Mechanics Flashcards
What is a normal inspiratory reserve volume?
1.9 to 2. 5 liters
What is a normal tidal volume?
0.4 to 0.5
What is a normal expiratory reserve volume?
1.1 to 1.5
What is a normal residual volume?
1.5 to 1.9
What is a normal total lung capacity?
4.9 to 6.4
What is a normal inspiratory capacity?
2.3 to 3.0
What is a normal functional residual capacity?
2.6 to 3.4
What is a normal vital capacity?
3.4 to 4.5
What are three important features of gases that can be derived from the Ideal Gas Law?
- a gas will exert a pressure or a force per unit area. 2. a gas occupies a volume, expressed in liters. 3. the volume of a gas is directly proportional to its temperature and inversely proportional to the pressure.
What is the re-written version of the ideal gas law, where concentration is written as a constant?
P = RTC
What is total pressure equal to in the gas fraction equation?
1.0 Sum of all partial pressures must equal one
What is Dalton’s Law?
PB=PN2+PO2+PCO2+PH2O
When is water vapor pressure included in the Dalton’s Law equation?
when calculating for saturated air, i.e. in the body.
What is the fractional gas concentration (Fg) equation?
Fg = Pg/PB Where Pg is the gas partial pressure sum and Pb is barometric pressure
What does BTPS stand for?
body temperature, ambient pressure and saturated with water vapor. Volumes of ventilated gas are typically expressed in BTPS conditions (e.g., pulmonary ventilation, tidal volume).
What does STPD stand for?
standard temperature (0 ̊C or 273 ̊K), standard pressure (760 mmHg) and dry (no water vapor present). Metabolic rates (oxygen consumption and carbon dioxide production) are expressed as gas volumes in STPD conditions since volumes at STPD are directly related to the number of millimoles of oxygen consumed or carbon dioxide produced (22.4 ml per mmole).
What does ATPS stand for?
ambient temperature, ambient pressure and saturated with water vapor. Many respiratory variables are measured in ATPS conditions and must be converted to BTPS or STPD conditions as appropriate.
Henry’s Law describes the concentration of a dissolved gas in solution (Cg). What is the equation?
Cg = K * Pg where K is the solubility constant (specific to a certain temperature, solvent and gas) and Pg is the gas pressure in contact with the solvent
What is tidal volume?
the change in volume with quiet inspiration and expiration
What is inspiratory reserve volume?
the additional air that can be inspired with additional effort (max)
What is residual volume?
the air that can never be expelled from thelung, no matter how much effort is expended
What is functional residual capacity?
The sum of the expiratory reserve volume and the residual volume, i.e. all the air in the lung left after quiet expiration
What is inspiratory capacity?
All the air that could go in the lung after quiet expiration, i.e. the sume of tidal volume and inspiratory reserve volume
What is vital capacity?
The total air that can move in and out of the lungs in physiologic conditions , ie. the sum of inspiratory capacity, expiratory residual volume and inspiratory residual volume
what is total lung capacity?
All the possible air that could fit into the lung if you ignored physiology, i.e. vital capacity plus residual volume
What effect does water pressure have on the partial pressures of other gases in a mixture?
PH20 in saturated air decreases the overall partial pressure attributable to other gases, i.e. it lowers PO2 by 10 mm Hg
Is water vapor pressure dependent on temperature or barometric pressure? why?
It is dependent on temperature because temperature is what determines how much water goes from liquid to gas form and barometric pressure is a negligible component of that phase change
Why do gases go down a partial pressure gradient and not a concentration gradient?
the sum of all fractional gas concentrations must equal to one, but the variables that determine these concentrations (mathematically) are pressure alone. In particular for the concentration of a gas in solution, it varies only by the solubility coefficient and partial pressure of the gases.
What is the simplest requirement for inspiratory flow, keeping in mind that gas flows down a pressure gradient?
Pb (mouth) > Pa (alveolar)
Same is true for the reverse flow
What causes changes in Pa?
movement of diaphragm and chest wall, which in turn change the pressure on the intrapleural space
What are two ways of measuring intrapleural pressure?
1) placing a small catheter connected to a pressure measuring device in the intrapleural region
2) placing a balloon in the thoracic esophagus and measuring intraesophegeal pressure
During pneumothorax, which releases the thorax from the lung, what happens to the lung?
it collapses.
