Respiration PDF

8/11/2019 Respiration PDF

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Respiratory system

Biomechanics of breathing

Negative intrapleural pressure and its importance

Lung volumes and capacities

Spirometry

Molecular properties of gasses

Daltons law

states that the total pressure exerted by a gaseous

mixture is equal to the sum of the partial

pressures of each individual component in a gas

mixture

=

=+++= n

iin ppppp

121 p

V

Vp ii =

partial pressurepi of the i-th component we can determine from volume concentration

Vi/Vand from total pressure of that mixturep


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total atmospheric pressure PB

= 101,325 kPa (760 Torr)

Partial pressures and contents of dry air

Example 1. Calculate partial pressure N2

andO2

at PB = 101,3 kPa; N2 = 78,03 %, O2 = 20,95 %:

pN2

= 0,7803 . 101,3 kPa = 79,11 kPa;

pO2

= 0,2095 . 101,3 kPa = 21,23 kPa.

Henrys law

At a constant temperature, the amount of a given gas dissolved in a given type

and volume of liquid is directly proportional to the partial pressure of that gas.

B

kip

p

VpV

=

at PB

= 101,3 kPa a T = 37 C je: O2

= 0,024 ; CO2

= 0,57

CO2

solubility in water is 24-times higher than for O2

In arterial blood pO2 = 12,0 kPa, pCO2 = 5,3 kPa;How much of O2 and CO2 is dissolved in 1L of blood:

Vp-O2 = 0,024 . 12000 / 101300 = 2,84 ml .l1

Vp-CO2 = 0,57 . 5300 / 101300 = 29,82 ml.l1


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Units of pressure and their conversion

1m

1m

Hg = 13 546 kg.m-3

h = 760 mm Hg = 760 torr . 1 atm = 101 325 Pa. 1 mm Hg (1 torr) = 133.322 Pa

h

H2O = 1000 kg.m-3

h = 10.329 m H2O . 1atm = 101 325 Pa. 1 cm H2O = 98.1 Pa

1 mm Hg = 1.36 cm H2O

p

SI unit: [Pa] = N/m2

using height of liquid with the same pressure effect

Torricelli pokus:

http://brunelleschi.imss.fi.it

p = h ..g

h =height

=density

g = gravitational acceleration

The Respiratory System

Respiratory systemdesigned for gasexchange

Regulates acid-basebalance

Regulates blood pressure

Prevention ofthromboembolism

- upper respiratory tract is above vocal cords

- lower respiratory tract is below vocal cords


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Pathway of RAAS

Human angiotensinogenis 118 amino acids long

Trachea and Bronchial Tree


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Terminal bronchiole Tree

300 million air sacs.Large surface area (60 80 m2).

Cells Types of the Alveoli

Type I alveolar cells

simple squamouscells where gas

exchange occurs

Type II alveolar cells(septal cells)

free surface hasmicrovilli

secrete alveolarfluid containingsurfactant

Alveolar dust cells

wanderingmacrophagesremove debris


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Alveolar-Capillary Membrane

Respiratory membrane = 1/2 m

Exchange of gas from alveoli to blood

4 Layers of membrane to cross- alveolar epithelial wall oftype I cells- alveolar epithelial basementmembrane- capillary basementmembrane- endothelial cells of capillary

Conductive and Respiratory Zones

Conductive zone (Dead volume)

- Conducts air to respiratory zone

- Humidifies, warms, and filters air

Components:

Trachea

Bronchial tree

Bronchioles

Respiratory zone

- Exchange of gases between airand blood

Components:

Terminal bronchioles Respiratory bronchioles

Alveolar sacs


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Intra-pleuralPressures

Helps keep parietal &visceral pleura sticktogether and alveoli inflated

Always subatmospheric(756 mm Hg)

As diaphragm contractsintrapleural pressuredecreases even more (754mm Hg)

Breathing or Pulmonary Ventilation

Air moves into lungs when pressure inside lungs is less than atmosphericpressure

Air moves out of the lungs when pressure inside lungs is greater than

atmospheric pressure

Atmosphericpressure = 1 atmor 760mm Hg

Summary of Breathing


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Compliance of the Lungs

Ease with which lungs & chestwall expand depends upon

1. Elastic recoil of lungs &

2. surface tension

Some diseases reducecompliance

tuberculosis forms scar tissue

pulmonary edema => fluid in lungs& reduced surfactant

Laplaces Law tells us that thepressure within a sphericalstructure with surface tension,such as the alveolus, is inverselyproportional to the radius of thesphere (P=2T/r). That is, at aconstant surface tension, smallalveoli will generate biggerpressures within them than willlarge alveoli.

