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19 Cards in this Set

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  • Back
Regional Distribution of Pulmonary Blood Flow 4-8
1. in a normal person in the upright position (seated or standing), with his/her lung volume at total lung capacity
a. blood flow is lowest at the top (apex)
b. increases progressively moving toward the bottom (base) of the lung.
2. pulmonary blood flow will be greater in the more dependent portions of the lungs, regardless of the position of the body i.e. in a person lying on his/her left side, the left lung receives more blood flow/unit volume a. gravity on the blood in the thin-walled
b. highly distensible and compressible pulmonary vessels.
The Interaction of Gravity & Extravascular Pressure: The Zones of the Lung 4-9
1. Intravascular pressures affected by hydrostatic pressures of the columns of blood above or below the level of the heart.
2. Intravascular pressures increase progressively from apex to base (top to bottom) of the upright lung.
3. Gravity has no effect (the air pressure within the alveoli) at different levels
4. @ end of a normal expiration with the glottis open; alveolar pressure = atmospheric pressure.
5. quiet breathing;
a. inspiration: alveolar pressure falls about 1 cm H2O below atmospheric
b. expiration: about 1 cm H2O above atmospheric pressure
6. Abnormal or more forceful breathing: greater changes in alveolar pressure, but gravity does not have an effect.
Interaction of Gravity & Extravascular Pressure: Zone 1 (4-9)
1. @ top of the upright lung, when it occurs.
2. Under certain conditions; ALVELOAR P > all intravascular pressures --> collapsing the smallest alveolar vessels (art/ven/cap) exposed to alveolar pressure --> zero flow in those vessels throughout the cardiac cycle.
3. Normally, intravascular pressures @ top of the upright lung are just great enough to prevent continuous vessel collapse; Flow is low, but not zero.
4. Abnormal conditions --> continuous vessel collapse, resulting in a Zone 1 at the top of the upright lung. Examples are low pulmonary artery pressure and sustained high alveolar pressure with positive pressure ventilation.
Interaction of Gravity & Extravascular Pressure: Zone 2 (4-9)
1. upper 1/3 of a normal upright lung w/o zone 1.
2. pulmonary artery diastolic, pulmonary venous P < Alveolar P < Pulmonary Artery systolic P.
3. The effective driving pressure for flow to the capillaries in zone 2: pulmonary artery P - alveolar pressure.
4. The hemodynamic state in Zone 2; “vascular waterfall” (pulmonary venous pressure is NOT a determinant of volume flow to the capillaries).
5. Flow is intermittent; when pulmonary arterial P > alveolar pressure.
6. Moving downward within Zone 2, following increase
a. intravascular P
b. blood flow values
c. # of open capillaries
Interaction of Gravity & Extravascular Pressure: Zone 3 (4-9)
1. lower 2/3 of a normal upright lung.
2. Alveolar P < pulmonary artery/ven/cap P (Intravascular P's continue to increase progressively with distance below the heart.)
3. The effective driving pressure for flow in this zone; pulmonary artery P - pulmonary venous P
4. @ very low lung V < functional residual capacity (FRC),
5. increased intrapleural P @ base of the lung may decrease transmural P in large vessels enough to reduce (but not prevent) blood flow to this region.*sometimes called “Zone 4”.
Hypoxic Pulmonary Vasoconstriction: Local alveolar hypoxia
vasoconstriction in the hypoxic region. (Alveolar hypoxia by low oxygen in the inspired gas, hypoventilation or atelectasis)
Hypoxic Pulmonary Vasoconstriction: Mechanism of Hypoxic Pulmonary Vasoconstriction
hypoxia inhibits (closes) certain K+ channels in pulmonary vascular smooth muscle cell membranes --> depolarization, Ca2+ ion influx, and contraction.
Hypoxic Pulmonary Vasoconstriction: Physiologic Function of Hypoxic Pulmonary Vasoconstriction (4-10)
Hypoxic pulmonary vasoconstriction diverts blood away from poorly ventilated or poorly oxygenated alveoli to other alveoli (better ventilated or oxygenated)
vasodilation of systemic arterioles in response to hypoxia
1. opposite to hypoxic pulmonary vasoconstriction
2. helps increase blood flow to the tissues under hypoxic conditions.
3. vascular smooth muscle of Systemic arterioles;
a. different type of K+ channels, or
b. same type but fewer than pulmonary arterioles.
4. Systemic arterioles also dilate in response to the accumulation of metabolic substances by hypoxic tissue cells
Pulmonary Edema 4-11
1. extravascular accumulation of fluid in the lung, caused by one or more physiologic abnormalities; result is inevitably impaired gas transfer.
