Mechanics of Breathing

buxufuni's version from 2017-01-04 09:16


Question Answer
What muscles are involved in inspiration?diaphragm (contracts) moves down, external intercostal muscles contracts (elevate the ribs), anterior serrati and scalenes move ribs and the sternocleidomastoid muscle (elevates the sternum)
What muscles are involved in expiration?expiration is usually passive however with forceful expiration the internal intercostal muscles (depress ribs) and the rectus abdominis (depress ribs)
Which nerve supplies the diaphragm?Phrenic nerve
Which nerve supplies the intercostals? intercostal nerve
Describe the muscles involved in restful breathing? during inspiration the diaphragm contracts and then expirations is caused by the elastic recoil of the lung pulling the relaxed diaphragm and thorax inward (passive)
Describe the muscles involved in mildly deep breathing?during inspiration the diaphragm and external intercostal muscles contract and then during expiration you get lung elastic recoli and contraction of the internal intercostal muscles
Describe the muscles involved in very deep/forceful breathing?during inspiration the diaphragm, external intercostals, sternocleidomastoid and pectorialis major contract and then during expiration you get lung elastic recoil along with contraction of the internal intercostals and abdominal muscles
What is a pneumothorax?when outside air rushes into the pleural cavity due to a disruption in the chest wall and parietal pleura or if there is a disruption of the visceral pleurae
What is a pleural effusion?when there is a build up of fluid in the pleural cavity causing the lung to collapse
What is ventilation?The process of air exchange between the atmosphere and the alveoli
What is bulk flow (F) proportional to?proportional to the change in pressure between the two points or proportional to the inverse of the resistance
What is the equation for ventilation?F=(Palv-Patm)/R
What is the symbol for interpleural pressure?Ppl
When Palv < Patm what process is occuring?inspiration
When Palv > Patm what process is occuring?Expiration
What is the equation for boyles law?P1V1=P2V2
Using the principles of Boyles law describe inspiration?with inspiration there is an increase in volume and a decrease in pressure causing air to flow in
Using the principles of Boyles law describe expiration?with expiration there is a decrese in volume and an increase in pressure causing air to flow out
What are the two factors which determine lung volume?1) pressure difference between the inside and outside of the lung (transpulmonary pressure) 2) the stretchability of the lungs (compliance)
What is the symbol for transpulmonary pressure?Ptp
What is the transpulmonary pressure?the difference in pressure between the outside (Pip - pressure of the interpleural fluid) and the inside of the lung (Palv)
What is the equation to work out the transpulmonary pressure?Ptp = Palv - Pip (always positive)
What does a positive Ptp mean?the lung is able to increase its volume
What occures when Ptp is zero?the lung is at its smallest size
What is the symbol for transmural pressure?Pcw
What is transmural pressure?The difference between pleural pressure and atmospheric pressure
What is the equation to calculate transmural pressure?Pcw = Pip - Patm
Is Pip and Pcw positive or negative during quiet breathing?Pip is negative, hence Pcw is also negative
What is the equation used to calculate the pressure across the respiratory system?Prs = (Palv - Pip) + (Pip - Patm) which can be simplified to Prs = Palv - Patm
What is the elastic recoil of the lungs?The tendancy of an elastic structure to oppose the stretching and distortion
Why do the lungs still contain air at rest?because this opposes the lungs natural tendancy to collapse due to the elastic recoil
Does Ptp need to be positive or negative in order to oppose the natural elastic recoil?Ptp must be positive
What is the importance in maintaining a balance in Ptp?If Ptp is not in balance it may cause a pneumothorax or a pleural effusion
Describe the events which occur during inspiration?the diaphragm and inspiratory muscles contract > thorax expands > Pip becomes more subatmospheric > have an increased transpulmonary pressure > lungs expand > Palv becomes subatmospheric > air flows into the alveoli
What is interpleural pressure?The pressure of the pleural fluid surrounding the lung
Describe the events which occur during expiration?diaphragm and inspiratory intercostals stop contracting > chest wall recoils inwards > Pip moves back towards its pre-inspiratory size > air in the alveoli becomes compressed > Palv becomes greater then Patm > air flows out of the lungs
What is lung compliance (CL)?a measure of the elastic properties of the lung defined as the magnitude of the change in lung volume for each unit change in transpulmonary pressure