The rib cage EXPANDS because it is no longer tethered to the lung
The functional residual capacity is a compromise of which two forces in the normal thorax?
outward force of chest wall v. inward recoil force of the lung
What is a normal intrapleural pressure in passive FRC? What is the NET effect on the lung and the rib cage?
-3 to -6 cm H20
Lung: expansion
Rib cage: collapse
What is transpulmonary pressure and how do you calculate it?
Transpulmonary pressure: the pressure acting to inflate the lungs is the (PA - Pip).
Usually negative - causes lung EXPANSION
When the glottis is open and Pa is at equilibrium with Pb, what is the transpulmonary pressure equal to?
- Pip
How do you calculate the transthoracic pressure?
the force acting on the thoracic wall (Pip - PB). Since pleural pressure is generally negative, it “sucks” the chest wall inward.
What is the transrespiratory pressure? When do you measure it?
the difference between alveolar and atmospheric pressure measured (PA - PB).
-with the glottis closed and with the respiratory muscles relaxed
When transrespiratory pressure is negative, where will gas flow? Positive?
- negative: gas will flow into the alveoli when the glottis is opened.
- positive: gas will flow out of the lungs when the glottis is open.
What is elastance?
the inverse of compliance
What happens to the opposing force exerted by a rubber band (or a lung) when it is stretched?
it increases as the distance it is stretched increases
i.e. like a spring
What is the slope at any point when plotting pressure v. volume of a lung?
compliance at that volume
the following cause compliance to increases or decrease? a) respiratory distress syndrome
b) edema
c) atelectasis (i.e., alveolar collapse)
d) fibrosis
Decrease
The following cause compliance to decrease or increase?
a) age
b) emphysema
c) Increasing body size
Increase
Which law (from cardio) also describes surface tension on a curved surface, which decreases as the size of the surface increases?
la place’s law
Do surface forces repel or pull interstitial fluid into the alveolus?
pull (La Place’s Law)
Do lungs without an air-fluid interface (i.e. saline filled) Have greater or lesser compliance?
Greater (static) compliance
Define hysteresis?
hysteresis is the different relationship between pressure and volume during inflation compared to that during deflation.
1) reduces alveolar surface tension,
2) preserves alveolar integrity,
3) prevents continuous transudate (edema) from pulmonary
capillaries to alveoli
What does these 3 things in the lung?
surfactant
When is surfactant functional? when is it initially produced in the fetus?
Functional ~ week 30
Produced week 18 to 20 of gestation
What are two stimuli for the release of surfactant?
- lung distention
- stimulation of beta adrenergic receptors
What happens to surfactant on expiration?
As the surface available for surfactant spread decreases on expiration, the surfactant concentration increases, decreasing the surface tension further.
If lung volume is reduced below FRC on forced expiration, what happens to surfactant levels?
the surfactant is tightly compressed, the protein is extruded into the hypophase and the phospholipid undergoes a phase transition (becoming a surface solid); when this occurs, there is no fluid-air interface and surface tension is reduced nearly to zero.
As the surface area increases on the subsequent inspiration, the process is reversed.
What effect does surfactant have on work?
it reduces the work needed for inflation
What effect does reducing the pressure gradient across the chest (i.e. Pip increasing to 0) have on thoracic volume?
It increases it
When two compliant systems are in series, what happens to the total compliance?
It must be less than either component individually
What is the Pip like at the bases of the lung v. the apices?
PiP is less negative (i.e. less gradient) at the bases compared to the apices
Which part of the lung has the highest ventilation?
lower
What happens to airway resistance at larger lung volumes?
airway resistance is lower due to the greater dimensions of the airways since they are pulled open by the tension exerted on them from the parenchyma
During maximal expiratory effort, what happens to the maximum flow that can be generated at any given lung volume?
During a maximal expiratory effort, the maximum flow that can be generated at any given lung volume
decreases as lung volume decreases due to compression of the airways.
What must be true of Pairway and Pip for airway compression to occur?
Pairway < Pip
Emphysema increases lung copliance, which reduces tethering and increases dynamic compression. What does this do to flow limitation?
increases it
Which part of the lung is more sensitive to dynamic compression?
the small airways of the basilar parts of the lung
What causes the effort independent portion of the flow volume curve during expiration?
dynamic compression of the airways
As expiratory effort increases, Pip increases, thereby increasing airway compression (although U may increase) and limiting V
In some diseases, portions of a lung can collapse. If you anticipated this in a patient, would it make a difference whether you permitted collapse and then took measures to re-expand the lung or whether you took measures in advance to prevent collapse if you could?
