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Basic Sciences: Answers
129
References
Mathews L, Singh RK. Cardiac output monitoring. Ann Card Anaesth. 2008;11:56-68.
Cholley BP, Payen D. Noninvasive techniques for measurements of cardiac output. Curr
Opin Crit Care. 2005;11:424-9.
1.62 Answer: D
P
alv
is ambient atmospheric pressure, or zero reference pressure, and P
pl
is a negative
intrapleural pressure that becomes even more negative during inspiration. The lungs will
expand to a higher volume during inhalation as a result of an increase in the transpulmonary
pressure, or distending pressure (P
alv
P
pl
). Static compliance is measured under conditions of
no airflow (stepwise changes in volume with no airflow during measurement of distending
pressure). With each increase in distending pressure there is a corresponding increase in lung
volume. Compliance is V/P. Distending pressure divided by change in lung volume gives
the lung volume divided by recoil pressure (P
alv
P
pl
) equals compliance only during the first
linear part of the lung distention/pressure relationship. Generally speaking, volume/pressure
(V/P) does not equal V/P. Change in elastic recoil pressure is only part of the compliance
calculation.
References
Gattinoni L, Carlesso E, Caironi P. Stress and strain within the lung. Curr Opin Crit Care.
2012;18:42-7.
Albaiceta GM, Blanch L, Lucangelo U. Static pressure-volume curves of the respiratory
system: were they just a passing fad? Curr Opin Crit Care. 2008;14:80-6.
1.63 Answer: A
The volume of air remaining in the lungs after a maximal effort to exhale all the air
possible is the residual volume. Therefore, this volume is not part of the vital capacity and
cannot be measured directly by a spirometer, which measures only changes in volume. Since
you cannot voluntarily change your lung volume below the residual volume, the spirometer
cannot measure it. Other methods (e.g., body plethysmography, inert gas dilution) must be
used to measure residual volume. Expiratory reserve volume is vital capacity minus
inspiratory capacity, and the resting volume of the lungs is the sum of residual volume and
expiratory reserve volume. Lungs will recoil inward until the recoil pressure (P
alv
P
pl
)
equals zero, a volume significantly below the residual volume.
References
Clayton N. Lung function made easy: assessing lung size. Chron Respir Dis. 2007;4:151-7.
Kendrick AH. Comparison of methods of measuring static lung volumes. Monaldi Arch Chest
Dis. 1996;51:431-9.
1.64 Answer: A
In respiratory physiology, dead space is air that is inhaled by the body in breathing, but
does not partake in gas exchange. In adults, it is usually in the region of 150 mL. Not all the
air we breathe in is able to be used for the exchange of oxygen and carbon dioxide. About a
third of every resting breath is exhaled exactly as it came into the body. Because of dead
space, taking deep breaths more slowly (e.g., ten 500 mL breaths per minute) is more
Shahzad G. Raja
130
effective that taking shallow breaths quickly (e.g., twenty 250 mL breaths per minute).
Although the amount of gas per minute is the same (5 L/min), a large proportion of the
shallow breaths is dead space, and does not allow oxygen to get into the blood. Dead space
can be enlarged (and better envisaged) by breathing into a long tube. Even though one end of
the tube is open to the air, when one inhales, it is mostly the carbon dioxide from expiration.
Using a snorkel increases a diver's dead space in the airways (though usually not
significantly). Dead space can be divided into two components: "anatomic" and
"physiologic".
Anatomic dead space is the gas in the conducting areas of the respiratory system, such as
the mouth and trachea, where the air does not travel to the alveoli of the lungs. It is normally
about 150 mL (or 2.2 mL per kilogram of body weight). This is about a third of the resting
tidal volume (450-500 mL). Anatomic dead space is the volume of the conducting airways. It
may be measured by Fowler‘s method, a nitrogen washout technique. It increases with an
increase in tidal volume and is dependent on posture.
Physiologic dead space is equal to the anatomic dead space plus the alveolar dead space.
