MSAP Physiology Respiratory System Flashcards
Gauge scale vs Absolute Scale
Ex. °F °C
O° C= Point at which water freezes (arbitrary) (doesn’t mean anything in energy terms)
100°C= Point at which water boils Relativistic information (arbitrary scale)
0°K= no heat or movement associated with it
Kelvin is the better scale to use (absolute temperature scale) 0
Degrees Farenheight: how cold he could make water before it froze 100 Degrees F: temperature underneath his armpit (arbitrarily driven) Kelvin: 0°C= 273K
Gauge scale pulmonary physiology
mmHg, cmH2O (pressures) (P)
Atmospheric = 0
Gauge scale starts at zero
+ cmH2O (positive pressure) = higher atmospheric pressure
-cmH20 (negative pressure) = lower atmospheric pressure
What happens when you punch a balloon?
The hand is enveloped by the balloon
Something similar happens to the lungs
Lungs are surrounded by pleural membrane full of fluid
plural fluid allows lungs to inflate and have layers of pleural membrane rub against each other without damage
Viseral Pleura
covers the outside of the lung
Parietal Pleura
Covers the inside of the chest wall
Static Conditions in the Lung
Pleural space pressure = (-)ve at static conditions
Lungs are trying to collapse inwards and thorax is trying to push outwards; expansionist force is generated which decreases the pressure
Alveolar pressure= 0
Transmular pressure (pressure across the alveolar wall)= Pressure alveolar-Pressure pleural membrane= 0-(-5)=+5
How does pleural pressure, alveolar pressure, airflow and lung volume change during Inspiration?
As the thorax expands (recruited muscles to expand the thorax) the pleural pressure decreases even further; Pp= more (-)ve
Alveolar pressure= O
Transmular pressure=PA-PP=0-(-10)= +10 à this causes the alveolar walls to move outwards
Pressure inside alveolar drops and now there is a slight negative pressure inside; Barometric (atmospheric) pressure is still zero.
Pressure differential causes gases to start filling the lungs.
How does pleural pressure, alveolar pressure, airflow and lung volume change during expiration?
Relax muscles–> thorax decreases in volume–> increase pleural pressure–> decrease transmular pressure which makes the pressure inside the alveolar (+)-ve –>pressure differential allows air to go outwards into the atmosphere
Sequence of events for one breathing cycle
Expiration:
All driven by contraction of diaphragm muscle –> increase in thoracic volume–> drop in pleural pressure–> increase in transmeural pressure across the alveoli–> expansion of the alveoli –> drop in alveoli pressure–> pressure differential between alveolar pressure and atmospheric pressure allows for gas to start filling the lungs –> as gas continues to fill the lungs pressures then equilibrate–> flow will slow down and stop–> flow leaves–> lung volume declines–> back to normal lung volume
Movement related to atmospheric and alveolar pressures during the breathing cycle
Expiration
Elastic force cause alveolar to contract and causes positive pressure inside alveolar which moves air back into the atmosphere; once PA and PB have equilibrated then flow is stopped movement related to
Compliance
Change in volume per given change in pressure (think of a balloon)
As the mechanical properties of the lungs change, the compliance changes
What causes a drop in compliance
Clinically Lung Fibrosis; extra collagen gives us very stiff lungs that make them difficult to inflate; large pressure needed for small changes in volume
What causes high compliance?
High Compliance= little resistance to changes in volume
Clinically: Emphysema; the walls of the aveoli are eaten away by protease activity; lungs becomes like plastic bag (easy to inflate, but there is very tough low elasticity alveoli )
What is spirometry? What is a weakness of the system?
Main method through which we measure certain parameters of lung function
Weakness: have to be able to exhale that air to measure it
Spirometry: What is tidal volume?
Measure difference between shallow breaths
How much you breath in a average cycle (usually 500ml) ;how much we breath in and out during FRC
Spirometry: Total Lung Capactity
Breathing in as much as possible
Spirometry:Residual volume
Still 2L of gas in the lungs after we exhale fully
Important Clinical Parameters
4 main parameters to predict lung volume: Need to know height of pt, age,
sex, race
Spirometry: FRC
Function residual capactiy = rest volume of lungs
Spirometry: Vital Lung Cpacity
Vital lung capacity= total lung capacity- rest volume of lungs
- maximum dynamic volume (as much as you can breath in or out)
- Forced vital capacity (when pt is asked to force air out of lung) ; name reflects the method that the patient was asked to do
What is the VC in a normal pt?
80% VC from TLC is FEV1= In one second you should be able to get 80% of the vital capacity out of the lungs
What are the steps of spirometry?
Volume/Time spirometry; amount of air the pt can breath over time
Ask pt to go to total lung capacity (breathing in as much as possible) and then forcefully exhale for as long as possible
Measuring the volume that the pt exhales from total lung capacity over time
Spirometric abnormalities with restrictive lung diseases
Pt with Restrictive Lung Disease (low lung volumes):
Abnormalities: Dampening of entire curve so that FVC is low and FEV1 is low; both parameters lower than predicted, but FEV1 to FVC ratio is normal (80%)
Clinically: Lung Fibrosis (difficult to fill mechanically tight lungs)
Spirometric abnormalities with obstructive lung diseases
Pt with Obstructive Lung Disease (Problem with rate at which air can flow in and out of the lung):
Abnormalities: FVC is normal but FEV1 is very low and FEV1:FVC ratio is <<80%
Clinically: Asthma, COPD
Partial Pressure
Partial Pressure: In a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature
Dalton’s Law
Daltons Law: The total pressure of a mixture of gasses is equal to the sum of the partial pressures of the individual gases in the mixture
Fraction of inspired oxygen
the assumed percentage of oxygen concentration participating in gas exchange