Download Mechanics of respiration

Mechanics of respiration
By
Dr. M.B.Bhat.
Mechanics of
Respiration
• Ventilation –Breathing in & out of air from
lungs
• Inspiration –Taking in of air –Active
process
• Expiration –Given out of air –Passive
process (normally) –Active process in
forced expiration
• Normal respiration by
• Negative pressure breathing –
• Advantage –increase venous return
Normal Respiration
• During inspiration –
• By operation of respiratory pump
(Muscle Force)—Thorax expand –along
with Lungs also expand–
• Decreases pressure in thoracic cavity
• By over-coming resistance
• Rushing of air from atmosphere
through the respiratory tract into lungs
• Till intra-pulmonary & atmospheric
pressure equals
• During expiration – (cessation of
inspiratory activity)
• By elastic recoiling – Thorax
assumes its original position –Lungs
get compressed –
• Thoracic cavity pressure rises –
• Air goes out (through the same
routes) –till the air pressure between
intra-pulmonary & atmospheric are
equal
• Hence normal expiration is apassive
process
Mechanism of
respiration
• Involves 3 processes
• Creation of Force (for operation of
respiratory pump) –by respiratory
muscles
• Pressure changes (in the thoracic
cavities)
• Resistance to over come (for air
movements)
Respiratory muscles –Inspiratory
& Expiratory muscles
• Inspiratory muscles –
• Chief inspiratory muscles (operate during
quite respiration) –Diaphragm & External
inter-costal muscles
• Expiratory muscles –(operate only during
forceful expiration) –Internal inter-costal
muscles; Abdominal muscles
• Accessory respiratory muscles (operate only
in forceful respiration) –Scaleni, Sternocledomastoid, Anterior Serati, Extensor muscles of
vertebral columns
Diaphragm –Chief
inspiratory muscle
• Nerve supply –Phrenic nerve (C3,4&5)
• Contraction of diaphragm flatten it
towards abdomen by 1.5cm (during
quite respiration) & up to 7cm (during
forceful respiration)
• Result –increase in vertical
dimension of thoracic cavity
• Account for 75% change in
intrathoracic volume during quite
respiration (2/3rd of Tidal volume)
• Though important for respiration not
absolute necessity
External inter-costal muscles
• Origin –From the lower border of one
rib to -• Insertion— upper border of the rib
below
• Course –From origin pass obliquely
forwards & downwards to the lower
rib
• Nerve supply –Nerve to inter-costal
muscles (T1 to T12)
• Contraction –leads to upward &
forward movements of ribs
Thoracic cavity
• Thoracic lid –made up of 1st pair of ribs
jointed between vertebral column &
manubrium sterni –moves very little (in
hyperpnea manubrium moves upwards
–thereby increase antero-posterior
diameter)
• Upper costal area –2nd to 6th ribs –slope
obliquely downward & forward from
posterior to anterior
• Lower costal area –7th to 10th ribs –
swing outward & upwards
• As Thoracic lid is immovable –
• Contraction external inter-costal
muscles pull the lower ribs causing
upward & outward movements
• Upward movements push manubrium
upwards –increase antero-posterior
diameter –Pump-handle movement
• Outward movements –by virtue of the
bowed mid-part of ribs –increase
transverse diameter –Buckethandle movement
• By the contraction of diaphragm—
• Vertical dimension of thoracic cavity
increases – to about
• 1.5cm during quite respiration &
• 7cm during forceful respiration
• By the action of inter-costal muscles
& accessory muscles –
• Circumference of chest increases by –
• 1cm in quite respiration
• 5 to 11cm in forced respiration
• Expiration isa quiet passivemotion
• Cessation of inspiratory muscle activity –
• Due to elastic recoiling tendency of
lungs & chest –expiration takes place
• For forceful expiration –
• Internal inter-costal muscles
(arrangement of which is quiet opposite
to external inter-costal muscles) draws
the ribs inwards & downwards
• Abdominal muscles –increase intra
abdominal pressure and abdominal
contents push diaphragm upwards; &
draws the lower ribs downwards &
medially thereby decrease thoracic
dimension
Pressures of the
thoracic cage
• Two types of pressures
1. Intra-Pleural pressure (Or)
Intra-Thoracic pressure
(Pressure between two pleura)
2Intra-Alveolar pressure (Or)
Intra-Pulmonary pressure
(Pressure in the lungs –alveoli)
Pressures in the thoracic cage
Intra pleural pressure (or) Intra
thoracic pressure –
• Normal value—During quite
respiration
• At the beginning of inspiration= –3
cm H2O
(–2mm Hg)
• At the end of inspiration= –7.5 cm
H2O
(–6mmg)
• Max. in forced inspiration = –20 mm
Hg
• Ma. In forced expiration = +40 mm
Hg
Measurement of intra
pleural pressure
• Direct-• Indirect– Principle --pressure at lower 3rd of
esophagus beneath the lungs is same as
intra thoracic pressure –as esophagus also
present in the thoracic cavity.
