DMACC EMT Chapter 8

PREHOSPITALPREHOSPITAL
EMERGENCY CAREEMERGENCY CARE
CHAPTER
Copyright © 2014, 2010, 2008 by Pearson Education, Inc.
All Rights Reserved
Prehospital Emergency Care, 10th
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TENTH EDITION
Pathophysiology
8

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Learning ReadinessLearning Readiness
• EMS Education Standards, text p. 164

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ObjectivesObjectives
• Please refer to page 164 of your text to
view the objectives for this chapter.

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Key TermsKey Terms
• Please refer to pages 164 and 165 of
your text to view the key terms for this
chapter.

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Setting the StageSetting the Stage
• Overview of Lesson Topics
 Cellular Metabolism
 Components Necessary for Adequate
Perfusion

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Case Study IntroductionCase Study Introduction
EMTs Patty Mirabal and Gus Oakes are on
the scene of a 52-year-old man who is
complaining of difficulty breathing. The
patient is breathing shallowly and
rapidly. He gasps, "Need … help … can't
… breathe."

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Case StudyCase Study
• What purposes does breathing serve?
• In what ways does a problem with
breathing affect the body?

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IntroductionIntroduction
• Oxygen and glucose are necessary for
normal cell function.
• Illnesses and injuries can disturb the
delivery of oxygen and glucose and
removal of waste by-products.
• A fundamental purpose of emergency
care is maintaining adequate delivery
of oxygen and glucose.

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Cellular MetabolismCellular Metabolism
• Cellular metabolism is the process in
which the body breaks down molecules
of glucose to produce energy.
• Aerobic metabolism takes place when
oxygen is available.
• When there is a lack of oxygen, the
body uses a less effective process
called anaerobic metabolism.
continued on next slide

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• Aerobic metabolism
 The initial steps of cellular metabolism
do not require oxygen, but produce only
small amounts of energy.
 Oxygen is required to complete the
process of extracting energy from
glucose and removing the wastes
produced by the process.

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Aerobic metabolism. Glucose broken down in the presence of oxygen produces a large amount of energy (ATP).

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 The initial steps of cell metabolism take
place in the cytosol and are called
glycolysis.
 Glycolysis produces a small amount of
ATP.
 When oxygen is present, the process
continues in the mitochondria, where
larger amounts of ATP needed for cell
function are produced.

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• By-products of aerobic metabolism
include heat, carbon dioxide, and
water.
• Increased metabolism results in
increased respiratory rate to eliminate
the increased carbon dioxide.
• Heat and water can be used or
eliminated by the body.

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 An important cell function that requires
ATP is the sodium/potassium pump.

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The sodium/potassium pump. Energy (ATP) is required to pump sodium molecules out of the cell against the
concentration gradient. Potassium then moves with the gradient to flow into the cell. Sodium and potassium are
exchanged in a continuous cycle that is necessary for proper cell function. The cycle continues as long as the cells
produce energy through aerobic etabolism. When insufficient energy is produced, through anaerobic metabolism,
the sodium/potassium pump will fail and cells will die.

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• Sodium (Na+
) is primarily found outside
the cell.
• Potassium (K+
) is found primarily inside
the cell.
• Without a functioning
sodium/potassium pump, sodium that
finds its way into the cell cannot exit
and accumulates inside the cell.

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• When the concentration of sodium in
the cell is too high, potassium cannot
enter and the cell cannot function.
• Excess sodium in the cell allows excess
water to enter the cell.
• Excess water can cause the cell to
swell, rupture, and die.

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• In anaerobic metabolism, the
combination of inadequate energy
production and accumulating lactic acid
result in failure of cell processes.

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Anaerobic metabolism. Glucose broken down without the presence of oxygen produces pyruvic acid that converts
to lactic acid and only a small amount of energy (ATP).

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• Anaerobic metabolism
 The first stage of cell metabolism is
anaerobic.
 The waste product produced is pyruvic
acid.
 Without oxygen, pyruvic acid is
converted to lactic acid.
 Accumulation of lactic acid is harmful to
body functions.

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• Anaerobic metabolism
 In the presence of extensive anaerobic
metabolism, cells die, which can lead to
organ failure and death.