Compliance refers to the distensibility of the lung and is defined as the change inlung volume produced by a change in pressure.

Thin layer of fluid in alveolicauses inwardly directedforce = surface tension, watermolecules strongly attracted toeach other causes alveoli toremain as small as possible

Detergent-like substance calledsurfactant produced by Type IIalveolar cells lowers alveolarsurface tension

If surfacetension ishigh muchenergy mustbe used toexpandalveoli

Compliance of the Lungs

C = V /P

Emphysema is a disease characterized by dilation of the alveolar spaces anddestruction of the alveolar walls. With their loss, much of the elastic recoil of the lungis also lost.

Normal values are about 200 ml cmH2O-1

Airways resistancethis is a measure of the resistance to airflow in the airways expressed as the airpressure divided by the flow. Normal adult values are about 2 cmH2Ol

-1s


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Determination of PulmonaryDetermination of Pulmonary FFunctionunction

To evaluate symptoms and signs of lung disease

To assess the progression of lung diseaseTo monitor the effectiveness of therapy

To evaluate preoperative patients

Screen people at risk of pulmonary disease

To monitor for potentially toxic effects of certain

drugs/chemicals

Basic techniques:

peak air flow measurement

determination of lung volumes and capacities

forced expiratory volume measurement

flow/volume curve recording


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Tidal volume TV = amountair moved during quietbreathing

Minute ventilation MVR= isamount of air moved in aminute

Maximum voluntaryventilation MVV = volume of

air inspired per minute duringmaximum voluntary hyperventilation. The patient isasked to breathe at 50 min-1as deeply as possible for 15 s.The total volume of inspiredair is measured and multipliedby four. Normal values formen are about 150 l min-1,

Reserve volumes = amountyou can breathe either in orout above that amount of tidalvolume (IRV, ERV)

Residual volume RV = 1200mL permanently trapped air insystem (in the mouth, tracheaas well as the rest in thelungs) This volume increaseswith age and is slightly lowerin women.

Vital capacity & total lungcapacity are sums of theother volumes

Lung Volumes and Capacities

Lung Volumes and Capacities

Vital capacity (VC) is a change ofair volume in the lung which ismeasured between the maximuminspiration level and the maximumexpiration level. Thismeasurement which starts with

inspiration from the maximumexpiration level is called

inspiratory vital capacity (IVC).The examination which starts withexpiration from the maximuminspiration level is calledexpiratory vital capacity (EVC).

VC = IRV + TV + ERV

The functional residual capacity(FRC) is an amount of air whichremains in the lung after normalexpiration.

FRC = ERV + RV

The total lung capacity (TLC) is the air volume in the lung at the end of maximum inspiration.

TLC = IRV + TV + ERV + RV


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Forced Expiratory Volume Measurement

The forced expiration volume per second

(FEV1) is an air volume in liters which anexamined person expires in the first secondof forced expiration after maximuminspiration.

This measured expiratory volume is oftenexpressed as a percentage of the forcedvital capacity, FEV1 /FVC and is called theTiffenea index [%].

FEV1 is called the second vital capacity ordistributed forced expiration per first second.

FEV1/FVC = 80%

Dynamic values of lung ventilation - flow/volume curve recording

Respiration frequency (df) [min-1] is a number of breaths in a given timeinterval. It is usually given in units per minute. The normal respiration rate for a

baby is about 60 min-1 but, by the age of one year, this has fallen to 30-40 min-1

and, in an adult, 12-15 min-1.The respiration rate is not completely regular and changes with exercise, during talking and according tothe environment. The control centre for breathing is in the medulla of the brain and the major influence onthis is the CO2and O2 level in the blood. The medulla, through its influence on the nerves supplying the

respiratory muscles and the diaphragm, can increase or decrease respiration rate and tidal volume.

Maximum expiratory flow values at 25% FVC (MEF25, also FEF25 ) [l.s-1], at 50% FVC (MEF50,also FEF50), and at 75% FVC (MEF75, also FEF75).They are usually given in liters per second and informus about expiratory flows of important segments of adistributed forced expiration curve, respectively theflow volume curve.

