Author R Schumacher 2009 License Unless otherwise noted

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The First Breath: M 1 2009 Source Undetermined R. Schumacher M 1 Embryology Spring 2009

Beaker A

Pierre Simon Laplace • French mathematician, physicist, and astronomer • Taught Napoleon - Ecole Militaire de Paris • Traite de Mecanique Celeste – 1806 -7 in Tome IV discusses capillary action and relates surface tension and radius of curvature Source Undetermined

Laplace Relationship • ∆P =2γ/r • Trans-surface pressure = 2(surface tension) / radius of curvature Source Undetermined

Pulmonary Surfactant • A liquid film that comes in contact with air covers alveoli, hence surface tension forces are at work in the lung. • If surface tension can be lowered then the work of breathing should be easier. • Since the forces are due to molecular forces of attraction, one way to lower surface tension would be to physically separate the molecules. This is what pulmonary surfactant does.

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• If this surface film is compressed the phospholipids will be packed more tightly and more water excluded from the surface. This is ideal: the smaller the radius of curvature the more important surface tension forces become (La. Place), the smaller the radius of curvature the tighter the surfactant molecular pack and the greater the reduction in surface tension forces. Source Undetermined

LAWS OF LUNG DEVELOPEMENT • Law I- Airways – The airways are present by the 16 th week of intrauterine life • Law II - Alveoli – Alveoli develop principally after birth • At birth the alveoli are primitive • At birth there are 20, 000 alveoli, at age eight years- 300, 000 • Law III- Vascular – preacinar arteries follow the development of the airways – intraacinar arteries appear as alveoli grow

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Jean L. Poiseuille, Jean Léonard Marie (1799 -1869) was a French physiologist who made a key contribution to our knowledge of the circulation of blood in the arteries. Source Undetermined Poiseuille's Law of The Flow of Liquids Through a Tube: Where: l = the length of the tube in cm r = the radius of the tube in cm p = the difference in pressure of the two ends of the tube in dynes per cm 2 c = the coefficient of Viscosity in poises (dyne-seconds per cm 2) v = volume in cm 3 per second Then: v = r 4 p/8 cl

• Arteriogram: – Newborn lacks intraacinar arteries – Lacks background “haze” seen in the adult lung – So resistance is high Source Undetermined

Pulmonary vascular resistance “high” in the newborn because: 1. There is a relative lack of alveoli and intraacinar cross sectional area for blood flow (Pouseuille). 2. In smaller arterioles, pulmonary vascular smooth muscle exists the medial thickness of the arteriole is higher than the adult. (not from laws of development)

Pulmonary vascular resistance low in the newborn because: 1. Larger arteries are less muscular in the newborn than in the adult. 2. Vascular smooth muscle does not exist/extend to the same vascular “level” as it does in the adult.

“THE FIRST BREATH” 1. What has to happen? Think big easy general ideas 2. How does it happen? Think: “In the body, how can I move water from one place to another”

THE FIRST BREATH: Goal #1: Fluid out, Air in. Source Undetermined

Fetal Pulmonary Fluid: Chloride Secreting Epithelium • Prior to birth the lung is a fluid filled organ with transepithelial chloride secretion as the major driving force for active production of lung fluid. There is net flow of fluid out of the lungs. • Multiple (but not all) studies suggest decrease in Cl pump activity is responsible for decrease in lung water prior to labor.

Fetal Pulmonary Fluid: Na “Reabsorption” • At birth lung epithelia change from Cl secreting to Na reabsorption mode. • ENa. C expression is developmentally regulated with peak expression in the alveolar epithelium achieved at term gestation • αENa. C “pumps” increase activity. Why/ Not clear. Exposure to air? , Stretch? , Steroids? , β adrenergic influences • (Nasal Na epithelial activity in premies……)

Fetal Pulmonary Fluid: Na “Reabsorption” • At birth lung epithelia change from Cl secreting to Na reabsorption mode. • ENa. C expression is developmentally regulated with peak expression in the alveolar epithelium achieved at term gestation • αENa. C “pumps” increase activity. Why/ Not clear. Exposure to air? , Stretch? , Steroids? , β adrenergic influences • (Nasal Na epithelial activity in premies……)

What About the Squeeze? • 1917 radiographic studies suggest compression of thorax in labor. • 1935 -56 German texts state lung water is jetted from the mouth with squeezing. • Recent xray (rabbits) and MRI studies still suggest squeezing plays a role

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• At the time of birth some (but not the majority) of lung water may be squeezed from the fetal lung as the infant passes through the birth canal. This removes some fluid and “loads” the diaphragm (decrease radius of curvature and aligns sarcomeres) for “the first breath. ” Source Undetermined

• Starling forces at work to clear lung fluid Source Undetermined

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• Functional Residual Capacity is establishe d Source Undetermined

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Goal #2. Blood In • Fetal circulation: – “right-to-left shunting” at the level of the atria and the ductus arteriosus. Source Undetermined

Pulmonary Vascular Resistance Falls at Birth: Why? • Mechanical • Biochemical – Simple examples p. H, p. O 2 – More……. .

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