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Adequate PerfusionAdequate Perfusion
• Perfusion is the delivery of oxygen,
glucose, and other substances to the
cells and the elimination of waste
products from the cells.

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• Perfusion requires functioning
nutrient/oxygen delivery and waste
removal systems.

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• 11 components of these systems are:
1. Composition of ambient air
2. Patent airway
3. Mechanics of ventilation
4. Regulation of ventilation
5. Ventilation/perfusion ratio
6. Transport of oxygen and carbon dioxide
by the blood

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• 11 components of these systems are:
7. Blood volume
8. Pump function of the myocardium
9. Systemic vascular resistance
10.Microcirculation
11.Blood pressure

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• Any alteration in the components may
lead to poor cellular perfusion.
• Inadequate perfusion can shift cells
from aerobic to anaerobic metabolism.
• In anaerobic metabolism, production of
energy is reduced and harmful by-
products accumulate.
• Emergency care focuses on restoring
and maintaining the components.

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Gus quickly moves next to the patient to
better assess his condition, while Patty
unzips the airway kit and begins to select
equipment to begin patient care.

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• What, specifically, will Gus be assessing
to determine the patient's condition?
• How will Patty know what equipment
and treatment the patient needs?
• What is happening to the patient at the
cellular level?
• What will happen if the EMTs do not
intervene quickly?

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Composition of Ambient AirComposition of Ambient Air
• The concentration of oxygen in the
ambient air determines the amount of
oxygen that ends up in the alveoli for
gas exchange.
• Ambient air contains approximately
79% nitrogen, 21% oxygen, and trace
amounts of argon and carbon dioxide.

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Table 8-1 Partial Pressure of Gases in Ambient
Atmosphere at Sea Level

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• FiO2 is the fraction of inspired oxygen.
• A patient breathing air that contains 21
percent oxygen has an FiO2 of 0.21.
• One way to improve cellular
oxygenation to increase the patient's
FiO2 by administering supplemental
oxygen.

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• Some toxic gases displace the amount
of oxygen in the air, which suffocates
the patient.
• Carbon monoxide disrupts the ability of
the blood to carry oxygen to the cells.
• Cyanide interferes with oxygen use by
the cell.
• Each of these situations leads to
hypoxia.

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Patent AirwayPatent Airway
• A patent airway is open and not
obstructed by any substance.
• Establishing an open airway is one of
the first steps in emergency care.
• Failure to establish or maintain a patent
airway leads to cellular hypoxia and
patient death.

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Airway obstruction can occur at several levels of the upper and lower airway, including the nasopharynx,
oropharynx, posterior pharynx, epiglottis, larynx, trachea, and bronchi.

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Patent AirwayPatent Airway
• Airway obstruction can occur at several
levels and has many causes.
 Obstruction of nasopharynx,
oropharynx, or pharynx
 Swelling of epiglottis
 Laryngeal spasm or edema
 Obstruction of trachea or bronchi

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Mechanics of VentilationMechanics of Ventilation
• An intact thoracic cavity is integral to
normal ventilation.
 Thoracic cavity boundaries
 Mediastinum
 Parietal and visceral pleura

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• Boyle's law
 The volume of a gas is inversely
proportional to the pressure.
 Increasing and decreasing the volume of
the thoracic cavity changes the pressure
of air inside it.

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• Boyle's law
 Contracting the diaphragm and
intercostal muscles increases the
thoracic volume, creating negative
pressure.
 The negative pressure causes the pleura
and lungs within the thorax to expand,
creating negative pressure within the
lungs.

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• Boyle's law
 The pressure of atmospheric air is 760
mmHg at sea level.
 Just prior to inhalation, the pressure
within the chest is 758 mmHg.
 Air flows from the higher pressure of the
atmosphere toward the lower pressure
of the lungs.

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• Boyle's law
 On exhalation, the diaphragm and
intercostal muscles relax.
 The volume of the thorax and lungs
decreases.
 Pressure inside the chest rises to 761
mmHg.
 Air flows from the higher pressure in the
lungs to the lower pressure of the
atmosphere. continued on next slide

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A. The diaphragm relaxes.
B. The size of the chest cavity decreases.
C. Pressure within the chest decreases.
D. The intercostal muscles relax.
Click on the event that occurs just prior to theClick on the event that occurs just prior to the
movement of air into the lungs on inhalation.movement of air into the lungs on inhalation.

