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Respiratory Pump And Respiratory Cycle Notes

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Lecture 5 Respiratory pump and respiratory cycle

Describe the functional anatomy of the respiratory pump including innervation of diaphragm & intercostals muscles o Respiratory pump
 Mechanism that helps to pump blood back to the heart during inspiration
 Intrathoracic pressure decreases during inspiration, causing the pressure in the atria of the heart to drop to around 2.1kPa
 Aspirating blood towards the right atrium from the thoracic vein o Diaphragm
 Sheet of internal skeletal muscle that extends across bottom of the rib cage
 In inhalation, the diaphragm contracts, thus enlarging the thoracic cavity
 Reduces intra-thoracic pressure, & creates suction that draws air into lungs
 Innervation by phrenic nerve o Intercostal muscles
 Groups of muscles that run between the ribs, & help form & move chest wall
 External intercostal muscles, which aid in quiet and forced inhalation
 Internal intercostal muscles, which aid in forced expiration
 External & internal muscles are innervated by the intercostal nerves List muscles of inspiration and expiration t rest, during exercise & during respiratory distress o Diaphragm o Intercostal muscles
 External

• Assist in deep inspiration by increasing the anterioposterior diameter of the chest
 Internal

• Assist in expiration by pulling the ribcage down
 Innermost

• Aid in forced expiration o Accessory muscles of respiration
 Sternocleidomastoid; Scalene; Serratus anterior; Pectoralis major and minor; Upper trapezius; Latissimus dorsi; Erector spinae (thoracic); Iliocostalis lumborum; Quadratus lumborum; Serratus posterior superior and inferior; Levatores costarum; Transversus thoracis; Subclavius Describe the intrapleural space o Space between two membranes in the lung (visceral and parietal) o Contains a thin layer of fluid Explain why intrapleural pressure is negative o Intrapleural/Intrathoracic pressure at FRC= -5cmH2O (5cm water below atmosphere) o If FRC is atmospheric pressure, there is no gas flow

Lungs want to collapse and ribs want to expand, creating negative suction pressure o Breathing in is active, and breathing out is passive Outline the measurement of intrapleural pressure o Directly by introducing a needle to pleural cavity o Indirect method: by introducing the oesophageal balloon into oesophagus State typical values of intrapleural pressure at FRC & during inspiration for breathing at rest o At FRC= -5cmH2O o


During inspiration the pressure is even more negative (8 cmH2O end of inspiration)

Lung volume increases, the elastic recoil of the lungs increases as well

Describe & explain changes that occur in intrapleural pressure, alveolar pressure, gas flow & lung volumes during respiratory cycle o

Intrapleural pressure

Reaches its lowest point at the end of inspiration

Collapsing force of the lung is the difference between intrapleural &
intrapulmonary pressures


Always negative

If intrapleural pressure is increased by that much the lung will collapse

Alveolar pressure

Inspiration stops when the entering air causes alveolar pressure to rise to atmospheric pressure

During expiration, the cycle is reversed, with decrease in lung size causing an increase in alveolar pressure


Lung expansion causes alveolar pressure to become negative & air enters

Air flows out of the lungs, alveolar pressure returns to atmospheric pressure

Gas flow


Inspiration=into the lungs; Expiration=out of the lungs

Lung volumes

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