• Procedure - Catheter tipped with a balloon
is swallowed & kept at lower 3rd of
esophagus and inflate & connect the
catheter with manometer.
• Reasons for negative pressure (explain)
Significance of intra
pleural pressure
• Always negative (sub-atmospheric)
in normal respiration
• Prevents collapse of alveoli
• Prevents collapse of small air ways
• Aids in venous return (Respiratory
pump)
• In Pneumothorax it becomes equal
to atmospheric pressure –alveoli
collapse
Intra alveolar pressure (or)
Intra pulmonary pressure
• At the beginning of inspiration & at the
end of expiration –it is zero
• During inspiration= minus 1to 4 mm Hg
• During expiration – Plus 1to 4 mm Hg
• During forced inspiration – minus 20 mm
Hg
• During forced expiration – plus 40 mm
Hg
• Measurement – “Mouth pressure”
Trans-pulmonary
pressure
• Difference between intra
thoracic pressure & intra
pulmonary pressure
• Pressure operating inner &
outer wall of the alveoli
• Measure the elastic forces in
the lungs
Resistances
•
•
1.
2.
Elastic resistance &
Non-elastic resistances –are;
Air-way resistance
Non-elastic tissue resistance
Elastic resistance
• Resistance due to elastic
nature of lungs & thoracic cage
• Reciprocal of elastic resistance
is compliance
Compliance
• Compliance is the measure of
stretch ability or elasticity
• StaCompliance is change in
volume by unit change in
pressure (∆V/∆P) – L/cm H2O
• Specific compliance –
Compliance/FRC (in L per cm
H2O per L)
Types of compliances
• As both lungs & thoracic cage
has elastic nature –in the
respiratory system the various
compliances are;
• Lung compliance (L.C)
• Thoracic compliance (Th.C)
• Total compliance (T.C) -- (both
L.C & Th.C)
• Compliance is measured in
static condition
Lung compliance
• Volume of lung expansion for
each unit increase in intra
pleural pressure
• Normal value –0.22L / cm H2O
• (range – 0.09 to 0.26 / cm H2O)
• In infant – 0.005 / cm H2O
Factors affecting lung
compliance
• Size
• Phases of Respiratory cycle –
Deflation & Inflation
• Gravity –less at apices
• Factors Compliance -• Emphysema & Old age
• Factors Compliance -• Pul. Congestion, Pul. edema &
fibrosis --
Total compliance
• Normal value – 0.11L / Cm H2O
• Measurement -- ∆V / ∆P (Airway
pressure –Intra pulmonary
Pressure)
Thoracic compliance
•
•
•
•
Is due to Sterno-costal joints
Normal value – 0.22L / cm H2O
Cannot measure directly
Calculate by using the equation-
Factors determining
lung compliance
1. Elastic nature of pulmonary
tissue (contribute 1/3rd)
2. Surface tension (contribute
2/3rd)
Elastic nature of
pulmonary tissue
• Inter woven of elastin & collagen
fibers like nylon stocking
arrangement
• In emphysema –degradation of
elastin & collagen frame work –leads
to increase distensiblity
• In old age –change in physicochemical properties of elastin &
collagen –increase distensibility
• In pul.fibrosis –increase in interstitial
tissue –stiffness – distensibility
Surface tension
• Of pure water =70dynes/cm
• Of Alveolar fluid without
surfactant =50dynes/cm
• Of Alveolar fluid with surfactant
=5 dynes/cm
• Laplace law – P = 2T/r
• Average size alveoli (100µm) –
the collapsing pressure Or
distending pressure (P)-• with surfactant; P= 4cm H2O
(3 mm Hg)
• Without surfactant; P = 18cm
H2O
Surfactant
•
•
•
•
•
•
•
•
•
•
Surface tension lowering agent
Secreted from Type II cells
Contains –
Dipalmitoyl phosphatidyl choline (DPPC)
(Dipalmitoyl lecithin) – 62%
Phosphatidly glycerol –5%
Other phospholipids –10%
Neutral lipids –13%
Protein – 8%
Carbohydrate – 2%
And calcium ions
Mechanism of action of Surfactant
• Surfactant consist of mainly of–
Phospholipids
• Phospholipids have hydrophilic
(phosphate portion) & hydrophobic (lipid
portion) ends
• The hydrophilic end dissolves into the
alveolar fluid; while the hydrophobic
end facing the exterior.