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• Accessory muscles
 Used when extra effort is needed for
inhalation or exhalation
 Increases energy use
 If energy production fails from
insufficient oxygen, the muscles of
respiration fail.

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Table 8-2 Accessory Muscles

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• Compliance and airway resistance
 High resistance and low compliance
increase the effort needed to breathe
and lead to hypoxia.

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 Compliance is the ease with which the
lungs or chest wall expand.
 Pneumonia, pulmonary edema, and
some chest injuries can decrease
compliance.

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 Resistance is the ease of airflow into
and out of the airway structures.
 Edema of the airway and constriction of
the bronchioles can lead to increased
airway resistance.

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• Pleural space
 Negative pressure is maintained in the
pleural space.
 An injury to the chest wall or lung that
opens the space can draw air, by way of
negative pressure, into the space.
 The lung may collapse from the air
accumulation.

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• Minute ventilation, or minute volume, is
the amount of air moved in and out of
the lungs in one minute.
• Minute volume = tidal volume ×
frequency of ventilation

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• Average minute volume is:
• 500 mL × 12/minute = 6,000 mL (6 L)

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• A decrease in tidal volume decreases
the minute volume.
• A decrease in respiratory rate
decreases the minute volume.
• A decrease in minute volume reduces
the air available for gas exchange in
the alveoli.

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• A decrease in minute ventilation can
lead to cellular hypoxia.
• To ensure adequate ventilation, both
the tidal volume and respiratory rate
must be adequate.

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• An increase in ventilatory rate can
compensate for reduced tidal volume in
maintaining minute volume, to a point.
• With low tidal volume, the volume of
air may not be sufficient to reach the
alveoli for gas exchange.

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• Alveolar ventilation is the amount of air
moved in and out of the alveoli in one
minute.
• Air that does not reach the alveoli,
remaining in the trachea and bronchi, is
called dead space air.
• 150 mL of a 500 mL tidal volume
remains in the dead air space; 350 mL
reaches the alveoli.

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• Alveolar ventilation = (tidal volume –
dead air space) × frequency of
ventilation/minute

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• Dead air spaces fill first with
ventilation.
• If tidal volume decreases, alveolar
volume decreases.
• An increase in ventilation rate does not
mean more air volume is reaching the
alveoli.

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• Providing oxygen alone to a patient
with poor tidal volume does not correct
hypoxia.
• The patient needs assisted ventilation
to increase tidal volume.

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• Hypoxia can occur from:
 A low tidal volume
 A slow ventilatory rate
 A fast ventilatory rate

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• When the ventilatory rate is too fast
 There is inadequate time between
breaths to fill the lungs.
 A very fast rate requires a large amount
of energy that may not be able to be
sustained, setting up the patient for
respiratory failure.

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• When the ventilatory rate is too fast
 Ventilatory rates of 40/minute or
greater in the adult patient and greater
than 60/minute in the pediatric patient
are too fast to be sustainable or to allow
adequate time for a normal tidal
volume.

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Regulation of VentilationRegulation of Ventilation
• Breathing is an involuntary process
controlled by the autonomic nervous
system.
• Receptors measure oxygen (O2), carbon
dioxide (CO2), and hydrogen ions (pH).
• Receptors send signals to the brain to
adjust the rate and depth of
respiration.

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Respiration is controlled by the autonomic nervous system. Receptors within the body measure oxygen, carbon
dioxide, and hydrogen ions and send signals to the brain to adjust the rate and depth of respiration.

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• Chemoreceptors are specialized
receptors that monitor the pH, CO2, and
O2 levels in arterial blood.
• There are central chemoreceptors and
peripheral chemoreceptors.

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• Central chemoreceptors are located
near the respiratory center in the
medulla.
 Sensitive to CO2 and changes in the pH
of the cerebrospinal fluid (CSF)
 The pH in CSF reflects the CO2 level of
arterial blood.
 The more CO2 in the blood, the greater
the amount of acid

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• Small changes in pH stimulate a
response in the rate and depth of
breathing.
• Faster, deeper breathing eliminates
more CO2.
• Slower, shallower breathing eliminates
less CO2.

