Respiratory - Airway Physiology Flashcards
What is the conducting zone of the lungs?
anatomical dead space and does not participate in gas exchange
What is the respiratory zone of the lung?
where gas exchange takes place
Gas exchange can only occur in what type of tissue?
flat epithelium
What is the transitional zone of the lungs?
both an air conduit and allows some gas exchange
What anatomical structures make up the transitional zone of the lungs?
respiratory bronchioles and alveolar ducts
In order for gas exchange to occur, does pressure need to be greater inside or outside the lung?
pressure inside the airway needs to be greater than pressure outside the airway
What is pressure inside the lungs minus pressure outside the lungs called?
transpulmonary pressure TPP
What is pressure inside the lungs called?
alveolar pressure
What is pressure outside the lungs called?
intrapleural pressure
What is formula for TPP?
TPP = alveolar pressure - intrapleural pressure
What pressure is always positive to keep the lungs open?
TPP
What pressure is ways negative to keep the lungs inflated?
intrapleural
What instances causes intrapleural pressure to become positive? (2)
pneumo, forced expiration
When does alveolar pressure become positive? negative?
positive during expiration, negative during inspiration
During what phases of the respiratory cycle is there no airflow? (2)
FRC and end-expiration
What does contraction of inspiratory muscles do to thoracic pressure and thoracic volume?
decreases thoracic pressure, increases thoracic volume
What law explains the decrease in thoracic pressure, and increase in thoracic volume during inspiration?
Boyles
Contraction of what muscles are primarily responsible for inspiration? (2)
diaphragm and external intercostals
What are the accessory muscles of inspiration?
sternocleidomastoid ad scalene muscles
Is exhalation passive or active? How?
passive, recoil of chest wall
What muscles are responsible for forced exhalation? (TIREs)
transverse abdominus, internal oblique, rectus abdominis, external oblique
What muscles play a secondary role in active exhalation?
internal intercostals
What causes exhalation to become active?
increase in minute ventilation, lung disease, cough/clear secretions
What vital capacity is required to produce an effective cough?
15mL/kg
What is the process of exchanging gas between the atmosphere and the lungs, Oxygenation or ventilation?
ventilation
What are the two primary functions of ventilation?
acquire O2, remove CO2
Does the entire tidal volume participate in gas exchange? Why?
No, dead space.
What is the volume of dead space?
2mL/kg
What does increased dead space do to the PaCO2 - EtCO2 gradient?
widens the gradient and causes CO2 retention
What is the consequence of increased dead space?
more difficult to eliminate expired gas from the lungs
Where is anatomic dead space?
conducting airways (nose/mouth to terminal bronchioles)
What is physiologic dead space?
anatomic dead space and alveolar dead space
Do alveoli participate in dead space? How?
Yes, alveoli that are ventilated but not perfused
What is the formula for minute ventilation (VE)?
VE = tidal volume x respiratory rate VE = 500 x 10 = 5000mL/min
What is the fraction of VE that is available for gas exchange?
alveolar ventilation (VA)
What is the formula for VA?
VA = (Vt - Vd) x RR VA = (tidal volume - dead space) x respiratory rate
VA is directly proportional to what?
CO2 production
VA is indirectly proportional to what?
PaCO2
What is the Vd/Vt ratio?
fraction of tidal volume that contributes to dead space
Calculate the Vd/Vt for a 70kg patient spontaneously breathing a Vt of 0.45L
150mL / 450mL = 0.33
What affect does mechanical ventilation have on Vd/Vt ratio (increase or decrease)?
increase
Why does mechanical ventilation increase Vd/Vt ratio to 0.55?
increase alveolar pressure -> increases ventilation relative to perfusion
What is the most common cause of altered Vd under general anesthesia?
decreased cardiac output
How does a LMA affect dead space?
decreases Vd.
How does Atropine affect dead space?
Increases
How does atropine increase dead space?
bronchodilation increases the volume of the conducting airways
The table is being turned 180 during a craniotomy. You add extension tubing to your circle system. How is dead space affected? Why?
It isn’t! Anything proximal to the y piece does not affect dead space.
How can the circle system increase dead space?
faulty one way valve. The entire limb becomes dead space.
What equation is used to calculate physiologic dead space?
Bohr
What equation compares the partial pressure of CO2 in the blood vs partial pressure of CO2 in exhaled gas?
