This document discusses paralyzed diaphragm. It begins by describing how diaphragmatic paralysis can occur and the symptoms patients may experience depending on whether it is unilateral or bilateral. Common causes of paralysis include iatrogenic injury, malignancy, and certain medical conditions. Diagnosis involves imaging and tests of diaphragm movement. Treatment depends on a patient's symptoms, with conservative care used for mild cases and diaphragmatic plication surgery considered for more severe symptoms. Bilateral paralysis has a poorer prognosis than unilateral paralysis.

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4 THORAX 6 PARALYZED DIAPHRAGM — 1
6 PARALYZED DIAPHRAGM
Bryan F Meyers, M.D., F.A.C.S., and Benjamin D. Kozower, M.D.
.
Evaluation of Elevated Hemidiaphragm
Paralysis of the diaphragm is an unusual and challenging clinical compromise. Patients may sleep in a semirecumbent position or in
problem that may occur either in isolation or as part of a systemic the lateral decubitus position with the affected hemidiaphragm
disease. It can be caused by a number of disorders and should be down. Most patients have few respiratory symptoms at rest, but
considered in the differential diagnosis whenever a chest radi- some complain of dyspnea, cough, or chest pain with exertion [see
ograph shows an elevated hemidiaphragm. At one time, diaphrag- Figure 1]. Patients with left-side paralysis may experience GI com-
matic paralysis was generally considered to be a benign condition, plaints resulting from compression of the stomach [see Figure 2].
but it is now clear that many patients experience various pul- In addition, patients may suffer from recurrent pneumonia, bron-
monary, cardiac, and gastrointestinal symptoms. The symptoms chitis, or cardiac arrhythmias.
reported are typically nonspecific, and the correct diagnosis is Bilateral diaphragmatic paralysis, on the other hand, is poorly
often difficult to make. tolerated. Patients with this condition depend more on their acces-
It is helpful to remember that the clinical manifestations of sory muscles of respiration, avoid the supine position, and are
diaphragmatic paralysis are usually explained by the pathophysiol- more prone to chronic respiratory failure.5
ogy. Interruption of the phrenic nerve anywhere between the neck In children, diaphragmatic paralysis may cause severe respirato-
and the diaphragm results in paralysis of the ipsilateral hemidi- ry distress. Compared with adults, children have weaker inter-
aphragm [see Discussion, Diaphragmatic Anatomy, below]. costal muscles, a more compliant chest wall, and a more mobile
Because the diaphragm is a continuous muscular sheet, one might mediastinum. Accordingly, children must depend on their
suppose that paralysis of one side would adversely affect the other. diaphragms to achieve adequate tidal volumes. Unilateral
Actually, the two sides of the diaphragm function independently: diaphragmatic paralysis in a child usually necessitates mechanical
tension from one side is not distributed to the other across the ventilation; bilateral paralysis is often fatal without prompt venti-
central tendon.1 Bilateral diaphragmatic paralysis is rarely encoun- latory support.
tered by the thoracic surgeon. When it does occur, it is usually a
manifestation of neuromuscular or systemic disease. Common Causes of Diaphragmatic Paralysis
The functional effects of hemidiaphragmatic paralysis are simi- As noted (see above), bilateral diaphragmatic paralysis is usual-
lar to but less striking than those of bilateral paralysis [see ly a manifestation of a systemic disease, such as a neuromuscular
Discussion, Normal Diaphragmatic Function, below].2 An elevat- junction disorder, an immunologic phenomenon, or a myopathy.
ed hemidiaphragm compresses the hemithorax and results in a Because thoracic surgeons rarely treat these conditions, the ensu-
restrictive pattern of lung disease. In the seated position, the
patient’s vital capacity and total lung capacity decrease by approx-
imately 20%; in the supine position, vital capacity decreases by
nearly 40%.3 Ventilation and perfusion of the lower lobe are also
reduced on the affected side. Mismatching may widen the alveo-
lar-arterial oxygen difference and produce mild hypoxemia.4
Generally, adults with healthy lungs tolerate these changes well;
however, patients who are obese or have underlying lung disease
are more likely to be symptomatic.
Diaphragmatic paralysis is frequently described in the literature
in conjunction with eventration of the diaphragm. Eventration is a
condition in which all or a portion of one hemidiaphragm is per-
manently elevated while retaining its continuity and its normal
attachments to the costal margins. Although eventration and uni-
lateral paralysis are technically different, they often give rise to the
same physiologic disturbances and radiographic findings.
