Respiratory system Part 1 - Ventilation

Formas de la respiration , 1961; painting by Jorge de la Vega (Argentine)

Dr Denise Zahiu

Definition

The respiratory system is definite as a biological system consisting of specific organs and structures used for gas exchange.

Organization of the respiratory system

• The air pump consist in airways and lungs, the thoracic cavity and muscles of respiration. It delivers air to and remove the air from the alveoli

• The gas exchange surface is the alveoli

• The circulatory system transport O2 and CO2 between lungs and tissues. Red blood cells are highly specialized for O2 and CO2 transporting.

Organization of the respiratory system

• Mechanisms for locally regulating the distribution of ventilation and perfusion. Ventilation and perfusion are unequal throughout the lungs and the lungs attempt to regulate local air flow and blood flow by feedback-control mechanisms.

• Mechanisms for centrally regulating ventilation. Respiratory control centers in the central nervous system rhythmically stimulate the muscles of inspiration

Roles of the respiratory system

• Respiration

• Olfaction –ventilation delivers odorants to the olfactory epithelium

• Processing of inhaled air before it reaches the alveoli –humidify and heat the inspired air

• Highly compliant pulmonary vessels are like left ventricular reservoir (440 ml)

• Filtering small emboli from the blood

• Biochemical reactions

Respiration

= a process in living organisms involving the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances.

= the action of breathing

= life

Respiratory process stepsA. External respiration

1. Ventilation of lungs (pulmonary ventilation; breathing)

2. Exchange of gases between alveolar air and blood

3. Transport of O2 and CO2 in the blood to the tissues

4. Diffusion of gases between blood and tissues

B. Internal respiration

=Use of O2 in cellular metabolism = oxidative phosphorylation in the mitochondria

Pulmonary ventilation = mechanical process by which the atmospheric air moves into and out of the lungs

Inspiration = the air moves in the lungs

Expiration = the air moves out of the lungs

Pulmonary ventilation

Pulmonary ventilation is triggered and controlled by the respiratory centers located in the brain stem

….this subject will be presented in detail in the 3th lecture

The air flows in and out of the lungs due to the gradient of pressure between the alveoli and external medium

• Pressures involved in the air movement, in lungs:

Intrapleural pressure (PIP)

The chest wall – lung interaction determines the intrapleural pressure

Ortostatism – gravity effect!

Intrapleural pressure value is influenced by gravity and posture of the body

There is pleural fluid in the intrapleural space, secreted by the pleura and drained by limphatics

Alveolar pressure (intrapulmonary pressure) = is the pressure inside the alveoli

Lung at restInspiration

• At the end of expiration it is equal to atmospheric pressure

• It decreases during inspiration due to increase in the thoracic cavity volume.

• It increases during expiration

• The difference in barometric pressure and alveolar pressure determines air flow during inspiration.

Alveolar pressure

Transpulmonary pressure (PTP) is the difference between intrapleural pressure and alveolar pressure

PTP is the radial pressure difference across an airway wall at any point along the respiratory tree

Overview of pulmonary pressures

Collapse and reinflation of the lungs. In A, we assume that PIP rises to PB, so that PTP falls to zero, collapsing the lungs

The pneumotorax is a condition inwhich air accumulates in thepleural space, causing it to expandand thus compress the underlyinglung. With no vacuum to counterthe elastic recoil of lungs, alveoliwill colapse (atelectasis).To re-expand the lungs we have tobring the PTP at the normal value(4-5 mmHg) by any combinationof an increase in PA or decrease inPIP.

Conducting airways deliver fresh air to the alveolar spaces

The nose –humidify and heat the air

Larynx – vocal folds - speech

The time spent by the RBS in the peri-alveolar capillary is only 0.75 seconds

The dead space serve only to air flow.

The alveolar air spaces is the gas exchange region.

Pulmonary compliance (C)= the ability of the lungs to expand / stretch

Describes the distensibility of the lungs and chest wall (change of volume for a given change in pressure)

It is illustrated as a pressure-volume curve

It is related to elastance / elasticity; E =1/C

It has to 2 components: static and dynamic compliance

Static compliance is determined indifferent steady states, whenbreathing movements werestopped.