Alveolar dead space is the area in the alveoli that does receive air to be exchanged, but there
is not enough blood flowing through the capillaries for exchange to be effective. It is
normally very small (less than 5 mL) in healthy individuals. It can increase dramatically in
some lung diseases. Physiologic dead space can be measured by Bohr's method.
The product of tidal volume (volume moved in or out with each breath) times the
frequency or breathing rate (number of breaths/min) is the total ventilation per minute (also
called minute ventilation). In this clinical vignette, the total ventilation is 600 mL times 12
breaths/min = 7200 mL/min. As stated in the problem, the alveolar ventilation (air ventilating
the respiratory zone for gas exchange each minute) is 6000 mL/min. The difference is that
part of the total ventilation going only to non-exchanging conducting airways = 1200
mL/min. or 100 mL per breath at 12 breaths/min. This 100 mL is the dead space volume.
References
Hedenstierna G, Sandhagen B. Assessing dead space. A meaningful variable? Minerva
Anestesiol. 2006;72:521-8.
Williams EM, Hamilton RM, Sutton L, Viale JP, Hahn CE. Alveolar and dead space volume
measured by oscillations of inspired oxygen in awake adults. Am J Respir Crit Care Med.
1997;156:1834-9.
1.65 Answer: B
The response to a stab wound that punctures the lung demonstrates the elasticity of the
lung and chest wall. The tendency of the lung to collapse is normally balanced by the
tendency of the chest wall to spring out. Thus, intrapleural pressures are subatmospheric.
Introduction of air in this space allows the lung to collapse and not to expand outward. At the
same time the chest wall will spring outward, not inward. Lung collapse obviously results in
very low lung volume.
References
Haynes D, Baumann MH. Pleural controversy: aetiology of pneumothorax. Respirology.
2011;16:604-10.
Baumann MH. Pneumothorax. Semin Respir Crit Care Med. 2001;22:647-56.
Basic Sciences: Answers
131
1.66 Answer: E
Normally, O
2
is transferred from air spaces to blood via a perfusion-limited process.
Thus, O
2
moves across the alveolar-capillary membrane by a process of simple diffusion, and
the amount of gas taken up depends entirely on the amount of blood flow. Processes that
impair diffusion of O
2
transform the normal relationship to a diffusion-limited process. Thus,
if O
2
must move a greater distance because of a thickened barrier, as would occur with
increased extravascular lung water (pulmonary oedema) or cell components (interstitial
fibrosis or asbestosis), the diffusion process is limited. Chronic obstructive lung diseases have
little effect on pulmonary diffusion capacity. Breathing a hyperbaric gas mixture would
increase the driving force and may overcome diffusion limitation in patients with mild
fibrosis or interstitial oedema. Increasing the ventilatory rate will not have this effect and will
only serve to maintain a high gradient of O
2
from air to blood. Strenuous, but not mild
exercise, decreases passage time and may also favour diffusion limitation.
References
West JB. Understanding pulmonary gas exchange: ventilation-perfusion relationships. Am J
Physiol Lung Cell Mol Physiol. 2004;287:L1071-2.
Powell FL, Hempleman SC. Comparative physiology of oxygen transfer in lungs. Adv Exp
Med Biol. 1988;227:53-65.
1.67 Answer: D
Afferent fibres from pulmonary mechanoreceptors are carried with the vagal and
glossopharyngeal nerves to the brainstem and serve to limit inspiration. The respiratory centre
of the central nervous system consists of a diffuse group of neurons whose inherent activity is
not abolished even after all known afferent stimuli have been eliminated. Although sectioning
the brain and observing respiratory changes is a useful approach to locating important areas of
respiratory regulation, this approach interferes with many complex pathways which may
interact. Nonetheless, transection of the brain above the pons has little effect—an apneustic
centre may be located in the pons. Transection above the centre results in prolonged
inspiration, but not prolonged expiration. Apparently, a pneumotaxic centre in the upper pons
together with vagal afferents limit inspiration. The medullary centre is capable of initiating
and maintaining respiration even if separated from the pons.