Bohr
What is the formula for the Bohr equation?
Vd/Vt = (PaCO2 - PeCO2) / PaCO2
What airway devices increase dead space? (3)
facemask, HME, PPV
What airway devices decrease dead space? (3)
ETT, LMA, trach
What drugs cause a decrease in dead space?
anticholinergics due to bronchodilation (atropine)
How does age affect dead space?
old age increases dead space
What does neck flexion and extension do to dead space?
extension increases
flexion decreases
What are the pathophysiologic causes of increased dead space?
decreased CO, decreased pulm. blood flow, COPD, PE (air, thrombus, amniotic fluid, bone)
What patient positions decrease dead space? Increase?
decrease - supine, head down
increase - sitting
What is the normal V/Q ratio?
0.8 (ventilation 4L/min, Perfusion 5L/min)
What two mechanisms affect distribution of blood flow to the lungs?
gravity and hydrostatic pressure
How are V/Q ratios affected by the upright position?
Higher V/Q ratio in the apex, Lower V/Q in the base of the lungs
In which portion of the lung are alveoli best and least ventilated?
best base, least apex
In which portion of the lung is perfusion the greatest?
base due to gravity
How is compliance calculated?
compliance = change in volume / change in pressure
Describe alveolar ventilation in non-dependent and dependent regions of the lung.
Non-dependent: low
Dependent: high
Describe perfusion in non-dependent and dependent regions of the lung.
Non-dependent: low
Dependent: high
Describe V/Q in non-dependent and dependent regions of the lung.
Non-dependent: high
Dependent: low
Describe PAO2 in non-dependent and dependent regions of the lung.
Non-dependent: high
Dependent: low
Describe PACO2 in non-dependent and dependent regions of the lung.
Non-dependent: low
Dependent: high
Describe PAN2 in non-dependent and dependent regions of the lung.
Non-dependent: same
Dependent: same
What does the balance of ventilation and perfusion throughout the lung determine?
PaO2 and PaCO2
Describe the relationship of V and Q in the most dependent area of the lung?
V < Q
Describe the relationship of V and Q in the nondependent area of the lung?
V > Q
What is the most common cause of hypoxemia in the PACU?
Atelectasis (V/Q mismatch)
How does anesthesia affect FRC?
FRC is smaller -> atelectasis
What are consequences of a smaller FRC in the PACU?
atelectasis, R-to-L shunt, V/Q mismatch, hypoxemia
How do you treat V/Q mismatch from atelectasis?
humidified O2, mobility, cough, deep breath, incentive spirometry
What West Lung Zone does mechanical ventilation increase?
increases zone 1
How is CO2 and O2 affected by underventilated alveoli?
blood retains CO2 and does not take enough O2
Does CO2 or O2 diffuse faster?
CO2 diffuses 20x faster
How is CO2 and O2 affected by overventilated alveoli?
excessive diffusion of CO2, unproportionate uptake of O2
What is the PAO2-PaO2 gradient with V/Q mismatch?
large
What is the PACO2-PaCO2 gradient with V/Q mismatch?
small
How does the body compensate for V/Q mismatch?
bronchioles constrict to minimize dead space (zone 1), hypoxic pulmonary vasoconstriction reduces blood flow to minimize shunt (zone 3)
What law describes the relationship between pressure, radius, and wall tension?
Law of Laplace
How do you calculate tension in a cylinder?
pressure x radius
How do you calculate tension in a sphere?
(pressure x radius) / 2
What type of cells produce surfactant? When does it start?
type 2, 22-26 weeks
What does surfactant do? (2)
reduces alveolar surface tension, prevents alveolar collapse
What happens to surface tension as alveolar radius changes?
stays constant
In each individual alveoli, V/Q ratio is determined by relative pressures between what? (4)
alveolus, arterial capillary, venous capillary, interstitial space.
What zone of the lung is described by: PA > Pa > Pv
zone 1
What increases zone 1? (4)
HoTN, PE, excessive airway pressure
Finish the sentence: in west zone 1, there is ___ but no ___.
there is ventilation but no perfusion
How does the body react to a increase in Zone 1?
bronchioles constrict to reduce dead space
What zone of the lung is described by: Pa > PA > Pv
zone 2
What is the V/Q ratio of zone 2?
