Fetal Lung Development & Surfactant

• Surfactant is a mixture of phospholipids and lipoproteins produced in fetal lung cells

Physiological Adaptations

• Transition to extrauterine life begins at birth
• Total lungs develop and mature during the last trimester of pregnancy to support gas exchange at birth
• Surfactant production starts at 24 weeks gestation and is distributed throughout the lungs starting at 28-32 weeks
• Sufficient concentration of surfactant to prevent Respiratory complications occurs at 34-35 weeks
• Surfactant prevents alveoli from sticking together when taking the first breath and makes gas exchange easier
• Brown fat protects the infant from hypothermia
• Brown fat is deposited during the last week of gestation and is located in the scapular area, thorax, and behind the kidneys
• Glucose is stored in the liver as glycogen; a source of energy
• During labor, adrenal glands are stimulated to produce catecholamines hormones, dopamine, norepinephrine, and epinephrine
• These hormones increase surfactant levels in the lungs, blood flow to the heart, lung, and brain, and energy, and stimulate WBCs

Dijkstra's Algorithm

Introduction

• Dijkstra's algorithm finds the shortest path from a starting node to all other nodes in a weighted graph, provided there are no negative edge weights.

Algorithm

• Initialization:
  • The distance to the start node is set to 0 and to all other nodes to infinity.
  • All nodes are marked as unvisited.
• Iteration:
  • The unvisited node with the smallest distance is selected as the active node.
  • For each neighbor of the active node:
    • The distance from the start node to the neighbor is calculated via the active node.
    • If this distance is less than the previous distance to the neighbor, the neighbor's distance is updated.
  • The active node is marked as visited.
• Termination:
  • Step 2 is repeated until all nodes have been visited or the destination node has been visited.

Example Graph

• The following graph shows how one would calculate distances between nodes:
  • A is connected to B, distance 2
  • A is connected to C, distance 5
  • B is connected to D, distance 1
  • C is connected to D, distance 3
• With A as the starting node, the shortest paths to all other nodes are:
  • A -> B: 2
  • A -> C: 5
  • A -> D: 3 (A -> B -> D)

Properties

• It finds the shortest path from a start node to all other nodes.
• It only works with non-negative edge weights.
• It can be used to find the shortest path to a specific destination node; the algorithm can be terminated once the destination node has been visited.

Pseudocode

function Dijkstra(Graph, Startknoten):
    Distanz[Startknoten] = 0
    für jeden Knoten v in Graph:
        wenn v != Startknoten:
            Distanz[v] = Unendlich
    besucht = leere Menge
    solange es unbesuchte Knoten gibt:
        aktuellerKnoten = Knoten mit minimaler Distanz in (Graph - besucht)
        besucht.hinzufügen(aktuellerKnoten)
        für jeden Nachbarn n von aktuellerKnoten:
            neueDistanz = Distanz[aktuellerKnoten] + Gewicht(aktuellerKnoten, n)
            wenn neueDistanz < Distanz[n]:
                Distanz[n] = neueDistanz
    return Distanz