors of phrenic nerve activity
Expiratory phase has no phrenic nerve activty as diaphragm is relaxing.
What links the lungs to the chest wall?
Equilibrium volume = volume of the structure with no external infleunces
Elastic recoil of lungs - the lungs want to get smaller so lungs are being pulled away from equilibrium volume, so they are a very small volume (residual volume).
Elastic recoil of chest wall - chest wall has large equilbirium volume, chest wall will expand to large equilibrum volume. Chest wall wants to expand outwards.
Elastic recoil of lungs and chest wall in balance - Equal and opposite force sets the functional residual capacity (FRC). Due to pleural fluid, the 2 structures are couple together to create a combined equilbrlium volume.
Descrbie pleural membranes -
Perietal pleura lines the chest wall and is continous with membranes that cover structures eg heart. It allows seperate compartments between each lung, so they can act seperately.
Visceral pleura goes on surface of lungs, the surfactant allows movement between membranes.
Pleural space contains 10-17ml pleural fluid. It reduces friction (energy efficient), it is the ultrafiltrate of plasma, formation of fluid from parietal pleua circulation determined by starling forces; subatomic pleural pressure results in increased hydrostatic gradient, to pull fluid into pleural space. Stomata allows pleural fluid to drain between the parietal pleura and lymphatics.
Pleural fluid is important in coupling lungs to chest wall
Descrbie lungs and chest wall at equilibrium and FRC
LUNGS-
Lung equilibrium volume is small, at FRC lungs are stretched away from equilbrium volume. At FRC lunfs generate inward elastic reoil pressure (as they want to collapse inwards)
Chest wall -
Chest wall equilibrium volume is large, at FRC chest wall compressed away from equibrlium volume. At FRC chest wall generates anoutwatd elastic recoil pressure.
Intrapleural pressure and generation of intrapelural pressure
Generation of intrapelural pressure - At FRC lungs want to collapse to a smaller volume and chest wall wants to spring outwards.
Pleural pressure is more negative than the recoil pressures of the lungs and chest wall, pulling the 2 structures together.
Intrapleural pressure = Refers to the pressure within the pleural cavity. Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, in what is known as negative pressure. Gravity effects intrapleural pressure, more negatvie intrapleural pressure at top of lungs than base of lungs.
Describe lung distending pressure (Pdist)
Pdist = Pin - Pout
Pdist = PA - Ppl
INflation requires a postive Pdist (Pin>Pout)
Describe inspiration
IN quiet breathinng, expiration is the reverse of inspiration and is passive (doesnt require expiratory muscle contraction).
Inspiration muscles contract increasing thoracic volume, Ppl (pleural pressure) becomes more negative.
Lung distending pressure increases
Lungs inflate
Increase in lung volume causes P(A) to fall below P(B)
Air flows into lungs until P(A)=P(B).
During inspiration, the chest wall expands which drops intraplural pressure, increasing lung distending pressure which will increase lung volume. As lung volume goes up, it is being stretched away from its equiilbrlium volume. Recoil pressure will increase and as volume increases, alveolar pressure will decrease, causing apressure gradient for air flow to occur. THe opposite occurs in expiration.