V/Q = 1
What zone of the lung is described by: Pa > Pv > PA
zone 3
In zone 3 of the lung, blood flow is a function of what?
pulmonary arteriovenous pressure difference
In zone 3 most alveoli are better ___ than ____.
better perfused than ventilated (V < Q)
What is a shunt?
shunt is blood flow without perfusion
How does hypoxic pulmonary vasoconstriction react to a west lung zone 3?
reduces pulmonary blood flow to under-ventilated alveoli
Why should the PA catheter be placed in west lung zone 3?
pressure in the capillary is always higher than the alveoli, so the vessel is always open
What is an anatomic shunt?
any venous blood that directly empties into the left heart
Where are sites of normal anatomic shunt?
thesbian veins, bronchiolar veins, pleural veins
What zone of the lung is described by: Pa > Pist > Pv > PA
zone 4, pulmonary edema
What happens to lung pressure in pulmonary edema?
interstitial pressure exceeds pressure in the pulm. capillaries and alveoli d/t accumulation of fluid
What are the two causes of west zone 4?
increase in capillary hydrostatic pressure and reduction in pleural pressure
What causes an increase in capillary hydrostatic pressure leading to a west zone 4? (3)
fluid overload, mitral stenosis, pulmonary vasoconstriction
What causes a reduction in pleural pressure leading to a west zone 4? (2)
laryngospasm or inhalation against a closed glottis
Supplementing hypoventilation with O2 can lead to undetected ______.
hypercarbia
What equation determines the partial pressure of oxygen inside alveoli?
alveolar gas equation
How do you calculate alveolar oxygen?
PAO2 = FiO2 x (Pb - PH2O) - (PaCO2 / RQ)
= FiO2 x (760mmHg - 47mmHg) - (PaCO2 / 0.8)
What is a normal PAO2 value?
105.89 mmHg
What is the best way to treat hypercarbia?
increase alveolar ventilation and fix hypoxemia
How is the respiratory quotient (RQ) calculated?
CO2 production / O2 consumption
What is a normal RQ?
0.8
What causes a RQ > 1? RQ = 0.7?
RQ > 1 means overfeeding
RQ = 0.7 meas starvation
What is the A-a gradient?
difference between alveolar oxygen PAO2 and arterial oxygen PaO2
What does the A-a gradient help diagnose?
cause of hypoxemia
What is a normal A-a gradient at room air?
less than 15 mmHg
Calculate the A-a gradient. PAO2: 105 SaO2: 100 FiO2: 60 PaO2: 95
PAO2 - PaO2
105 - 95 = 10 mmHg
What increases the A-a gradient? (4)
aging, vasodilators, R-to-L shunt, diffusion limitation
What are examples of R-to-L shunts that would increase the A-a gradient?
atelectasis, pneumonia, bronchial intubation, intracardiac defect
How is the percentage of a shunt estimated?
shunt increases 1% for every 20mmHg of a A-a gradient
Are lung volumes based on total body weight, lean body weight, or ideal body weight?
ideal
how do you estimate vital capacity?
60-70mL/kg
How do you estimate FRC?
35mL/kg
IRV + TV + ERV + RV = ???
total lung capacity
IRV + TV + ERV = ???
vital capacity
IRV + TV = ???
inspiratory capacity
RV + ERV = ??
FRC
RV + CV = ??
closing capacity
what is the volume of total lung capacity?
5800
what is the volume of vital capacity?
4500
what is the volume of inspiratory capacity?
3500
what is the volume of FRC?
2300
what is the volume of IRV?
3000
what is the tidal volume?
500
what is the volume of expiratory reserve volume?
1100
what is the volume of residual volume?
1200
What is the amount of gas that can be forcibly exhaled after tidal inhalation?
IRV
what is the amount of gas that enters and exits the lungs during tidal breathing?
tidal volume
What is the volume of gas that can be forcibly exhaled after tidal exhalation?
ERV
What is the volume of air that remains in the lungs after complete exhalation, reservoir during apnea?
residual volume
What is the volume above residual volume where the small airways being to close?
closing capacity
How does obstructive lung disease affect lung volumes?
increased residual volume and TLC
Spirometry does not measure which lung volumes?
RV, TLC, FRC, closing volume, and closing capacity
What is the reservoir of oxygen that prevents hypoxemia during apnea?
