Ventilation and Lung mechanics Flashcards
what is ventilation?
process of inspiration and expiration.
Neurones in the _______________generate automatic rhythmic impulses which are responsible for the normal involuntary rhythmic breathing pattern.
respiratory center in the medulla of the brain
describe the different lung volumes!
ur notes
what r pulmonary capacities?
when describing events int he pulmonary cycle, it is sometimes desirable to consider 2 or more of the volumes together>> pulmonary capacities
anatomical dead space? value?
Only part of the tidal volume is available for gas exchange.
The rest fills the conducting airways, which extend from the nostrils to the terminal bronchioles.
The volume of the conducting airways is known as anatomical dead space bc no gas exchange occurs there
150ml
what is the alveolar dead space?
those alveoli which r not perfused or r damged, dont take place in gas exchange! & ventelation in those parts r wasted!
what is the total dead space?
total of all dead spaces !
Total dead space = Anatomical dead space + alveolar dead space.
what is minute ventilation? how much is it?
amount of air flows in or out of the tract in 1 min!
500ml or 6L
what is minute repiratory volume? how do we calculate it?
total amount of new air moved into the respiratory passages each minute
Tidal volume x respiratory rate
normal TV is 500ml
normal RR is 12 breaths per min
500x12= 6L/min
what is alveolar ventilation? equation
what is its signficance?
total volume of NEW air entering the alveoli & adjacent gas areas each min.
OR
The RATE at which air reaches those areas is Alveolar ventilation
AV = (TV – Ads) x RR
(look at ex in ur book)
it is one of the mafor factors determining the concentrations of O2 and Co2 int he alveoli
“At rest, (at the end of quiet expiration, when the respiratory muscles are relaxed)
the lung is subject to 2 equal and opposing forces.
One is directed inwards and the other outwards.
Explain this concept and what happens in change of pressures
Inward: the lung’s elasticity and ST generate an inwardly directed force that favours small lung volumes.
Outward: The muscles and various connective tissues associated with the rib cage also have elasticity, these elastic elements favour outward movement of the chest wall
Net effect: At rest the two opposing forces balance each other, and also creates a negative pressure within the intrapleural space relative to atmospheric pressure. “
describe the mechanism of normal quiet inspiration and the role of inspiratory muscles
diaphragm and external intercostal contract>> causes thoracic cavity to be large and rib cage rises>> causing LARGE VOLUME and LOW pressure (cuz u got more space)
This low P. in lungs will cause influx of air from out to in!
vise versa with expiration
Describe the mechanism of quiet expiration and the role of elastic recoil
In quiet expiration, when the muscle contraction ceases, the elastic recoil of the lung results in the thoracic cavity and lung returning to the original equilibrium position.
Thus quiet expiration is a passive process.
in quiet inspiration, how many % is the diaphragm involved?
what about the muscles in quiet expiration
70%
tricked you! quiet expiration is a PASSIVE process! no muscles used!
describe the mechanism of forced inspiration and forced expiration and the accessory muscles of inspiration and expiration
Forced inspiration (during excersize)>>
- sternocleidomastoid & scalene of neck
- serratus anterior & pectoralis major of chest wall
Forced expiration
- internal intercostal muscles
- abdominal wall muscles (ex & in oblique & rectus abdominus)
what does the pleural space contain?
Explain the importance of the pleural seal in respiration
10 ml of pleural fluid spread as a thin film over the visceral and parietal pleural surfaces
the 2 pleural membranes contribute to the pleural seal
The ST between the molecules of this fluid forms a seal, holding the outer surface of the lungs to the inner surface of the chest wall.
It is this seal which ensures that the chest wall and lungs move together.
Just like if there was a little bit of watter btw ur cup and coaster, its gets stuck to gther and when u life the cup the coaster is stuck to it
Explain why the pressure within the pleural cavity is lower than atmospheric p. at rest and changes in pleural pressure during respiratory cycle.
****continual suction of excess fluid into lymphathic channels maintains a slight suction in the pleural cavity. therefore the lungs r held to the thoracic wall and glued there!****
sooooo. ..
* the pleural pressure is always in (slight suction) meaning a slightly negative p.,*
the normal pleural pressure at beginning of inspiration is -5 cm of water, which is required to keep the lung open to their resting levels!
in inspiration>expansion of chest cage pull lungs outwards
creating a MORE negative p. of -7.5cm of water
define elastic recoil
tendency of BOTH elastin and collagen fibres to return to their original size when stretched)
define Radial traction
Pressure changes in the pleural cavity & alveoli during inspiration & expiration
intraplural presure
inspiration: -4 becomes -6 decreases
expiration: -6 becomes -4 increases
intrapulmonary pressure
inspiration: 0 becomes -1 decreases
expiration: 0 becomes +1 increases
Explain how a pneumothorax occurs and why this results in collapse of the lung
.At rest, (i.e. the end of a quiet expiration), the intra-pleural pressure is slightly below atmospheric pressure, and the ST of the small amount of pleural fluid creates a seal which keeps the lung adherent to the chest wall.
If an opening is created which allows the pleural cavity to communicate with the air outside, air will flow into the pleural cavity down the pressure gradient until the pressure in the pleural cavity reaches atmospheric pressure.
When the pleural seal is broken, and the elastic recoil of the lung causes it to collapse towards the hilum, as the negative pleural pressure and outward recoil of the chest wall can no longer counteract it.
Define the term ‘compliance’ of the lungs
in order to acheive complience of the lungs, what must happen?
- stretchiness of the lungs*
- To stretch the lungs the elastic recoil of the lung must be overcome.*
The elastic properties of the lungs arise from two sources:
- Elastic tissue in the lungs
- ST of the fluid lining the alveoli
what is surfactant? what is its role?
Surfactant, is secreted by type II pneumocytes in the lung.
It is a complex mixture of phospholipids & proteins with detergent properties.
The hydrophilic ends of these molecules lie in the alveolar fluid with their hydrophobic ends projecting into the alveolar gas.
As a result, they float on the surface of the lining fluid
ROLE: the surfactant molecules, which are interspersed between the fluid molecules, disrupt the interaction between fluid molecules on the surface thereby reducing the surface tension.
surfactant is absent in fetuses younger than_______
25 wks
