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Page 9 / Case 11.02

DISCUSSION

THE DIAPHRAGM

Embryology
The precursor is first noted @ 3wks of gestation -- the septum transversum. The definitive diaphragm is derived from 4 structures.
1. Septum transversum which gives the central tendon
2. Two pleuroperitoneal membranes
1. The esophageal mesentery with incorporated crura
2. The body wall component which give the majority of the muscular portion

Nerve supply to the diaphragm
The Phrenic nerve is the only nerve supply it originate from C4 mainly but also C3&C5 contributes to it. At the level of diaphragm each phrenic nerve divide into 3 motor branches:
1. Sternal
2. Anterolateral
3. Posterior

Physiology of diaphragm
Diaphragm and insp.muscles contract in concert.
Abdominal pressure (Pab) rises and Plural pressure( Ppl) falls, the ratio of the pressure change is Pab/Ppl <-1
When the diaphragm is paralyzed : Pab=Ppl and so Pab/Ppl = +1 and the ratio is positive. This is why the abdomen moves paradoxically inward which is opposing the inflation of the lungs.

Eventration of the Diaphragm
This is an abnormally thin and elevated section of or complete hemi-diaphragm. The left side is more common affected than the right side.

Evantration is due to:
1. Maldevelopment of diaphragmatic muscle.
2. Phrenic nerve interruption from birth or operative injury
Embryologically : there is a complete or partial absence of muscular development in septum transversum with normal pleura above and peritoneum below. The two membranes may be separated by a thin fibrous sheath.

Gross pathological analysis shows absence or diminution of the diaphragmatic muscle. It becomes fibrous, thin and abnormally elevated. The Phrenic nerve is smaller than normal.

Mechanics
The diaphragm elevated with minimal or no functional contraction, but usually without paradoxical movement initially. The mediastinam shift towards the contralateral lung and diminishes the efficiency of the opposite diaphragm and lung.

At first diaphragmatic excursions are synchronous. Later there is paradoxical movement and mediastinal flutter (pendelluft)

Diaphragmatic paralysis
This generally results in infants or young children from brachial plexus injury at birth or trauma related to cardiac surgery.

Congenital malformations, which occur rarely, include:
1-Agenesis of phrenic nerve
2. Localized dystrophy of the muscle
3. Structural abnormality of cervical cord

Bilateral diaphragmatic paralysis
Conditions that are associated with include:
1. Amyotrophic lateral sclerosis
2. Spinal muscular atrophy
3. Limb girdle dystrophy
4. Acid maltase deficiency
5. Post open heart surgery or birth trauma.


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