FRC
What is static equilibrium?
at FRC the inward elastic recoil of the lungs is balanced by outward recoil of the chest wall
How can FRC be indirectly measured?
nitrogen washout, helium wash in, body plethysmography
What causes a reduction in FRC?
reduced outward lung expansion or reduced lung compliance (restrictive lung diseases), increased zone 3
How does PEEP affect FRC?
restores FRC by reducing zone 3
How does position, induction, NMB, and surgical displacement affect FRC?
Upright position < supine < anesthetic induction < NMB < surgical displacement
How does general anesthesia affect FRC?
decreases
What causes general anesthesia to decrease FRC?
diaphragm shifts cephalad 4cm d/t decreased inspiratory muscle tone and increased expiratory muscle tone
How does obesity affect FRC?
decreases
What causes obesity to decrease FRC?
decreased chest wall compliance, increased airway collapsibility
How does pregnancy affect FRC?
decreases
What causes pregnancy to decrease FRC?
diaphragm shifts up, decreased chest wall compliance
Is FRC in neonates increased or decreased?
decreased
What causes FRC in neonates to be decreased?
less alveoli, decreased compliance, ribcage prone to collapse
How is FRC affected by old age?
increased
What causes FRC to increase in old age?
decreased elastic lung tissue -> air trapping -> increased RV -> increased FRC
What positions increase and decrease FRC?
Decrease: supine, lithotomy, trendelenburg
increase: prone, sitting, lateral
How does paralysis affect FRC?
decreases
What causes paralysis to decrease FRC?
diaphragm moves cephalad, decreased lung volumes
How does inadequate anesthesia affect FRC?
decreases
What causes inadequate anesthesia to decrease FRC?
Straining -> forceful expiration -> decreased lung volumes
How does excessive IV fluids affect FRC?
decreases
What causes excessive fluids to decrease FRC?
Fluid accumulation in dependent lung favors zone 3
How does high FiO2 affect FRC?
decreases
What causes high FiO2 to decrease FRC?
absorption atelectasis -> shunt
What causes reduced pulmonary compliance to decrease FRC?
acute lung injury, pulm. edema, pulm. fibrosis, atelectasis, P-Effusion
How does obstructive lung disease affect FRC?
increases
What causes obstructive lung disease to increase FRC?
air trapping -> increased RV -> increases FRC
How does PEEP affect FRC?
increases
How do sigh breaths affect FRC? How?
increases by recruiting collapsed alveoli
Describe closing volume?
during exhalation: the point where pleural pressure exceeds airway pressure
In which zone of the lung do airways collapse first?
zone 3, dependent areas due to high pleural pressure
What factors increased CV? (CLOSE-P)
COPD, LV failure, Obesity, Supine, Extremes of age, Pregnancy
What is closing capacity?
sum of closing volume and residual volume
The relationship between what two variables determines if airways collapse during tidal breathing?
FRC and CC
What situation causes the airways to close during tidal breathing?
FRC > CC or FRC < CC
FRC < CC
In a young healthy patient, airway closure occurs just above ____
residual volume
How can we measure CV and CC?
washout of tracer gas (nitrogen or xenon-133)
Where is CV and CC measured?
as patient exhales from total lung capacity
What is oxygen content (CaO2)?
measure of how much O2 is present in 1 dL of blood.
What are the two ways O2 is transported in the blood?
dissolved in plasma 3%, reversibly binds with Hgb 97%
What is the formula for CaO2?
CaO2 = (1.34 x Hgb x SaO2) + (PaO2 x 0.003)
What is a normal value of CaO2?
20mL O2/dL
How is O2 dissolved in the plasma measured?
PaO2
What law explains how oxygen is dissolved in the plasma?
Henrys
What law states that the concentration of gas in solution is directly proportional to the partial pressure of the gas above the solution?
Henry
How much oxygen does each gram of Hgb carry?
1.39mL
What is normal Hgb and Hct in males?
Hgb 15g/dL, Hct 45%
What is normal Hgb and Hct in females?
Hgb 13g/dL, Hct 39%
How is DO2 calculated?
CaO2 x CO x 10
What is a normal value of DO2?
1000 mL O2/min
What is the difference between the amount of O2 that leaves the lungs and the amount that returns?
VO2 (O2 consumption)
How is VO2 calculated?
