Lung resistance and Neonatal Respiratory Disease Flashcards
What are volume and pressure changes?
- Respiratory muscles initiate changes in the intraplueral pressure which sets up a partial pressure gradient enables air to flow
- 1cm diaphragm movement creates a change in 3 cmH20 which is enough
- The more muscular effort the more work
- Ideally the lungs would be stretchy to allow inflation
Normal respiratory pressure around 1 L
What is Boyle’s Law?
The pressure of a given mass of a n ideal gas is inversely proportional to its volume at a constant temperature.
What are the two resistances that breathing effort work needs to overcome?
- Elastic resistance ( Lungs and Chest wall = surface tension and surfactant) - contributes to 65% resistance (Static state)
- Tissue - Lungs, Pleura
- skeletal, muscular skin
Dynamic state - Tissue Viscous Resistance and Airway Resistance:
- 35% of resistance - tissue viscuous resistance and airway resistance
- 20% = Lungs, Ribs,, Diaphragm and organs
- Airways, Gas flow
What is compliance and specific compliance?
Compliance: Distensibility (stretch) of the lunge i.e. the change in lung volume that occurs with each unit change in transpulmonary pressure e.e. V/P i.e. for both lung by 200 mL.
- Specific compliance - the corrected for volume at that time e.e. compliance / V
- This standardises compliances for different volumes
What is Elastance?
-Property of resisting deformation (resistance) or desite to return to original shape
E = 1/C
What is the V/P (compliance) relationship (TP CHNAGES)?
- Shows the capacity of the lungs to adapt to transpulmonary pressure changes
- You need muscular effort so the work of breathing is the area in this loop plus the hatched area
- Resistance are overcome
What is static resistance of the chest wall?
- Stiffness of chest wall
- Force of movement of chest wall is opposite that of lung
- Chest wall has tendency to expand but held by negatove pleural pressure
- Unopposed reaches 70% of TLC (resting position)
- When thorax is intact, in equilibrium with the lungs, its restinf level is Functional Residual Capacity (FRC)
What are some causes of increased chest wall resistance?
- Structural abnotmality - decreased flexibility/expansion
- Deformities of thorax
- Ossification of the costal cartilage
- Paralysis of intercostal muscles
- Chest trauma - paralysis, strain, pain
- Loss of elasticity
- Burns
- Blockage of the smaller respiratory passages with mucus or fluid
- Raised abdominal pressure
- Obesity
- Pregnancy
What is the static resistance of the lungs?
-Elastic recoil 0 the tendency of an elastic structure to oppose stretching
- The lungs naturally have a tendency to collapse because of elastic recoil
- Held open by the negative intraplueral pressure (established by lymphatic pumping of fluid)
- Collapse caused by :
- Elastin and collagen in lung tissues (1/3 of this)
- Surface tension (2/3 of this resistance)
Describe elastin and collagen in lung tissues
- Interwoven in the lung parenchyma
- Tendency to oppose stretching
What is surface tension in lungs?
- Caused by an air-liquid interface
- Small alveoli are unstable and have a greater tendency to collapse and empty its air into connected larger alveoli (i.e. atelectasis)
- Reduction of ST forces allows interdependent/stability
What are the benefits of surfactant?
- 3 X less transmural pressure needed to expamd lungs
- Keeps alveoli dry - lowers the inwardly directed pressure which draws water into the alveoli
- Maximises area for ventilation and perfusion
- ST of small alveoli are reduced more than larger alveoli as syrfactant molecules crowd into the smaller space
- Maintains ‘alveolar interdependence’
- Aided by fibrous tissue seprtal and septal walls between alveoli of different sizes which act as additional splints
What are some disorders that influence surface tension?
- Neonatal Respiratory Distress Syndrome (NRDS)- Alters or destroys surfactant
- Adult respiratory distress syndrome
- Oxygen toxicity
What is NRDS?
- Increasing respiratory distress commencing at or shortly after birth. Increases in severity until progressive resolution occurs among survivors, usually around 2nd to 7th day . Caused by deficiency of surfactant
- Can be primary or secondary
- Mortality is 50% in infants <1 kg
- Incidence and severity is inversely proportional to gestational
What are the symptoms of NRDS?
Cyanosis
Preterm birth
Tachypnea
Nasal flaring
Chest retractions and grunting
