Download Pulmonary Ventilation and Pulmonary Circulation

Pulmonary Ventilation and Pulmonary
Circulation
Chapter 27
Mechanics of Pulmonary Ventilation
• The lungs can be expanded and contracted in 2 ways:
– 1. Downward and upward movement of diaphragm
– 2. Elevation and depression of ribs
Lung movements
Pressures that cause movement of air
in/out of lungs
• lung floats in the thoracic cavity
• surrounded by thin layer of pleural fluid
– lubricates
Pleural pressure
• Pressure of fluid in narrow space between lung pleura
and chest wall pleura
– slight suction of excess fluid into lymphatic channels
produces negative pressure
– keeps lungs in place
Alveolar Pressure
• Pressure inside lung alveoli
• no air flowing in or out of lungs = atmospheric pressure
• inspiration- alveoli pressure slightly below atm.
pressure (-1)
• expiration- alveoli pressure slightly above atm. pressure
(+1)
Compliance of the lungs
• Compliance- extent to which lungs expand for each unit
increase in transpulmonary pressure (pleural press. alveolar press.)
• Compliance diagram-inspiratory compliance curve and
expiratory compliance curve
Compliance
Diagram
• Characteristics determined by:
– elastic forces of lung tissue
– elastic forces caused by surface tension of fluid that lines the inside
walls of alveoli
Elastic forces of lung tissue
• Determined by the elastin and collagen fibers
interwoven among lung parenchyma
– deflated lungs- contracted and kinked
– expanded lungs- stretched and unkinked (elongating)
• Elastic forces caused by surface tension
– “surfactant”
“Surfactant”, surface tension and
collapse of lungs
• Inner surfaces of alveoli- water surface attempting to contract
– forces air out of alveoli
– net effect- causes elastic contractile force of entire lungs- “surface
tension elastic force”
• “Surfactant”- spreads over surface of a fluid and greatly
reduces the surface tension
– secreted by special epithelial cells in alveoli
– reduces amt. of press. to keep lungs expanded
The “work” of breathing
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1. Compliance work/elastic work
2. Tissue resistance work
3. Airway resistance work
Normal quiet respiration- only 3 to 5% of total work
energy expended by body is for pulmonary ventilation
process
• heavy exercise- 50x increase
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Pulmonary Volumes
Tidal volume
Inspiratory reserve volume
Expiratory reserve volume
Residual volume
Pulmonary capacities
Inspiratory capacity
Functional residual capacity
Vital capacity
Total lung capacity
Alveolar ventilation
• Rate at which new air reaches gas exchange areas of
the lungs where the air is in close proximity to the
pulmonary blood
• new air moves from terminal bronchioles into the alveoli
by diffusion
The respiratory passages
Rate of alveolar ventilation
• VA= Freq x (VT-VD)
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VA- vol. of new air entering the alveoli/min
freq.- no. of respirations /min.
VT- tidal volume
VD- dead space volume
Functions of the Respiratory Passageways
• Trachea- multiple cartilage rings- keeps trachea from
collapsing
• Bronchi- less extensive cartilage plates
• Bronchi and bronchioles- walls of smooth muscle
– terminal bronchioles (respiratory bronchioles)- only a few
smooth muscle fibers
– Sympathetic control weak- few nerve fibers there
– however, norepinephrine and epinephrine cause dilation of
bronchial tree
– parasympathetic- Ach- mild to moderate constriction
– other constriction factors: histamine, slow-reacting
substance of anaphylaxis
Mucus layer
• Moistens respiratory passages
• Secreted in part by goblet cells in epithelial lining
– also traps small particles
• Cough reflex- removes foreign particles
– sometimes velocities as high as 75-100 mph
Respiratory function of the nose
• 1. Warm air
• 2. Humidify air
• 3. Filter air
– together called air conditioning function of upper respiratory
passageways
Vocalization
• 2 mechanized functions:
– 1. Phonation- larynx- vocal cords
– 2. Articulation- structures of mouth
The pulmonary blood circulation
• Pulmonary vessels
– larger diameters than systemic arteries
– very thin and distensible- large compliance-accomodates 2/3
of stroke volume output of right ventricle
– lymphatics
– prevent edema- remove particulate matter and leaking plasma
protein
Blood flow through lungs and its
distribution
• Lung blood flow essentially equal to cardiac output
– factors controlling cardiac output also control pulmonary blood flow
• blood distributed to best oxygenated alveoli
– when concentration of O2 in alveoli falls below normal, vessels
constrict- sends blood to areas of lungs that are better aerated
• Hydrostatic pressure gradients and
regional pulmonary blood flow
• Pulmonary capillary dynamics
• Pulmonary edema
Pulmonary capillary dynamics
• So many capillaries in alveolar walls that they almost touch each
other
• capillaries different than other capillaries
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1.Cap. pressure very low-7mm vs. 17mm Hg
2 Interstitial fluid press. slightly more negative
3 Relatively leaky to protein molecules
4.Alveolar wall very thin- allows dumping of fluid fr. Interstitial spaces
into alveoli
• The net filtration pressure at capillary membrane causes a
slight continual flow of fluid from pulmonary cap.’s- pumped
back into circulation through lymphatic system
• Slight negative pressure in interstitial spaces that sucks any
fluid from alveoli to lymphatics
– keeps alveoli “dry” except for sm. amt that moistens lining surfaces of
alveoli
Pulmonary edema
• Most common causes:
– 1.left heart failure or disease of mitral valve
• inc. cap. press-floods interstitial spaces and alveoli
– 2.damage to pulmonary cap. Membranes
• pneumonia
• breathing noxious substances (chlorine gas, sulfur dioxide gas)
• Edema occurs when capillary pressure rises from
negative range into positive range
– death can occur within hours
– acute left heart failure- capillary pressure rises as high as
50mm Hg-death within 1/2 hour
The fluids in the pleural cavity
• Very thin layer of mucoid fluid between parietal and
visceral pleurae
– allows lungs to slide back and forth within cavity during
breathing
• negative force on outside of lungs- keeps them
expanded
– neg. press. created by pumping of fluid from pleural space by
lymphatics
The interpleural spaces