VO2 = CO x (CaO2 - CvO2
How does a left shift on the oxyhemoglobin curve affect affinity?
increased affinity (left love)
How does a right shift on the oxyhemoglobin curve affect affinity?
decreased affinity (right release)
How will changes in temperature shift the oxyhemoglobin curve?
decreased left
increased right
How will changes in 2,3-DPG shift the oxyhemoglobin curve?
decreased left
increased right
How will changes in CO2 shift the oxyhemoglobin curve?
decreased left
increased right
How will changes in H+ shift the oxyhemoglobin curve?
decreased left
increased right
How will changes in pH shift the oxyhemoglobin curve?
increased left
decreased right
How will HgbMet, HgbCO, and Hgb F affect the oxyhemoglobin curve?
shift left
At a SpO2 of 90%, PaO2 =
60
At a SpO2 of 80%, PaO2 =
50
At a SpO2 of 70%, PaO2 =
40
What is P50 on the oxyhemoglobin curve?
PaO2 where 50% Hgb is saturated with O2
Maximum O2 loading occurs at a PaO2 of what?
100mmHg
What principle states that increased CO2 and decreased pH cause the erythrocyte to release O2?
Bohr effect
How does hypoxia affect 2,3-DPG?
increases 2,3-DPG, right shift of curve
How does banked blood affect the oxyhemoglobin curve?
banked blood has low 2,3-DPG -> left shift
How is ATP produced in the body?
oxidation of proteins, carbohydrates, and fats
Describe the phosphate bond.
high energy bond
What is the primary substrate for ATP synthesis?
glucose
What are the three key processes in glucose metabolism?
glycolysis, Krebs cycle, electron transport
What is the primary goal of glycolysis?
convert 1 glucose into 2 pyruvic acid
In the absence of oxygen, pyruvic acid is converted to what?
lactate
Where does the Krebs cycle take place?
mitochondria matrix
What is the primary goal of the glycolysis and the Krebs cycle?
liberate hydrogen from glucose
What are the end products of oxidative phosphorylation?
CO2, water and 34 ATP
What is the primary byproduct of aerobic metabolism?
CO2
Is PvCO2 higher or lower than PaCO2?
PvCO2 is 5mmHg higher than PaCO2
Is venous or arterial blood more acidic?
venous
What are the three mechanisms of CO2 transport?
Bicarbonate 70%
bound to Hgb 23%
dissolved in plamsa 7%
What ion is transported in erythrocytes to maintain electroneutrality?
chloride
What physics principle states that oxygen causes the erythrocyte to release CO2?
Haldane effect
Can venous or arterial blood carry more CO2 according to the Haldane effect?
venous blood can carry more
What causes increased CO2 production? (7)
sepsis, overfeeding, MH, shivering, prolonged seizures, thyroid storm, burns
What causes decrease CO2 elimination? (8)
Airway obstruction, increased dead space, increased Vd/Vt, ARDS, COPD, respiratory center depression, drug
overdose, inadequate NMB reversal
What part(s) of the anesthesia machine can allow rebreathing of CO2?
incompetent one way valves, exhausted soda lime
How does hypercapnia affect the oxyhemoglobin curve?
shifts right
What affect does hypercapnia have on cardiac and smooth muscle?
myocardial depression and vasodilation
How does hypercapnia affect the SNS?
increases SNS and increased catecholamine release
How does hypercapnia affect minute ventilation?
increases
How does hypercapnia affect potassium levels?
increases
How does hypercapnia affect calcium levels?
Acidosis release Ca: increases inotropy
Alkalosis binds calcium: decreases inotropy
How does hypercapnia affect ICP?
increases. CO2 diffuses across the BBB -> increased CBF and volume
How does hypercapnia affect level of consciousness
decreases
How does hypercarbia increase right ventricle workload?
CO2 causes vasoconstriction in the lungs causing pulm. HTN increasing RV workload
How does a 10 mmHg increase in PaCO2 in acute respiratory acidosis affect pH?
decreases pH 0.08
How does a 10 mmHg increase in PaCO2 in chronic respiratory acidosis affect pH?
decreases pH 0.03
What is the relationship between PaCO2 and minute ventilation?
CO2 ventilatory response curve
Where are chemoreceptors located?
medulla, carotid bodies, transverse aortic arch
What do chemoreceptors monitor?