The peak expiratory flow (PEF) [l.s-1], also calledthe top expiratory velocity is the greatest flowachieved during forced expiration from themaximum inspiration.


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FORCED EXPIRATION TEST

Simplest test

One of the most informative

Requires minimal equipment Trivial calculations

Majority of patients with lung disease: abnormal forcedexpiration

Classification of ventilation defects

obstructive

restrictive

combined

With purely obstructive ventilation defect, the expiratory flows aresignificantly reduced, while the vital lung capacity is relatively well maintained.

The basic criterion for specifying the obstructive ventilation defect, that means areduced ability to ventilate lungs, is reduction of the FEV1 value.

A low degree of the obstructive ventilation defect is considered a reduction of

the FEV1 value from 60 % to the bottom limit of the standard, respectively to 80%of the standard reference value.

A medium severe degree is considered a FEV1 reduction from 45 % to 59 % ofthe reference value,

a severe degree is then a FEV1 reduction under 45 %.

These criteria are accurate enough only in the case that FEV1/VC index is lowerthan the bottom limit of the standard (approximately 60 % and depends on age ).

Obstructive ventilation defect


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AsthmaCOPD (chronic bronchitis, emphysema and the overlap between them)Cystic fibrosis

Common Obstructive Lung Diseases

-Airflow is reduced because the airways narrow and the FEV1 is reduced-Spirogram may continue to rise for more than 6 seconds because lung takelonger to empty-FVC may also be reduced because gas is trapped behind obstructed bronchi butthis reduction to a lesser extent than FEV1

Asthma is characterized by airwayhyperresponsiveness, which results in reversibleincreases in bronchial smooth muscle tone, andvariable amounts of inflammation of the bronchialmucosa.During an acute

asthma attack, the alreadyinflamed airways narrowfurther due to bronchospasm,which leads to increased

airway resistance

COPD

http://www.youtube.com/watch?v=aktIMBQSXMo


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Large Airway Obstruction

1. Fixed obstruction2. Variable extrathoracic obstruction

3. Variable intrathoracic obstruction

Fixed obstruction1. Post intubation stenosis2. Endotracheal neoplasms3. Bronchial stenosis

Maximum airflow is limited to a similar extent in both inspiration and expiration

Variable extrathoracic Obstruction1. Bilateral and unilateral vocal cord paralysis2. Vocal cord constriction3. Airway burns

The obstruction worsens in inspiration because the negative pressure narrows thetrachea and inspiratory flow is reduced to a greater extent than expiratory flow

Large Airway Obstruction

In variable intrathoracic obstruction1. Tracheomalacia2. Polychondritis3. Tumors of the lower trachea or main bronchus.

The narrowing is maximal in expiration because of increased intrathoracic pressurecompressing the airway.

The flow volume loop shows a greater reduction in the expiratory phase


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Restrictive ventilation defect

With a classic restrictive ventilation defect during forced expiration, the patientexpires a smaller air volume from lungs and this happens at normal or only slightlylower speed.

The criterion for a restrictive ventilation defect for a tentative screeningexamination of a lung function is a lower absolute value of the vital capacity VC withnormal values of FEV1/VC or FEV1/FVC indexes.

The vital capacity is considered lower if its value drops under 80 % of the referencevalue.

When assessing seriousness, a low degree of RVD is considered a VC reductionfrom 60 % to the bottom limit of the standard, respectively to 80 % of the reference

value.

A medium severe degree of RVP is considered a VC reduction from 45 % to x60%,

a severe degree of RVP is considered a reduction under 45 %.

Restrictive Lung DiseasesRestrictive Lung Diseases

A. Intrinsic Restrictive Lung DisordersSarcoidosis

Idiopathic pulmonary fibrosisInterstitial pneumonitisTuberculosis

Pnuemonectomy (loss of lung)Pneumonia

B. Extrinsic Restrictive Lung DisordersScoliosis, Kyphosis

Ankylosing SpondylitisPleural EffusionPregnancy

Gross ObesityTumorsAscitesPain on inspiration - pleurisy, rib fractures


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C. Neuromuscular Restrictive Lung DisordersGeneralized Weakness malnutrition

Paralysis of the diaphragm

Myasthenia GravisMuscular DystrophyPoliomyelitisAmyotrophic Lateral Sclerosis


Restrictive lung disease :

Full lung expantion is prevented by fibrotic

tissue in the lung parenchyma and the FVCis reduced .

