Respiratory physiology

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Respiratory physiology
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Respiration is the process by which the body
takes in and utilizes oxygen (O2) and gets rid of
carbon dioxide (CO2).
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Respiration can be divided into four major
functional events

• Ventilation Movement of air into and out of
  lungs
• Gas exchange between air in lungs and blood
• Transport of oxygen and carbon dioxide in the
  blood
• Internal respiration Gas exchange between the
  blood and tissues

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Respiratory System Functions

• Gas exchange Oxygen enters blood and carbon
  dioxide leaves
• Regulation of blood pH Altered by changing blood
  carbon dioxide levels
• Voice production Movement of air past vocal
  folds makes sound and speech
• Olfaction Smell occurs when airborne molecules
  drawn into nasal cavity
• Protection Against microorganisms by preventing
  entry and removing them

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Section 1 Pulmonary Ventilation Pulmonary
ventilation means the inflow and outflow of air
between the atmosphere and the lung alveoli,
which is determined by the activity of the
airways, the alveolus and the thoracic cage.
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I Functions of the Respiratory Passageways
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Respiratory System Divisions

• Upper tract
• Nose, pharynx and associated structures
• Lower tract
• Larynx, trachea, bronchi, lungs

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Conducting Zone

• All the structures air passes through before
  reaching the respiratory zone.
• Cartilage holds tube system open and smooth
  muscle controls tube diameter
• Warms and humidifies inspired air.
• Filters and cleans

Insert fig. 16.5
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Respiratory Zone

• Region of gas exchange between air and blood.
• Includes respiratory bronchioles and alveolar
  sacs.

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Airway branching
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Bronchioles and Alveoli
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Thoracic Walls and Muscles of Respiration
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Breathing

• Occurs because the thoracic cavity changes volume
• Insipiration uses external intercostals and
  diaphragm
• Expiration is passive at rest, but uses internal
  intercostals and abdominals during severe
  respiratory load
• Breathing rate is 10-20 breaths / minute at rest,
  40 - 45 at maximum exercise in adults

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Thoracic Volume
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Pleura
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• Pleural fluid produced by pleural membranes
• Acts as lubricant
• Helps hold parietal and visceral pleural
  membranes together

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Ventilation

• Movement of air into and out of lungs
• Air moves from area of higher pressure to area of
  lower pressure
• Pressure is inversely related to volume

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Alveolar Pressure Changes During Respiration
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Principles of Breathing
Functional Unit Chest Wall and Lung
Follows Boyles LawPressure (P) x Volume (V)
Constant
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Principle of Breathing
Follows Boyles Law PV C
At Rest with mouth open Pb Pi 0
Pb
Airway Open
A
Pi
PS
D
1
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Principle of Breathing
Follows Boyles Law PV C

• At Rest with mouth open Pb Pi 0
• Inhalation
• Increase Volume of Rib cage
• Decrease the pleural cavity pressure- Decrease
  in Pressure inside (Pi) lungs

Pb
Airway Open
A
Pi
PS
CW
D
2
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Principle of Breathing
Follows Boyles Law PV C

• At Rest with mouth open Pb Pi 0
• Inhalation
• Pb outside is now greater than Pi- Air flows
  down pressure gradient
• Until Pi Pb

Pb
Airway Open
A
Pi
CW
PS
D
3
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Principle of Breathing
Follows Boyles Law PV C

• At Rest with mouth open Pb Pi 0
• Exhalation Opposite Process
• Decrease Rib Cage Volume

Pb
Airway Open
A
Pi
CW
PS
D
4
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Principle of Breathing
Follows Boyles Law PV C

• At Rest with mouth open Pb Pi 0
• Exhalation Opposite Process
• Decrease Rib Cage Volume
• Increase in pleural cavity pressure -
  Increase Pi

Pb
Airway Open
A
Pi
CW
PS
D
5
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Principle of Breathing
Follows Boyles Law PV C

• At Rest with mouth open Pb Pi 0
• Exhalation Opposite Process
• Decrease Rib Cage Volume
• Increase Pi
• Pi is greater than Pb
• Air flows down pressure gradient
• Until Pi Pb again

Pb
Airway Open
A
Pi
CW
PS
D
6
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Mechanisms of Breathing How do we change the
volume of the rib cage ?

