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21 Cards in this Set
- Front
- Back
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Describe the muscles used in breathing
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Inspiration-active; uses diaphragm muscles and external intercostals
Expiration-passive at rest; abdominals and internal intercostals during severe respiratory load |
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Describe the pleural cavity
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Very small space; Maintained at negative pressure; Transmits pressure changes; Allows lung and ribs to slide
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Describe the process of breathing at rest
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Follows Boyle’s Law: Pressure (P) x Volume (V) = Constant
at rest: pressure outside the lungs (Pb) = pressure inside the lungs (Pi) |
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Describe the process of inhalation
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Increase Volume of Rib cage
Decrease the pleural cavity pressure Decrease in Pressure inside (Pi) lungs; Pb outside is now greater than Pi Air flows down pressure gradient into lungs until Pi = Pb |
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Describe the process of exhalation
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Decreased Rib Cage Volume
Increased pleural cavity pressure Increased Pi; Pi is greater than Pb Air flows down pressure gradient out of lungs until Pi = Pb |
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Describe the pulmonary pressure and volume changes that occur during breathing
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A. pleural pressure
inspiration-decreases expiration-increases B. lung volume inspiration-increases expiration-decreases C. alveolar pressure (sigmoidal curve) inspiration-initially decreases before returning to normal expiration-initially increases before returning to normal |
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Describe how pleural pressure relates to alveolar pressure
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Pleural pressure must always be smaller than alveolar pressure; if not, lung will be collapsed (pneumothorax)
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Describe compliance of the lungs
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measure of distensibility of the lungs
Compliance (C)= change in lung volume (V)/ change in lung pressure (P) Different compliances for inspiration & expiration based on elastic forces of lungs Compliance reduced-higher or lower lung volumes, higher expansion pressures, venous congestion, alveolar edema, atelectasis & fibrosis Compliance increased-age & emphysema secondary to alterations of elastic fibers |
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Describe the elastic forces of the lungs
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can be divided into 2 parts
1. elastic tissue of lung and thoracic wall 2. surface tension of fluid that lines the inside wall of alveoli |
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Describe surface tension
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Within fluid all forces balance
At surface unbalanced forces generate tension Effect of surface tension on alveolar size-causes smaller alveoli to collapse, and larger alveoli to expand (air would flow into larger alveoli) |
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Describe the law of LaPlace
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P= (2 X T)/r
Pressure in alveoli is directly proportional to surface tension and inversely proportional to radius of alveoli Pressure in smaller alveolus would be greater than in larger alveolus, if surface tension were same in both |
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Describe surfactant
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Phospholipid produced by alveolar type II cells
Reduces attractive forces of hydrogen bonding by becoming interspersed between H20 molecules; surface tension in alveoli is reduced prevents alveolar collapse; equalizes pressure in small and large alveoli (more surfactant in small alveoli) Functions: 1. Lowers surface tension of alveoli & lung-increases compliance of lung; reduces work of breathing 2. Promotes stability of alveoli-reduces forces causing atelectasis (collapse); assists lung parenchyma interdependant support 3. Prevents surface tension forces from drawing fluid into alveoli from capillary |
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Describe the factors involved in the relaxation pressure-volume curve
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Elastic properties of both the lung and chest wall determine their combined volume
At end of expiration, the inward pull of the lung is balanced by the outward spring of the chest wall |
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Describe airway resistance
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A. causes
1. internal friction between gas molecules 2. friction between gas molecules and airway walls B. sites of airway resistance Major resistance is at the medium-sized bronchi Most of pressure drop occurs at seventh division Very small bronchioles have very little resistance-due to large number of small airways in parallel; air velocity becomes low, diffusion takes over |
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Describe laminar flow
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parallel streams of in the small airways; velocity in center is twice as fast as velocity at the walls
Poiseuille's law: R=(8nl)/(pi * r^4); l=length; r=radius; R=resistance reducing r 50% will increase R 16-fold pressure increases proportional to flow rate and gas viscosity |
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Describe turbulent flow
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Turbulence occurs at higher flow rates in large airways (nose, mouth, trachea)
stream lines of flow become disorganized pressure is no longer proportional to flow Increases in density, velocity & airway resistance make turbulence more probable Breath sounds heard with a stethoscope reflect the turbulent airflow; Laminar flow is silent |
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Describe the factors that affect airway resistance
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A. Any factor that decreases airway diameter, or increases turbulence will increase airway resistance:
1. Rapid breathing-air velocity and hence turbulence increases 2. Narrowing airways (asthma, parasympathetic stimulation) 3. Emphysema-decreases small airway diameter during forced expiration B. Lung Volume-linear relationship b/t lung volume & conductance of airway resistance; as lung volume is reduced, airway resistance increases C. Bronchial Smooth Muscle-contraction of airways increases resistance D. Density & Viscosity Of Inspired Gas-increased resistance to flow with elevated gas density; changes in density rather than viscosity have more influence on resistance |
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Describe the dynamic compression of airways and isovolume pressure-flow curves
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A. dynamic compression of airways-at some lung volume, flow rate will be the same not matter what the expiratory effort is
B. isovolume pressure-flow curves 1. high lung volume-rise in intrapleural pressure results in greater expiratory flow 2. mid and low lung volumes-flow becomes independent of effort after a certain intrapleural pressure has been exceeded |
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Describe equal pressure point
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equal pressure point (EPP)-establishes driving pressure in the airways
established at peak expiratory flow (PEF); occurs when pressure inside airway equals pressure outside airway (pleural pressure) divides airways into downstream and upstream segments; upstream segment-alveoli to the EPP; downstream segment-EPP to mouth driving pressure for airflow is alveolar pressure minus pleural pressure Airways are subjected to compression during forced expiration from the EPP to the trachea (when pleural pressure exceeds airway pressure) In emphysema, there is decreased alveolar pressure, so less of a pressure gradient is established |
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Contrast obstructive vs restrictive airway disease
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A. Obstructive airway diseases-Increased airway resistance; diseases include Asthma, Emphysema, Bronchiectasis, Bronchitis, and Chronic obstructive pulmonary disease (COPD)
residual volume (RV) is greatly increased; effort-independent portion of curve is depressed inward B. Restrictive Airway Disease-restricts lung expansion-->decreased lung volume, decreased compliance, increased work of breathing Diseases include Pulmonary Fibrosis, Asbestosis, Silcosis peak expiratory flow (PEF) and total lung capacity (TLC) are decreased; effort-independent part of curve is similar to normal |
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Describe the work of breathing
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Work is required to move lung & chest
Work is represented as pressure * volume (W=P*V) Work is measured from a pressure–volume curve-represented by the area above pressure-volume curve (inspiratory work of breathing) restrictive disorder-inspiratory work of breathing is increased Airway resistance is increased in an obstructive disorder (requires more energy to force air out of lungs during expiration) difficult to directly measure total work of breathing done by movement of lung & chest wall; oxygen consumption measurements can be used O2 cost of quiet breathing is 5% of total resting oxygen consumption; Hyperventilation increases O2 cost to 30%; High O2 cost in obstructive lung disease limits exercise ability |
