Unit 5 - Breathing PART G Flashcards
Factors affecting pulmonary ventilation
- Lung compliance (CL)
a. Stretchability and elasticity of the lung tissue
b. Alveolar surface tension - Airway Resistance
a. Breathing mechanics
b. Smooth muscle tone
c. Pathological states
Lung compliance (CL)
Ability of lung to stretch and expand/distend (if compliance is high – lung stretches easily, like inflating a balloon, if compliance is low, it stretches less easily, like trying to inflate a car tire – greater pressure is required to inflate the tire than the balloon).
Lung compliance (CL)
Measured as the…
change in lung volume that occurs as a result of a change in transpulmonary pressure.
Lung compliance (CL)
Calculated as
CL = D lung volume / D transpulmonary pressure (Tp)
CL =DV/DP
Lung compliance (CL)
CL =DV/DP
Large changes in lung volume as a result of…
small changes in Tp indicate high compliance. Small changes in lung volume as a result of larger changes in Tp indicate low compliance.
Obstructive lung diseases have…
high compliance, but low elastic recoil (lungs expand easily, but do not recoil easily – like a worn out rubber band).
Restrictive lung diseases have…
low compliance and high elastic recoil (lungs do not expand easily, but recoil easily – like a brand new rubber band).
Lung compliance (CL)
Results from:
a. Stretchability and elasticity of the lung tissue
b. Alveolar surface tension
Lung compliance (CL)
Results from:
a. Stretchability and elasticity of the lung tissue
- decreases as we age and due to restrictive lung diseases (diseases which reduce/restrict ability of lung to expand).
- Lung tissue is surrounded by connective tissue that contains elastin and collagen protein fibers. Elastin allows lungs to stretch and recoil. Collagen is not elastic and provides strength.
- loss or build up of these connective tissue fibers produces changes in lung compliance (loss increases compliance; addition, particularly of collagen in the form of fibrous scar tissue, decreases compliance).
Stretchability and elasticity of the lung tissue
E.g.1: Aging
as we age, there is a LOSS of elastin and collagen that decreases the elastic recoil of the lungs (lungs become like a worn out elastic band that does not return to its original shape and is permanently stretched out). Result is an increased CL and impaired expiration.
Stretchability and elasticity of the lung tissue
E.g.2: Pulmonary fibrosis
stiffening of lung caused by chronic inhalation of fine particulate matter (asbestos, cigarette smoke, etc.) deep into the lung.
•Triggers an inflammatory process that leads to build up of collagen (scar tissue). Result is decreased CL and impairment of inspiration.
•Scar tissue also thickens membranes between alveoli, which slows diffusion of gases (poor gas exchange)
Lung compliance (CL)
Results from:
b. Alveolar surface tension
- attractive forces (H+ bonds) between adjacent water molecules on the surface of alveoli resist alveolar expansion and increase the work of inspiration (i.e. decrease compliance)
- Stretch of Type II alveolar cells causes them to secrete surfactant (which is a mixture of phospholipids and proteins). Surfactant molecules disrupt the H+ bonds between water molecules, and therefore decrease the cohesive forces that resist alveolar expansion. As a result, surfactant increases CL which makes inspiration easier, and prevents alveolar collapse.
Stretch of Type II alveolar cells causes them to secrete surfactant (which is a mixture of phospholipids and proteins). Surfactant molecules disrupt the H+ bonds between water molecules, and therefore decrease the cohesive forces that resist alveolar expansion. As a result, surfactant increases CL which makes inspiration easier, and prevents alveolar collapse.
Synthesis begins…
~24th week of fetal development and reaches adequate levels by week 34.
Deficiency in premature infants causes…
low CL that leads to newborn respiratory distress syndrome (NRDS). Treatment for NRDS includes spraying artificial surfactant into the lungs or artificial ventilation.
- have “stiff” (low-compliance) lungs
- have alveoli that collapse each time they exhale
Airway Resistance
Increasing airway resistance reduces air flow and therefore decreases pulmonary ventilation. Decreasing resistance increases ventilation.