References
Kreit JW, Eschenbacher WL. The physiology of spontaneous and mechanical ventilation.
Clin Chest Med. 1988;9:11-21.
Mitchell RA. Neural regulation of respiration. Clin Chest Med. 1980;1:3-12.
1.68 Answer: D
The relationship between alveolar ventilation (VA) and alveolar CO
2
pressure (PACO
2
) is
represented as:
VA = (VCO
2
/PACO
2
) x K
where K is a constant such that PACO
2
= FACO
2
x K. (FACO
2
is the fraction of alveolar CO
2
).
Since VCO
2
is constant if CO
2
production remains unchanged, PACO
2
will double if VA is
Shahzad G. Raja
132
halved. In normal persons, alveolar CO
2
pressure (PACO
2
) is virtually identical to arterial CO
2
pressure (PaCO
2
). Therefore, PaCO
2
will also double if VA is halved. On the other hand,
alveolar CO
2
pressures (PACO
2
) would decrease if ventilation were increased. Unless inspired
air is enriched with O
2
, arterial O
2
pressure (PaO
2
) and alveolar O
2
pressure (PAO
2
) will
decrease.
References
Yamaguchi K, Kawai A, Mori M, et al. Distribution of ventilation and of diffusing capacity to
perfusion in the lung. Respir Physiol. 1991;86:171-87.
Piiper J. Alveolar-capillary gas transfer in lungs: development of concepts and current state.
Adv Exp Med Biol. 1994;345:7-14.
1.69 Answer: A
Breathing 100% O
2
should increase the PaO
2
to almost 670 mm Hg in healthy persons
(same as alveolar PAO
2
). Diffusion abnormalities and ventilation/perfusion inequality are also
common causes of hypoxaemia. Breathing 100% O
2
will greatly relieve the hypoxaemia in
these cases, but not if the patient has an anatomic right-to-left shunt (for example, a
ventricular septal defect). One hundred percent O
2
also greatly increases the PaO
2
in profound
hypoventilation. The PaO
2
will greatly increase in the normal individual as well. In
abnormalities of diffusion (e.g., alveolar wall thickening) the PaO
2
will be below 670 mm Hg,
but not as low as 125 mm Hg. In ventilation/perfusion abnormalities, PAO
2
will be quite high
in all communicating air spaces after 100% O
2
, and both alveolar and arterial PO
2
will be
quite high. Only in true right-to-left shunting would breathing 100% O
2
not substantially
elevate the PaO
2
, which could be as low as 125 mm Hg. The small rise over normal PaO
2
comes mainly from a small amount of additional dissolved O
2
in blood passing through
ventilated areas.
References
Kumar RK, Sandoval J. Advanced pulmonary vascular disease: the Eisenmenger syndrome.
Cardiol Young. 2009;19:622-6.
Moons P, Canobbio MM, Budts W. Eisenmenger syndrome: A clinical review. Eur J
Cardiovasc Nurs. 2009;8:237-45.
1.70 Answer: D
Bohr‘s equation states that
VD/VT = (PACO
2
PECO
2
)/PACO
2
where VD/VT is dead space/tidal volume, PECO
2
is mixed expired CO
2
, PACO
2
is alveolar CO
2
pressure.
In a normal person, PaCO
2
is virtually identical to PACO
2
. Thus
VD/VT = (PaCO
2
PECO
2
)/PaCO
2
Basic Sciences: Answers
133
Since by Fowler‘s method, VD/VT = 0.25 in the patient described in the question, the
(PaCO
2
PECO
2
)/PaCO
2
= (40 PECO
2
)/40 = 0.25. Therefore PECO
2
= 30 mm Hg. If
considerable inequality of blood flow and ventilation were present, PECO
2
could be much less
than 30 mm Hg, and the patient‘s physiologic dead space would exceed the anatomic dead
space.
References
Whipp BJ. Physiological mechanisms dissociating pulmonary CO2 and O2 exchange
dynamics during exercise in humans. Exp Physiol. 2007;92:347-55.
