Breathing

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  • Created by: LBCW0502
  • Created on: 16-02-19 16:12
What are the intercostal layers?
3 layers - external layer, internal layer, innermost layer. (Diaphragm)
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What is the function of the intercostal muscles?
During breathing, provides structural support and moves ribs
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What is the function of a diaphragm?
Closes thoracic outlet, separates thoracic/abdominal cavities. Contracts (increase thorax volume, decrease intra-thoracic pressure) - air into lungs
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What is Dalton's Law? (1)
Pressure gas mixture = sum of partial pressures of individual components of the gas mixture. P = P nitrogen + P oxygen + P carbon dioxide. Room air (gas volume percentage). Nitrogen - 78%, oxygen - 21%, carbon dioxide - 0.03%, water vapour - 0.05%
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What is Dalton's Law? (2)
P atm - 760 mm Hg (sea level). P oxygen (760) (0.21) = 160 mm Hg. P carbon dioxide - 0.3 mm Hg. In lung, humidified
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Describe the process of expiration
Volume of thorax decreases, increased pressure in lungs. Forces air out of lungs. Resting conditions - passive (muscles not active), Diaphragm relaxes, internal intercostals relax
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Describe the process of inspiration (1)
Thorax expands in 3 planes. Top/bottom (superior/inferior). Side/side (medial/lateral). Front/back (anterior/posterior). Increase top/bottom (diaphragm contraction). Side/side and front/back (external intercostals)
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Describe the process of inspiration (2)
Rotation around rib (vertebral column joints). Analogies - pump handle (top/bottom) and bucket handle (side/side)
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Which instrument is used to measure lung volumes?
Spirometer. When subject inhales, air moves into the lungs. The volume of the bell decreases and the pen rises on the trace
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What is tidal volume?
Volume of air in and out with each resting breath (~ 500 mL)
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What is inspiratory reserve volume?
Maximum amount of air which can be inhaled ~ 3000 mL
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What is expiratory reserve volume?
Maximum amount of air which can be exhaled ~ 1100 mL
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What is residual volume?
Volume of air remaining in the lungs (prevents lungs from collapsing) ~ 1200 mL
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What is functional residual capacity?
Total of expiratory reserve volume and residual volume ~ 2300 mL
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What is vital capacity?
Total of inspiratory and expiratory reserve volumes ~ 4600 mL
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What is total lung capacity?
Total from residual volume to inspiratory reserve volume ~5800 mL
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What is flow directly proportional to?
Change in pressure/R. Alveolar pressure or intrapleural pressure can be measured. Single respiratory cycle - one inspiration followed by one expiration
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What is the intrapleural pressure?
- 3 mm Hg (subatmospheric). Opposing forces due to elastic recoil of chest wall trying to pull chest wall outwards and elastic recoil of lung creates an inward pull
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Describe features of a pneumothorax
Due to collapsed lung that cannot function normally. Pierce through interpleural space, air enters, lung collapses to unstretched size, ribcage expands slightly. Also leads to mediastinal shift
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What is compliance?
Ability to stretch. High compliance (stretches easily). Low compliance (requires more force). E.g. restrictive lung diseases, fibrotic lung diseases, inadequate surfactant production
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What is elastance?
Returning to its resting volume, when stretching force is released
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What is elastic resistance?
Resistance to stretch of lung tissues and air-liquid interface lining the alveoli
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What is airway resistance?
Resistance due to friction between layers of flowing air and airways
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What is elastic resistance (stiffness) measured as?
Compliance (stretchiness). Lung compliance = change in volume/change in transmural pressure gradient (P = alveolar pressure - intrapleural pressure)
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How do you calculate airway resistance?
Alveolar pressure - mouth pressure / airflow at mouth (pressure gradient driving air along airways (=alveolar - mouth)
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Which type of air flow takes place at rest?
Laminar flow at rest - air flow in normal airways
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Which type of air flow takes place during exercise?
High linear velocities in wide airways like the trachea may produce turbulent flow and noisy breathing
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Describe features of airway resistance (1)
Laminar flow in a tube. Flow = change in pressure/R where R is directly proportional to length x viscosity / radius to the power of 4. Importance of radius, if halved resistance increases x16 and with same pressure gradient flow is reduced to 1/16 th
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Describe features of airway resistance (2)
Main sites of airway resistance (health) - whole respiratory system (nose, pharynx, larynx), within lungs (medium sized bronchi). Smaller more distal airways have higher individual resistance but large numbers in parallel mean net resistance is low
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Which factors affect resistance of airways? (1)
Factors within airways (bronchial smooth muscle tone, hypertrophied epithelium and glands. Factors causing constriction (vagal stimulation, pulmonary stretch receptors, irritant receptors, histamine, PGs, leukotrienes etc.)
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Which factors affect resistance of airways? (2)
Or relaxation (CO2, adrenaline, sympathetic stimulation - there are very few sympathetic fibres)
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How do respiratory conditions affect compliance?
Lung fibrosis (scarred/stiff) - low compliance. Emphysema (tissue destruction/floppy) - high compliance. Asthma doesn't usually affect compliance
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Outline features of pressure volume curves
Graphs show narrow range of pressure and volume. Intrapleural curve is always negative and alveolar pressure/lung volume are positive (inspiration/expiration)
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What is the law of LaPlace?
It two bubbles have the same surface tension, the small bubble will have higher pressure. Surface tension is created by the thin fluid layer between alveolar cells and the air
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Describe features of surfactant (1)
More concentrated in smaller alveoli, mixture containing protein and phospholipids. Insoluble fatty acid end and hydrophilic end (floats on surface of alveolar lining fluid)
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Describe features of surfactant (2)
Newborn respiratory distress syndrome (premature babies, inadequate surfactant - causes lungs to collapse, artificial surfactant needed)
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Describe features of ventilation (1)
Total pulmonary ventilation > alveolar ventilation (due to dead space). Total pulmonary ventilation = ventilation rate x tidal volume
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Describe features of ventilation (2)
End of inspiration (dead space filled with fresh air). First exhaled air comes out of dead space, only 350 mL leaves alveoli, exhale 500 mL (tidal volume). End of expiration, dead space filled with stale air from alveoli. Inhale 500 mL of fresh air
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Describe features of ventilation (3)
Tidal volume. First 150 mL of air into alveoli stale air from dead space. Only 350 mL of fresh air reaches alveoli, dead space filled with fresh air
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How do you calculate alveolar ventilation?
Ventilation rate x (tidal volume - dead space volume)
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What happens to P oxygen and P carbon dioxide as alveolar ventilation increases?
Alveolar P oxygen increases and P carbon dioxide decreases. Normal ventilation at 4.2 L/min. Hypoventilation (high PCO2, low PO2), hyperventilation (high O2, low CO2 - issue due to removal of CO2/driving force for respiration)
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