What is the total compliance oh a healthy lung?200ml air/cm water meaning that each time Ptp increases by 1cm of water the lung volume expands by 200ml
What happens to the compliance if half of the lung is removed?If corrected for volume the compliance will remain the same
Why is inspiration and expiration two seperate curves on the compliance curve?because inspiration is an active process while expiration is a passive process
In terms of compliance and pressure, what occurs with emphysema?pressure decreases and compliance increases. this is good for inspiration as the lung is very stretchy however it is bad for expiration as the elastic recoil is lost
In terms of compliance and pressure, what occurs with fibrosis?there is an increase in pressure and a decrease in compliance. This is bad for inspiration as the lung is considerably less stretchy but good for expiration as there is a high elastic recoil
What are the two major determinants of lung compliance?1) strechability or elastic recoil 2) surface tension at the air-water interface of the alveoli
What is surface tension in the lung?water molecules in the lung are attracted to each other and this attracting tends to collapse the alveoli and force air out
What is the equation for the law of LaPlace?P = 2T/r P=pressure T=surface tension R=sphere radius
Why is surface tension in the lung usually not a problem?because the lungs contain surfactant which gets between the water molecules of the lung to reduce the surface tension
Which cells secrete sufactant?Type II surfactant secreting epithelia (phospholipoprotein)
What percentage of the alveolar surface is made up by type II cells?around 5%
What is surfactant?A complex mixture of phospholipids, protiens and ions
What is the function of the phospholipid in the surfactant?responsible for reducing the tension by 1/6
Why is surfactant so important in small alveoli?it reduces the surface tension by half, therefore reducing the pressure and preventing the alveoli from collapsing
By lowering the surface tension of the lung what does sufactant also do?it increases the compliance and decreases the work of breathing
What is atelectasis?collapse
How does surfactant prevent the transudation of fluid into the alveoli?it reduces the surface hydrostatic pressure as well as preventing the surface tension forces from drawing fluid into the alveoli from the capillary
What is new born respiratory distress syndrome?when an infant is born prematurely it is deficient in surfactant which leads to alveoli collapse
How can new born respiratory distress syndrome be treated?artificial respiration or artificial surfactant given through the infants trachea
Which three factors govern resistance in laminar flow?1) length of the tube 2) viscosity of the liquid 3) radius of the tube
How does lung volume during inspiration effect airway resistance?lung volume increases with inspiration leading to the airway radius becoming larger, reducing the resistance causing lug expansion
How does radial traction effect airway resistance?The airways are connected by elastic tissue to the alveoli walls and are pulled open when the alveoli expand during inspiration therefore decreasing resistance
What has more radial traction? inspiration or expiration?Inspiration, this means it also has a decreased resistance
How does forceful expiration effect alveolar resistance?airway compression occurs; with an increase in interpleural pressure they small bronchioles collapse as they contain no cartilage, this increases the resistance
What is asthma?The smooth muscles of the airway contract strongly increasing the resistance and causing chronic inflammation, may be due to allergens, viral infections or sensitivity to the environment
How can asthma be treated?Can reduce inflammation with glucocorticoids (preventative) or can use bronchodilators to relax the smooth muscle and block the action of bronchoconstrictors (relievers)
What is emphysema?destruction of the elastic tissue in alveolar and capillary walls causing a reduction in the number of alveoli
What are the physiological effects of emphysema?reduced radial traction (narrow airways, small airways collapes), airway resistance increases, lund volume increases, and in order to achieve a normal tidal volume there needs to be a more negative Palv during inspiration and a more positive Palv during expiration
Which branch of the autonomic nervous system regulates airway resistance?parasympathetic
What does increased parasympathetic activation do to airway resistance?increases bronchoconstriction which increases the resistance (eg. cough or asthma)
What does decreased parasympathetic activation do to airway resistance?decreases broncoconstriction which decreases the resistance (eg. exercise)
Describe the hormonal control of airway resistance?during exercise adrenaline acts on airway smooth muscle causing bronchodilation and an increase in resistance (this is a secondary effect to the increase in dead space)