Clinical Evaluation
HISTORY
Figure 1 Shown is a postoperative radiograph from a 55-year-
In adults, the clinical presentation of uni- old woman who underwent left upper lobectomy. Because the
lateral paralysis of the diaphragm is highly tumor was directly adherent to the phrenic nerve, a 2 cm portion
variable. Right and left hemidiaphragmatic of the left phrenic nerve was resected along with the tumor.
paralysis seem to occur with equal frequency Recovery was uneventful, and the only late symptom was mild
and usually cause little or no respiratory dyspnea with exertion.

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4 THORAX 6 PARALYZED DIAPHRAGM — 2
Evaluation of Elevated Hemidiaphragm
Patient presents with elevated hemidiaphragm on chest x-ray
Obtain clinical history:
• Previous operations (iatrogenic phrenic nerve injury)
• Malignancy involving phrenic nerve
• Respiratory symptoms (exertional dyspnea, cough, difficulty
in sleeping)
• GI symptoms (dysphagia, dyspepsia)
• Cardiac symptoms (dysrhythmia)
Perform physical examination:
• Auscultation for decreased breath sounds
• Percussion to assess diaphragmatic excursion
Order investigative studies:
• Inspiratory and expiratory chest x-ray (to confirm elevated
hemidiaphragm)
• Fluoroscopy and sniff test (to distinguish diaphragmatic
paralysis from weakness)
• Cervical phrenic nerve stimulation (to clarify diagnosis in
patients on mechanical ventilation when sniff test is
inconclusive—rarely necessary)
Patient is asymptomatic or Patient has significant symptoms (e.g., dyspnea,
has only mild symptoms recurrent pneumonia, chronic bronchitis, chest pain,
poor exercise tolerance, cardiac dysrhythmia, or
Treat conservatively: functional gastric disorder)
• Physical therapy
• Pulmonary rehabilitation Order further tests as required:
• Weight loss • Pulmonary (pulmonary function tests)
• Cardiac (ECG, echocardiography)
• GI (gastric motility study)
Treat surgically with diaphragmatic plication (open or
thoracoscopic).

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4 THORAX 6 PARALYZED DIAPHRAGM — 3
inite connection between the two has not been established.
The outcome of phrenic nerve injury incurred during cardiac
surgery has been well studied. In many cases, the injured phrenic
nerves recover; typical recovery times for diaphragmatic function
range from 6 months to 2 years.6,8 In 20% of cases, however, the
injury is permanent [see Figure 3]. Although morbidity is usually
minimal, bilateral diaphragmatic paralysis after cardiac surgery
has occasionally resulted in death. It should be kept in mind that
diaphragmatic paralysis after cardiac surgery is a more serious
problem in children than in adults. In pediatric patients, phrenic
nerve injury usually results in respiratory distress, which may pre-
vent weaning from mechanical ventilation.9
In current usage, the term iatrogenic phrenic nerve injury refers
to either (1) unintentional injury to the nerve during an operation
or (2) intentional resection of the nerve to permit complete exci-
sion of a chest neoplasm. In the past, however, phrenic nerve
injury was sometimes deliberately induced to elevate or disable a
hemidiaphragm for therapeutic purposes, either permanently or
temporarily. Therapeutic phrenic nerve paralysis was originally
achieved by crushing the nerve at the level of the diaphragm with
Figure 2 Shown is a postoperative radiograph of a 70-year-old a surgical clamp; subsequently, temporary paralysis was achieved
man who underwent left upper lobectomy for removal of a periph- by exposing the phrenic nerve in the neck and infiltrating the area
eral 3 cm lesion. The phrenic nerve was injured with the electro- around it with local anesthetics. This technique was employed in
cautery during mediastinal lymph node dissection. The radi- the treatment of pulmonary tuberculosis and was occasionally
ograph shows permanent elevation of the left hemidiaphragm
performed to elevate a hemidiaphragm and help obliterate a diffi-
with gastric bloating 3 years after operation. The patient is neither
dyspneic nor dyspeptic and does not require surgical intervention.
cult pleural space problem. It must be emphasized that in current
practice, therapeutic phrenic nerve paralysis is of historic interest
only. It is never necessary, and it is no longer considered appro-
ing discussion focuses on conditions associated with isolated priate or beneficial.