2. As the edema fluid builds up, order of
a. interstitium
b. alveoli,
- diffusion of gases—particularly oxygen—decreases
3. capillary endothelium is much more permeable to water and solutes than is the alveolar epithelium, so edema first in interstitium 2nd in alveoli.
Matching Ventilation and Perfusion
1. dotV A / dotQ ratio determine Alveolar PO2 and PCO2 values; then determine the Systemic arterial PO2 and PCO2 values; idealy 1.0 ratio
2. Only some regions of the normal lung in the upright posture have the ideal ratio of 1.0. Numerous respiratory diseases ~ abnormal ratios, affecting the values of arterial blood gases.
3. Ventilation-Perfusion Relationships: alveolar ventilation rate to pulmonary capillary blood flow rate
Consequences of High and Low dotV A / dotQ (5-1)
1. ratio > 1.0: the alveolar gas tensions in that region become more similar to those of inspired air (i.e., air in the conducting airways).
2. ratio < 1.0: the alveolar gas tensions in that region become more similar to those of mixed systemic venous blood (i.e., blood in the right ventricle).
3. Fig 5-2: more quantitative version of Figure 5-1, emphasizing a continuum of PO2 and PCO2 values existing between 0 and inifinity for the ratio
1. normally arterial PO2 is normally a few mm Hg less than the alveolar PO2 (not entirely equal as been told before)
2. normal anatomic shunt, some degree of ventilation-perfusion mismatch and diffusion limitation in some parts of the lung
3. dotV A / dotQ mismatch is usually the most important, with a small contribution from shunts and very little from diffusion limitation.
4. Larger-than-normal differences; significant ventilation-perfusion mismatch; can also be caused by anatomic or intrapulmonary shunts, diffusion block, low mixed venous PO2s, breathing higher than normal oxygen concentrations, or shifts of the oxyhemoglobin dissociation curve
The Alveolar – Arterial Oxygen Difference: (A – a) DO2 (SLIDE 11,12)
1. alveolar PO2 Calculated by the alveolar gas equation MINUS the Actual measured arterial PO2.
2. An abnormally large Difference: presence of a ventilation-perfusion inequality in the lung.
3. The size Difference may also indicate the severity of any ventilation-perfusion inequality.
4. P AO2 = P IO2 -1.25 PaCO2
5. equation works for ideal alveolar P O2, if there was no abnormalities of alveolar ventilation or pulmonary capillary blood flow
Regional dotV A / dotQ Differences & Their Consequences in the Lung (3-12, 5-6)
part 1
1. intrapleural surface P not uniform throughout the thorax; less (-) in the (lower, gravity-dependent) regions of the thorax VS (upper, nondependent) regions; form gradient created by gravity
2. transpulmonary pressure (alveolar minus intrapleural) is greater in upper regions of the lung than it is in lower regions of the lung
3. alveoli (upper) apply more distending pressures; they have greater Volumes than the alveoli in more dependent regions.
Regional dotV A / dotQ Differences & Their Consequences in the Lung (3-12, 5-6)
part 2
4. abscissa: the transpulmonary pressure (alveolar pressure minus intrapleural pressure).
5. ordinate: the volume of the alveolus expressed as a percent of its maximum.
6. @ FRC, the alveolus in the upper part of the lung is on a less steep portion of the alveolar pressure-volume curve (less compliant) VS more compliant alveolus in the lower region of the lung.
7. Thus, any change in transpulmonary pressure during a normal respiratory cycle will cause a greater change in volume in the alveolus in the lower, gravity-dependent region of the lung
Regional Differences in the Ventilation-Perfusion Ratios in the Upright Lung (5-7)
1. dotV A / dotQ ratios at locations between apex and base of the lung
2. blood flow values increase from lung apex to base more steeply than the ventilation values increase
3. values decrease progressively from apex to base
4. ideal raio 1.0 @ rib 3
Consequences of Regional Ventilation-Perfusion Differences in the Normal Upright Lung (5-8)
1. alveolar gas compositions in various regions of normal lungs in the upright posture affected by ratio
2. values for end pulmonary capillary blood PO2 and PCO2 at each of the levels in the diagram will be essentially the same as the alveolar values.
3. The blood in these pulmonary capillaries then mixes to form the pulmonary venous blood.
4. This mixture determines the values for PO2 and PCO2 in the blood entering the left atrium and ventricle. --> pumped into the systemic arteries.
ventilation-perfusion mismatching
(primer figure)
1. non-ideal dotV A / dotQ ratio affect gas tensions in end pulmonary capillary blood and systemic arterial blood
2. Region A < 1.0 ; will not be able to completely restore the O2 content and PO2 of arterial blood to normal.
Region B > 1.0 ; most common cause of arterial hypoxemia
inequalities in the lungs cause mixed alveolar and systemic arterial blood gas tensions to become more different from one another than they would be if ratio was = to 1.0 for the whole lung.