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Mechanism of breathing..
• BREATHING is an involuntary process which
involves two processes – Inspiration and
• The two processes involves certain bones and
• At rest an adult breathes at a rate of 12-14
breaths/min and the amount of air inspired or
expired per breath is approx. 500ml. Thus 6-7
litres of air is breathed in or out of the lungs per
minute called PULMONARY VENTILATION
• An active process .
• Thoracic cavity expands.
• Pleural cavity pressure decreases.
• Movement of ribs outwards and upwards.(rib
• Descent of diaphragm.(diaphragmatic movements)
• Due to these movements the volume inside the lungs
increases , leading to decrease in pressure inside the
• This decrease in pressure in the lungs relative to
atmospheric pressure(760 mm hg) leads to movement of
air from atmosphere to the lungs.
• 1ST pair of ribs moves and bring about increase in
• 2nd -6th ribs slope downwards and forwards from their joints
with the spinal column.(pump handle movements).
• 7th _10th ribs swing outwards and upwards.(bucket handle
• Responsible for 75% of inspiratory effort
• Thin dome-shaped muscle attached to the lower ribs, xiphoid
process, lumbar vertebra
• Innervated by Phrenic nerve (Cervical segments 3,4,5)
• During contraction of diaphragm
– Abdominal contents forced downward & forward causing increase in
vertical dimension of chest cavity
– Rib margins are lifted & moved outward causing increase in the
transverse diameter of thorax
– Diaphragm moves down 1cm during normal inspiration
– During forced inspiration diaphragm can move down 10cm
• Patients with bilateral nerve palsy but, with intact innervation of
intercoastal muacles have their respiration somewhat laboured but,
it is adequate to maintain
• Transection of spinal chord above 3rd spinal segment is fatal but,
below 5th cervical segment is not because phreic nerve remains
– Pump handle: ribs are stuck down in the front and up in the back
– Bucket handle: ribs are stuck down and in
– Caliper: ribs are stuck pincing in
• Inhalation dysfunction:
– Pump handle: ribs are stuck up in the front and down in the back
– Bucket handle: ribs are stuck up and out
– Caliper: ribs are stuck pincing out
Accesory muscles of inspiration.
These muscles assist with forced inspiration during
periods of stress or exercise
• Attach cervical spine to apical rib
• Elevate the first two ribs during forced inspiration
• Attach base of skull (mastoid process) to top of
sternum and clavicle medially
• Raise the sternum during forced inspiration
The Passive Phase Of Breathing Cycle
• Chest muscles & diaphragm relax contraction.Elastic recoil of thorax & lungs
return to equilibrium.
• Pleural & alveolar pressures rise.Gas flows passively out of the lung.
Active expiration requires abdominal & internal intercostals muscle
Rectus abdominus/abdominal oblique muscles
– Contraction raises intra-abdominal pressure to move diaphragm upward
– Intra-thoracic pressure raises and forces air out from lung Internal
– Assist expiration by pulling ribs downward & inward
– Decrease the thoracic volume
– Stiffen intercostals spaces to prevent outward bulging during straining.
--adductor muscles of vocal chords.
--their contraction is not complete so their main function is protective.
Pressure changes during ventillation-
intra –pulmonary pressure.
• In quiet breathing at end inspiration and expiration this is
equal to atmospheric .ie.760 mm hg.
• As inspiration begins,the volume increases and the pressure
decreases to about 1 mm hg below the atmospheric.
• When expiration follows passively,the elastic recoil causes the
intra-pulmonary pressure to swing slightly towards the
positive side.ie.761 mm hg.
• At the end expiratory position, tendency of lungs to recoil from the
chest wall is just balanced by the tendency of the chest wall to
recoil in the opposite direction.
• This causes a slight subatmospheric pressure of about -2mm hg
between the 2 layers pf pleura at the start of inspiration.
• -ve intra pleural pressure is directly proportional to the amount of
thorasic expansion which occurs.
• During quiet inspiration, lungs are pulled into a more expanded
condition causing intra pleural pressure to decrease to about -
• At end expiration, where the recoil pressure of lungs and chest wall
balance ,intra pleural pressure returns back t0 -2mmhg.
INTRA PLEURAL PRESSURE.
• Vertical expansion is achieved by lowering of
Bucket handle movement
• Transverse (Lateral) increase happens at the rib
• This movement is sometimes referred to as
• The movement comes from the lower portion
due to CARTLIDGE as well as the shape of the
• Lower ribs are shaped in direction of movement.
• Upper ribs are more horizontal.
• It is the outward movement which assists the
diaphragm as well as providing more space for
Pump handle movement
• This movement is less efficient (5-10%)
• Increases the size of the cavity from the
upper chest, from sternum.
• It is called PUMP HANDLE MOTION.
• It is less flexible not as much breath can be
• The expansion will not allow the intake of
Factors affecting intra pulmonary and
intra pleural pressure.Valsalva manouvre- forced expiration against a closed glottis, may
produce a positive intra pulmonary pressure of more than 100 mm hg
above the atmospheric value.
Muller’s manouvre- forced inspiration against a closed glottis can reduce
the intra pulmonary pressure to less than 80 mm hg below the
DEEP INSPIRATION-pressure lowers as much as 30 mm hg.
VALSALVA MANOUVRE-pressure increases by 60 – 70 mm hg.
EFFECT OF GRAVITY.-in standing pressure decreases by -7mmhg, and
sitting pressure decreases by – 2 mm hg.
EMPHYSEMA-loss or decrease in lung elasticity, so it increases intra
INJURY TO THORACIC WALL-causes equalzation of intrapleural and
atmospheric pressure thus causing collapse of lungs , thus causing
• Breath itself is nominal. It is a concept. It is
about shaping the shapeless, snatching order
from chaos. Creation. Breath is the
intellectual emanation that creates the eye of
the storm. How can an emanation support
the physical action of speaking? Through
allowance, ease and trust.
• thank u ..