VENTILATION / PERFUSION RELATIONSHIPS

BALBOA, Elaine. BANTOLO, AlenaPias. BAQUILOD, Martin Lorenzo Miguel. BARRETTO, Diana. BAUTISTA, Caroline. BAUTISTA, Teodoro Jr. BONTIA, Ana Jane

1A - MEDICINE

INTRODUCTION AND IMPORTANT CONCEPTS• Narration of the Introduction and

Important Concepts. (1st and 2nd paragraph)

• Molecules of O2 and CO2 enters / exits thru the conduction system and the lungs thus showing a glimpse of ventilation and perfusion.

• Proper labeling of important concepts will be shown.

INTRODUCTION AND IMPORTANT CONCEPTS

• Molecules of O2 and CO2 enters from the conduction system to the lungs showing a glimpse of ventilation and perfusion.

• Ventilation perfusion Formula will be shown.

• Proper labeling of important concepts will be shown.

• Ventilation perfusion ratio is defined as the ratio of ventilation to blood flow. This ratio can be defined for a single alveolus, for a group of alveoli, or for the entire lung. At the level of a single alveolus, the ratio is defined as the alveolar ventilation divided by the capillary flow. At the level of the lung, the ratio is defined as the total alveolar ventilation divided by the cardiac output.

Profiles for alveolar ventilation and bloodflow in healthy adults. The y-axis represents

flow (either blood flow or airflow) in L/min. The ventilation-perfusionratio is shown on the x-axis, plotted on a logarithmic scale.

The optimal V˙ A/Q˙ ratio is 0.8 in healthy lungs.

INTRODUCTION AND IMPORTANT CONCEPTS

•Proper labeling of important concepts will be shown.

• Normal values will be highlighted.

• In normal individuals, alveolar ventilation and blood flow are each distributed uniformly to the gas-exchanging units, and the alveolar ventilation is slightly less than the pulmonary blood flow. In normal resting individuals, alveolar ventilation is about 4.0 L/min and pulmonary blood flow is about 5.0 L/min. Thus, in the normal lung, the overall ventilation:perfusion ratio is about 0.8, but the range of ratios varies widely in different lung units. If ventilation and blood flow are mismatched, both O2 and CO2 transfer are impaired.

• When ventilation exceeds perfusion, the ventilation:perfusion ratio is greater than 1 and when perfusion exceeds ventilation the ventilation:perfusion ratio is less than 1.

• In individuals with cardiopulmonary disease, mismatching of pulmonary blood flow and alveolar ventilation is the most frequent cause of systemic arterial hypoxemia.

TYPES OF V/Q RELATIONSHIP

IDEAL V/Q or V/Q OF 1An ideal is a condition wherein the respiratory unit receives equal amount of ventilation and perfusion. In this situation gas exchange between the alveolar gas and pulmonary capillary blood is optimal that is why it is known as an ideal .For example, if a respiratory unit receives 3 lpm of ventilation and 3 lpm of blood flow, then the relationship is 3/3 or 1.

Ventilation and perfusion of molecules will be demonstrated as described.

TYPES OF V/Q RELATIONSHIP

LOW V/Q or V/Q<1This condition exists when the respiratory unit receives inappropriate low ventilation relative to its perfusion such as in partial obstruction of the airways. For example, a respiratory unit receives 2 lpm of ventilation and 3 lpm of blood flow, then the relationship is 2/3 or V/Q less than 1.This may be caused by a low respiratory unit ventilation due to low compliance such as in pulmonary fibrosis and lack of surfactant or due to high airway resistance found in asthma and chronic obstructive pulmonary disease.

ZERO V/QThis conditon exists when the respiratory unit receives no ventilation but perfusion remains normal. For example, a respiratory unit receives 0 lpm of ventilation and 3 lpm of blood flow, then the relationship is 0/3 or V/Q = 0.This may be caused by alveolar flooding found in pneumonia and ARDS, complete obstruction of the airway, and extrinsic compresion of alveoli present in compression atelectasis due to hydrothorax or pneumothorax.

