VENTILATION/PERFUSION RELATIONSHIPS
At lower lung volumes, alveoli in dependent areas are _____ but not ____.
Perfused, ventilated.
Due to intrapulmonary shunting
Alveoli near the top of the lung have higher transpulmonary pressure, don't inflate as much.
Areas closer to the ____ of the lung receive greater blood flow than areas closer to the ____.
Hilum, Periphery.
A V/Q ratio of 0 is also known as ______
intrapulmonary shunt
What 3 forms are Carbondioxide transported through in the blood?
dissolved in solution 7%
bicarbonate 70%
bound to protein 23%
The basic breathing rhythm originates in the _____.
Medulla.
A dorsal respiratory group, which is primarily active during inspiration, and a ventral respiratory group, which is active during expiration.
Two pontine areas influence the doral (inspiratory) medullary center: A lower pontine (apneustic) center is excitatory. An upper pontine (pneumotaxic) center is inhibitory
The pontine centers appear to fine-tune respiratory rate and rhythm
At the base of the lung, pleural pressure is ____ negative, so the transpulmonary pressure is _____.
Less, Smaller
The lower (dependent) areas of both lungs tend to be better ventilated than do the upper areas because of a gravitationally induced gradient in intrapleural pressure (transpulmonary pressure).
At rest, the transpulmonary pressure is +5cm H2O.
Becuase alveolar ventilation (Va) is normally about __ L/min, and pulmonary capillary perfusion (Q) is __ L/min, the overall V/Q ratio is about __
4 L/min, 5 L/min, 0.8
Because perfusion increases at a greater rate than ventilation, nondependent (apical) areas tend to have higher V/Q ratios than do dependent (basal) areas
How is the alveolar-to-arterial (A-a) O2 gradient changed in one-lung ventilation?
Widened
What are 3 factors that shift the hemoglobin–oxygen dissociation curve to the right.
increased 2,3-DPG, Acidosis, Hyperthermia.
Other causes: hypercarbia, sickle cell, pregnancy, volatile anesthetic, chronic anemia
The PaCO2 at which ventilation is zero is called the ______.
Apneic threshold.
Opiods and general anesthesia increase the apneic threshold.
Pre-alveolar cause of a shunt: ____
Alveolar cuase of a shunt: _____
Most common cause of increased dead space ventilation: ___
bronchospasm, mucus plugs
atelectasis, pneumonia, consolidation
Hypotension
_____ is the process whereby desaturated, mixed venous blood from the right heart returns to the left heart without being resaturated with O2 in the lungs.
Shunting
This leads to decreased or dilute arterial O2 content.
At high altitudes, and in patients with extensive destruction of alveolar-capillary membrane, O2 uptake is limited by _____.
Diffusion
The oxygen-Hgb dissociation curve is roughly flat when the Po2 is between ___ and ___ mmHg
60, 100
The carotid bodies (peripheral chemoreceptors) lie at the ______ and interact with the central respiratory centers via the _______.
bifurcation of the common carotid arteries, glossopharyngeal nerve.
The two sets of peripheral chemoreceptors include the carotid bodies and the aortic bodies.
In zone 2 (Pa __ PA __ Pv)
PA=Alveolar pressure
Pa =arterial pulmonary pressure
Pv= venous pulmonary pressure
(Pa > PA > Pv)
In zone 1 (PA > Pa > Pv), Alveolar pressure (PA) is greater than both the arterial pulmonary pressure (Pa) and venous pulmonary pressure (Pv), resulting in obstruction of blood flow and creation of alveolar dead space.
In zone 2 (Pa > PA > Pv), resulting in blood flow that is dependent on the differential between Pa and PA.
The bulk of the lung is described by zone 3 (Pa>Pv>PA), resulting in blood flow independent of the alveolar pressure.
Zone 4, the most dependent part of the lung, is where atelectasis and/or interstitial pulmonary edema occur, resulting in blood flow that is dependent on the differential between Pa and pulmonary interstitial pressure.
____ shunt refers to anatomic shunts and lung units where V/Q is zero. A _____ shunt is an area of the lung with a low V/Q ratio.
Clinically, hypoxemia from a ____ shunt can usually be partially corrected by increasing the inspired O2 concentration; hypoxemia caused by an ____ shunt cannot.
Absolute, relative
relative, absolute
The most common mechanism for hypoxemia is an increased _______.
alveolar–arterial gradient.
The A–a gradient for O2 depends on the amount of right-to-left shunting, the amount of V/Q scatter, and the mixed venous O2 tension
Decreased cardiac output
Increased oxygen consumption Decreased hemoglobin concentration
Decreased O2 binding to hemoglobin causes increased affinity for CO2 and H+ is the ______ effect
Haldane effect
Central chemoreceptors respond to changes in ___ concentration in the ____.
Peripheral chemoreceptors primarily respond to changes in _____.
H+, cerebrospinal fluid.
PaO2.
Central chemoreceptors are thought to lie on the anterolateral surface of the medulla.
Peripheral chemoreceptors produce reflex increases in alveolar ventilation in response to reductions in Pao
Factors affecting dead space:
Posture: upright vs supine
Position of airway: Neck extension vs flexion
Age
Artificial airway
Positive-pressure ventilation
Anticholinergic
Pulmonary perfusion: Pulmonary emboli, Hypotension
Pulmonary vascular disease: Emphysema
Posture: upright (Inc) vs supine (Dec)
Position of airway: Neck extension (Inc) vs flexion (Dec)
Age (Inc)
Artificial airway (Dec)
Positive-pressure ventilation (Inc)
Anticholinergic (Inc)
Pulmonary perfusion: Pulmonary emboli (Inc) Hypotension (Inc)
Pulmonary vascular disease: Emphysema (Inc)
_____ is the amount of mixed venous blood that would have to be mixed with pulmonary end-capillary blood to account for the difference in O2 tension between arte- rial and pulmonary end-capillary blood.
Venous admixture
General anesthesia commonly increases venous admixture to 5% to 10%, probably as a result of atelectasis and airway collapse in dependent areas of the lung.
PEEP is often effective in reducing venous admixture and preventing hypoxemia during general anesthesia
The A–a gradient for O2 is directly proportional to ____, but inversely proportional to _____.
shunt, mixed venous O2 tension.
the greater the shunt, the less likely the possibility that an increase in Fio2 will prevent hypoxemia.
Other than alkalosis, hypothermia, and decreased DPG, what are 3 causes of a left shift of the O2-Hb disassociation curve?
CO-Hb, Met-Hb, Sulf-Hb, fetal-Hb, myoglobin
The pulmonary endothelium metabolize a variety of vasoactive compounds, including _____, _____, and _____.
norepinephrine, serotonin, bradykinin,
and a variety of prostaglandins and leukotrienes.
The lungs also convert angiotensin I to angiotensin II.