Pulmonary 2 Flashcards by Denisse Tiangco

HIGH PRESSURE
LOW FLOW
Branches of thoracic aorta
Systemic arterial blood

Trachea, bronchial tree, supporting tissues of the lungs

1-2% of total cardiac output

Bronchial arteries

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LOW PRESSURE
HIGH FLOW
Venous blood from the right ventricle
Pulmonary capillaries for gas exchange
5cm
Thin walls, large diameter -> large compliance 7 ml/mmHg

Pulmonary artery

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Blood volume in the lungs

450 ml 9% of total blood volume

70ml is in the pulmonary capillaries

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Decreased alveolar oxygen reduces local alveolar blood flow and regulates pulmonary blood flow distribution

Alveolar O2 below 70 percent of normal (73mmHg)

Alveolar hypoxia -> vasoconstriction of adjacent pulmonary vessels

To redistribute blood flow where it is most effective

Hypoxic vasoconstriction

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In the upright position, when the effects of gravity are apparent, the lung apices are relatively

underperfused owing to low arterial hydrostatic pressure at lung apices

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Whereas in the upright position, the lung bases are relatively

overperfused

for this reason, pulmonary blood flow is often described as being divided into three different zones

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Palveoli > Partery > P vein

Zone:

Zone 1

Lung apices are relatively underperfused

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Partery > Palveoli > Pvein

Zone 2

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Partery> P vein> Palveoli

Zone 3

Lung bases are relatively overperfused

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No blood flow during the cardiac cycle
A pathologic condition that does not normally occur in the healthy lung

The lack of perfusion in this zone pulmonary blood flow quickly leads to tissue necrosis and lung damage

Occur when hydrostatic arterial and venous pressures are lower than alveolar pressure

Zone 1

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Seen with severe hemorrhage and positive-pressure ventilation

Occur in lung apices, where arterial hydrostatic pressure are reduced relative to the pressures in arteries supplying the lower lung fields

Under these conditions, the blood vessel is completely collapsed and there is no blood flow during either systole or diastole

Zone 1 blood flow

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This zone has intermittent blood flow during the cardiac cycle
No blood flow during diastole

This is typically exhibited by the upper 2/3 of the lungs
Alveolar pressures cause collapse of pulmonary capillaries during diastole, but pulmonary capillary pressures during systole exceed alveolar pressures, resulting in perfusion during systole

No blood flow during diastole because of collapse of pulmonary capillaries

Zone 2 blood flow

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This zone has continuous blood flow during the cardiac cycle

This pattern of blood flow is characteristic of the lung bases which are situated below the heart

Pulmonary capillary pressures are greater than alveolar pressures during systole and diastole, which means that the pulmonary capillaries remain patent throughout the cardiac cycle.

Zone 3 blood flow

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Causes by any factor that increases fluid filtration out of the pulmonary capillaries or impede pulmonary lymphatic function

Most common causes:

LSHF of mitral valve disease
Damage to the pulmonary blood capillary membranes

Pulmonary edema

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Normal pleural fluid

50 ml

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Excess fluid is pumped away by lymphatics:

Mediastinum
Lateral surface of parietal pleura
Superior surface of the diaphragm

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This comes from the pumping of fluids out of the pleural space by the lymphatics

Negative pressure

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Blockade of lymphatic drainage from the pleural cavity
Cardiac failure
Greatly reduced plasma colloid osmotic pressure
Infection or any other cause of inflammation

Pleural effusion

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Important for efficient gas exchange

For gas exchange to occur efficiently at the pulmonary membrane, pulmonary ventilation and perfusion should be well matched

Optimal matching minimizes unnecessary ventilation of nonperfused regions and perfusion of nonventilated areas

Inefficient to perfuse unventilated alveoli or ventilate nonperfused alveoli

V/Q matching

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V/Q at rest

0.8 with alveolar ventilation of about 4L/m and cardiac output of 5L/minute

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The lung apices at rest are

underperfused and relatively overventilated (V/Q ratio = 3.3) but compared with the lung bases, they do not receive as much perfusion

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The high V/Q ratio indicated discrepancy between the

amount of blood flow and ventilation

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Conversely, the lung bases at rest are relatively

overperfused (V/Q ratio, 0.6)

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Optimal matching of pulmonary ventilation and perfusion is achieved by

hypoxia-induced vasoconstriction and by changes in response to exercises

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Mechanisms of Maintaining V/Q Matching

Hypoxia-induced vasoconstriction | Changes during exercise

Shunts blood to better-ventilated lung segments

Hypoxia-Induced Vasoconstriction

Recruitment | Distention

Changes during exercise

In most capillary beds, hypoxia stimulates vasodilation (eg. myogenic response of autoregulation) In pulmonary vasculature, hypoxia stimulated

vasoconstriction of pulmonary arterioles, essentially preventing the perfusion of poorly ventilated lung segments (eg. as might occur in pulmonary disease) This allows the lungs to optimize V/Q matching for more efficient gas exchange