The static compliance isdetermined by the : Elastic forces of the lung tissue

itself Elastic forces caused by surface

tension of the fluid that linesthe inside wall of the alveoliand other lung air spaces

Pulmonary compliance in pulmonary diseases

• in emphysema destruction of elastic fibers↓ elastance and ↑ compliance

• in restrictive lung diseases (fibrotic lung diseases, inadequate production of surfactant in the alveoli) ↓ compliance

Dynamic pulmonary compliance

Dynamic pulmonary compliance -Hysteresis

Surface tension

Surface tension• There is a thin fluid layer between alveolar cells and air

• Surface tension (T) at air-fluid interface arises because of hydrogen-bonds between water molecules (cohesive forces )

• Surface tension tends to decrease the surface of the air-fluid interface…

• Interplay between cohesive and adherent forces collapsing force

• In a water bubble surface tension exerts a force directed toward the center of the bubble (Law of LaPlace)

• T increases the resistance of lungs to stretch (↓ compliance)

P =2T

r

P Pressure in sphere

r Radius of sphere

T Surface tension of liquid

Law of LaPlace:

Surface tension

• Surfactants disrupt cohesive forces between water molecules ↓ T prevent small alveoli from collapsing & ↑ lungs compliance

• Different concentrations of surfactant in inflated or deflated alveoli differences in T changes in pulmonary compliance

P

x x xx

Surfactant decreases the work of breathing

Surfactant

Measurements of ventilator functionSpirometry

Workings of a simple

spirometer.

Lung volumes and capacities

Functional residual capacity (FRC)• FRC = air/oxygen reservoir

• FRC ↓ = low air/oxygen reserve = rapid desaturation

• Low FRC:

• Sex (woman have a 10% decrease in FRC when compared to men)

• Diaphragmatic muscle tone (individuals with paralyzed diaphragms have less FRC when compared to normal individuals)

• Posture (FRC greatest standing > sitting > prone > lateral > supine)

• Certain lung diseases in which elastic recoil is diminished (e.g., interstitial lung disease, thoracic burns, and kyphoscoliosis,)

• Increased abdominal pressure (e.g., obesity, ascites, pregnancy)

Residual Volume – Helium dilution

• It can’t be measured directly by spirometry

• Mass conservation law! (Lavoisier & Lomonosov)

• Mass = Ct. = concentration x distribution volume

Flow-volume loop

FVC Patients with obstructive lung disease usually have a normal

or only slightly decreased vital capacity. Patients with

restrictive lung disease have a decreased vital capacity.

PEFR expiratory muscle strength

large airway patency (trachea, main bronchi)

overall test validity

also low in obstructive diseases

Forced Expiratory Flow at 25% (FEF25%) flow through medium-size to large bronchi

FEF50% and FEF25%-75%. medium-small airway status

FEF75% smallest airway status

FEV1 normal > 70% of FVC

It is reduced in obstructive lung disease because of

increased airway resistance.

It is reduced in restrictive lung disease because of the low

vital capacity.

FEV1/FVC

LOW: OBSTRUCTIVE (20-30% in severe obstructive

airway disease.)

NORMAL OR ALMOST NORMAL: RESTRICTIVE

>70%

Obstructive disorders- FEV1 LOW ; FVC NORMAL OR

SLIGHTLY higher

Restrictive disorders- FEV1 LOW; FVC LOW

FET 6 s

Higher in obstructive lung disease

Flow-volume in obstructive lung disease:is concave, FEF25-75 too low, FVC normal

Flow-volume in restrictive lung disease:shape normal, FVC low, FEV1 low, FEV1/FVC normal

F/V loop in mixed lung disease: FVC, PEF, FEV1 and FEF25-75 low

Large airway obstruction

• A typical shape of the flow-volume loop is seen in cases of obstruction of the large airways.

• Three different shapes of flow-volume loops can be distinguished.

Variable Extrathoracic Obstruction

• Typically the expiratory part of the F/V-loop is normal: the obstruction is pushed outwards by the force of the expiration.

• During inspiration the obstruction is sucked into the trachea with partial obstruction and flattening of the inspiratory part of the flow-volume loop.

• Vocal cord paralysis, extrathoracic goiter and laryngeal tumours.

Flattening of the inspiratory part of the flow-volume loop

Variable Intrathoracic Obstruction

• This is the opposite situation of the extrathoracic obstruction.

• A tumour located near the intrathoracic part of the trachea is sucked outwards during inspiration with a normal morphology of the inspiratory part of F/V-loop.

• During expiration the tumour is pushed into the trachea with partial obstruction and flattening of the expiratory part of the F/V loop.

Flattening of the expiratory part of the F/V loop.

Fixed Large Airway Obstruction

• This can be both intrathoracic as extrathoracic.

• The flow-volume loop is typically flattened during inspiration and expiration.

• Tracheal stenosis caused by intubation and a circular tracheal tumour.

The flow-volume loop is typically flattened during inspiration and expiration