In the lungs, much like in the blood vessels, resistance is determined primarily by the…
radius (diameter) of the airway. Bronchodilation decreases resistance, bronchoconstriction increases resistance. Remember that F = D P/R
Resistance (bronchoconstriction/dilation) is influenced by:
a. Breathing mechanics
b. Smooth muscle tone
c. Pathological states
Resistance (bronchoconstriction/dilation) is influenced by:
a. Breathing mechanics
Airways (bronchi, bronchioles) are connected to alveolar walls by elastic connective tissue. As a result, airways are pulled in the direction of the alveoli (RADIAL TRACTION).
On inspiration, expansion of the thoracic cavity and of the alveoli pulls on the the airways (increases RADIAL TRACTION) so they become more open (increases diameter). As a result airway resistance decreases, which increases air flow.
During Expiration
↓ Alveolar Expansion
↓ Radial Traction
↓ Airway Diameter
↑ Resistance
During Inspiration
↑ Alveolar Expansion
↑ Radial Traction
↑ Airway Diameter
↓ Resistance
Resistance (bronchoconstriction/dilation) is influenced by:
b. Smooth muscle tone
- decreased smooth muscle tone = BRONCHODILATION
- increased smooth muscle tone = BRONCHOCONSTRICTION
Bronchodilation
increased CO2 in expired air relaxes bronchiolar smooth muscle & causes bronchodilation
Broncoconstriction
increases resistance to air flow & decreases the amount of fresh air that reaches the alveoli
Smooth muscle tone is controlled by:
i. Nervous control
ii. Paracrine agents
ii. CO2
Nervous control
- PARASYMPATHETIC stimulation increases smooth muscle tone in the airways and causes BRONCHOCONSTRICTION
- There is little SYMPATHETIC innervation of bronchiolar smooth muscle, however STIMULATION OF b2-receptors BY EPINEPHRINE relaxes smooth muscle causing BRONCHODILATION.
Paracrine agents
HISTAMINE release by mast cells causes CONTRACTION of bronchiolar smooth and STIMULATES MUCUS SECRETION, both of which will decrease the diameter of the airway (BRONCHOCONSTRICTION) and increase resistance to air flow.
Histamine =
bronchoconstrictor
- released by mast cells in response to either tissue damage or allergic rxns
CO2
↑ PCO2 bronchioles dilate ↓ PCO2 bronchioles constrict
Bronchodilated airway
SNS
EPINEPHRINE + B2 receptors
↑ PCO2
Bronchoconstricted airway
PSNS
Histamine
↓ PCO2
Resistance (bronchoconstriction/dilation) is influenced by:
c. Pathological states
i. Asthma
ii. Chronic Obstructive Pulmonary Diseases (COPDs)
Resistance (bronchoconstriction/dilation) is influenced by:
c. Pathological states
i. Asthma
- Episodes of inflammation and strong BRONCHOCONSTRICTION due to hyper-responsiveness of bronchiolar smooth muscle to irritants (dust, cold, emotions, etc).
- Asthma also chronically increases the number of mast cells (therefore there is increased histamine release which reinforces the BRONCHOCONSTRICTION).
Resistance (bronchoconstriction/dilation) is influenced by:
c. Pathological states
ii. Chronic Obstructive Pulmonary Diseases (COPDs)
1) Emphysema
2) Chronic bronchitis (often co-occurs with emphysema)
Resistance (bronchoconstriction/dilation) is influenced by:
c. Pathological states
ii. Chronic Obstructive Pulmonary Diseases (COPDs)
1) Emphysema
- Destruction and collapse of alveoli and smaller airways
- Loss of elastic fibers and elastic recoil which increases CL, but impairs expiration. Some air is trapped in lungs (produces abnormally high residual volume).
Resistance (bronchoconstriction/dilation) is influenced by:
c. Pathological states
ii. Chronic Obstructive Pulmonary Diseases (COPDs)
2) Chronic bronchitis (often co-occurs with emphysema)
Inflammation of airways and accumulation of mucus (mast cells secreting proinflammatory cytokines) causes increased resistance
