pulmonary ventilation is the first unit in dr. kaminski's guest lecture on the physiology of respiration. it reviews the mechanisms for breathing and introduces a slew of terminology and ideas with which we can analyze the process of respiration. the first part was the review of the mechanics of breathing, which occurs when the pleura is expanded via the lowering of the diaphragm and the raising / expansion of the ribcage. the muscles involved in raising the ribcage are the external intercostals, sternocleidomastoid, scalenes, and serratus anterior while the muscles involved in lowering the ribcage are the rectus abdominis and the internal intercostals. the forces that are at play in the thoracic region are then looked at: the elastin in the alveoli causes it to collapse inward, countered by the elasticity of the ribcage pushing outward. the surface tension of water on the inside of the alveoli draws it inward, countered by the surfactant that is secreted in the alveoli which reduces surface tension. finally, the negative pressure (less than atmospheric) in the pleural cavity draws the lungs outward and the pleura inward.
the idea of respiratory work is then introduced. in mechanics, work = force x distance, and in respiration this is analogous to work = intrapleural pressure x displaced air. the total work of inspiration is the idealized work if all the energy of inspiration is converted directly into air movement. tissue resistance work is the work done to move the ribcage, muscles, bones, cartilage, etc. airway work is the work done to move the air itself and is analogous to the "resistance" of Q=P/R, especially in the sense that increasing or decreasing the radius of brochi has a huge effect on airway resistance and thus work. tissue resistance + airway work represents the deviation from the idealized compliance work-- these two factors create the delay after the pleura expands, before the increasingly negative pressure in the intrapleural cavity causes the lungs to expand.
the free work of expiration is the idealized work from expiration minus the tissue resistance and airway work. maybe the most important term in this section is the total work of breathing, which is the sum of the work from inspiration and expiration (and is graphically represented by the area between the two curves).
next we look at the different terms given to the breakdown of lung capacity. total lung capacity is the total air possible in the lung and is generally ~5500mL. of this, ~1000mL is untouched by respiration and is called the residual volume. what's left is the vital capacity, which is generally 4500mL. the vital capacity is made up of the tidal volume, inspiratory reserve volume, and expiratory reserve volume. the tidal volume represents the volume of air that comes in and out of the lungs during normal breathing, generally 500mL. the inspiratory reserve is the amount you can breathe in after the tidal volume, which is generally 3000mL. the expiratory reserve is the amount you can breathe out after the tidal volume, generally 1000mL. some factors that can influence vital capacity-- anatomy can play a role in that a larger body size or shape can increase VC while abnormalities like scoliosis or lung paralysis can decrease VC. physiology plays a role in that muscle strength or exertion can increase VC while decreased compliance or bronchoconstriction can reduce VC.
the last set of terms that are introduced seem to be more geared toward measurement of respiratory function. forced vital capacity represents the time it takes to exhale the vital capacity, while forced expiratory volume represents the volume or percentage of vital capacity that is exhaled within a unit time, generally 1 or 3 seconds. the FEV (1sec) for a normal, young adult is 80-90% of the vital capacity. forced expiratory flow is a measure of the flow rate during the middle of the exhalation of the vital capacity. minute respiratory volume is the volume of fresh air that is actually being exchanged in the lungs, and is analogous to cardiac output -- represented by breathing rate x tidal volume. minute alveolar volume is the same, except looking at the fresh air that is being exchanged specifically in the alveoli. finally, anatomical dead space is the volume of air from respiration that does not take place in gas exchange.
questions
1. what are the two mechanisms for respiration?
2. what are the muscles that raise the ribcage?
3. what are the muscles that lower the ribcage?
4. restful breathing is mostly ___ while vigorous breathing is mostly ___.
5. describe the force dynamics operating in the thoracic cavity due to elasticity, surface tension, and negative intrapleural pressure.
6. what is compliance, tissue resistance, and airway work?
7. what is the total work of inspiration?
8. what is the free work of expiration?
9. what is the "total work of breathing"?
10. what proportion of total body work is the work of breathing?
11. tidal volume...
12. inspiratory reserve volume...
13. expiratory reserve volume...
14. vital capacity...
15. residual volume...
16. total lung volume...
the factors that influence vital capacity:
17. normal anatomical factors...
18. normal physiological factors...
19. abnormal anatomical factors...
20. abnormal physiological factors...
21. what is forced vital capacity?
22. what is forced expiratory volume?
23. what is a normal value (percentage of vital capacity) of 1 second FEV for healthy, young, people?
24. what is forced expiratory flow?
25. what is minute respiratory volume?
26. what is minute alveolar volume?
27. what is anatomical dead space?
answers
1. diaphragm lowering and raising, ribcage raising and lowering.
2. external intercostals, parasternal internal intercostals, scalenes, sternocleidomastoid, serratus anterior
3. rectus abdominis, internal intercostals.
4. diaphramatic, rib-cage based.
5. elastin in alveolar septa causes inward recoil while elasticity in ribs and chest promotes outward expansion. water on inner surface of alveoli causes inward force, surfactant produced by alveoli counters this surface tension. negative intrapleural pressure causes alveoli to expand and chest/ribs to shrink.
6. in the respiratory system, the W=F x D equation is translated into W=Pressure X air displacement. compliance work represents the ideal work done if all energy is converted into air movement. tissue resistance work is the work done to move the bones, muscles, cartilage, etc. airway work is the work done to move the air itself and is analogous to the "R" in the Q=P/R from hemodynamics.
7. the combination of compliance, tissue resistance, and airway work.
8. the compliance work from expiration minus the tissue and airway work from expiration.
9. the work of the entire breathing cycle (the area inside the inspiration / expiration curves)
10. ~3%, no more than 5% even in heavy exercise.
11. the regular amount of air ventilated per breath, generally ~500mL
12. amount of air that can be inhaled after tidal volume, ~3000mL
13. amount of air that can be exhaled after tidal volume, ~1000mL
14. expiratory reserve + tidal volume + inspiratory reserve ~4500mL
15. amount of air still in lungs after complete exhalation, ~1000mL
16. vital capacity + residual volume, ~5500mL
17. larger body size or type increases VC
18. muscle strength or vigor of effort increases VC
19. kyphosis, scoliosis, respiratory paralysis lowers VC
20. pulmonary congestion, reduced compliance (asthma, bronchitis, etc.) lowers VC
21. time it takes to get the vital capacity out.
22. the amount of vital capacity exhaled in a given unit of time, which includes tissue resistance and airway work.
23. 90-100% of VC
24. average flow during the middle part of the FVC
25. tidal volume X respiratory rate (analagous to cardiac output), generally ~6L/min
26. the amount of fresh air that is reaching the alveoli
27. the air that filled the airways but does not participate in gas exchange, generally ~150mL
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