Physiology of respiration
DR/Noha Elsayed
2015--2016
Gas exchange occur as a result of pressure gradient changes across
the AC(alveolar-capillary) membrane .
• Alveolar pco2=40
alveolar po2=100
• Capillary pco2=5
Capillary po2=40
So,Gas diffusion from high concentration to lower seeking
equilibrium
Factors affect the diffusion of gases across the membrane
V/Q (ventilation /perfusion mismatch):May be due to inadequate ventilation or perfusion or both
Three Types of
Ventilation-Perfusion Mismatch
• Low ventilation-perfusion ratio
– Perfusion exceeds ventilation
• High ventilation-perfusion
– Ventilation exceeds perfusion
• Silent unit
– Result of decreased ventilation and perfusion (pneumothorax,
ARDS)
Inhalation
Exhalation
External intercostal muscles (Between
the ribs): Contract
Ribs & Sternum: Move upwards &
outwards
Width of chest: Increases
Depth of chest: Increases
Diaphragm: Descends
Elastic tissue of lungs: Stretched
Air pressure within alveoli <
Atmospheric pressure ---- & so air is
sucked into alveoli from atmosphere
External intercostal muscles: Relax
Ribs & Sternum: Move downwards &
inwards
Width of chest: Decreases
Depth of chest: Decreases
Diaphragm: Ascends
Elastic tissue of lungs: Relax
Air pressure within alveoli >
Atmospheric pressure ---- & so air is
forced out of alveoli
Neurocontrol of Respiration
Lung volumes are classified into:
1.
Tidal volume (TV):Is the amount of air inspired during normal,
relaxed breathing
2.
Inspiratory reserve volume (IRV): Is the additional air that can be
forcibly inhaled after the inspiration of the normal tidal volume
3.
Expiratory reserve volume (ERV): Is the additional air that can be
forcibly exhaled after the expiration of the normal tidal volume
4.
Residual volume (RV): Is the volume of air still remaining in the
lungs after the expiratory reserve volume is exhaled
Lung capacities are classified into:
1.
Total lung capacity (TLC): Is the maximum amount of air that can fill the
lungs
2.
Vital capacity (VC): Is the total amount of air that can be expired after
full inhalation
3.
Inspiratory capacity (IC): Is the maximum amount of air that can be
inspired
4.
Functional residual capacity (FRC): Is the amount of air remaining in the
lungs after normal expiration
peak expiratory flow (PEF)or peak expiratory flow rate (PEFR) is a person's
maximum speed of expiration
Respiratory Cycle, Capacities, and Volume
Ventilation
Process of moving air into and out of lungs
 Two phases
 Inhalation (inspiration)
 Exhalation (expiration)
You must ensure adequate ventilation.
Oxygenation
• The process of loading oxygen molecules onto
hemoglobin molecules in blood stream
• Fraction of inspired oxygen (FIO2)
– Percentage of oxygen in inhaled air
– Increases with supplemental oxygen
– Commonly documented as a decimal number
Adequate breathing
• Adequate breathing
– Patient is responsive, alert, able to speak
– Rate between 12 and 20 breaths/min
– Adequate depth
– Regular pattern of inhalation and exhalation
– Clear and equal breath sounds
Normal and Abnormal Respiratory
Patterns
• Rate
– Eupnea: Normal breathing, 12–20 breaths/min in adults
– Tachypnea: Abnormally fast; caused by fever, hypoxemia,
pneumonia
– Bradypnea: Abnormally slow; caused by narcotics, fatigue,
CNS lesions
– Apnea
Normal and Abnormal Respiratory Patterns (
• Depth
– Hyperpnea: Deeper than normal breath; can lead to
respiratory alkalosis
– Hypopnea: Shallow breath; can lead to respiratory acidosis
• Pattern
– Present with characteristic alterations of respiratory rate,
depth, or regularity
Normal and Abnormal Respiratory Patterns
Causes of Inadequate Breathing
– Severe infection
– Trauma
– Brainstem insult
– Renal failure
– Upper and/or lower airway obstruction
– Respiratory muscle impairment
– Central nervous system impairment
– Oxygen-poor environment
Recognizing Inadequate Breathing
•
Breathing rate of less than 12 breaths/min or more than 20 breaths/min
•
Cyanosis: indicator of low blood oxygen
•
Note the following:
– Position
– Chest rise/fall
– Flared nostrils
– Pursed lips
– Retractions
– Use of accessory muscles
– Quick breaths, long exhalation
– Labored breathing
•
Assess for pulsus paradoxus.
– Systolic blood pressure drops more than 10 mm Hg during inhalation.
Recognizing Inadequate Breathing
• Airway management steps:
– Open the airway.
– Clear the airway.
– Assess breathing.
– Provide appropriate intervention(s).
• Evaluation includes:
– Observe
– Palpate
– Auscultate
Arterial Blood Gas Analysis
• Blood is analyzed for pH, PaO2, HCO3−, base excess, and SaO2.
End-tidal Carbon Dioxide (ETCO2)
Assessment
• Detects carbon dioxide in exhaled air
– Adjunct for determining ventilation adequacy
– Confirms advanced airway placement
• Capnometer
– Numeric reading of exhaled CO2
• Capnographer
– Graphic representation of exhaled CO2
End-tidal Carbon Dioxide (ETCO2) Assessment
• Capnography can:
– Indicate effectiveness of chest
compressions
– Detect return of spontaneous
circulation
• Use is limited with cardiac
arrest
Disease State Categories
• Obstructive diseases
– Difficulty moving air out of lungs
– Involve increase in airway resistance
– Examples
• Asthma
• COPD
• Cystic fibrosis
• Bronchioectasis
Disease State Categories
• Restrictive diseases
– Difficulty moving air into lungs
– Result in loss of chest or lung compliance
– Examples
• Occupational lung diseases
• Idiopathic pulmonary fibrosis
• Pneumonia
• Atelectasis
Types of Hypoxia
• Hypoxic hypoxia
– Insufficient oxygen in blood
• Anemic hypoxia (hypemic hypoxia)
– Reduced or dysfunctional hemoglobin
• Stagnant hypoxia
– Reduced cardiac output, resulting in tissue hypoxia
• Histotoxic hypoxia
– Cells unable to use oxygen due to inactivation or destruction of key
enzymes
THANKS
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