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• Peripheral chemoreceptors are located
in the aortic arch and the carotid
bodies.
• As O2 in the blood decreases, peripheral
chemoreceptors signal the respiratory
center in the brainstem to increase the
rate and depth of respiration.

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• A significant decrease in the arterial
oxygen content causes an increase in
the rate and depth of respiration.

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• Normally, rate and depth of breathing
are regulated by the amount of CO2 in
the blood.

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• COPD patients have a tendency to
retain CO2
 They become insensitive to small
changes in CO2.
 Their respirations are controlled by
decreased oxygen levels; this is called
the hypoxic drive.

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• Three types of receptors within the
lungs provide impulses to regulate
respiration.
 Irritant receptors
 Stretch receptors
 J-receptors

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• Irritant receptors
 Found in the airways
 Sensitive to irritating gases, aerosols,
and particles
 Simulate coughing, bronchoconstriction,
and increased ventilatory rate

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• Stretch receptors
 Found in the smooth muscle of the
airways
 Protect against over inflation of the
lungs

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• Stretch receptors
 Measure the size and volume of the
lungs
 Stimulate a decrease in the rate and
volume of ventilation when stretched by
high tidal volumes

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• J-receptors
 Found in the capillaries surrounding the
alveoli
 Sensitive to increases in capillary
 When activated, they stimulate rapid,
shallow ventilation

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• Respiratory control centers in the
brainstem
 Dorsal respiratory group (DRG)
 Ventral respiratory group (VRG)
 Pontine respiratory center (pneumotaxic
center)

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• Ventral respiratory group
 Located in medulla oblongata
 Receives sensory input and sends it to
the spinal cord to stimulate the
diaphragm and intercostal muscles
 Contains inspiratory and expiratory
neurons
 Controls basic pattern of breathing

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• Dorsal respiratory group
 Located in medulla oblongata
 Receives sensory input and
communicates it to the VRG for further
input on rate and depth of breathing

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• Pontine respiratory center
 Sends inhibitory impulses to the
inspiratory neurons of the VRG to turn
off the inhalation
 Promotes a smooth transition between
inhalation and exhalation

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• Illness or injury can disrupt the
respiratory centers in the brainstem.
• Pattern and depth of ventilation can be
affected.
• Gas exchange may be inadequate;
cellular hypoxia may result.

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The patient is working hard to breathe,
and has pale, moist skin. He is using
accessory muscles to breathe, but seems
to be moving very little air. The patient
seems on the verge of complete
exhaustion, and appears sleepy.
Patty selects a bag-mask device to assist
the patient's ventilations, and connects it
to supplemental oxygen.

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• What medical problems could lead a
patient to have such severe difficulty
breathing?

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Ventilation/Perfusion (V/Q) RatioVentilation/Perfusion (V/Q) Ratio
• V/Q ratio is the relationship between
alveolar ventilation and perfusion of the
alveolar capillaries.
• The relationship influences gas
exchange.
• Can be used to explain causes of
hypoxemia

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Overview of ventilation and perfusion.

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Ventilation/Perfusion RatioVentilation/Perfusion Ratio
• In an ideal state the amount of
ventilation is equally matched to the
amount of perfusion.
• Physiologically, based on gravity and
the nature and distribution of alveoli in
the lungs, a perfect match does not
occur.
• Overall, perfusion exceeds ventilation,
but the situation is highly functional.

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• When ventilation is better than
perfusion, there is wasted ventilation.
• When perfusion is better than
ventilation, there is wasted perfusion.

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• Pressure imbalance
 If the air pressure in an alveolus
exceeds the blood pressure in the
capillary bed, blood flow through the
capillary stops.
 Occurs normally in the apex of the lungs
 Occurs when the systemic blood
pressure decreases

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Possible causes of ventilation disturbances.

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• Ventilatory disturbances
 A condition that decreases the amount
of air reaching the alveoli, such as
asthma, results in wasted perfusion.
 Hypoxemia and hypoxia result.
 Treatment is aimed at increasing lung
ventilation.

