Respiratory Pathophysiology
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| Primary Function of Respiratory System | Exchange gasses between the environment (air) and
the blood in the lungs.
Deliver oxygen (O2) to tissue and remove waste gas – carbon dioxide (CO2).
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| Common Problems-airway | Obstruction, occlusion
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| Common Problems-ventilation | Gas trapping, ineffective chest excursion,
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| Common Problems-oxygenation | Inability to diffuse gas across alveolar capillary
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| Defense Mechanisms-Upper respiratory tract | mucosa and nasal hairs = humidification, removes
particles.
Epiglottis = prevents aspiration/foreign bodies from entering trachea/bronchial tree.
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| Defense Mechanisms-Lower respiratory tract | Mucous blanket – protects trachea, bronchi, traps
foreign particles.
Cilia – propel mucus and entrapped particles upward to oro/nasopharynx.
Irritant receptors – nose = sneeze; trachea/bronchi = cough [upper/lower].
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| Gas-Exchange airways | Respiratory bronchioles –
no cilia, no goblet cells,
little smooth muscle
– Alveolar ducts – lead to
– Alveoli – primary gasexchange
units of the lung
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| Pulmonary Blood Flow | Desaturated blood
from right ventricle
(RV) to lungs
– Capillary beds feed
alveoli, exchange gas
– Return saturated blood
to left atrium (LA)
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| Pulmonary & Bronchial Circulation | Facilitates gas exchange,Delivers nutrients to lung tissue
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| Systemic Circulation | Saturated hemoglobin travels to L heart,
then into circulation.
At peripheral capillary level, O2 and CO2
exchanged.
Returned to R heart
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| Hemodynamics | Low pressure vs. high pressure across lung.
Pulmonary catheter used to more
precisely measure pressure in R heart as
a measure of L heart
function.
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| Lung Volume & Capacities | Tital volume (VT)=volume inhaled/exhaled during normal breathing.
Expiratory reserve volume (ERV)=volume expired from relaxed lung from forceful exhalation.
Inspiratory reserve volume (IRV)=volume of forceful inhalation.
Residual volume (RV)=remaining
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| Muscles & Chest Excursion | Expansion of thorax creates negative pleural
pressure = lung volume.
At end of inspiration, normal elasticity retract lung = elastic recoil.
Air is moved into and out of lung via the airways in a bellows like fashion.Lungs have natural tendency to
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| Lung Compliance | Measure of lung and chest wall distensibility.
Determined by alveolar surface tension and elastic recoil of lung/chest wall.
Abnormally high = lung has lost elastic recoil, e.g.emphysema.
Abnormally low = “stiff” lung, e.g. ARDS,pneumonia,pulm edema.
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| Airway resistance | Similar to resistance found in blood flow
– Related to airway length, area & gas
characteristics
– Normally low ~ ½ or more from nose
– Most common cause is edema, obstruction
(mucus plugging), bronchospasm.
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| Neurological Control of Breathing | Automatic and voluntary control
– Brain stem – basic automatic rhythm
– Medulla – control diaphragm and
inspiratory intercostal muscle
– CNS chemoreceptors and peripheral
chemoreceptors in carotids and aortic
bodies respond to D pH, PaCO2, PaO2
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| Gas Transport - O2 | Ventilation of lungs
– Diffusion of O2 across alveolocapillary
membrane to blood
– Attachment of O2 to hemoglobin
– Transport via LA/LV of heart to arteries,
arterioles, capillaries
– Diffusion of O2 across capillaries to cells
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| Gas Transport - CO2 | Diffusion of CO2 from cells to capillaries as
carbonic acid
– Transport via venous system to RA/RV then
to pulmonary artery
– Diffusion of CO2 across alveolocapillary
membrane
– Removal of CO2 through exhalation
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| Alveolocapillary Membrane | Large surface area, very
thin membrane.Partial pressure of oxygen
is higher in alveolar gas
PAO2 than in capillary
blood PaO2. Create high diffusion
gradient.Blood remains in capillary
0.75 sec but only 0.25 sec
needed to equilibrate across cap mem
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| Arterial Oxygenation | During equilibration, O2 dissolves into
capillary plasma
Binds with available hemoglobin until
saturated (SaO2)
Small residual dissolved O2 in plasma
20 ml of O2 in 100 ml of blood
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| Gas Pressure | Result of random collisions of gas molecules
L-space = ^ pressure for constant volume
^temperature = ^pressure for constant
volume
Sea level barometric pressure = 760 mm Hg
(sum of all gasses and water vapor pressure)
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| Gas Pressure Characteristics | Composition of air: O2
= 20.9%, N = 78.1%,
trace gasses = remainder
Water vapor pressure = 47 mm Hg
Partial pressure of O2 at sea level =
0.209 x (760 – 47) = 159
mm Hg
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| Blood Gasses | Arterial
PaO2 100
PaCO2 40
SaO2 96-98%
Venous
PvO2 40
PvCO2 46
SvO2 75%
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| Oxygen Delivery | Cellular respiration
^ oxygen demand = ^ cardiac output AND/OR
higher tissue uptake (except myocardium and
brain tissue) [short term]
^oxygen demand = ^hemoglobin production
[long term]
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| Oxyhemoglobin | In lungs – hemoglobin has affinity for oxygen
(oxyhemoglobin association) = saturation
At tissues – hemoglobin is release(oxyhemoglobin dissociation) = desaturation
Conditions that cause greater release of oxygen -L-pH,H-temp,H-CO2
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| Diagnostic Tests | Spirometry
– Arterial blood gas
– (mixed-venous continuous monitoring)
– Chest XRay or CT scan
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| Conditions that increase affinity | L-temp, L-CO2, carboxyhemoglobin, increase pH
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