Wasserman K, Sietsema KE. Assessing cardiac function by gas exchange. Cardiology.
1988;75:307-10.
1.71 Answer: C
Vital capacity is the sum of inspiratory reserve volume, tidal volume, and expiratory
reserve volume. Therefore, in order to calculate inspiratory reserve volume, the tidal volume
and expiratory volume have to be subtracted from the vital capacity. All of these values can
be measured by spirometry. The other choices are not sufficient to calculate inspiratory
reserve volume. Residual volume cannot be measured by spirometry.
References
Clayton N. Lung function made easy: assessing lung size. Chron Respir Dis. 2007;4:151-7.
Kendrick AH. Comparison of methods of measuring static lung volumes. Monaldi Arch Chest
Dis. 1996;51:431-9.
1.72 Answer: D
Patients suspected of having emphysema/chronic obstructive pulmonary disease should
undergo pulmonary function testing to confirm airway obstruction and to quantify its severity
and reversibility. Pulmonary function testing is also useful for following disease progression
and monitoring response to treatment. The primary diagnostic tests are FEV
1
, which is the
volume of air forcefully expired during the first second after a full breath; forced vital
capacity (FVC), which is the total volume of air expired with maximal force; and flow-
volume loops, which are simultaneous spirometric recording of airflow and volume during
forced maximal expiration and inspiration. Reduction of FEV
1
, FVC, and the ratio of
FEV
1
/FVC are the hallmark of airway obstruction. Flow-volume loops show a concave
pattern in the expiratory tracing. FEV
1
declines up to 60 mL/yr in smokers, compared with a
less steep decline of 25 to 30 mL/yr in nonsmokers, beginning at about age 30. In middle-
aged smokers who already have a low FEV
1
, the decline occurs at a more rapid rate. When
the FEV
1
falls below about 1 L, patients develop dyspnoea with activities of daily living;
when the FEV
1
falls below about 0.8 L, they are at risk of hypoxaemia, hypercapnia, and cor
pulmonale. FEV
1
and FVC are easily measured with office spirometry and define severity of
disease because they correlate with symptoms and mortality. Normal reference values are
determined by patient age, sex, and height.
Other test abnormalities may include an increased total lung capacity, functional residual
capacity, and residual volume, which can help distinguish COPD from restrictive pulmonary
disease, in which these measures are diminished; decreased vital capacity; and decreased
single-breath diffusing capacity for carbon monoxide (DLCO). Decreased DLCO is nonspecific
Shahzad G. Raja
134
and is reduced in other disorders that affect the pulmonary vascular bed, such as interstitial
lung disease, but can help distinguish COPD from asthma, in which DLCO is normal or
elevated.
References
Turato G, Zuin R, Saetta M. Pathogenesis and pathology of COPD. Respiration.
2001;68:117-28.
Thurlbeck WM. Pathophysiology of chronic obstructive pulmonary disease. Clin Chest Med.
1990;11:389-403.
1.73 Answer: B
The thoracic duct conveys the greater part of the lymph and chyle into the blood. It is the
common trunk of all the lymphatic vessels of the body, excepting those on the right side of
the head, neck, and thorax, and right upper extremity, the right lung, right side of the heart,
and the convex surface of the liver. In the adult it varies in length from 38 to 45 cm. and
extends from the second lumbar vertebra to the root of the neck. It begins in the abdomen by
a triangular dilatation, the cisterna chyli, which is situated on the front of the body of the
second lumbar vertebra, to the right side of and behind the aorta, by the side of the right crus
of the diaphragm. It enters the thorax through the aortic hiatus of the diaphragm, and ascends
through the posterior mediastinal cavity between the aorta and azygos vein. The thoracic duct
has several valves; at its termination it is provided with a pair, the free borders of which are
turned toward the vein, so as to prevent the passage of venous blood into the duct.
References
Chapter 2. The Thorax: Part 1-The Thoracic Wall. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 34-57.