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• Perfusion disturbances
 Ventilation is normal, or even increased,
but blood flow through the lungs is
decreased.
 There is wasted ventilation, leading to
hypoxemia and hypoxia.
 Administering oxygen may help, but the
perfusion disturbance must be
corrected.

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• Various conditions lead to V/Q
mismatch and resultant hypoxia.
• Treatment is aimed at improving
ventilation, oxygenation, and perfusion
to the lungs.

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Gas TransportGas Transport
• Oxygen must be continuously delivered
by the blood to the cells for normal
cellular metabolism.
• Carbon dioxide must be carried back to
the lungs to be blown off in exhalation.
• A disturbance in the transport system
may lead to cellular hypoxia and
hypercarbia.

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• Gases move from areas of higher
concentration to areas of lower
concentration.

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• Oxygen Transport
 1,000 mL of O2 are delivered to the cells
every minute.
 O2 is transported in the blood in two
ways.
• 1.5 to 3% is dissolved in plasma.
• 97 to 98.5% is attached to hemoglobin
molecules.

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Oxygen is transported in the blood two ways: attached to hemoglobin and dissolved in plasma. Carbon dioxide is
transported in the blood three ways: as bicarbonate, attached to hemoglobin, and dissolved in plasma.

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• Hemoglobin is a protein molecule that
contains iron.
• There are four iron sites per
hemoglobin molecule for oxygen to
bind to.
• Each molecule can carry up to four
oxygen molecules.

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• If one oxygen molecule is attached to
the hemoglobin molecule, it is 25%
saturated; if four molecules are
attached, it is 100% saturated.
• Attachment of one oxygen molecule to
hemoglobin increases the affinity for
the other sites to also bind with
oxygen.

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• Hemoglobin to which oxygen is bound
is called oxyhemoglobin.
• Hemoglobin with no oxygen attached is
called deoxyhemoglobin.

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• Without hemoglobin, the blood cannot
carry enough oxygen to sustain life.
• Loss of hemoglobin, such as through
bleeding, can lead to cellular hypoxia,
even though an adequate amount of
oxygen is available in the alveoli.

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• Carbon dioxide is transported in the
blood in three ways.
 7% is dissolved in plasma.
 23% is attached to hemoglobin in RBCs.
 70% as bicarbonate.

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• The largest amount of CO2 diffuses from
the cell, into the blood, and then into
RBCs.
• In the RBC, CO2 combines with water to
form carbonic acid, which then
dissociates into hydrogen and
bicarbonate.

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• Bicarbonate exits the RBC and is
transported in plasma.
• When blood reaches the lungs,
bicarbonate diffuses back into RBCs,
where it combines with hydrogen and
then dissociates into water and CO2.
• CO2 diffuses from the blood into the
alveoli and is released through
exhalation.

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• Alveolar/capillary gas exchange
 After inhalation, the alveolar air is high
in O2 and low in CO2.
 Venous blood in the capillaries
surrounding the alveoli is low in O2 and
high in CO2.

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• Gas molecules move from areas of high
concentration to areas of low
concentration.
 O2 moves into the capillaries where the
oxygen content is very low.
 Simultaneously, CO2 moves in the
opposite direction.

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• Blood ejected from the left ventricle
into the arteries is high in O2 and low in
CO2.
• This blood travels into the capillaries in
the tissues to reach the cells.

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• As a result of metabolism, cells are
higher in CO2 and lower in O2.
• O2 leaves the blood and enters the
cells; CO2 leaves the cells and enters
the blood.

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A. Bound to hemoglobin
B. In the form of bicarbonate
C. Dissolved in plasma
D. Carried by white blood cells
Click on the mechanism by which most ofClick on the mechanism by which most of
the oxygen in blood is transported.the oxygen in blood is transported.

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Blood VolumeBlood Volume
• A determinant of blood pressure and
perfusion is blood volume.
 Adults have 70 mL of blood/kg of body
weight.
 A 70-kg adult has 4,900 mL (4.9 L) of
blood.