• As the hydrophobic portion (lipid) has
attraction towards gas, the inward
attraction of the molecules of the
surface area can be minimized &
thereby lowering the surface tension.
Significance of surfactant
• Surface tension (by 1/12th –1/2)
• Compliance
• Respiratory work load is
• Helps in stability of alveoli of unequal size
• Prevent collapse of alveoli during
expiration
• Prevent bursting of alveoli during
inspiration
• Keeps the alveoli dry (prevent pul.
Congestion)
Factors affecting surfactant
• Factors surfactant –
1. Occlusion of main bronchus
2. Occlusion of pulmonary artery
3. Long-term inhalation of 100% O2
4. Cutting of both vagi
5. Cigarette smoking
Factors surfactant –
1. Thyroid hormone -- production
2. Glucocorticoids – accelerate
maturation
Clinical significance of
surfactant
• (Infant) Respiratory distress
syndrome (IRDS) or
• Hyaline membrane disease
(due to deficiency of surfactant
in fetal life)
Pulmonary Resistance
1. Non-elastic tissue resistance
(Viscous resistance)
2. Air-way resistance
Resistance are measured during
dynamic condition
R = ∆P/ V (flow) in liter/sec
Pulmonary resistance
(Total resistance)
• Air way resistance + viscous
resistance
• Obtained by using intra pleural
pressure
• 3.5cm H2O per liter per second
Air way resistance
• Due to friction between molecules of
flowing gas & also with walls of the
tube
• Raw = (Pmouth – Palv) / V in L/sec
• Normal value = 0.6 to 2.4 cm H2O per
Liter per second
• LFTs used in determine Raw are –
• PEFR; MVV; FEV
• Raw --Increases in obstructive type
respiratory diseases
Factors determining air way resistance
•
•
•
•
•
•
•
Factors air way resistance
Decrease lung volume
Decrease in diameter
Total cross sectional area
Increase in Density & viscosity
Types of flow -Dynamic compression of air
ways
Non-elastic tissue
resistance
• Resistance offered by the nonelastic tissue of the thoracic cavity –
Lungs, rib-cage, diaphragm &
abdominal content
• Responsible for the Hysteresis
(closed loop) type of pressurevolume relation of respiratory cycle
• Account for 20% of total pulmonary
resistance
• Itis increased greatly in Emphysema
Thoracic resistance
• Pulmonary resistance (Airway
resistance + viscous resistance)
+ chest wall resistance
• Thoracic cage resistance –no
measurement developed so far
Work done of breathing
• Work done = Pressure x volume
• Normal value of total work done = 0.3 to
0.8 kg m/min
• Elastic work –65%
• Non-elastic work –35%; out of this
• Airway resistance work –28%
• Viscous resistance work (Inertia work)–7%
• Work of breathing increases in –
• Emphysema, asthma, congestive cardiac
failure with dyspnea & orthopnea
• During heavy breathing – air
way work is more
• In obstructive –airway work
increases
• In fibrosis –elastic & nonelastic tissue work increase
• In pulmonary diseases all
types of work are increased
• Work of breathing can be
calculated from relaxation
pressure curve
• During respiration, work done
not only to overcome elastic
resistance, but alsofor
frictional airway & non-elastic
resistance, the respiratory
curve is hysteresis loop
Efficiency of respiratory muscle
• Efficiency = work done per unit
oxygen consumption
• = Useful work X 100/ Total energy
expended (O2 cost)
• O2 cost is 0.5 to 1ml/L of pulmonary
ventilation
• Mechanical efficiency is 8%
• Voluntary hyper ventilation it is —
30%
• In exercise though total work rises;
the energy cost still represents <3%
of total energy expanded.
Thank you