1.74 Answer: C
The sternal angle is the point where the costal cartilage attaches the second rib to the
sternum. This is an important anatomical landmark to remember-it is used to find the valves
when auscultating the heart! The costal margins are formed by the medial borders of the 7th
through 10th costal cartilages. They are easily palpable and extend inferolaterally from the
xiphisternal joint. The sternal notch/jugular notch is the notch located at the superior border
of the manubrium, between the sternal ends of the clavicles. The sternoclavicular joints are
simply the joints connecting the sternum with the clavicles. Finally, the xiphoid process is the
bone that makes the inferior part of the sternum.
References
Chapter 2. The Thorax: Part I-The Thoracic Wall. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 34-57.
1.75 Answer: A
The costodiaphragmatic recess is the lowest extent of the pleural cavity or sac. It is the
part of the pleural sac where the costal pleura changes into the diaphragmatic pleura. Because
this is the most inferior part of the pleural sac, fluid in the pleural sac will fall to this region
when a patient adopts erect posture. The costodiaphragmatic recess is also the area into which
Basic Sciences: Answers
135
a needle is inserted for thoracocentesis, and it is found at different levels at different areas of
the thorax. At the mid clavicular line, the costodiaphragmatic recess is between ribs 6 and 8;
at the midaxillary line it is between 8 and 10; and at the paravertebral line it is between 10
and 12.
The costomediastinal recess is found where the costal pleura becomes the mediastinal
pleura. The cupola is the part of the pleural cavity which extends above the level of the 1st rib
into the root of the neck. The hilar reflection is the point at the root of the lung where the
mediastinal pleura is reflected and becomes continuous with the visceral pleura. Finally, the
middle mediastinum is the space in the mediastinum which contains the heart, pericardium,
great vessels, and bronchi (at the roots of the lung).
References
Chapter 3. The Thorax: Part II-The Thoracic Cavity. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 58-112.
1.76 Answer: D
A needle inserted for aspiration of fluid from the pleural space will pass through the skin,
subcutaneous tissue, external intercostals, internal intercostals, innermost intercostals and
parietal pleura in that order from superficial to deep.
References
Chapter 2. The Thorax: Part I-The Thoracic Wall. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 34-57.
1.77 Answer: E
Latissimus dorsi is a triangular, flat muscle that covers the lumbar region and the lower
half of the thoracic region. It has an extensive origin from the spinous processes of the lower
six thoracic vertebrae, from the posterior layer of the lumbodorsal fascia, from the external lip
of the crest of the ilium lateral to the margin of the sacrospinalis, and from the three or four
lower ribs by fleshy digitations, which are interposed between similar processes of the
external oblique. Through the posterior layer of the lumbodorsal fascia it is attached to the
spines of the lumbar and sacral vertebrae, to the supraspinal ligament, and to the posterior
part of the crest of the ilium. From this extensive origin the fibres converge and form a thick,
narrow tendon which crosses the inferior angle of the scapula, and usually receives a few
fibres from it. The muscle curves around the lower border of the teres major, and is twisted
upon itself, so that the superior fibres become at first posterior and then inferior, and the
vertical fibres at first anterior and then superior. It is inserted into the bottom of the
intertubercular groove of the humerus above the tendon of the pectoralis major through a
quadrilateral tendon that is about 7 cm. long. The lower border of its tendon is united with
that of the teres major, the surfaces of the two being separated near their insertions by a bursa;
another bursa is sometimes interposed between the muscle and the inferior angle of the
scapula. The tendon of the muscle gives off an expansion to the deep fascia of the arm.
The latissimus dorsi is supplied by the sixth, seventh, and eighth cervical nerves through
the thoracodorsal (long subscapular) nerve. When the latissimus dorsi acts upon the humerus,
it depresses and draws it backward, and at the same time rotates it inward. It is the muscle
which is principally employed in giving a downward blow, as in felling a tree or in sabre
Shahzad G. Raja
136
practice. With the arm fixed, the muscle may act in various ways upon the trunk; thus, it may
raise the lower ribs and assist in forcible inspiration; or, if both arms are fixed, the two
muscles may assist the abdominal muscles and pectorales in suspending and drawing the
trunk forward, as in climbing.
