Respiratory Anatomy and Physiology
The thoracic cavity is a closed structure bounded by the chest wall and
diaphragm.
The trachea begins below the larynx and ends in an inverted Y (carina)
branch or bronchus, which then branches into the bronchioles,
terminating in the gas exchange units called alveoli.
Located behind the trachea is the esophagus, which connects to the
stomach.
THORACIC CAVITY- 3 sections
 Mediastinum-encloses the esophagus, trachea, heart, aorta,
thymus gland, lymph nodes, vagus, cardiac and phrenic nerves
and the great vessels-flexible partition that extends from front to
back and top to bottom of the cavity
 2 Lung Chambers-cavities that contain each lung-each lung
connects to the mediastinum through its vessels and bronchus
*because each lung is in a separate chamber the unaffected lung
will remain expanded
 Right lung has 3 lobes—Left lung has 2 lobes
 Lower lobes or bases are positioned posteriorly
Surfactant-is important re: lung inflation
 Keeps the surface tension in the alveoli lower than normal
 Allows the alveoli to expand more easily
 Prevents the alveoli from collapsing
Processes of Respiration-gas exchange occurs in 4 steps:
1. Ventilation-movement of air between the atmosphere and the
alveoli and distributing air within the lungs to maintain
appropriate pressures of oxygen and carbon dioxide in the alveoli.
Requires patent conducting airways and intact neuromuscular
system and thoracic cage.
2. Diffusion-movement of oxygen and carbon dioxide across the
alveolar-capillary membrane. Occurs from an area of high
concentration to an area of lower concentration. Relies on
adequate ventilation and perfusion.
3. Perfusion-Movement of blood through the pulmonary capillary
bed and transporting the blood to and from the tissue capillary
bed. Requires adequate cardiac output, sufficient haemoglobin
and a perfusing vascular system.
4. Diffusion-movement of oxygen and carbon monoxide across the
cellular membrane. Occurs from an area of high to low
concentration. Relies on adequate arterial oxygen pressures and
adequate perfusion.
Ventilation
-the respiratory control center is located in the pons and medulla of
the brain stem (respiratory center)
-autonomic regulation is controlled by lung receptors-there are 2
groups of chemoreceptors-central and peripheral chemoreceptors
 Central chemoreceptors sense changes in Co2 and pH
 Peripheral chemoreceptors sense changes in arterial O2
-ventilation is primarily affected by changes in the Co2 level
-chronic Co2 retainers will rely on stimulus provided by blood
oxygen levels
Hypoxia
-refers to a reduction in tissue oxygenation
Causes:
1. Hypoxemic hypoxia in which the oxygen content of the blood is
reduced.
2. Stagnant or ischemic hypoxia, in which circulation of oxygen in
the blood is impaired.
3. Anemic hypoxia in which the ability to transport oxygen in the
blood decreases.
4. Histotoxic hypoxia in which the cells are unable to utilize
oxygen.
Signs and Symptoms of Acute Hypoxia
Increase in ventilation (Chemoreceptor mediated)
Decreases in judgement and motor proficiency
Dyspnea, fatigue, headache, nausea, vomiting, decreased visual
acuity
Cyanosis of lips and nail beds if adequate hemoglobin
Insomnia and cheyne stokes breathing
Disorientation, hallucinations, convulsions with extreme hypoxia
Signs and Symptoms of Chronic Hypoxia
Dyspnea, fatigue, cyanosis
Pulmonary hypertension (d/t alveolar hypoxia and vasoconstriction)
and polycythemia
Body adapts to hypoxia with increased ventilation, pulmonary
vasoconstriction, and increased production of RBC’s
Adventitious Sounds
-additional breath sounds superimposed on normal sounds
-indicate changes in the tracheobronchial tree
-vary in pitch, intensity, duration, and the phase of the respiratory
cycle in which they occur
Examples: crackle, wheeze, rhonchus, pleural friction rub
Voice Sounds
-auscultation of voice sounds through the normally air-filled lung
produces a muffled, unclear sound because sound vibrations travel
poorly through air
-vocal resonance is increased when the sound must travel through a
solid or liquid medium, as it does in clients with a consolidated area
of the lung, pneumonia, atelectasis, pleural effusion, tumor, or
abscess
Bronchophony-abnormally loud and clear transmission of
voice sounds through an area of increased density—assess by
having client repeat the number 99 while auscultating
Whispered Pectoriloquy-enhanced voice heard through the
chest wall—perceived by having the client whisper one, two,
three—whispered words should be faint and indistinct, if they
are heard loudly and distinctly, the nurse suspects
consolidation of lung tissue
Egophony-enhanced vocal resonance with a high-pitched,
bleating, nasal quality—assess by having client repeat the
letter E-if the letter is heard as a flat, nasal sound of A through
the stethoscope this is egophony-this indicates an area of
consolidation, pleural effusion, or abscess
Abnormal Rates and Rhythms
Bradypnea-slow breathing-less than 12/min
Tachypnea-rapid breathing-more than 24/min
Hypoventilation, inadequate ventilation-less than body
requirements-leaves too much CO2 in blood-acidosis
Hyperventilation-inadequate ventilation-more than body
requirements-causes too much CO2 to be blown off-alkalosis
Cheyne Stokes-periods of deep breathing alternating with apnea
Ataxic-unpredictable irregularity, may be shallow or deep and may
be apneic
Sighing-breathing punctuated by deep sighs
Obstructive-prolonged expiration with increased rate, less time to
expire-leads to air trapping and shallow breathing
Arterial Blood Gases
Normal
pH 7.35-7.45
pO2 80-100mmHg
pCO2 35-45 mmHg
HCO3-22-26mEq/L
Base excess 0 (+2 alkalosis, -2 acidosis)
SaO2-95-99%
Respiratory Acidosis (pH<7.35, pCO2>50mmHg)
-accumulation of carbonic acid (CO2 and H2O) due to
hypoventilation
Respiratory Alkalosis (pH>7.45, pCO2<35mmHg)
-Decrease in carbonic acid (CO2 and H2O) due to hyperventilation
Metabolic Acidosis
-Accumulation of renal acids, lactic acids, and ketoacids
Metabolic Alkalosis
-Associated with hypokalemia, volume contraction or administration
of alkalis
Interpreting ABGs
1. Determine if pH is low (acidosis), normal or high (alkalosis)
2. Determine if the PaCO2 is low (alveolar hyperventilation), normal
or high (alveolar hypoventilation)
3. If pH is low and PaCO2 is normal-consider metabolic causes—
low pH and HCO3 less than 22-metabolic acidosis
4. If pH is high and PaCO2 is normal-consider metabolic causes—
high pH and HCO3 greater than 26-metabolic alkalosis
5. Determine if PaO2 is low (hypoxemia), or normal
6. Determine if SpO2 is low, or normal and correlate with
hemoglobin result
pH—acidotic or alkalotic?
PaCO2—low or high?-respiratory
PaCo2—normal & HCO3 low or high?--metabollic