Surface forces tend to make the walls of collapsed alveoli “stick” together until a large pressure (remember the critical opening pressure?) is applied. Since these pressures are not easily generated, particularly by a sick patient, it would be better to prevent the collapse. There are tradeoffs, however, for example increasing thoracic (i.e., intrapleural) pressure (e.g. using positive airway pressure in an adult) can reduce venous return and compromise cardiac output.
In the presence of obstruction to expiratory airflow what would you expect to happen to the FRC?
FRC will tend to increase, thereby increasing the elastic recoil of the lung, which will aid the expiratory effort and reduce dynamic compression of the airways (remember mechanical interdependence?).
A patient with emphysema has a lung compliance of 0.4 liters/cm H2O and a chest wall compliance of 0.2
liter/cm H2O. What is the compliance of the chest wall and lung together?
The lung and the chest wall constitute two compliant systems in series. The resultant compliance is less since the system is more difficult to inflate than either component individually. From the equation given in lecture.
1=1+1=1+1 C Clung Cchest wall 0.4 0.2
C1 = 7.5 cmH2O/l C = 0.133 liters/cmH2O (i.e. <clung wall></clung>
If the two lungs of a subject together have a compliance of 0.2 liter/cm H2O and the two lungs have equal compliance, what is the compliance of each lung?
The right and left lungs are arranged in parallel. The resultant compliance should be greater since the system is easier to inflate. C = Cleft lung + Cright lung = 0.2 liters/cmH2O
Cleft lung = Cright lung = 0.1 liters/cmH2O
In an abnormal lung in which the only pathologic change is loss of elastic tissue, would compliance be increased or decreased?
If the only change is a decrease in elastic tissue, then the compliance would increase. Clinically, a loss of elastic tissue is frequently associated with an increase in fibrous tissue. In this case, lung compliance could decrease.
At the end of expiration, what is true of intrapleural pressure relatvie to atmospheric pressure?
lungs are at FRC with relaxed respiratory muscles, so Pip < Patm
At the end of expiration, what is true of the lung volume?
it equals FRC
At the end of expiration, what should be true of C fiber activity?
nothing. absent other stimulus, C fiber activity should always be minimal
What is true of recoil forces on the lung at the end of expiration?
inward recoil of the lungs must equal outward recoil of the chest wall = FRC volume
i.e. Pip should always be slightly negative due to force of lungs pointing inwards
At what PaO2 are peripheral chemoreceptors stimulated?
values below 60 mmHg
A mountain climber standing on Mt Everest has no supplemental oxygen. In this climber, what would you expect of his central chemoreceptor activity? Peripheral chemoreceptors?
Central chemoreceptors will not be stimulated by the low PO2, but increased ventilation rate will stimulate peripheral chemoreceptors to lower PCO2, which will increase pH at the central chemoreceptors. The increased [H] will not diffuse across the brain blood barrier, but the resultant decrease in PCO2 at the level of the brain will decrease central activity
what is an advantage of a large FRC?
reduce falls in alveolar and arterial pressures of gas during expiration
during a breath hold, does the volume of the lungs increase, decrease or remain the same, assuming metabolism is unchanged?
if R=1, then O2 consumed equals CO2 produced and volume doesnt change
if R <1, then lung volume decreases because more O2 is consumed than CO2 is produced
if R>1, then lung volume increases because more CO2 is produced than O2 is consumed
Which action is active rather than passive during normal breathing: inspiration or expiration?
inspiration is active, expiration is passive
What nerves innervate the diaphragm? from what level of the spine?
the phrenic nerves of C3, 4 and 5 (C 3 4 5 keeps you alive)
Which nerves innervate the external intercostals? what part of breathing do they help with? what happens if they are paralyzed?
intercostal nerves off the spinal cord
aid in inspiration
breathing is not very affected by paralysis (main issue is diaphragm paralysis)
What is “paradoxical movement” on inspiration?
When the diaphragm is paralyzed or held still as in sniffing, and contracts up and in rather than down and out
When looking at a pressure volume loop for breathing, what is the lung volume during deflation compared to inflation at any given point?
