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LYMPHATIC SYSTEM: BIOS 255 Anatomy And Physiology III With Lab
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BIOS255 – Anatomy & Physiology IIIProfessor Haneen Salhieh, M.S.
Week 7 - The Respiratory System: Physiology
Introduction to Spirometry
To assess the severity of respiratory diseases or to track improvements, clinicians measure the patient’s
pulmonary ventilation through the process of spirometry. The patient will breathe into a device called a
spirometer that captures expired breaths and records different variables such as speed of expiration,
depth and rate of breathing, and rate of oxygen consumption.
One category of measured values is lung volumes, Lung volumes which refer to the amount of air in the
lungs at various points in the respiratory. The main lung volumes are: TIRE
Tidal Volume (TV): volume of air that is inhaled or exhaled during a normal, quiet breath. It
represents the basic amount of air moved with each breath (~500mL).
Residual Volume (RV): volume of air that remains in the lungs after a maximal exhalation. This
is air that does not leave to maintain lung elasticity and prevent lung collapse (~1,300mL).
Inspiratory Reserve Volume (IRV): maximum volume of air that can be inhaled after a normal
inhalation. It represents the extra air that can be inhaled beyond a regular breath (~3,000mL).
Expiratory Reserve Volume (ERV): maximum volume of air that can be exhaled after a normal
exhalation. It represents the extra air that can be exhaled beyond a regular breath (~1,200mL)
Another category of measured values is lung capacities, which are combinations of two or more lung
volumes. The primary lung capacities include: TIFV
Total Lung Capacity (TLC): maximum amount of air the lungs can hold, representing the sum of
all lung volumes (TLC = RV + VC). Typical value is 6,000mL.
Inspiratory Capacity (IC): maximum volume of air that can be inhaled after a normal exhalation
(IC = TV + IRV). Typical value is 3,500mL.
Functional Residual Capacity (FRC): volume of air left in the lungs after a normal exhalation
(FRC = RV + ERV). Typical value is 2,500mL.
Vital Capacity (VC): maximum volume of air a person can exhale after a maximal inhalation (VC
= ERV + TV + IRV). Typical value is 4,700mL.
Pulmonary Dead Spaces
It is important to note that not all inhaled air reaches the alveoli to become available for gas exchange.
Pulmonary dead spaces refer to the portions of the respiratory system where no gas exchange occurs.
There are two types of dead spaces:
Anatomical Dead Space: This is the volume of air (~150mL) that remains in the conducting
airways such as the pharynx, larynx, trachea, bronchi, and bronchioles and does not reach the
alveoli for gas exchange. The primary function of the anatomical dead space is to humidify and
filter the inhaled air. As this ‘trapped air’ is sitting in these conducting zone structures, the
beginning of your exhaled air will consist of this air and will thus have more O 2 than CO2, which is
why mouth-to-mouth resuscitation can be effective.
Physiological Dead Space: Physiological dead space includes the anatomical dead space and
any alveoli that do not participate in gas exchange due to inadequate blood flow or other factors.
Sometimes, the alveoli are healthy but do not receive blood or air flow at that time. In other
instances, the alveoli can be damaged because of some pathology. Physiological dead space
can increase in conditions like pulmonary embolism or certain lung diseases where blood flow to
some areas of the lungs is compromised.
, BIOS255 – Anatomy & Physiology III
Professor Haneen Salhieh, M.S.
Ventilation Rates
Anatomical dead space can change depending on different stimuli. When someone is relaxed,
the parasympathetic nervous system will keep the airways slightly constricted to minimize the dead
space. When someone is in an active state, such as during arousal or exercise, the sympathetic nervous
system will dilate the airway to increase airflow.
One calculation that considers the dead space is called the alveolar ventilation rate (AVR), which
accounts for how much air is ventilating the alveoli. This calculation is determined by multiplying the
amount of air that reaches the alveoli by the respiratory rate. This measure is most directly relevant to the
body’s ability to partake in gas exchange.
For example: A patient inhales 500mL of air, and 150mL of it is in the dead space. This leaves 350mL
that reaches the alveoli. With a respiratory rate of 12 breaths per minute, this gives us a total of 4,200mL
(4.2L) of air that will ventilate the alveoli per minute (350mL/breath x 12 breaths/min = 4,200mL/min).
Another calculation that can be determined from spirometry measurements is minute respiratory
volume (MRV), which considers the amount of air inhaled per minute. This will directly determine the
alveolar ventilation rate. It can be measured by multiplying the tidal volume by respiratory rate.
Let’s continue with the example from above. The patient inhaled 500mL of air and took 12 breaths in the
minute. The MRV would be 500mL x 12 bpm = 6,000mL or 6L/min.
Lung Disorders
Spirometry helps distinguish between and assess restrictive and obstructive disorders.
Restrictive lung disorders are characterized by reduced lung compliance, meaning that the lungs
become less able to expand. This results in a decreased ability to inhale an adequate volume of air,
showing a reduced vital capacity in spirometry. Some examples include black lung disease, idiopathic
pulmonary fibrosis, and tuberculosis.
Obstructive lung disorders are characterized by airway obstruction, making it difficult for a person to
exhale air effectively. This results in increased air trapping in the lungs. It is difficult to inhale or exhale a
given amount of air. Common examples are chronic bronchitis, cystic fibrosis, COPD, and asthma.
Emphysema is an example of a lung disorder that shares characteristics of both restrictive and
obstructive disorders.
Composition of Air: Dalton’s Law
Atmospheric air consists of approximately 78.6% nitrogen (N 2), 20.9% oxygen (O2), 0.04% carbon dioxide
(CO2), and trace amounts of other gases such as helium, argon, neon, ozone, and methane. Each of
these individual gases contributes its own toward the total atmospheric pressure of 760 mm Hg. This
principle is known as Dalton’s Law.
The separate contribution of each gas is called its partial pressure. This is usually symbolized with a P
and followed by the formula of the gas (e.g., Po 2 represents the partial pressure of oxygen). To calculate
the partial pressure of a gas, you will need to multiply the sea-level atmospheric pressure by the
percentage of the gas in decimal form. For example:
If the atmospheric pressure is 760 mm Hg, and about 20.9% of the atmosphere consists of oxygen, the
Po2 is
O:0.209 x 760 mm Hg = 159 mm Hg.
CO2: 0.0004 x 760 mm Hg = 0.3 mm Hg
N2: 0.786 x 760 mm Hg = ~597 mm Hg
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