PHYSIOLOGY OF RESPIRATORY SYSTEM (Lecture II)

Universiti Malaysia Kelantan, Faculty of Vet. Medicine

Dr. Erkihun Aklilu (Lecturer)

11 April 2013

Respiratory physiology

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Spirometer

Lung Volumes

Functional Residual Capacity

The volume of gas left in the lungs at the end of normal tidal expiration

Maintains relatively constant gas tensions with each breath

Preventing rapid changes in alveolar gas with changes in ventilation or inspired gas

Increasing the average lung volume during quiet breathing, reducing work of breathing due to shape of compliance curve

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Lung Volumes

Functional Residual Capacity

FRC and RV usually increase together

An increase in RV, without an increase in TLC leads to a reduced VC

The normal ratio RV/TLC ~ 15-30% (1.2/6.0 l)

Hyperinflation, in itself, does not produce pulmonary disability

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Lung Volumes

Disadvantages of a high FRC

Reduced rate of alteration of alveolar gas composition - eg. anaesthetic induction

Mechanical disadvantage for respiratory muscles,

Limits ability to increase ventilation on demand

Increase dead space

Increase mean intrathoracic pressure & reduce venous return

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Lung Volumes

Factors Affecting FRC

Body size

Sex

Age

Diaphragmatic muscle tone

Posture

Lung disease

Chest wall

Alveolar-ambient pressure gradientPage 7

Floating Property of the Lung

Lungs of dead animalso Because of remains of residual volume in the lung ,

excised lung sections of dead animal or slaughtered animals floats in water

Fetal lungs o Consistency – like liver, no air, sink in watero After birth, the first one breath leaves residual air the

lungs making it to float in water (determine whether newborn animal was born dead?)

Pneumonic lungso Due to consolidation, lung tissues sink in water

Respiratory System

Mechanisms of Respiration

Ventilation:

Involves inspiration and expiration processed

Inspiration:

Is the active part of the breathing process, which is initiated by the respiratory control centre in medulla oblongata (Brain stem).

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Mechanisms of Respiration

Pulmonary ventilation- Breathing- air movement in and out of body

External respiration- Includes all processes involved in exchanging O2and CO2 with the environment Respiratory gas transport

Internal respiration /Cellular respiration- Involves the uptake of O2 and production of CO2 within

individual cells

Variations in breathing state depends on: Frequency of respiratory cycle Depth of inspiration Both

Eupnea: Normal quiet breathing

Dyspnea : Difficulty in breathing

Hyperpnea : Depth & frequency – notable after physical exertion

Polypnea : Rapid shallow breathing (panting)

- Similar to hyperpnoea in regard to frequency but not in depth

Apnea: Transient cessation of breathing

Tachypnea: Excessive rapidity of breathing

Bradypnea: Abnormal slowness of breathing

Terminology for States of breathing

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Respiratory SystemBreathing / Inspiration

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Respiratory System

Respiratory rate: Frequency of Respiration per minute

Number of respiratory per minute

A respiratory cycle------- Inspiration + Expiration

Respiratory rate indicates the health status of an individual

Proper interpretation is required as it is subject to numerous variations

Respiratory rate varies from species to species

Normal resting respiration rate of animals

Animal Cycles/min Range

Horse 15 8 – 16

Cattle 20 15 – 30

Calf 30 24 --36

Pig 15 10 - 20

Piglet 30 24 - 36

Dog 24 18 - 30

Puppy 12 15 - 35

Cat 22 20 - 24

Sheep 15 20 – 30

Lamb 40 36 – 48

Goat 30 25 -35

Factors Affecting Respiratory Rate

Body size

Age

Exercise

Excitement

Environmental temperature

Pregnancy

Degree of digestive fill –- Pregnancy and digestive fill -- restrict the movement of diaphragm

during inspiration; therefore adequate ventilation is maintained by increasing frequency

State of health

Lung Sounds

Lung sounds are used to assess the normal functioning of the lungs

Sound made by high velocity, turbulent air flow in the trachea andbronchi

Low velocity flow in the bronchioles makes no sound

Adventitious sounds- Crackles -- due to edema/exudate within the airways- Wheezes -- due to broncho-constriction, bronchial wall thickening,

external air way compression or pneumonia

Bronchodilation- Dilation of bronchial airways- Caused by sympathetic ANS activation - Reduces resistance

Bronchoconstriction- Constriction of the bronchi- Caused by:

- Parasympathetic ANS activation- Histamine release (allergic reactions)- Asthma in human (difficulty in breathing - rales and rushing sound can be

heard even without stethoscope; vasodilators)

Lung Sounds

Abnormal Appearances of the Lungs

Pneumothorax:- allows air into pleural cavity- Hemothorax - if filled with blood

Atelectasis:- Also called a collapsed lung- Results from pneumothorax

Respiratory Pressures

Partial pressure

The pressure exerted by a particular gas in a mixture of gases

The sum of partial pressures of the gases within a mixture equals the total pressure.- PaO2 = Partial pressure of oxygen in arterial blood- PvCO2 = Partial pressure of carbondioxide in venous

blood

Respiratory Pressures

Partial pressure

Gas content in arteries approximately the same becausenone of it has reached capillary system where gasexchanges (loss of O2 and gain of CO2) take places.

Gas content in venous blood – differ depending on thelocation because of different metabolism associatedwith the function of body part

Respiratory PressuresAtmospheric Pressure

760 mm Hg under standard temperature and pressure

**Gas composition of dry air (atmospheric air) and alveoliGas Atmospheric Alveolar partial

pressure(mm Hg)

Content (%)

Partial pressure(mmHg)

Oxygen 21 159 104 (PO2 )Carbondioxide 0.03 0.23 40 (PCO2)Nitrogen 79 600 569 (PN2 )

47 (PH2O )Total(appoximate)

100 760 760

Humidification (presence of water vapor; PH2O) causes dilution of theother gases. Note: the component of vapor pressure (PH2O) which causesdifference from atmospheric values