diaphragmatic paralysis [see Table 1].The two most common caus-
es of unilateral diaphragmatic paralysis are (1) iatrogenic injury Malignancy involving phrenic nerve Neoplastic involve-
after a cardiothoracic or cervical procedure and (2) malignancy. ment of the phrenic nerve accounts for one third of cases of
diaphragmatic paralysis.10 Bronchogenic carcinomas are the
Injury to phrenic nerve Common mechanisms of phrenic lesions that most commonly affect the phrenic nerve, and paraly-
nerve injury during cardiac procedures include stretching, crush- sis is usually secondary to mediastinal lymph node involvement or
ing, transection, and hypothermia. During the mid-1980s, topical direct mediastinal invasion by central tumors. Other mediastinal
ice slush was frequently employed in cardiopulmonary bypass pro- tumors that may affect the phrenic nerve include thymomas, lym-
cedures, and this practice dramatically increased the incidence of phomas, and germ cell tumors. It is reassuring to note that in
phrenic nerve injury. After cooling jackets replaced topical ice slush patients with unilateral diaphragmatic paralysis of no clear origin,
in this setting, the incidence of elevated hemidiaphragms fell from malignancy turns out to be the cause in fewer than 5% of cases.
23% to 2%.6,7 It has been suggested that harvesting the internal Although patients with unexplained diaphragmatic paralysis are
mammary artery may contribute to phrenic nerve injury, but a def- unlikely to have an occult malignancy, they are also unlikely to
recover their diaphragmatic function.10
PHYSICAL EXAMINATION
Table 1—Causes of Isolated Diaphragmatic Patients with diaphragmatic paralysis may be asymptomatic or
Paralysis may present with some of the nonspecific clinical findings men-
tioned (see above). Physical examination usually reveals decreased
Idiopathic paralysis
Phrenic neuropathy
breath sounds on the affected side, a mediastinal shift during inspi-
Phrenic nerve injury ration, or a scaphoid abdomen. Percussion may demonstrate an
Iatrogenic elevated hemidiaphragm with decreased excursion on inspiration.
Malignancy (invasion or compression)
Trauma
Therapeutic (tuberculosis) Investigative Studies
Mononeuritis In the majority of cases, an asympto-
Viral infection (Guillain-Barré syndrome) matic person is referred to the surgeon
Vasculitis
because a chest radiograph demonstrates
Diabetes
an elevated hemidiaphragm. It is impor-
Connective tissue disease
Anterior horn cell lesions
tant to remember that there is a broad dif-
Herpes zoster ferential diagnosis for an elevated hemidi-
Poliomyelitis aphragm and that diaphragmatic paralysis
Amyotrophic lateral sclerosis is relatively rare [see Table 2].
Workup usually begins with inspiratory and expiratory chest

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4 THORAX 6 PARALYZED DIAPHRAGM — 4
a b
c
Figure 3 Shown are three chest radi-
ographs of a 25-year-old man with residual
anterior mediastinal mass after treatment
for germ cell tumor. (a) Preoperative view
shows normal diaphragmatic positioning
bilaterally. (b) Immediate postoperative view
demonstrates an elevated right hemidi-
aphragm, attributed to stretch injury and
electrothermal injury caused by dissection of
mass from the vicinity of the phrenic nerve
at the right hilum. (c) Late view, 3 months
after operation, reveals gradual restoration
of normal diaphragm positioning. Patient is
asymptomatic.
radiographs. However, fluoroscopic examination is the most prac- sniff test, a definitive diagnosis can be made by employing cervi-
tical method of assessing the movement of the diaphragm. The cal phrenic nerve stimulation in conjunction with electromyo-
excursion of the domes of the diaphragm averages 3 to 5 cm and graphic measurement of phrenic nerve latency.13 This final test is
may range from 2 to 10 cm.11 The examination is typically per- rarely necessary.
formed with the patient standing, but it is more sensitive when the
patient is supine because the effect of gravity is removed. In a
patient with unilateral paralysis, the paralyzed hemidiaphragm Management
moves upward with rapid inspiration and downward with expira-
CONSERVATIVE VERSUS SURGICAL
tion. This paradoxical motion passively follows changes in
TREATMENT
intrapleural and intra-abdominal pressure.