• To Inhale is an ACTIVE process
• Diaphragm

• External Intercostal Muscles

Both actions occur simultaneously otherwise not
effective
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II Respiratory Resistance Including Elastic
Resistance and Inelastic resistance
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Elastic Resistance A lung may be considered as an
elastic sac. The thoracic wall also can be
considered as an elastic element. So during
inspiration the inspiratory muscles must expand
the thoracic cage which are together with the
elastic resistance.
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Elasticity

• Tendency to return to initial size after
  distension.
• High content of elastin proteins.
• Very elastic and resist distension.
• Recoil ability.
• Elastic tension increases during inspiration and
  is reduced by recoil during expiration.

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Compliance

• Distensibility (stretchability)
• Ease with which the lungs can expand.
• The compliance is inversely proportional to
  elastic resistance
• Change in lung volume per change in
  transpulmonary pressure.
• DV/DP
• 100 x more distensible than a balloon.

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Static lung compliance
C DV/DP
100
deflation
Lung volume (TLC)
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normal breathing
inflation
0
0
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Transpulmonary pressure (cmH2O)
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• The elastic forces can be divided into two parts
• the elastic forces of the lung tissue itself
• 2) the elastic forces caused by surface tension
  of the fluid that lines the inside wall of the
  alveoli.
• The elastic forces caused by surface tension are
  much more complex. Surface tension accounts for
  about two thirds of the total elastic forces in a
  normal lungs.

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Surface Tension

• Force exerted by fluid in alveoli to resist
  distension
• Lungs secrete and absorb fluid, leaving a very
  thin film of fluid.
• This film of fluid causes surface tension..
• H20 molecules at the surface are attracted to
  other H20 molecules by attractive forces.
• Force is directed inward, raising pressure in
  alveoli.

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What is Surface Tension ?
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Surface Tension

• Law of Laplace
• Pressure in alveoli is directly proportional to
  surface tension and inversely proportional to
  radius of alveoli.
• Pressure in smaller alveolus would be greater
  than in larger alveolus, if surface tension were
  the same in both.

Insert fig. 16.11
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Effect of Surface Tension on Alveoli size
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Surfactant

• Phospholipid produced by alveolar type II cells.
• Lowers surface tension.
• Reduces attractive forces of hydrogen bonding by
  becoming interspersed between H20 molecules.
• Surface tension in alveoli is reduced.
• As alveoli radius decreases, surfactants ability
  to lower surface tension increases.

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Area dependence of Surfactant action
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Surfactant prevents alveolar collapse
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Factors Contributing to Compliance - Hysteresis
Volume L
6
3
Without surfactant
RV
0
Pleural Pressure
- 30 cm H2O
0
- 15
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Inelastic Resistance The inelastic resistance
comprises the airway resistance (friction) and
pulmonary tissue resistance (viscosity, and
inertia). Of these the airway resistance is by
far the more important both in health and
disease. It account for 80-90 of the inelastic
resistance.
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Airway Resistance

• Airway resistance is the resistance to flow of
  air in the airways and is due to
• 1) internal friction between gas molecules
• 2) friction between gas molecules and the walls
  of the airways

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Types of Flow
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Laminar flow

• is when concentric layers of gas flow parallel
  to the wall of the tube. The velocity profile
  obeys Poiseuilles Law (pg 4311)

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Poiseuille and Resistance

• Airway Radius or diameter is KEY.
• ? radius by 1/2 ? resistance by 16 FOLD - think
  bronchodilator here!!

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Airway resistance increase

• Any factor that decreases airway diameter, or
  increases turbulence will increase airway
  resistance, eg
• Rapid breathing because air velocity and hence
  turbulence increases
• Narrowing airways as in asthma, parasympathetic
  stimulation, etc.
• Emphysema, which decreases small airway diameter
  during forced expiration

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Control of Airway Smooth Muscle

• Neural control
• Adrenergic beta receptors causing dilatation
• Parasympathetic-muscarinic receptors causing
  constriction
• NANC nerves (non-adrenergic, non-cholinergic)
• Inhibitory release VIP and NO ? bronchodilitation
• Stimulatory ? bronchoconstriction, mucous
  secretion, vascular hyperpermeability, cough,
  vasodilation neurogenic inflammation

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Control of Airway Smooth Muscle (cont.)

