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Physiology
Phys - Vent Lung Mechanics
| Question | Answer |
|---|---|
| ventilation | exchange of air btw external environment and alveoli |
| bulk flow of fluid | :Flow (F) = pressure gradient/R |
| pressure gradient for the respiratory system | difference btw atmospheric pressure and alveolar pressure (all pressures in the respiratory system are given relative to atmospheric pressure) |
| R | resistance to air flow in the airways, the most impt factor determining airway resistance is diameter (or radius), remember resistance is inversely proportional to the 4th power of the radius |
| ventilation, gas exchange, gas transport, gas exchange, cellular respiration | exchange of air by bulk flow, exchange of O2,CO2 in lung capillaries by diffusion, trasport of O2,CO2 thru pulmonary and systemic circulation by bulk flow, exchange of O2/CO2 by diffusion, cell utilization of O2 and production of CO2 |
| pressure gradients during inspiration and expiration | F=(Palv-Patm)/R, inspiration: Patm > Palv, expiration: Palv > Patm |
| Boyle's Law | at constant temp, the pressure exerted by a fixed # of gas molecules varies inversely w/ volume of container (increase volume decreases gas' pressure) |
| how does air flow during ventilation according to Boyle's Law | volume of the container (lungs) is made to change and the pressure of the air in the alv changes in accordance w/ Boyle's.. changes in alv pressure alter the pressure gradient. air flows in or out of alv depending on pressure gradient |
| transpulmonary pressure | changes in this changes lung volume to move air, measured btw in and out of lungs (not btw alv and outside chest wall) Ptp=Palv-Pip |
| inside pressure, outside pressure | pressure of air in the alveoli, pressure of the intrapleural fluid |
| the stable balance between breaths | at end of expiration, lung tendency to expand bc of pos. transpulmonary pressure is exactly balanced by the chest wall's elastic recoil force |
| what is inspiration initiated by | neurally induced contraction of the diaphragm and "inspiratory" intercostal muscles btw the ribs which results in increase in thorax size (volume) |
| change in volume | decreases intrapleural pressure, increases transpulmonary pressure, this upsets the balance of forces present at the end of expiration, lungs expand |
| expansion of lung | increases the volume of the alveoli and (by Boyle's law) the alveolar pressure decreases |
| the decrease in alveolar pressure | increases the pressure gradient btw the alv and external environment (alv pressure less that atm pressure), results in air movemt into lungs |
| what is expiration initiated by | the relaxation of the diaphragm and inspiratory intercostal muscles, the chest wall is no longer being pulled outward, its volume decreases passively due to its elastic recoil properties |
| what happens to transpulmonary pressure during expiration | decreases and results in a decrease in the volume of the lungs, thus the alv volume decrease and (by Boyle's law) the pressure of air in the alv increases |
| the increase in alv pressure | increases the pressure gradient btw the alv and external environment (alv pressure > atm pressure), air is expelled from lungs |
| with normal quiet breathing, expiration is | an entirely passive process |
| at the end of expiration | Palv, Patm are equal, no air flow |
| at mid-inspiration | chest wall expanding, lowers Pip, makes Pip more positive, this results in Palv becoming negative and inward air flow results |
| at end-inspiration | chest wall is no longer expanding, hasnt started its passive contraction bc lung size is not changing and glottis is open to atm, Palv is again equal to Patm, no air flow |
| mid-expiration | resp. muscles relaxing, lungs and chest wall are passively collapsing due to elastic recoil, Palv increases, Palv greater than Patm, air is forced out |
| Lung compliance (CL) | CL=magnitude of change in lung volume/change in the transpulmonary pressure |
| low lung compliance | a greater-than-normal transpulmonary pressure must be generated to produce a given amount of lung expansion |
| determinants of lung compliance | elasticity of pulmonary connective tissue and alveolar surface tension |
| elasticity of pulmonary oonnective tissue | this elasticity is compromised in patients with connective tissue diseases and as a result, they commonly develop respiratory problems as well |
| alveolar surface tension | at interface btw alv air and the liquid matrix of the cells lining the alveoli. increasing surfactant reduces surface tension in alv thus increasing lung compliance (deep breaths enhance the secretion of surfactant by stretching Type II cells |
| airway resistance | determined by physical, neural, and chemical factors. airway resistance normally very low, thus small pressure gradients can result in movement of large volumes of air |
| airway resistance physical factors | transpulmonary pressure distends the airways esp. those w/o cartilage and reduces resistance, lateral traction forces by elastic connective tissue fibers attached to exterior of airways help distend the airways |
| airway resistance neural factors | epinephrine relaxes airway smooth muscle (B-adrenergic receptors) thus reduces airway resistance, leukotrienes produced by inflammatory contract airway smooth muscle |
| airway resistance chemical factors | asthma disease smooth muscle contracts strongly. COPD causes difficulties w/ventilation & w/oxygenation of blood. emphysema destruction of alv, enlargemt of alv air spaces, loss of pulm capillaries. chronic bronchitis excessive mucus produced in bronchi a |
| total lung volume's tidal volume | volume of air moved in and out of the lungs during quiet breathing (normally about 500ml) |
| total lung volume's inspiratory reserve volume | the additional volume of air that can be inspired by max exertion of inspiratory muscles following a normal inspiration |
| total lung volume's expiratory reserve volume | the additional volume of air that can be exhaled by max contraction of expiratory muscles following normal expiration |
| total lung volume's residual volume | the amount of air that's left in the lungs at the end of a max expiration |
| lung capacities | various combinations of individual lung volumes |
| inspiratory capacity | sum of tidal volume and inspiratory reserve volume, it represents the amount of air that can be inspired from the end of a normal expiration |
| functional residual capacity | sum of expiratory reserve volume and the residual volume, it represents the amount of air that remains in lungs at end of normal expiration (sum of inspiratory capacity and functional residual capacity is the total lung volume) |
| vital capacity | total amount of air that can be inspired after performing a max expiration, it's the total amount of air that can be physiologically controlled, and is the sum of the expiratory reserve volume, tidal volume, and inspiratory reserve volume |
| total lung capacity | same as the total lung volume and is the sum of the four individual lung volumes |
| forced expiratory volume in 1 second | FEV1 is the amount of air an individual can exhale in 1 sec. by max respiratory exertion following a max inspiration |
| impt clinical measurement of FEV1 | as a percentage of the vital capacity. normal value is about 80% |
| FEV1 in obstructive lung disease | FEV1 is significantly less than 80% due to narrowing (obstruction) of respiratory airways |
| restrictive lung disease | the airway resistance is normal but respiratory movements are impaired. vital capacity is reduced but a normal ratio of FEV1 to vital capacity is present |
| minute ventilation | the total amount of air moved into and out of the lungs over a 1 minute period. minute ventilation (ml/min) = tidal volume (ml/breath) x respiratory rate (breaths/min) |
| anatomic dead space | volume of conducting airways (about 150ml) where no gas exchange takes place, thus not all of the tidal volume inhaled on a normal breath goes into the alveoli |
| alveolar ventilation | amount of fresh air that moves into the alveoli during a 1 minute period. alveolar ventilation (ml/min) = [tidal volume - dead space] (ml/breath) x respiratory rate (breaths/min) |
| determination of the efficacy of respiratory activity | should always be focused on the alveolar minute ventilation |
| alveolar dead space | volume of air contained in alveoli that have little or no blood supply |
| physiologicic dead space | the total dead space, the sum of the anatomic dead space and the alveolar dead space |
Created by:
oupharm2013