Body Systems L19 Notes Flashcards
Name the factors effecting pulmonary compliance
Ease of lung expansion
Describe how the elasticity of connective tissue of the lungs is measured
- Measure -> Elastic recoil
- Lung volume changes -> pressure change
What is the equation for calculation of compliance?
- Compliance = δV / δP (litres/cm H2O)
Eg. Patient inhales 500ml air. Intrapleural pressure before insp. = -5cm H2O & -8cm at
end. Calc. compliance of lungs.
»_space; δV = 500 ml = 0.5L (0->500)
»_space; δP = (-8) – (-5) = -8 + 5 = -3cm
= δ = 3cm
»_space; Compliance = 0.5 / 3 = 0.1667L/cm H2O
Describe how surface tension is created
Surface tension
- Caused -> Intermolecular forces between mol. of liquid
- Air-fluid interface surface -> fluid
» Under tension -> (similar to stretching thin mem. Eg. Fluid layer between
alveolar cells & air)
What is Laplace’s law?
- Laplace’s Law:
» Relationship between pressure (P) , Surface Tension (T) & Radius (r) of an
alveolus (bubble).
What does Laplace’s law state?
> > At equilibrium -> Tendency of Incr. pressure expands alveolus
»_space; Balances tendency of surface tension to collapse alveolus
What is the equation for Laplace’s law?
> > P = 2T / r
Name a major factor influencing surface tension & describe what effect it has
- Pulmonary Surfactant:
» Reduces surface tension
-> Incr. compliance
Describe the role of pulmonary surfactant in reducing surface tension
> > Equalises pressure differences between large & small alveoli.
Maintains uniform alveolar size
Tension decreases as alveoli decr. in size
Enables adjustment of alveoli -> rates of inflation & deflation.
How does pulmonary surfactant maintain uniform alveolar size?
> > Maintains uniform alveolar size
- > Higher conc. -> Smaller alveoli - > Lower surface tension helps equalise pressure -> alveoli of different sizes. - > Easier inflation -> Smaller alveoli - > Energy required -> Alveolae expansion reduced with incr. no. of breaths.
Name the two factors which cause resistance to breathing
Lung volume
Bronchial Smooth muscle
What is airway resistance?
Airway Resistance
Major non-elastic source -> Gas flow resistance
Describe the effect of air resistance on gas flow
Incr. resistance -> Decr. gas flow
What is airway resistance determined by?
Resistance determined -> radius
Name the influencing factors on the radius of the airway
Lung volume
Bronchial Smooth muscle
Describe how lung volume influences airway resistance
- Lung Volume:
|»_space; Dilation -> Bronchi -> Lung expansion
Describe the two ways by which bronchial smooth muscle is influenced in order to influence airway resistance
Parasympathetic Nerves
Sympathtic nerves & adrenaline
Describe how the parasympathetic nerves effect the bronchial smooth muscle to influence airway resistance
- Bronchial Smooth Muscle:
» Parasympathetic Nerves
-> Bronchoconstriction
Describe how the sympathetic nerves & adrenaline effect the bronchial smooth muscle to influence airway resistance
> > Sympathetic Nerves & Adrenaline
-> Bronchodilation
What causes stimulation of bronchodilation by via the sympathetic nervous system & adrenaline?
> > Sympathetic Nerves & Adrenaline
- > Bronchodilation - ->> Caused - > Smoke & Dust irritance - > Histamine (Allergic response)
What is the equation for measuring air resistance?
Measuring Airway Resistance:
- ( FEV1 / FVC ) x 100
What two equational factors influence airway resistance?
- Forced Vital Capacity (FVC)
- Forced Expiratory Volume (FEV1)
What is the forced vital capacity?
- Forced Vital Capacity (FVC)
» Forceable exhalation
» Little difference to VC
What is the forced expiratory volume?
- Forced Expiratory Volume (FEV1)
|»_space; Vol. of air expired per second
What is the forced expiratory volume used for?
> > Used -> Assess changes in airflow resistance
Eg. Athsmatic patients.
Expressed as & of FVC
What affect does inspiration have on lung volume & intra-pleural pressure?
Incr. Lung vol (ml)
Decr. Intra-pleural pressure (cm H2O)
What affect does expiration have on lung volume & intra-pleural pressure?
Decr. Lung vol (ml)
Incr. Intra-pleural pressure (cm H2O)
What kind of shape represents lung volume on a graph?
- Lung volume:
Positive Bell shaped curve -> Inspiration & Expiration
What is the peak value of lung volume on a graph?
> > Peak -> 500ml
What shape does intra-pleural pressure create on a graph?
- Intra-pleural pressure:
Negative (irregularly-shaped) bell curve -> Inspiration & Expiration
What is the peak value of intra-pleural pressure on a graph?
> > Peak -> -8 cm
What shape represents intra-pleural pressure on a graph if no airway resistance present?
> > If no airway resistance -> V-shaped graph