PaCO2
At what levels is CO2 a respiratory depressant?
PaCO2 > 80-100
What is MAC of CO2?
200mmHg
A left shift and increased slope of the CO2 ventilatory response curve will create what ABG reading?
respiratory alkalosis
A right shift and decreased slope of the CO2 ventilatory response curve will create what ABG reading?
respiratory acidosis
What is the highest PaCO2 at which a person will not breathe?
apneic threshold
How does a left shift on the CO2 ventilatory response curve affect the apneic threshold?
decrease
How does a right shift on the CO2 ventilatory response curve affect the apneic threshold?
increases
What causes a left shift on the CO2 ventilatory response curve?
hypoxemia, Met. acidosis, surgical stimulation, inter cranial HTN, salicylates, aminophylline, doxapram, NE
What causes a right shift on the CO2 ventilatory response curve?
Met. alkalosis, CEA, sleep, volatiles, opioids, NMBs
Where is the respiratory control center located?
medulla
Where are central chemoreceptors located?
medulla
Where are peripheral chemoreceptors located?
carotid bodies, and aortic arch
What CN is responsible for lung stretch receptors?
CN 10
What CN is responsible for peripheral chemoreceptors?
CN 9, 10
What is the respiratory center that causes inspiration? Where is it located?
dorsal respiratory. Tractus solitarius of medulla
What is the respiratory center that causes expiration? Where is it located?
ventral respiratory. Tractus solitarius of medulla
When is the ventral respiratory center most active?
when exhalation demand increases
What respiratory center inhibits the dorsal respiratory center? Where is it located?
pneumotaxic. upper pons
What respiratory center stimulates the dorsal respiratory center? Where is it located?
Apneustic. Lower pons
What is the function of the pneumotaxic center?
triggers the end of inspiration
What is the function of the apneustic center?
causes inspiration
What do central chemoreceptors respond to?
PaCO2
What do peripheral chemoreceptors respond to?
PaO2
Which chemicals free diffuse through the BBB and which do not?
CO2, H, HCO3
CO2 diffuses
H+ and HCO3 do not
What is the most important stimulus for central chemoreceptors?
hydrogen concentration in the CSF
As H+ concentration increases in the CSF what happens to the rate and depth of breathing?
rate and depth increase
How long does it take HCO3 to equilibrate between the blood and CSF?
few hours, peaks in 2 days
At a PaO2 < 60, the hypoxic ventilatory response closes oxygen-sensitive potassium channels in what cells?
type 1 glomus cells
What does the hypoxic ventilatory response do to action potentials, calcium channels, and neurotransmitter release?
increase action potentials, opens Ca channels, and increases Ach and ATP release
What nerves are responsible for the hypoxic ventilatory response?
Herings, and CN 9
What conditions impair the hypoxic ventilatory response?
CEA and sub-anesthetic doses of inhalation and IV anesthetics
What does not stimulate the hypoxic ventilatory response?
reduction in CaO2 in anemia and CO poisoning
Stretch receptors in the lungs transmit information via which nerve to the dorsal respiratory center?
vagus nerve
The dorsal respiratory center sends signals to the diaphragm via which nerve?
phrenic (C3-C5)
What reflex turns off the dorsal respiratory center and and stops further inspiration?
Hering-Breuer
What activates the Hering Breuer reflex?
lung inflation > 1.5L above the FRC (3x normal Vt)
J receptor stimulation causes what type of breathing?
tachypnea
What reflex causes the newborn to take their first breath?
paradoxical reflex of the head
What reflex causes apnea, bradycardia, and vasoconstriction?
dive reflex (face submerged in cold water)
What activates hypoxic pulmonary vasoconstriction?
reduced alveolar O2 tensions, PAO2
What is the only region in the body that responds to hypoxia with vasoconstriction?
pulmonary vascular beds
What drugs impair hypoxic pulmonary vasoconstriction?
volatile anesthetics > 1.5 MAC, vasodilators, PDE inhibitors, dobutamine, some CCB, phenylephrine, epinephrine, dopamine
How does fluid status effect hypoxic pulmonary vasoconstriction?
Hypervolemia (LAP > 25) impair
Hypovolemia causes HPV
What ventilator settings impair hypoxic pulmonary ventilation?
excessive PEEP and high tidal volume –> increased dead space