The so-called sniff test is then performed to confirm that the Treatment is individualized and depends
abnormal diaphragm excursion is the result of paralysis rather on the degree to which the patient is inca-
than of weakness. During this test, the patient inhales forcefully pacitated. Most healthy adults with isolated
and rapidly through the nose with the mouth closed. A sharp and diaphragmatic paralysis are asymptomatic or suffer only from mild
brief downward motion in both hemidiaphragms is the normal exertional dyspnea. The vast majority of these patients do not
response when paralysis is absent. If an entire hemidiaphragm require surgical treatment and are best treated conservatively (e.g.,
exhibits a paradoxical upward motion greater than 2 cm, howev- with physical therapy, pulmonary rehabilitation, and counseling on
er, diaphragmatic paralysis is likely.12 The diagnosis of diaphrag- weight loss, if necessary). Just as many patients with normal lung
matic paralysis may be difficult to make in patients with severe function can tolerate major pulmonary resections, most patients
chronic obstructive pulmonary disease, in whom normal hemidi- who are otherwise fit can tolerate unilateral diaphragmatic paraly-
aphragms move very little. The sniff test may also be inconclusive sis without the need for surgical intervention.
in weak, debilitated patients, who often are incapable of produc- Operative management may, however, be indicated for children
ing a forceful sniff. In patients who are undergoing mechanical and for adults who have significant symptoms (e.g., dyspnea,
ventilation and in whom the diagnosis remains in doubt after a recurrent pneumonia, chronic bronchitis, chest pain, poor exercise

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4 THORAX 6 PARALYZED DIAPHRAGM — 5
tolerance, cardiac arrhythmias, or functional disorders of the There was a small improvement in tidal volume after bilateral pli-
stomach).14 The classic treatment is diaphragmatic plication, cation, but this was probably attributable to improved rib cage
which may be performed either via a thoracotomy or thoraco- efficiency secondary to diaphragmatic fixation.
scopically. Plication of the diaphragm was first performed in 1947 These findings may explain why bilateral plication has been
to treat congenital eventration of the diaphragm, and the basic more beneficial for adults than it has been for children,20 who
principles of the procedure have changed little since then.15 depend more on the diaphragmatic contribution to respiration.
In infants, the small improvement in rib cage efficiency may not
PLICATION OF DIAPHRAGM
be large enough to allow them to be weaned from mechanical ven-
tilation. In children with hemidiaphragmatic paralysis, however,
Open plication is essential for improving diaphragmatic efficiency and
A standard diaphragmatic plication is performed through a preventing complications associated with long-term mechanical
posterolateral thoracotomy in the eighth intercostal space. The ventilation.20
lung and the mediastinum are examined to exclude any unsus-
pected pathologic conditions. The uncut diaphragm is plicated Thoracoscopic
with four to six parallel rows of heavy nonabsorbable sutures.The In 1996, a thoracoscopy-assisted approach to diaphragmatic
stitches are placed in an anterolateral-to-posterolateral direction, plication was first described. The goal was to achieve an equiva-
and each row takes several bites of the diaphragm to form pleats. lent degree of plication by less invasive means.21 Three patients
The sutures are tied only after all the rows have been placed. were treated in this fashion.The procedure made use of a double-
When all of the sutures are placed and tied, the diaphragm should lumen endotracheal tube, two thoracoscopic ports, and a 5 cm
be tight, and much of the plicated tissue should lie within the cen- minithoracotomy. The diaphragm was invaginated and stitched
tral tendon. with two rows of continuous sutures. The results were excellent,
Open diaphragmatic plication is an effective procedure for and the average hospital stay was 8 days. All three patients showed
treating diaphragmatic paralysis. In a study of 17 patients who significant improvements in FVC and FEV1: FVC improved by
underwent plication for exertional dyspnea,16 no major complica- 9% to 22%, and FEV1 improved by 11% to 14%.These improve-
tions were reported during a mean hospital stay of 11 days. At 6 ments were maintained for a minimum of 17 months.
months’ follow-up, patients exhibited significant improvements Since this first description, several reports of successful
with respect to dyspnea score, forced vital capacity (FVC), total diaphragmatic plication with a purely thoracoscopic approach
lung capacity (TLC), functional residual capacity (FRC), and (using three or four ports) have been published.14,22 These case
arterial oxygenation. Furthermore, the subjective and objective reports documented symptomatic improvement and reduced
improvements were maintained for at least 5 years. In a subse- length of stay (4 days); however, they did not document significant
quent series from the United Kingdom, similar results were improvements in FVC or FEV1.Thoracoscopic diaphragmatic pli-
observed at a mean follow-up of 10 years: 14 of 15 patients were cation appears to be the surgical method of the future, but larger
satisfied with their plication and had returned to work.17 In addi- series with longer follow-up periods are needed. The main con-
tion, FVC, forced expiratory volume in 1 second (FEV1), FRC, traindication to thoracoscopic plication is extensive pleural adhe-
and TLC improved by 12%, 15%, 26%, and 13%, respectively. sions from inflammatory reactions or previous operations.