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• Blood composition
 45% formed elements
• 42% to 48% red blood cells
• White blood cells
• Platelets
 55% plasma
• 91% water
• Plasma proteins
• Albumin, clotting factors, antibodies

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• Hydrostatic pressure is the force inside
the vessel or capillary bed generated by
the contraction of the heart and the
blood pressure.
• Hydrostatic pressure exerts a "push"
inside the vessel or capillary.
• High hydrostatic pressure promotes
edema.

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• In left heart failure, the ventricle does
not empty completely, so it cannot
receive the full amount of blood
returning from the lungs.
• Blood backs up into the pulmonary
circulation, resulting in increased
hydrostatic pressure.

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• Plasma oncotic pressure keeps fluid
inside the vessels to oppose hydrostatic
pressure.
• The large plasma proteins have the
effect of "pulling" water into the
capillaries.

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• Hydrostatic and oncotic pressures must
be balanced.
 High hydrostatic pressure pushes fluid
out of capillaries and promotes edema.
 Low hydrostatic pressure pushes less
fluid out of the vessel.

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• Hydrostatic and oncotic pressures must
be balanced.
 High oncotic pressure draws excessive
amounts of fluid into the capillary and
promotes blood volume overload.
 Low oncotic pressure does not exert
enough pull to counteract the push of
hydrostatic pressure, promoting loss of
vascular volume and edema.

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Myocardial FunctionMyocardial Function
• The myocardium must be an effective
pump to maintain perfusion.
 Cardiac output (CO) is the amount of
blood ejected from the heart in one
minute.
 CO = heart rate × stroke volume

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• Several factors affect the heart rate.
 Sympathetic and parasympathetic
nervous systems affect heart rate
through the cardiovascular control
system in the brain stem.
 The cardiovascular control center is
composed of the cardioexcitatory center
and the cardioinhibitory center.

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• An increase sympathetic stimulation
increases the heart rate.
• A decrease in sympathetic stimulation
decreases the heart rate.
• An increase in parasympathetic
stimulation decreases the heart rate.
• A decrease in parasympathetic
stimulation increases the heart rate.

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• Stroke volume is the amount of blood
ejected from the heart with each
contraction.
• Stroke volume is determined by
preload, myocardial contractility, and
afterload.

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• Preload
 Preload pressure is created by the blood
volume in the left ventricle at the end of
diastole.
 The available venous volume plays a
major role in determining preload.
 An increase in preload increases stroke
volume, which increases the cardiac
output.

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• Frank-Starling law of the heart
 As blood fills the left ventricle, it
stretches the muscle fibers.
 The stretch of the muscle fiber
determines the force available to eject
the blood from the ventricle.
 There is a limit to the Frank-Starling
law.

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• Damage to the heart from heart failure
or myocardial infarction can decrease
the myocardial contractility, thereby
decreasing stroke volume and cardiac
output.

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• Afterload is the resistance in the aorta
that must be overcome by contraction
of the left ventricle to eject the blood.
• High diastolic blood pressure creates
high afterload, which increases
myocardial workload.
• Over time, high afterload can lead to
left ventricular failure.

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• Factors that decrease cardiac output
 Decreased heart rate
 Decreased blood volume
 Decreased myocardial contractility
 Parasympathetic nervous stimulation
 Beta1 blockade (beta blockers)
 Higher diastolic BP over time

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• Factors that increase cardiac output
 Increased heart rate (to a point)
 Increased blood volume
 Increased myocardial contractility
 Sympathetic nervous system stimulation
 Beta1 stimulation from epinephrine
 Lower diastolic BP

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Systemic Vascular ResistanceSystemic Vascular Resistance
• SVR is the resistance to blood flow
through a vessel.
• Vasoconstriction increases SVR,
increased SVR increases BP.
• Vasodilation decreases SVR, decreased
SVR decreases BP.

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• Sympathetic stimulation increases the
SVR and BP.
• Epinephrine and norepinephrine
stimulate alpha1 receptors, which cause
vasoconstriction and increased SVR.
• Parasympathetic stimulation decreases
SVR and BP.

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• If the volume of blood decreases,
decreasing the vessel size to increase
SVR can help maintain BP.
• Decreasing vessel size through
vasoconstriction decreases cellular
perfusion and increases anaerobic
metabolism.
• Patients with anaerobic metabolism
may have a poor general appearance.

