Gas Exchange: Johnson Flashcards
Pressure gradients created by muscular contraction allow for the air to travel into the lungs to get to the alveoli.
???
the partial pressure of the gases in the alveolar air space and in the pulm capi perfusing the alveoli will determine the movement of the air
Alveolar ventilation is what?
product of vt and frequecy gives oupulm vent
The PP of the CO2 and O2 will favor the goal. So O2 will always be set up to go to the tissues and CO2 to leave the body to be expired.
???
Gas laws
Boyle’s Law: P1V1= P2V2
Dalton’s Law: total pressure exerted by a gas mixture is the sum of pressures exerted by individual gases that make up the mixture
Henry’s Law: amount of gas absorbed by a liquid to which it is not chemically combined is directly proportional to the positive pressure of the gas in the liquid; gives the partial pressure of O2 in the arterial blood
What are the components of the alveolar capillary gas exchange surface?
- liquid layer containing surfactant
- alveolar epithelium
- epithelial basement membrane
- thin interstitial space between alveolar epithelium and the capillary membrane
- capillary basement membrane that fuses with the alveolar epithelial basement membrane
- capillary endothelial membrane
NET diffusion of gases from high to low concentration in the alveolar air depends on what?
on the partial pressure of the gases NOT contraction of any muscle
What forces the oxygen within the air mixture to go into the pulmonary blood?
the partial pressure of oxygen must be higher in the alveolar gas mixture forcing it into the blood of the alveolar capillaries
O2 and CO2 move in_________ directions.
opposite
Oxygen is constantly being absorbed into the pulmonary blood from the alveolar air.
Carbon Dioxide is continuously diffusing from the pulmonary blood into the alveolar air.
O2 has a partial pressure gradient for net diffusion into the blood
Air is conditioned to be taken for gas exchange.
humidifier with water vapor to help condition help before it gets to alveoli
What is the normal barometric pressure? What gas components comprise this pressure?
760 mL mmHg
N2, O2, CO2, H2O
We do not want huge swings in partial pressure of gases. Normally we have FRC at the onset of every inspiratory effort. What prevents huge changes in the blood gases?
only a portion of functional residual capacity is changed over with each breath ????
rate of ven affects how fast or slow the partial pressure of gases in alveolar air will fluctuate
which will affect blood gas subsequently
CO2 is eliminated and O2 brought in to maintain physiological balance pH
????
Why does gas exchange continue even when respiration is temporarily interrupted (apneic pause)?
you have FRC
Functional residual capacity (FRC) is defined, in classical physiology, as the volume of gas remaining in the lungs at the end of expiration. In other words, FRC is the volume at which the elastic recoil pressure of the chest wall equals that of the lung and, at FRC, the system is in equilibrium.
Majority gas in air is?
nitrogen
Water vapor pressure is what? It does not change!!
47 mmHg
Partial pressures for what are denoted by Pa and PA?
Pa= arterial blood PA= alveolar air
How do calculate for the amount of air that participates in gas exchange?????
subtract the dead space (stays in conducting tubes) volume from tidal volume times frequency
What gas is continuously produced by tissues as metabolic waste and eliminated by ventilation?
CO2
What is the relationship between partial pressure of CO2 and ventilation?
they are inversely proportional
What is the progressive changes in partial pressure of O2 in expired air from the conducting zone to the respiratory zone?
conducting zone (dead air space, humidified): 150 mmHg
gradual mixing of dead space with alveolar air
respiratory zone (alveolar air): 100 mmHg
What is the progressive changes in partial pressures of CO2 in expired air from the conducting zone to the respiratory zone?
conducting zone (dead air space, humidified): 0 mmHg
gradual mixing of dead space with alveolar air
respiratory zone (alveolar air): 40 mmHg
For every respiratory cycle you have fresh and stale air. What is the fresh and stale air?
fresh air: the air you breath in
stale: the air remaining after each expiratory effort; does not participate in gas exchange
so with every breathe you are constantly refreshing the stale air in the dead air space
What occurs in the Fowler’s method of dead space measurement?
- Subject takes a single breath of 100% O2 and then exhales into a tube that continuously measures the [N2] in the expired gas.
- Anatomic dead space containing 100% O2 and 0% N2 empties first followed by alveolar emptying.
- Alveolar emptying results is a rise in [N2] and a decline in [O2] until a plateau is reached (indicates alveolar gas only).
- The volume with initially 0% N2 plus 50% of the rising N2 volume is equal to the anatomic dead space.
How do you increase the amount of blood available for gas exchanges?