Research has also been performed on changes in respiratory
SURGICAL PROPHYLAXIS AFTER PHRENIC NERVE INJURY
mechanics after diaphragmatic plication. In 1980, one group
noted that plication was more successful for hemiparalysis than
for bilateral diaphragmatic paralysis.18 These clinical results sub- Phrenic Nerve Repair versus Prophylactic Plication
sequently led another group to hypothesize that normal function- An area of investigation that, to date, has not been sufficiently
ing of the contralateral hemidiaphragm might be required to explored is the potential role of prophylactic procedures in cases
derive significant benefit from diaphragmatic plication.19 These where one is confident that a phrenic nerve has been injured dur-
investigators demonstrated that plication for unilateral paralysis ing an operation and wishes to reverse or at least mitigate the
improved the strength of the normal contralateral hemidi- effect of the injury.
aphragm, so that the contralateral hemidiaphragm functioned as a If the injury resulted from sharp dissection, so that the entire
better pressure generator and thus made a greater contribution to nerve is present but divided, one may elect to repair the nerve. On
breathing. However, they found that bilateral plication for bilater- occasion, we have invited colleagues from plastic surgery to per-
al paralysis did not yield significant improvements with respect to form microsurgical anastomoses between the cut ends of the sev-
diaphragmatic function, lung compliance, or work of breathing. ered nerves, but we have never attempted a formal analysis of this
practice. Such a repair would not, of course, be feasible in a case
where the phrenic nerve was resected in the course of excision of
an attached invasive tumor.
Table 2—Differential Diagnosis of Elevated If the nerve was resected or was injured beyond hope of recov-
Hemidiaphragm on Chest Radiograph ery, one may reasonably consider plicating the diaphragm during
the same operation so as to minimize the impact of the diaphrag-
Volume loss (atelectasis, lobar collapse, hypoplasia)
Splinting
matic paralysis without having to perform another operation later.
Pleural disease (subpulmonic effusion, mass) This strategy has not yet been studied in the surgical literature, but
Diaphragmatic hernia it should be kept in mind for the rare instances of phrenic nerve
Eventration resection or injury during pulmonary or mediastinal resection.
Phrenic nerve paralysis
Abdominal disease (dilated viscera, abscess) PACING OF DIAPHRAGM
Single-lung transplantation for pulmonary fibrosis Although pacing of the diaphragm requires an intact phrenic
nerve and thus is not useful in cases of classic diaphragmatic

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4 THORAX 6 PARALYZED DIAPHRAGM — 6
paralysis, it is an established mode of ventilatory support with requires normal lungs with the ability to oxygenate and ventilate
which the thoracic surgeon should be familiar.The two main indi- in response to diaphragmatic movement; severe restrictive lung dis-
cations for diaphragmatic pacing are central alveolar hypoventila- ease and major chest wall deformities are contraindications
tion and high cervical spinal cord injury; less common indications to pacing. In addition, it is crucial that the patient be cooperative and
are intractable hiccups and end-stage chronic obstructive pul- motivated and have adequate support from nursing staff and family.
monary disease. Central alveolar hypoventilation is a form of sleep Phrenic nerve pacing involves the use of an extracorporeal gen-
apnea resulting from failure of the respiratory drive itself rather erator with an antenna that transmits radiofrequency signals to a
than from an anatomic obstruction. It is also known as Ondine’s subcutaneous radio receiver; the receiver then translates the
curse (from the German myth about the water nymph Ondine, radiofrequency signal into direct current, which is delivered
who, finding that her mortal husband had been unfaithful, placed through electrodes to the phrenic nerves. The electrodes are
a fatal curse on him so that he would only breathe while awake).23 placed on the phrenic nerves via bilateral anterior thoracotomies
The underlying cause is impaired sensitivity of the brain’s respira- or neck incisions. Several different commercial pacing systems are
tory control center to alterations in oxygenation.The clinical result available, but they all work according to the same basic concept.
is persistent hypoventilation with sleep apnea and the develop- Phrenic nerve pacing remains a relatively rare procedure. The
ment of pulmonary hypertension. largest series published to date included 165 patients, of whom
The use of electricity to induce diaphragmatic contraction was 27% were paced on a full-time basis and 63% on a part-time
first suggested by Hufeland in 1783.24 Besides an intact phrenic basis.25 Phrenic nerve pacing met the ventilatory requirements of
nerve and a functioning diaphragm, diaphragmatic pacing also 47% of the patients and was partially successful in 36%.