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• SVR and pulse pressure
 Pulse pressure is the difference between
the systolic and the diastolic BP
readings.
 Systolic BP is an indicator of cardiac
output.

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 A narrow pulse pressure is less than
25% of the systolic BP.
 With a BP of 132/74 mmHg, the pulse
pressure is 58 mmHg (132 – 74 = 58).
 A narrow pulse pressure for that patient
is 33 mmHg (132 × 25% = 33 mmHg).

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 In a patient with blood or fluid loss,
narrow pulse pressure is a significant
sign.
• Blood loss lowers venous volume, which
lowers preload, which lowers stroke
volume, which lowers cardiac output
• Systolic BP decreases from the drop in
cardiac output.

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 In a patient with blood or fluid loss,
narrow pulse pressure is a significant
sign.
• Increased SVR increases diastolic BP.
• The result is a narrow pulse pressure.

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Microcirculation is the flow of blood through the smallest blood vessels: arterioles, capillaries, and venules.
Precapillary sphincters control the flow of blood through the capillaries.

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• Precapillary sphincters control the
movement of blood through the
capillaries.
 If the precapillary sphincter is relaxed,
blood moves through the capillary.
 If the precapillary sphincter is
contracted, the blood is shunted away
from the true capillary.

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• Precapillary sphincters help to maintain
arterial pressure.
 Three regulatory influences control
blood flow through the capillaries.
• Local factors
• Neural factors
• Hormonal factors

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Blood PressureBlood Pressure
• Blood pressure (BP) = cardiac output
(CO) × systemic vascular resistance
(SVR)
 Increased CO increases BP.
 Decreased CO decreases BP.
 Increased HR increases CO and BP.
 Decreased HR decreases CO and BP.

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• Blood pressure (BP) = cardiac output
(CO) × systemic vascular resistance
(SVR)
 Increased SV increases CO and BP.
 Decreased SV decreases CO and BP.
 Increased SVR increases BP.
 Decreased SVR decreases BP.

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• BP is monitored and regulated by
baroreceptors and chemoreceptors.
 Baroreceptors located in the aortic arch
and carotid sinuses detect changes in
blood pressure.
 Signals are sent to the vasomotor and
cardioregulatory centers in the
brainstem.

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• An increase in BP results in signals to
decrease the heart rate and dilate
blood vessels.
• A decrease in BP results in signals to
increase the heart rate and constrict
blood vessels.

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• Chemoreceptors
 A decrease in blood oxygen level
stimulates the sympathetic nervous
system.
 Heart rate increases and blood vessels
constrict.
 Hypoxia can present with pale, cool
skin, and increased heart rate.

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Review of Aerobic MetabolismReview of Aerobic Metabolism
ComponentsComponents
• Oxygen content in ambient air
• Patency of the airway
• Minute ventilation
 Ventilatory rate
 Tidal volume
• Alveolar ventilation
 Ventilatory rate
 Tidal volume

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• Systemic vascular resistance
 Sympathetic nervous system stimulation
 Parasympathetic nervous system
stimulation
• Gas exchange between the capillaries
and the cells

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Case Study ConclusionCase Study Conclusion
The patient has a history of chronic
obstructive lung disease and heart
failure. He has been increasingly short of
breath for two days, with a sudden
worsening today.
With the assistance of an engine crew,
Patty and Gus continue assisting the
patient's ventilations and providing
supplemental oxygen.

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Case Study ConclusionCase Study Conclusion
The crew recognizes the seriousness of
the patient's condition and is prepared to
take further measures, if needed, to
maintain the patient's airway.
Gus calls in a report to the receiving
hospital. When they arrive at the ED, a
physician, nurse, and respiratory
therapist are waiting to continue the
patient's care.

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Lesson SummaryLesson Summary
• Cells require oxygen and glucose to
produce energy and perform work.
• Without adequate ventilation and
perfusion, cells engage in anaerobic
metabolism, which produces less
energy and more waste.
• A fundamental purpose of emergency
care is to restore and maintain cell
perfusion.

DMACC EMT Chapter 8

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