References
Chapter 2. The Thorax: Part I-The Thoracic Wall. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 34-57.
1.78 Answer: D
Pulmonary embolism is a blockage of an artery in the lungs by a blood clot, fat, air or
clumped tumour cells. By far the most common form of pulmonary embolism is a
thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes
dislodged from its site of formation and embolises to the arterial blood supply of one of the
lungs. Symptoms may include dyspnoea, pain during breathing, and more rarely circulatory
instability and death. A clot originating in the leg vein will travel up the inferior vena cava,
into the right atrium, through the tricuspid valve, into the right ventricle, through the
pulmonary trunk, into the left pulmonary artery, into the left superior lobar artery, to finally
reach the left apical segmental artery and block it.
References
Chapter 3. The Thorax: Part II-The Thoracic Cavity. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 58-112.
1.79 Answer: C
Most of the veins of the heart open into the coronary sinus. This is a wide venous channel
about 2.25 cm. in length situated in the posterior part of the coronary sulcus, and covered by
muscular fibres from the left atrium. It ends in the right atrium between the opening of the
inferior vena cava and the atrioventricular aperture, its orifice being guarded by a semilunar
valve, the valve of the coronary sinus (valve of Thebesius). Its tributaries are the great, small,
and middle cardiac veins, the posterior vein of the left ventricle, and the oblique vein of the
left atrium, all of which, except the last, are provided with valves at their orifices.
The great cardiac vein begins at the apex of the heart and ascends along the anterior
longitudinal sulcus to the base of the ventricles. It then curves to the left in the coronary
sulcus, and reaching the back of the heart, opens into the left extremity of the coronary sinus.
It is the largest tributary of the coronary sinus. It receives tributaries from the left atrium and
from both ventricles: one, the left marginal vein, is of considerable size, and ascends along
the left margin of the heart.
The small cardiac vein runs in the coronary sulcus between the right atrium and ventricle,
and opens into the right extremity of the coronary sinus. It receives blood from the back of the
right atrium and ventricle; the right marginal vein ascends along the right margin of the heart
and joins it in the coronary sulcus, or opens directly into the right atrium.
The middle cardiac vein commences at the apex of the heart, ascends in the posterior
longitudinal sulcus, and ends in the coronary sinus near its right extremity.
The posterior vein of the left ventricle runs on the diaphragmatic surface of the left
ventricle to the coronary sinus, but may end in the great cardiac vein.
Basic Sciences: Answers
137
The oblique vein of the left atrium (oblique vein of Marshall) is a small vessel which
descends obliquely on the back of the left atrium and ends in the coronary sinus near its left
extremity; it is continuous above with the ligament of the left vena cava, and the two
structures form the remnant of the left Cuvierian duct.
The following cardiac veins do not end in the coronary sinus: (1) the anterior cardiac
veins, comprising three or four small vessels which collect blood from the front of the right
ventricle and open into the right atrium; the right marginal vein frequently opens into the right
atrium, and is therefore sometimes regarded as belonging to this group; (2) the smallest
cardiac veins (veins of Thebesius), consisting of a number of minute veins which arise in the
muscular wall of the heart; the majority open into the atria, but a few end in the ventricles.
References
Chapter 3. The Thorax: Part II-The Thoracic Cavity. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 58-112.
1.80 Answer: A
Atrial septal defect (ASD) is a congenital heart defect that results in a communication
between atria of the heart and may involve the interatrial septum. The interatrial septum is the
tissue that separates the right and left atria from each other. Without this septum, or if there is
a defect in this septum, it is possible for blood to travel from the left side of the heart to the
right side of the heart, or the other way around, resulting in mixing of arterial and venous
blood. During development of the foetus, the interatrial septum develops to eventually
separate the left and right atria. The foramen ovale remains open during foetal development to
allow blood from the venous system to bypass the lungs and go to the systemic circulation.