Discussion
Diaphragmatic Anatomy
The left and right phrenic nerves arise from the C3–C5 nerve
For the purposes of discussion, the diaphragm may usefully be roots and travel a distance of 30 to 40 cm between their cervical
divided into left and right hemidiaphragms. In anatomic terms, origin and their termination on the surface of the diaphragm. A
the diaphragm is a dome-shaped muscle that can be described as firm understanding of the anatomy of the phrenic nerves is cru-
having both muscular and tendinous components. The muscular cial for the thoracic surgeon because iatrogenic injury during
portion of the diaphragm is divided into three parts, each of which operation is a leading cause of diaphragmatic paralysis. Both
originates from one of the three structural elements forming the nerves originate on the middle scalene muscle and cross to the
lower thoracic aperture: the pars lumbalis diaphragmatis (origi- anterior scalene muscle, where they descend within an investment
nating from the lumbar spine), the pars costalis diaphragmatis of fascia. At the base of the neck, the left phrenic nerve crosses the
(from the ribs), and the pars sternalis diaphragmatis (from the thoracic duct, descending into the thorax on the anterior surface
sternum). The pars lumbalis is the most powerful region of the of the left subclavian artery. It then travels between the left com-
diaphragm.26 All three parts insert into a central aponeurosis mon carotid and subclavian arteries, crosses in front of the vagus
known as the central tendon. This tendon has a cloverleaf shape, nerve, and passes lateral to the aortic arch, where it descends
with one leaf directed anteriorly and two leaves directed laterally along the pericardium to a point just above the diaphragm. At the
(one into each hemithorax). thoracic inlet, the right phrenic nerve is located behind the
The diaphragm possesses three major apertures, which allow innominate vein and usually crosses in front of the internal mam-
passage of the inferior vena cava, the esophagus, and the aorta. mary artery. It descends to the right of the innominate vein and
The caval orifice is located in the right portion of the central ten- the superior vena cava before reaching the pericardium, anterior
don, typically at the level of T8. Diaphragmatic contraction to the lung. Finally, the right phrenic nerve descends along the
stretches this orifice and may facilitate the return of blood to the inferior vena cava toward the diaphragm. Both phrenic nerves
heart during inspiration. The right phrenic nerve and some lym- branch just proximal to the diaphragm, and small terminal
phatic vessels also pass through this orifice.The esophageal hiatus branches innervate the muscle.
is located behind the central tendon at the level of T10.This aper-
ture, unlike the other two, is ventrally framed by muscle.The aor-
tic opening is anterior to T12, between the crura and behind the Normal Diaphragmatic Function
median arcuate ligament. The aortic opening also allows passage The diaphragm is the most important respiratory muscle.
of the azygos vein, the thoracic duct, and lymphatic channels as During inspiration, the diaphragm contracts and moves caudally
they descend from the thorax into the abdomen. in a pistonlike fashion.This motion forces the abdominal contents
The arterial supply to the cranial surface of the diaphragm down and forward, increasing the vertical dimension of the chest
consists of the pericardiophrenic, musculophrenic, and superior cavity. In addition, the ribs lift the lateral aspect of the diaphragm
phrenic arteries. The posterior aspect of the diaphragm is sup- during inspiration, causing the transverse diameter of the thorax
plied by small direct branches from the aorta.The caudal surface to increase. As the diaphragm contracts, pleural pressure decreas-
of the diaphragm is supplied by the inferior phrenic arteries, es, facilitating lung inflation. Normal diaphragmatic function
which arise from the aorta or the celiac trunk; these arteries are accounts for 75% of air movement during normal respiration and
much larger than the superior phrenic arteries. Occasionally, the is responsible for 60% of minute volume in the supine position.
right inferior phrenic artery originates from the right renal Diaphragmatic excursion averages about 1 cm during normal
artery.27 The venous drainage from the diaphragm mirrors the tidal breathing, but it can increase to 10 cm during forced inspi-
arterial supply. ration and expiration.28

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4 THORAX 6 PARALYZED DIAPHRAGM — 7
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