Respiratory Physiology II PDF

4 Hiba misleh Adel Abu-Awad & Rawan Asrawi Yanal shafagoj Compliance of lungs Compliance of lung means how easy to inflate the lung (It about stretch ability) -if you inflate lungs with little force  Compliant lung -if you inflate lungs with too much force  uncompliant lung But, How we can inflate...

4 Hiba misleh Adel Abu-Awad & Rawan Asrawi Yanal shafagoj Compliance of lungs Compliance of lung means how easy to inflate the lung (It about stretch ability) -if you inflate lungs with little force  Compliant lung -if you inflate lungs with too much force  uncompliant lung But, How we can inflate lungs? Lung is like a balloon, we put it in a closed box, its floor is mobile, moves upward or downward. The pressure in the box is 0 (760mmHg), if we increase Airway the volume the pressure will decrease depending on boyle's law of gases V×P =constant which will result in decreasing the pressure. Imp: We change the pressure that surrounds the lung and we measure changing in volume of the lung (how much pressure we need to inflate the lung) ΔV/ ΔP Increase V We always put the independent variable on x axis (P) and the dependent variable (V) on y axis. The Slope= ΔV/ ΔP which is the Compliance (C) As we said, lung is an elastic balloon which has resting state (when we don't have any force applied on it) *resting volume of lung= 150 ml we also call it minimal volume (MV) or unstressed volume At resting volume Lung loses its tendency to collapse because it’s at resting state. What is the benefit of MV? When a baby was born and took only one breath ,then died he will have minimal volume ,then Medical Resting volume for a hollow examiner ( ‫ )الطبيب الشرعي‬will take some pieces of the dead baby’s Lung and put it in water, if these organ is the volume that is not pieces flow  they have minimal volume. tending to collapse nor to expand But if the baby was born dead (stillbirth), he didn’t take any breath, his lung pieces will sink down  don’t have minimal volume. Resting volume and residual volume of lung  can normal people like us reach minimal volume? No we can’t , we only can reach residual volume 1.1L. are not the same To inflate the lung there are 3 stages: Stage 1 :the lung is Uncompliant Note: it is not wise to inflate a totally deflated lung because it will make too much effort (too much work means too much ATP ) and ATP should not overcome 2% in this case it will reach 20%. Hysteresis Stage 2 :Compliant lung Note :it is wise to inflate a partially inflated lung little force and too much changing in V (high compliance) Stage 3 : Uncompliant lung  it is not wise to inflate a totally inflated lung Deflation curve is not the same as inflation curve Deflation we call it hysteresis (when backward process is different than forward process) ** By convention we take compliance we take the Deflation curve and not the inflation Approximately the lung's compliance is 200ml/1cmH2O Respiratory system is composed of two balloons, internal balloon is the lung and the external balloon is the thorax. *it's too difficult to inflate 2 balloons one inside the other rather than inflating one balloon only so the compliance in vitro (outside the body) Total Compliance(CT) =100 CT= Total Compliance CL= compliance of lung CT= compliance of thorax The lung at FRC(functional residual capacity 2.2L) has this much tendency to collapse (number 1) Resting volume of thorax is 4.5 L (75% of the TLC ) as if the thorax is compressed this is How much is the Tendency of thorax to expand (number 2) 2 1 So we have Lung-Thorax System For lung-thorax system, the tendency of thorax to expand equals the tendency of lung collapse and opposites in direction so the system is at rest ** Resting volume of the thorax when it is no more tending to expand Resting volume of the lung 150 ml Resting volume of the thorax 4.5 L Resting volume of the system 2.2 L Characteristics (features) of elastic structure: to move it from resting state you must apply force  Active But to bring it back to its resting state you just take the force away  Passive (recoil tendency of any elastic structure) Past question: If a person took tidal volume (500ml) What will be the tendency of the lung to collapse comparing to FRC (2.2L ) Answer: Increase What will be the tendency of the thorax to expand comparing to FRC Answer : decrease What will be the tendency of the lung-thorax system ? Answer : It has a tendency to collapse compared to FRC because it’s its resting volume  FRC is very important according to what we are talking about FRC is resting state of the system at which the tendency of lung to collapse equals and opposite to the tendency of thorax to expand it’s value 2.2 L it’s the volume of air present in the lungs before taking tidal volume. Emphysema The airways are open due to elastic fibers made from protein elastin. **Smoking inhibits anti proteases (for example anti trypsin)  proteases are now free to act and will start destroying elastic fibers Emphysema has high compliance and this is a problem which result : Collapsing tendency decreased to half while thorax tendency does not affected in this case  system is not at rest , what is the solution ?? The solution is to increase FRC for two purposes: 1. To increases the tendency to collapse of lung 2. To decrease the tendency to expand of thorax To make them equal and have new equilibrium FRC’ in Emphysema patient is more than in a healthy person Emphysema patient will have Active Expiration ,he will need compression and muscle contraction for expiration  energy expenditure is more while in a healthy person Expiration is Passive Another patient has collapsing tendency more than normal opposite to Emphysema like in Fibrosis , RDS ( Respiratory Distress Syndrome ) will have two arrows in the tendency to collapse FRC will decrease This will lead to : 1. Decrease in tendency to collapse of lung 2. Increase in tendency to expand of thorax So the tendency of lung collapsing will equal the tendency of thorax expansion. At residual volume what is the tendency to collapse of lung compared to FRC(always we compare to FRC)?? Tendency of lung to collapse decreases Tendency of thorax to expand increases The tendency for the system to expand  increases Here Inspiration is Passive Work in the respiratory system is of 2 major types : 1. Work to overcome elastic forces Static (70%): that required to expand the lungs against the lung and chest elastic forces. Two third is duo to surface tension and one third is duo to elastic fibers. 2. Work to overcome non-elastic forces dynamic (30%) that required to overcome: a. The viscosity of the lung and chest wall structures (20%). b. Airway resistance work (80%): that required to overcome airway resistance to movement of air into the lungs. From slides: Past questions: The maximum expiratory flow- volume curves in the diagram above were obtained from a healthy individual (curve A) and a 57 year old man who complains of shortness of breath (curve B). -Which of the following disorders does the man most likely have? A. Asbestosis B. Emphysema C. Fibrosis D. Acute asthmatic attack E. ARDS In normal male adult person Which of the following Is it true at functional residual capacity? A- Lung compliance is low B- It is about 4.5 C- The elastic recoil of the long thorax system is inward D- The elastic recoil of the chest wall is outward. B D End of sheet #4