- recruit more blood vessels OR
- distend the ones already participating (increase their capacity)
What are the factors that influence gas diffusion through tissue according to Fick’s law?
gas diffusion is:
- directly related to surface area of the tissue
- diffusion constant for the gas
- partial pressure difference of gas on each side of tissue
- inversely proportional to tissue thickness
You have to use the barometric pressure for the environment you are in.
???
What does Stand Temperature Pressure Dry (STPD) mean?
it is not saturated with water vapor (47 mmHg which is standard)
Why is there no gas exchange in the trachea?
there is no blood supply in the conducting zone
in order for gas exchange to occur you have to have alveoli, capillaries, and membrane to cross
How can the partial pressure of gases be altered?
- alter the barometric pressure
- alter the concentration of gas being inspired by subject (giving supplemental O2 to patient that has higher concentration than normal to help them breathe)
What is the suitcase of air that stays in your alveoli at all times?
functional residual capacity which contain 2.5-3L of gas
The partial pressures (PO2 and PCO2) in the alveolar air are determined by what 3 factors?
- alveolar ventilation
- O2 consumption
- CO2 production
How does the gas volume change with increasing number of bronchioles?
gas volume increases just like the cross-sectional area increases
What is the alveolar gas equation?
partial pressure of oxygen in the alveolus (PAO2) is given by the alveolar gas equation
PAO2= PIO2 - (PACO2/R)
PIO2 inspired partial pressure of oxygen which is equal to the FIO2 times the difference between PB and PH2O.
R is the respiratory exchange ratio (respiratory quotient).
R = (0.8) the ratio of CO2 excreted (VCO2) to the oxygen taken up (VO2) by the lungs.
FIO2= fraction of inspired oxygen
Respiratory quotient depends on dietary intake.
R for carbs is 1 and for fat is 0.7
Need to know
PA=alveolar air
Pa= arterial blood
PAO2= 100 PACO2= 40
PaO2= 100 PaCO2= 40
????
tells you how well your lung is functioning to generate gradients that will allow oxygen to be delivered to tissues and CO2 to be expelled from body
The fraction of CO2 in alveolus is function of what?
CO2 production from cellular metabolism and the rate of elimination by the lungs, termed alveolar ventilation
What must occur during exercise to prevent respiratory acidosis?
increase alveolar ventilation to maintain blood gas concentrations and eliminate CO2 properly as the metabolic CO2 concentration increases with exercise
How can respiratory acidosis occur with reference to PaCO2 and ventilation?
increase in PaCO2 due to either:
- increase in CO2 production OR
- decrease in alveolar ventilation
What is hypercapnia and hypocapnia?
hypoventilation leads to hypercapnia (increased PaCO2)
hyperventilation leads to hypocapnia (decreased PaCO2)
Why must you monitor patients closely and make appropriate adjustments to the ventilator rate?
so that blood gases remain in physiological range and prevent acid-base disturbances.
heterogeneity of alveoli
gravity
position of body????
lung elastic recoil and chest wall outward spring are equal at FRC
What are the phases and what does each represent in the single breath N2 test?
Subject exhales to RV, takes a single maximal inspiration of 100% O2, and subsequently exhaled air is measured for N2
Phase I: conducting airway; 0% N2
Phase II: Dead space & alveolar gas; gradual rise in N2
Phase III: Entirely alveolar gas from dependent regions of lung
Phase IV: Abrupt increase in [N2] reflecting end of dependent zone and start of apical emptying. Start Phase IV identifies airway closure “closing volume”. ~15%VC
Compare the volume changes during a single breath between a normal, increased resistance, and reduced compliance alveoli.
- normal 97%
- reduced compliance 50%
- increased total airway resistance 80%
What occurs with ventilation in terminal respiratory unit with variability in resistance and compliance?
non-uniform ventilation
How do the phases in the single breath N2 test change in a patient with early and severe COPD?
early COPD: slope phase III becomes 3%
severe COPD: no phase IV as there is no closing volume; slope phase III becomes 11%
In the UPRIGHT lung, the alveolar ventilation per unit of volume is greatest where?
base
- best ventilation comes at base at lungs (receives the greatest amount of ventilation of fresh air as it can take in the largest amount of tidal volume when the pressure gradient is established
- alveoli at lung base rest at a smaller volume than those at the apex
Distribution is not even due to what?
gravitational forces
The pleural surface pressure increases +0.2 cm H2O from the apex to the base of the lung. Why?
due to gravity and the weight of the lung tissue
Why are there regional differences in alveolar ventilation?
Pleural pressure affects the alveolar size