Elastic recoil may increased by fibrotictissue lead to increase the airflow

Both FEV1 and FVC may be reducedbecause the lungs are small and stiff ,butthe peak expiratory flow may be preserved

or even higher than predicted leads totall,narrow and steep flow volume loop inexpiratory phase.


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A combined, restrictively obstructive ventilation defect

reduced FVC and also FEV1 but the FEV1 is lowered disproportionately morethan the FVC and therefore the FEV1/FVC ratio is also lower.

Normal

Reduced

Reduced

Restriction

ReducedReducedFEV1/FVC

ReducedNormalFVC

ReducedReducedFEV1

MixedObstructionParameter


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Age:

FVC and flow rates decline with age. The value of FVC increases up to 24years of age and remain stable to age 35.-Elastic tissues deteriorate:

reducing lung compliancelowering vital capacity

-Arthritic changes:restrict chest movementslimit respiratory minute volume

-Emphysema:affects individuals over age 50depending on exposure to respiratory irritants (e.g., cigarette smoke)

Height:All spirometric measurements increase with body weight. It is due to anincrease in number and/or size of alveoli relative to airways, the larger lungsare likely to take longer than smaller one.

Sex:Most pulmonary function values are lower in female than male.

Weight:A spirometric results are positively correlated with weight to the extent thatincreased weight means growth or muscle mass. Beyond this (in obesity)

spirometric values (and lung values specially ERV) decrease with greaterweight.

Instrumentation for measuring lung ventilation volumes, airflows

- Bell spirometers closed system

- Pneumotachographs with volume - flow integration open system

- Whole-body plethysmograph

Pneumocomes from Greek and means lungs, so that the pneumograph is an instrument which gives agraph of lung function; this is actually a graph of lung volume against lime. Tachois also a Greek word andmeans speed so that the pneumotachograph produces a graph of the speed of airflow into or out of thelungs. Spiro is the Latin word meaning breath so that the spirometer is an instrument which measuresbreath. The measurement is usually of volume. Plethois another Greek word meaning fullness so that theplethysmograph is an instrument which gives a graph of fullness. The body plethysmograph gives ameasurement of lung fullness.


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Bell spirometers closed system

An inverted cylindrical container floats in a liquidand the volume of gas in the container can becalculated from the vertical displacement of thecylinder.

Actually a correction factor has to be applied toallow for the fact that the air cools and thuscontracts when it passes from the patient intothe spirometer.

http://ulb.upol.cz/videa/spirometry.mpg

Pneumotachographs with volume - flow integration open system

measures flow rate by means of a transducer through which the patient breathes.The air passes through a fine mesh which offers a small resistance to flow, with theresult that there will be a pressure drop across the mesh in proportion to the flow

rate.

the instrument also calculates volume by integrating the flow signal


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http://www.nationalasthma.org.au/HTML/management/spiro_res/vid_spiro.asp


http://www.nationalasthma.org.au/HTML/management/spiro_res/vid_spiro.asp



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Whole-body plethysmograph

A body plethysmograph consists of a box inwhich the patient sits and breathes through

a hole in the side. Each time the patientinhales volume V, the total volume of their

body increases and so the pressure in thebox increases. If the initial pressure in thebox, Pb, and the air volume, Vb, are known,then the reduction in volume, V, can becalculated from the pressure rise, p, duringinspiration.

PbVb = (Pb+p)(Vb-V)

Boyles law (P V = constant)

Residual Volume Measurement

Helium dilution

Spirometer of known volume and

helium concentration connected to thepatient

Closed circuit

Law of conservation of mass

At beginning After several minutes

Unknown lung volume can be calculated

[He] initial Vs = [He] final (Vs + VL)

We solve for the volume after (the volume of the lung and spirometer), subtract outthe volume of the spirometer, and we get the volume of the lung.Helium poorly soluble in water and thus diffuses very poorly across the alveolar wall.Subjects breath a gas that cannot escape from the lungs


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RV = FRC - ERV

RESIDUAL VOLUME

Peak-flow meter

Peak-flow meters are instruments used to measure peak expiratory flow rate(PEFR).The patient expires as forcefully as possible into the flowmeter which balances thepressure exerted by the flow of air past a movable vane against a spiral spring.

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