A condition of relative hypoventilation exists in both the LOW and ZERO V/Q

Ventilation and perfusion of molecules will be demonstrated as described.

TYPES OF V/Q RELATIONSHIP

HIGH V/Q or V/Q>1This condition exists when the respiratory unit receives inappropriate low perfusion relative to its ventilation. For example, a respiratory unit receives 3 lpm of ventilation and 2 lpm of blood flow, then the relationship is 3/2 or V/Q greater than 1.Hypotensive states or a partial obstruction of pulmonary blood vessels present in pulmonary embolism may be responsible for a high V/Q.

V/Q of InfinityThis condition exists when the respiratory unit receives no perfusion but ventilation remains normal. For example, a respiratory unit receives 3 lpm of ventilation and 0 lpm of blood flow, then the relationship is 3/0 or V/Q of infinity.This may be found when there is a complete obstruction of the pulmonary blood vessels

A condition of relative hyperventilation exists in both the HIGH and INFINITE V/Q

Ventilation and perfusion of molecules will be demonstrated as described.

TYPES OF V/Q RELATIONSHIP

The effect of changes in the ventilation-perfusion ratio on the alveolar PO2 and PCO2. A: Normal V/Q. B: V/Q = 0. C: V/Q is infinite.

TYPES OF V/Q RELATIONSHIP

CONSEQUENCES OF V/Q RELATIONSHIP IN O2 AND CO2 TENSION

• Narration of the consequences of V/Q relationship in O2 and CO2 tension- Ideal V/Q - V/Q decreases - V/Q = 0 - V/Q increases - V/Q is infinite

• Relationships, Values, Important Concepts will be emphasized.

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNGIntroduction

A normal lung has different V/Q ratios in its different regions. This may be attributed to the pull of gravity and the heart’s location relative to the lung.The volume of the lung at the apex is less than the volume at the bases. Thus, airflow and blood flow increase down the lung, but the differences in perfusion are greater than the differences in ventilation. Blood flow shows about a 5-fold difference between the top and bottom of the lung, while ventilation shows about a 2-fold difference. Blood flow is proportionately greater than ventilation at the base, reflecting a lower V/Q ratio and ventilation is proportionately greater than blood flow at the apex, demonstrating a higher V/Q ratio.

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNGPhysiologic Basis

To help explain these differences, the lung is often divided into three zones. In each zone, the patterns of blood flow are quite different. In Zone 1, there isno blood flow during all portions of the cardiac cycle because the local alveolar capillary pressure in that area of the lung never rises higher than the alveolar air pressure during any part of the cardiac cycle In Zone 2, there is intermittent blood flow only during the pulmonary arterial pressure peaks because the systolic pressure is then greater than the alveolar air pressure, but the diastolic pressure is less than the alveolar air pressure InZone 3, there is continuous blood flow because the alveolar capillary pressure remains greater than alveolar air pressure during the entire cardiac cycleNormally, the lungs have only zones 2 and 3 blood flow—zone 2 (intermittent flow) in the apices, and zone 3 (continuous flow) in all the lower areas.

•Narration on the Physiologic basis of the V/Q regional differences

•Important Concepts will be emphasized

•Animations will be made as described by the narration.

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNGPhysiologic Basis - Summary

Thus, the ratio decreases from the apex to the base of the lung. Nonetheless, there is normally more gas exchange in lower regions of the lung because they receive more blood flow. This difference in ventilation perfusion ratios are associated with a difference in alveolar O2 and CO2 contents between the apex and the base.

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNGO2 and CO2 content

Because of the decreased blood flow at the apex, the oxygen consumed and the CO2 produced are also decreased in this region. Because the CO2 produced is more closely linked to ventilation, whereas the oxygen consumed is more closely linked to perfusion, the CO2 produced is higher because ventilation exceeds perfusion. As a result, the respiratory quotient (CO2 produced/O2 consumed) is higher at the apex than at the base. During exercise, when blood flow to the apex increases and becomes more uniform in the lung, the differences between contents of gases in the apex and in the base of the lung diminish.