Only about 1/3 of the pulmonary capillaries are open at rest. Recruitment: opening of previously closed pulmonary capillaries because of increased pulmonary arterial pressures as may occur with exercise. During exercise, additional capillaries are Capillaries that are already open dilate to accomodate more blood

Open (recruitment) because of increased pulmonary artery blood pressure Distention

During exercise, ventilation and perfusion (and hence gas exchange) occur more frequently efficiently because

With increased cardiac output, blood flow is increased to the relatively underperfused lung apices Ventilation is increased to the relatively underventilated lung bases. V/Q matching occurs more efficiently during exercise.

Blood that bypasses the lungs or for another reason does not participate in gas exchange

Shunt

Two types of shunts:

Anatomic shunt | Physiologic shunt

Blood flow bypasses lungs Ex Fetal blood flow Intracardiac shunting (L->R, R->L)

Anatomic shunt

Blood flow to unventilated portions of lungs Ex Bronchial artery circulation Pneumonia Pulmo edema

Physiologic shunt

Oxygen content of systemic arterial blood at sea level

200 ml O2 197 ml from O2 bound to hemoglobin (98.5%) 3 ml from O2 physically dissolved (1.5%) Cardiac output = 5L/min O2 carried to tissues/min = 5L/min x 200 ml O2/L = 1000 ml O2/min

SpO2 of 90% = pO2

pO2 60 mmHg

Any increase in pO2 will cause minimal increase in spO2

Shift to the right

A slight decrease in pO2 causes a profound change in SpO2

Shift to the left

Onset of cyanosis

SpO2 85%

Bohr Effect | Increased O2 delivery to tissues when CO2 and H+ shift O2-Hgb dissociation curve

Shift to the right

EPO is produced in the

peritubular capillaries of the kidneys

Strongest stimulus of EPO

Hypoxia

Composition of air:

79% nitrogen 21% oxygen 0% CO2

In a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction Total pressure =

sum of the partial pressures of each gas 760 mmHg

Oxygen binding curve is

sigmoidal for both Hb-F and Hb-A

Has higher affinity for oxygen because it binds to DPG less strongly

Hb-F

Factors that lower oxygen bindng to hemoglobin

``` Dec pH Inc CO2 Inc H ion concentration Inc BPG/DPG Inc temperature ```

Conditions where oxygen is low, O2-Hgb curve shifts to the right such that Type of effect

more oxygen is readily available for distribution to the peripheral tissues Bohr Effect

Shift to the right HCO3 leaves the RBCs into the plasma HCO3 is replaced by chloride Chloride shift

Chloride shift | Partial pressure of CO2

Effect of allosteric factor to oxygen-binding curve

Increase in temperature increases O2 release | Shift to the right

Hypothermia causes shift to the

Left because it reduces oxygen requirements due to slow cellular metabolism

Increase 2,3 DPG decreases O2-Hb affinity leading to a shift to the

right

One DPG molecule binds to each Hb and stabilizes T form promoting

O2 release

Relaxed form Hgb

Binds better to O2

Tense/taut form

Decreased binding with O2 | Shift to the right

Has an affinity for Hb 200 times that of oxygen Once bound, does not readily dissociate Affects O2 transport

Carbon monoxide

ETC happens in

Inner mitochondria | Oxidative phosphorylation

Complex IV involves

Cytochrome oxidase

Inhibits cytochrome oxidase

carbon monoxide | Cyanide

Final acceptor in ETC

oxygen

Binds only to metHb Prevents reduction to active form Impairs ability of blood to transport O2

Cyanide

Drug associated with cyanide poisoning

sodium nitroprusside

Antidote for cyanide poisoning

Thiosulfate Hydroxocobalamin Amyl nitrite

Describes the relationship between the rate of diffusion and the three factors that affect diffusion The rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane

Fick’s Law of Diffusion

Receives entire cardiac output Has markedly lower pressures Smaller pressure drop across the pulmonary bed

Pulmonary circulation | Mean = 15

Most perfused area of the lung

Base | Zone 3

Most ventilated area of the lung

Apex

Increased hydrostatic pressure leads to

Edema

Secretion in pulmonary edema

Frothy | Blood tinged/pinkish secretion

First line drug for pulmonary edema

Furosemide

Transudative pleural fluid

Low albumin hypoalbuminemia Liver cirrhosis Nephrotic syndrome

Most common cause of V/Q mismatching

Hypoxia

Pulmonary 2 Flashcards

(72 cards)