PHYSIOLOGY OF RESPIRATORY SYSTEM (Lecture II) Universiti Malaysia Kelantan, Faculty of Vet. Medicine Dr. Erkihun Aklilu (Lecturer) 11 April 2013
PHYSIOLOGY OF RESPIRATORY SYSTEM (Lecture II)
Universiti Malaysia Kelantan, Faculty of Vet. Medicine
Dr. Erkihun Aklilu (Lecturer)
11 April 2013
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
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