This is because prior to birth, the oxygenation of the blood is via the placenta and not the
lungs. A layer of tissue begins to cover the foramen ovale during foetal development, and will
close it completely soon after birth. After birth, the pressure in the pulmonary circulation
drops, and the foramen ovale closes. In approximately 25% of adults the foramen ovale does
not seal over. In this case, elevation of pressure in the pulmonary circulation (i.e., pulmonary
hypertension due to various causes, or transiently during a cough) can cause opening of the
foramen ovale. This is known as a patent foramen ovale (PFO).
References
Lesions with normal segmental connections. Wilcox BR, et al. eds. Surgical Anatomy of the
Heart. Cambridge University Press. UK. 2004:131-214.
1.81 Answer: C
A muscular band, well-marked in sheep and some other animals, frequently extends from
the base of the anterior papillary muscle to the ventricular septum. From its attachments it
was thought to prevent overdistension of the ventricle, and was named the "moderator band".
However, more recent research has indicated that it is more properly considered part of the
electrical conduction system of the heart, and in that capacity it is called the "septomarginal
trabecula".
Shahzad G. Raja
138
References
Surgical anatomy of the conduction system. Wilcox BR, et al. eds. Surgical Anatomy of the
Heart. Cambridge University Press. UK. 2004:99-112.
1.82 Answer: B
Intercostal nerves are the ventral primary rami of spinal nerves T1-T11. They provide
motor innervation to intercostal muscles, abdominal wall muscles (via T7-T11) and muscles
of the forearm and hand (via T1). They provide sensory innervation to the skin of the chest
and abdomen on the anterior and lateral sides. The other nerves listed do not innervate the
chest wall. Dorsal primary rami provide motor innervation to true back muscles and sensory
innervation to the skin on the back. The lateral pectoral nerve provides motor innervation to
pectoralis major only, while the medial pectoral nerve provides motor innervation to
pectoralis major and minor. The thoracodorsal nerve provides motor innervation to latissimus
dorsi.
References
Chapter 2. The Thorax: Part I-The Thoracic Wall. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 34-57.
1.83 Answer: A
The costodiaphragmatic recess is the lowest extent of the pleural cavity or sac. It is the
part of the pleural sac where the costal pleura changes into the diaphragmatic pleura. Because
this is the most inferior part of the pleural sac, fluid in the pleural sac will fall to this region
when a patient sits up. The costodiaphragmatic recess is also the area into which a needle is
inserted for thoracocentesis, and it is found at different levels at different areas of the thorax.
At the mid clavicular line, the costodiaphragmatic recess is between ribs 6 and 8; at the
midaxillary line it is between 8 and 10; and at the paravertebral line it is between 10 and 12.
The costomediastinal recess is found where the costal pleura becomes the mediastinal
pleura. The cupola is the part of the pleural cavity which extends above the level of the 1st rib
into the root of the neck. The hilar reflection is the point at the root of the lung where the
mediastinal pleura is reflected and becomes continuous with the visceral pleura. Finally, the
middle mediastinum is the space in the mediastinum which contains the heart, pericardium,
great vessels, and bronchi (at the roots of the lung).
References
Chapter 3. The Thorax: Part II-The Thoracic Cavity. Snell RS, ed. Clinical Anatomy By
Regions. 9
th
edition. Baltimore, USA. Lippincott William & Wilkins. 2012: 58-112.
1.84 Answer: D
The oblique sinus is an area of the pericardial cavity located behind the left atrium of the
heart where the serous pericardium reflects onto the inferior vena cava and pulmonary veins.
If you slide your fingers under the heart, they will be in the oblique sinus. The other
pericardial sinus that you should be familiar with is the transverse sinus. The transverse sinus
is an area of the pericardial cavity located behind the aorta and pulmonary trunk and anterior
to the superior vena cava. It separates the outflow vessels from inflow vessels.