• Local factors
• histamine binds to H1 receptors-constriction
• histamine binds to H2 receptors-dilation
• slow reactive substance of anaphylaxsis-constricti
  on-allergic response to pollen
• Prostaglandins E series- dilation
• Prostaglandins F series- constriction

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Control of Airway Smooth Muscle (cont)

• Environmental pollution
• smoke, dust, sulfur dioxide, some acidic elements
  in smog
• elicit constriction of airways
• mediated by
• parasympathetic reflex
• local constrictor responses

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III Pulmonary Volume and Capacity
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Pulmonary Volumes

• Tidal volume
• Volume of air inspired or expired during a normal
  inspiration or expiration (400 500 ml)
• Inspiratory reserve volume
• Amount of air inspired forcefully after
  inspiration of normal tidal volume (1500 2000
  ml)
• Expiratory reserve volume
• Amount of air forcefully expired after expiration
  of normal tidal volume (900 1200 ml)
• Residual volume
• Volume of air remaining in respiratory passages
  and lungs after the most forceful expiration
  (1500 ml in male and 1000 ml in female)

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Pulmonary Capacities

• Inspiratory capacity
• Tidal volume plus inspiratory reserve volume
• Functional residual capacity
• Expiratory reserve volume plus the residual
  volume
• Vital capacity
• Sum of inspiratory reserve volume, tidal volume,
  and expiratory reserve volume
• Total lung capacity
• Sum of inspiratory and expiratory reserve volumes
  plus the tidal volume and residual volume

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Minute and Alveolar Ventilation

• Minute ventilation Total amount of air moved
  into and out of respiratory system per minute
• Respiratory rate or frequency Number of breaths
  taken per minute
• Anatomic dead space Part of respiratory system
  where gas exchange does not take place
• Alveolar ventilation How much air per minute
  enters the parts of the respiratory system in
  which gas exchange takes place

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Dead Space

• Area where gas exchange cannot occur
• Includes most of airway volume
• Anatomical dead space (150 ml)
• Airways
• Physiological dead space
• anatomical non functional alveoli

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Basic Structure of the Lung
NO GAS EXCHANGE
DEAD SPACE
Formula Total Ventilation Dead Space
Alveolar Space VT VD VA
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Similar Concept Physiological Dead Space
Healthy Lungs
Diseased lungs
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FVC - forced vital capacity

• defines maximum volume of exchangeable air in
  lung (vital capacity)
• forced expiratory breathing maneuver
• requires muscular effort and some patient
  training
• initial (healthy) FVC values approx 4 liters
• slowly diminishes with normal aging
• significantly reduced FVC suggests damage to lung
  parenchyma
• restrictive lung disease (fibrosis)
• constructive lung disease
• loss of functional alveolar tissue (atelectasis)
• FVC volume reduction trend over time (years) is
  key indicator
• intra-subject variability factors
• age
• sex
• height
• ethnicity

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FEV1 - forced expiratory volume (1 second)

• defines maximum air flow rate out of lung in
  initial 1 second interval
• forced expiratory breathing maneuver
• requires muscular effort and some patient
  training
• FEV1/FVC ratio
• normal FEV1 about 3 liters
• FEV1 needs to be normalized to individuals vital
  capacity (FVC)
• typical normal FEV1/FVC ratio 3 liters/ 4
  liters 0.75
• standard screening measure for obstructive lung
  disease (COPD)
• FEV1/FVC reduction trend over time (years) is key
  indicator
• calculate predicted FEV1/FVC (age and height
  normalized)
• reduced FEV1/FVC suggests obstructive damage to
  lung airways
• episodic, reversible by bronchodilator drugs
• probably asthma
• continual, irreversible by bronchodilator drugs
• probably COPD

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Spirometry
Total Lung Capacity
Forced Vital Capacity - FVC
Residual Volume
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Assessment of RESTRICTIVE Lung Diseases
These are diseases that reduce the effective
surface area available for gas exchange
eg fibrosis / pulmonary oedema
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Assessment of OBSTRUCTIVE Lung Diseases
These are diseases that reduce the diameter of
the airways and increase airway resistance
- remember Resistance increases with 1/radius 4
eg asthma / bronchitis
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Forced Vital Capacity - FVC
FEV1 gt 80 of FVC is Normal or in words - you
should be able to forcibly expire more than 80
of your vital capacity in 1 sec.
Forced Expiratory Volume in 1 sec - FEV1
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OBSTRUCTIVE lung disease
FEV1 lt 80 of FVC
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