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNGO2 and CO2 content

The heart can affect regional V/Q differences because it is situated midway between the top and bottom of the lungs, causing the arterial pressure to be about 11 mm Hg less at the lungs’ apex (15 cm above the heart) and about 11 mm Hg more than the mean pressure in the middle of the lungs at the lungs’ base (15 cm below the heart). Such pressure differences have profound effects on blood flow through the different areas of the lungs.The low arterial pressure results in reduced blood flow in the capillaries at the lung’s apex, while capillaries at the base are distended and blood flow is augmented.

ZONES V/Q PAO2 PACO2 SIGNIFICANCE

UPPER ZONE 1 HIGH >104 <40 ALVEOLAR DEAD SPACE

MID ZONE 2 ALMOST IDEAL 104 40

LOWER ZONE 3 LOW <104 >40 ALVEOLAR SHUNT EFFECT

V/Q RELATIONSHIP OF A NORMAL UPRIGHT LUNG

Lungs are composed of millions of respiratory units, which are interconnected to each other. When a single respiratory unit is affected by a disease, wherein it might either have a decreased ventilation (LOW V/Q) or a decreased perfusion (HIGH V/Q), the ventilation or the perfusion that is supposed to be for the “diseased” respiratory unit will be diverted to the normal or unaffected respiratory unit. (from V/Q of 1 to high V/Q for low ventilation states and from V/Q of 1 to low V/Q for low perfusion states.) This is because the “diseased” respiratory unit is connected to the normal or unaffected respiratory unit (V/Q of 1).

Thus, primary low V/Q (shunt) gives rise to secondary high V/Q (dead space) and vice versa. Alveolar dead space and intrapulmonary shunt represent the two extremes of ventilation-perfusion ratios, infinite and zero, respectively.

CONCEPTS OF V/Q MISMATCH

Low regional ventilation-perfusion (V˙ A/Q˙ ) ratio. A partially blocked airway causes this region to be underventilated, relative to blood flow. A low regional V˙ A/Q˙ ratio causes venous admixture and will increase the physiological shunt. A partially obstructed pulmonary arteriole will cause an abnormally high V˙ A/Q˙ ratio in a lung region. Restricted blood flow causes this region to be overventilated relative to blood flow, which leads to an increase in physiological dead space.

CONCEPTS OF V/Q MISMATCHSHUNT AND DEAD SPACE

COMPENSATORY MECHANISMS DURING PATHOLOGICAL RELATIONSHIP

• HIGH V/Q – alveolar dead space Mechanisms: HypocapnicBronchoconstriction (increasing airway resistance)

Diminished Surfactant Production (decreasing alveolar compliance)– regional abnormality: (wasted ventilation), relative hyperventilation in the respiratory unit with high V/Q– regional effect: PACO2 (alveolar hypocapnia)– regional result: V A and V A/Q (compensation)– partial obstruction of the pulmonary blood vessels or pulmonary embolism and hypotensive states.

• LOW V/Q – shunt Mechanisms: Hypoxic Pulmonary VasoconstrictionDiminished Surfactant Production (decreasing alveolar compliance)

– regional abnormality: V A/Q (wasted perfusion)– regional effect: PAO2 (alveolar hypoxia)– regional result: Q and V A/Q (compensation)

– low compliance such as in pulmonary fibrosis and lack of surfactant and when there is high airway resistance such as in asthma and chronic obstructive pulmonary disease (COPD)

A brief enumeration will be done with the corresponding pictures and animations shown for the compensatory mechanisms.

Could be used for showing movement of molecules illustrating ventilation and perfusion

Other Sample Illustrations

Other Sample Illustrations

Model to explain the uneven distribution of blood flow in the lung based on the pressures affecting the capillaries (LUNG ZONES)

Blood flow at different levels in the lung of an upright person at rest and during exercise. When the person is at rest, the blood flow is very low at the top of the lungs; most of the flow is through the bottom of the lung.

Other Sample Illustrations

Gravity causes uneven pulmonary blood flow inthe upright individual. The downward pull of gravity causes a lower blood pressure at the apex of the lungs. Consequently, pulmonary blood flow is very low at the apex and increases toward the base of the lungs.