Pulmonary ventilation
Download
Report
Transcript Pulmonary ventilation
Chapter 13 – Part 3
The Respiratory System
Events of Respiration
The major function of the respiratory
system is to supply the body with O2 and
to dispose of CO2.
To do this, at least four events must occur
(collectively called respiration):
1. Pulmonary ventilation
2. External respiration
3. Respiratory gas transport
4. Internal respiration
Events of Respiration
1. Pulmonary ventilation – moving air in
and out of the lungs
Commonly called breathing
2. External respiration – gas exchange
between pulmonary blood and alveoli
O2 loading and CO2 unloading
Events of Respiration
3. Respiratory gas transport – transport
of oxygen and carbon dioxide via the
bloodstream to and from the lungs and
body tissues
4. Internal respiration –
gas exchange between
blood and tissue cells in
systemic capillaries
Mechanics of Breathing
(Pulmonary Ventilation)
Completely
mechanical process
Depends on volume
changes in the
thoracic cavity
Mechanics of Breathing
(Pulmonary Ventilation)
Volume changes lead to pressure
changes, which lead to the flow of gases
to equalize pressure
A gas always conforms to the shape of its
container
In a large volume, the pressure will be low.
If the volume is reduced, the gas molecules
will be closer together and the pressure will
rise.
Mechanics of Breathing
(Pulmonary Ventilation)
Two phases
1. Inspiration – flow of air into the lungs
2. Expiration – air leaving the lungs
Inspiration (Inhalation)
Diaphragm and intercostal
muscles contract resulting in
the increased size of the
thoracic cavity
As the diaphragm contracts, it moves
inferiorly and flattens out
Contraction of the intercostals lifts the rib
cage and thrusts the sternum forward
Inspiration (Inhalation)
The increased volume results in a
decreased gas pressure within the lungs,
which produces a partial vacuum
External air is pulled into the lungs due to
an increase in intrapulmonary volume
Air continues to pull into the lungs until the
intrapulmonary pressure equals the
atmospheric pressure.
Inspiration (Inhalation)
Exhalation (Expiration)
Largely a passive process
which depends on natural
lung elasticity
As muscles relax, air is pushed out of the
lungs
Forced expiration can occur mostly by
contracting internal intercostal muscles to
depress the rib cage
Exhalation (Expiration)
Pressure Differences in the
Thoracic Cavity
Normal pressure within the pleural
space (intrapleural pressure) is always
negative
Differences in lung and pleural space
pressures keep lungs from collapsing
If for any reason, the intrapleural pressure
becomes equal to the atmospheric
pressure, the lungs will collapse
Atelectasis
Atelectasis – lung collapse
The lung is useless for
ventilation
Usually occurs when air
enters the pleural space from:
1. A chest wound
2. A rupture of the visceral pleura
Is reversed by drawing air out of the
intrapleural space with chest tubes, which
allows the lungs to re-inflate and resume its
normal function
Nonrespiratory Air Movements
Can be caused by reflexes or
voluntary actions
Examples
Cough - Clears the lower respiratory
passages of debris
Sneeze – Clears the upper
respiratory passages of debris
Laughing
Crying
Yawn – Increases ventilation to the
lungs; May be initiated by a need to
increase oxygen levels in the blood
Hiccup – Sudden inspiration; Results
from spasms of the diaphragm
Respiratory Volumes and Capacities
Tidal volume (TV) – Amount of air
inhaled of exhaled with a normal breath
Normal breathing moves about 500 ml of air
(about a pint) with each breath
Many factors that affect respiratory capacity
1. A person’s size
2. Sex
3. Age
4. Physical condition
Respiratory Volumes and Capacities
Inspiratory reserve volume (IRV) Amount of air that can be taken in forcibly
over the tidal volume
A person can inhale much more air than is
taken in during a normal, or tidal, breath
Usually between 2100 and 3200 ml
Respiratory Capacities
Respiratory Volumes and Capacities
Expiratory reserve volume (ERV) Amount of air that can be forcibly
exhaled
After a normal
expiration, more
air can be
exhaled
Approximately
1200 ml
Respiratory Volumes and Capacities
Residual volume - Air remaining in the
lungs after expiration
Even after the most strenuous expiration,
about 1200 ml of air still remains in the lungs
The residual volume cannot be voluntarily
expelled
Is important because:
1. It allows gas exchange to go on
continuously even between breaths
2. It helps to keep the alveoli open
(inflated)
Respiratory Capacities
Respiratory Volumes and Capacities
Vital capacity - the total amount of
exchangeable air
Vital capacity = TV + IRV + ERV
Typically around 4800 ml in healthy young
males
Respiratory Volumes and Capacities
Dead space volume - Air that remains
in conducting zone and never reaches
alveoli
About 150 ml in a normal tidal breath
Functional volume - Air that actually
reaches the respiratory zone and
contributes to gas exchange
Usually about 350 ml
Respiratory Volumes and Capacities
Respiratory capacities
are measured with a
spirometer
As a person breathes,
the volumes of air
exhaled can be read on an indicator
Spirometer testing is useful for evaluating
losses in respiratory functioning and in
following the course of some respiratory
diseases