Pulmonary Ventilation Flashcards
lungs can be contracted or expanded in two ways which are
(1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity, and (2)
by elevation and depression of the ribs to increase and
decrease the anteroposterior diameter of the chest cavity
quite breathing is accomplished by
movement of diaphragm
during inspiration diaphragm moves?
pulls the lungs downwards
during expiration the diaphragm?
, the diaphragm simply relaxes, and the
elastic recoil of the lungs, chest wall, and abdominal structures compresses the lungs and expels the air
during inspiration the rib cage moves?
forwards and upwards away from the sternum ( increasing the anteroposterior thickness of chest by 20%)
the muscles that elevate
muscles of inspiration (opposite are muscles of expiration)
The most important muscles that raise the rib cage
are
external intercostals, but others that help are the
(1) sternocleidomastoid muscles, which lift upward on the
sternum; (2) anterior serrati, which lift many of the ribs;
and (3) scaleni, which lift the first two ribs
The muscles that pull the rib cage downward during
expiration are mainly
(1) the abdominal recti, which have
the powerful effect of pulling downward on the lower ribs
at the same time that they and other abdominal muscles
also compress the abdominal contents upward against the
diaphragm, and (2) the internal intercostals
tell the contraction and relaxation of intercoastal muscles and external coastal muscles during inspiration
external intercoastal muscles contract
inter intercoastal muscles relax
ribs move forward (elevate)
pleural pressure
Pleural pressure is the pressure of the fluid in the thin
space between the lung pleura and the chest wall pleura.
The normal
pleural pressure at the beginning of inspiration is
-5 cm of h2o
During normal inspiration, expansion of the chest cage
pulls outward on the lungs with greater force and creates
more negative pressure, to an average of abou
-7 cm of h20
whne the glottis is open what is the pressure inside the lungs?
the pressures in all parts of the
respiratory tree, all the way to the alveoli, are equal to
atmospheric pressure, which is considered to be zero reference pressure in the airways—that is, 0 centimeters
of water pressure.
the cause inspiration the pressure falls inside the alveoli to
-1 cm of h20 (makes 0.5 liter of o2 to flow inwards into the lungs)
transpulmonary pressure
transpulmonary pressure is the pressure difference between that in the alveoli and that on the outer surfaces of the lungs (pleural pressure), and it is a measure
of the elastic forces in the lungs that tend to collapse the lungs at each instant of respiration, called the recoil pressure.
what is lung compliance
a measure of the lung expandability
It refers to the ability of the lungs to stretch and expand
The total compliance of both lungs together
200 milliliters of air
per centimeter of water transpulmonary pressure.
The characteristics of the compliance diagram are
determined by the elastic forces of the lungs. These forces
can be divided into two parts:
- elastic forces of lung tissue
2) elastic forces caused by surface tension of the
fluid that lines the inside walls of the alveoli and other lung
air spaces.
if the lungs are filled with saline what happes
there is no interaction between the air and the alveolar fluid so there is no surface tension present
surface tension elastic force
the nect effect is to cause an elastic contractile force of the entire lung
function of surfactant
reduces the surface tension of water molecules
It is
secreted
type II alveolar epithelial cells,
most important component of surfactant
phospholipid dipalmitoyl phosphatidylcholine,
surfactant apoproteins, and calcium ions.
dipalmitoyl phosphatidylcholine,
surfactant apoproteins works how
They perform this function by not dissolving uniformly
in the fluid lining the alveolar surface. Instead, part of the
molecule dissolves while the remainder spreads over the
surface of the water in the alveol
respiratory distress syndrome of the newborn.
the less the radius of the alveoli the more will be the alveolar pressure
so premature infants have alevoli radii less than 25% of that an adult and have no production of surfactants (starts at 7-6th month of gestation or later) so their lungs have more tendency to collapse
compliance of lungs and thorax
110 ml/cm of H2O
Thus,
under resting conditions, the respiratory muscles normally
perform “work” to cause ……… and why?
inspiration because during inspiration the respiratory muscles contract and while expiration its recoil effect of the lungs, chest wall and other muscles
The work of inspiration can be divided into three fractions:
(1) that required to expand the lungs against the lung
and chest elastic forces, called compliance work or elastic
work; (2) that required to overcome the viscosity of the lung
and chest wall structures, called tissue resistance work; and
(3) that required to overcome airway resistance to movement of air into the lungs, called airway resistance work.
tidal volume
is the volume of air inspired or
expired with each normal breath; it amounts to
about 500 milliliters in the average adult male.