Deflation volume >> inflation volume
If the pressure around a lung is raised above atmospheric pressure, what will happen to air loss? In what kind of lungs is this most pronounced?
Air loss won’t continue because the small airways will close.
Larger lung volumes with increasing age or during disease makes this effect more pronounced
On the pressure volume curve, what is indicated by the slope?
compliance
What happens to compliance of the lung at higher pressures?
It decreases because the lung is stiffer (thus the slope of the line flattens out towards the top)
What effect does alveolar edema have on compliance?
it decreases compliance by preventing inflation of the alveoli
What effect would atelectasis have on compliance?
compliance will drop if the lung has a low volume and is unventilated for a long time
also caused by increased surface tension
Why is the pressure surrounding the lung less than atmospheric pressure in the living chest or during measurement for pressure volume loops?
due to the elastic recoil effect of the lung
What effect do emphysema or aging have on the lung compliance?
increased compliance due to changes in elastic tissue geometry
Which will generate a higher pressure due to surface tension: an alveolia with a radius of 1 mm or of 0.5 mm?
0.5 mm - radius is inversely related to pressure generated
therefore gas will move from small alveoli to larger, along the pressure gradient
What effect does decreasing area of the alveolia surface have on surface tension? why?
decreasing area = decreasing tension
due to the effect of SURFACTANT (without surfactant this would be the opposite)
What effect does surface tension (in the absence of surfactant) do to the hydrostatic pressure of tissue outside the capillaries? what effect does this have?
surface tension reduces hydrostatic pressure outside the capillaries, which increases the driving force for liquid to exit the capillary into the alveoli and cause edema
surfactant prevents this by reducing surface tension
What is mechanical interdependence?
the tendency of any reduction or increase in volume of one area of the lung to be opposed by the rest of the lung
How does the interpleural pressure change at the base of the lung?
It is “higher” (i.e. less negative) becauuse the lung is supported by the diaphragm, which opposes the pull of gravity
Is the resting interpleural pressure at the apex of the lung more or less negative? What does this mean for it’s ability to expand on inspiration?
it is MORE Negative and therefore has a large resting volume but a very small change in volume on inspiration
Considering that the base of the long has a less negative interpleural pressure, a larger change in volume on inspiration, and smaller resting volume, what can we say about the ventilation of the base of the lung compared to the apex?
the base has more ventilation, because ventilation is the change in volume per unit resting volume
At very low lung volumes (i.e. residual volumes) what happens to the ventilation distribution of the lung in the apex v. the bases?
it is inverted: now the apex is better ventilated than the base, because the base has such a positive interpleural pressure that it is now higher than airway pressure and is actually being compressed and cannot expand at all
Why does airway closure happen at larger volumes in the elderly (i.e. at FRC)? what effect does this have on gas exchange?
Aging causes the loss of elastic recoil in the lung and interpleural pressures are less negative, so airway closure happens at higher volumes. This means that some parts of the base of the lung are ventilated intermittently, impeding good gas exchange in these areas
At volumes above FRC, what is true of interpleural pressure?
it is positive
At volumes below FRC, what is true of the interpleural pressre?
it is subatmospheric (i.e. negative)
In laminar flow, what is true of the relationship between resistance and radius?
resistance is inversely proportional to the fourth power of the radius
what is the major site of resistance to air flow in the lungs?
the medium sized bronchi
Define FEV1
It is the flow rate during maximal expiration
i.e. the volume of gas that can be exhaled during 1 second at a maximal expiration
What effect would removing a lobe have on total pulmonary compliance?
it would reduce it
During normal expiration at resting conditions, does intrapleural pressure become more negative?
no
During normal expiratin at resting conditions, where is flow velocity greater: in the large airwyas or the terminal bronchioles?
the large airways
When a normal subject develops a spontaneous pneumothorax of their right lung, would you expect their chest wall to expand?
no
if a normal subject develops a pneumothorax of their right lung, what would you expect to happen to blood flow to the right lung?
it would be reduced by increased pressure on the lung
When a normal subject makes an inspiratory effort against a closed airway, would you expect the intrapleural pressure to increase (become less negative) or would you expect the pressure inside the pulmonary capillaries to fall?
the pressure inside the pulmonary capillaries to fall