The inspiratory reserve volume i
e is the extra volume
of air that can be inspired over and above the
normal tidal volume when the person inspires
with full force; it is usually equal to about 3000
milliliters.
The expiratory reserve volume
is the maximum
extra volume of air that can be expired by forceful
expiration after the end of a normal tidal expiration;
this volume normally amounts to about 1100
milliliters.
The residual volume
is the volume of air remaining
in the lungs after the most forceful expiration; this
volume averages about 1200 milliliters
inspiratory capacity
equals the tidal volume
plus the inspiratory reserve volume. This capacity is
the amount of air (about 3500 milliliters) a person
can breathe in, beginning at the normal expiratory
level and distending the lungs to the maximum
amount.
The functional residual capacity
expiratory reserve volume plus the residual volume. This
capacity is the amount of air that remains in the
lungs at the end of normal expiration (about 2
vital capacity
expiratory reserve volume plus the residual volume. This
capacity is the amount of air that remains in the
lungs at the end of normal expiration (about 2
The total lung capacity
is the maximum volume to
which the lungs can be expanded with the greatest
possible effort (about 5800 milliliters); it is equal to
the vital capacity plus the residual volume
4 pulmonary capacities
inspiratory capacity
function residual capacity
vital capacity
total lung capacity
The minute respiratory volume is
s the total amount of new
air moved into the respiratory passages each minute and
is equal to the tidal volume times the respiratory rate per
minute
what is normal respiratory volume
Therefore, the minute respiratory volume averages about 6 L/min.
The ultimate importance of pulmonary ventilation
is to continually renew the air in the gas exchange areas of the lungs, where air is in proximity to the pulmonary blood. These areas include the alveoli, alveolar sacs, alveolar ducts, and respiratory bronchioles.
alveolar ventilation
The rate at which new
air reaches these areas alveoli, alveolar sacs, alveolar ducts, and respiratory bronchioles.
dead space
Some of the air a person breathes never reaches the gas
exchange areas but simply fills respiratory passages where
gas exchange does not occur, such as the nose, pharynx,
and trachea. This air is called dead space air because it is
not useful for gas exchange.
normal dead space volume
150ml
physiological dead space
the non functional alveoli are counted in the anatomical dead space then it is called the physiological dead space
Alveolar ventilation per minute
is the total volume of new
air entering the alveoli and adjacent gas exchange areas
each minute.
resistance to airflow in bronchial tree is usually caused by
larger bronchiole than smaller because there are many small bronchioles comparatively to larger ones
In some disease conditions, the smaller bronchioles play
a far greater role in determining airflow resistance because
(1) muscle contraction in their walls, (2) edema occurring
in the walls, or (3) mucus collecting in the lumens of the
bronchioles
sympathetic stimulation of bronchiole tree
norepinephrine and epinephrine has a direct affect on the bronchiole causing them to dilate
parasympathetic effect
acethylcholine causes the brioncholes to constrict
in asthma the parasympathetic effect worsens the situation
drug the blocks the effect of acytelcholine
atropine
Sometimes the parasympathetic nerves are also activated by reflexes that originate in the lungs which are
irritation of the epithelial membrane of
the respiratory passageways, initiated by noxious gases,
dust, cigarette smoke, or bronchial infection. Also, a bronchiolar constrictor reflex often occurs when microemboli
occlude small pulmonary arteries.
local secretory factors causing contraction in bronchiole are
histamine and slow reacting substance of anaphylaxis released during allergic reactions like asthma causes constriction or cause’ of some irritant like SO2 or acidic elements in smog
cough reflex
The bronchi and trachea are so sensitive to light touch that
slight amounts of foreign matter or other causes of irritation initiate the cough reflex. The larynx and carina (i.e., the point where the trachea divides into the bronchi) are especially sensitive, and the terminal bronchioles and even the alveoli are sensitive to corrosive chemical stimuli
such as sulfur dioxide gas or chlorine gas. Afferent nerve
impulses pass from the respiratory passages mainly through the vagus nerves to the medulla of the brain
