Pulmonary Blood Flow Distribution

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Questions and Answers

What is the effect of chronic hypoxia on pulmonary vascular resistance?

Has no effect on pulmonary vascular resistance

Decreases pulmonary vascular resistance

Increases oxygen saturation in blood

Causes pulmonary hypertension (correct)

Which pharmacologic agent primarily causes vasodilation in pulmonary vessels?

Dobutamine

Aminophylline (correct)

Phenylephrine

Norepinephrine

What occurs to pulmonary vascular resistance when pulmonary artery pressure (PAP) increases?

Pulmonary vascular resistance increases

It becomes dependent on blood viscosity

Pulmonary vascular resistance decreases (correct)

There is no change in pulmonary vascular resistance

Which of the following is an active mechanism affecting pulmonary vascular resistance?

Hypercapnia Signup and view all the answers

In terms of lung volume changes, what happens to extraalveolar vessels as lung volume increases?

They distend, decreasing resistance Signup and view all the answers

Which factor primarily influences pulmonary vascular resistance in response to acidosis?

pH levels Signup and view all the answers

What is the relationship between LA pressure changes and pulmonary vascular resistance?

Increased LA pressure results in decreased pulmonary vascular resistance Signup and view all the answers

Which pathologic condition is NOT associated with an increase in pulmonary vascular resistance?

Decreased alveolar ventilation Signup and view all the answers

Collectively, what is the main effect of low lung volumes on extraalveolar vessels?

They increase resistance significantly Signup and view all the answers

Which of the following conditions would result in recruitment of previously closed pulmonary vessels?

Increase in PAP Signup and view all the answers

What primarily influences blood flow distribution in the pulmonary system?

Alveolar pressure combined with gravity Signup and view all the answers

In Zone 1 of the pulmonary blood flow distribution, which statement is correct?

It is categorized as a dead space due to insufficient blood flow. Signup and view all the answers

How does increased ventricular end-diastolic pressure (VEDP) affect cardiac output (CO)?

It may increase CO according to the Frank-Starling law. Signup and view all the answers

Which of the following best describes ventricular afterload?

The force opposing blood flow during ventricular contraction. Signup and view all the answers

What does the Frank-Starling law illustrate about myocardial fibers?

Within limits, greater stretch enhances contractility. Signup and view all the answers

What condition contributes to the categorization of Zone 2 in pulmonary blood flow distribution?

Higher pulmonary arterial pressure than alveolar pressure. Signup and view all the answers

If vascular resistance (R) increases, what is the most likely effect on blood pressure (BP)?

BP increases, which may elevate afterload. Signup and view all the answers

Which factor is least likely to influence myocardial contractility?

Alveolar pressure Signup and view all the answers

What physiological role does myocardial contractility play in terms of cardiac output?

Enhancing contractility results in increased cardiac output. Signup and view all the answers

Which of the following describes the relationship between systemic vascular resistance (SVR) and mean arterial pressure (MAP)?

Higher SVR indicates higher MAP. Signup and view all the answers

Study Notes

Distribution of Pulmonary Blood Flow

Blood flow is influenced by gravity, cardiac output (CO), and pulmonary vascular resistance (PVR).
Blood flow is gravity dependent.
The distance from the apex to the base of the lung is 30 cm, generating a pressure difference of 30 cmH2O or 22 mmHg.
Intraluminal pressure (pressure within the blood vessel) in the gravity-dependent areas is greater.

Distribution in Three Zones

Zone 1 (Apex)
- Alveolar pressure (Palveolar) is sometimes greater than both arterial and venous intraluminal pressure, preventing blood flow through the region (Deadspace).
- Conditions that can lead to Zone 1:
  - Positive pressure ventilation
  - Dehydration
  - Hemorrhage
- In normal conditions, pulmonary artery pressure (PAP) is high enough to overcome Palveolar.
Zone 2 (Mid Portion)
- Arterial pressure (P arterial) is greater than Palveolar, allowing for pulmonary capillary perfusion.
Zone 3 (Bases)
- Gravity-dependent area.
- Both arterial and venous pressure are greater than Palveolar, resulting in constant blood flow.

Determinants of Cardiac Output

Stroke volume (SV) is influenced by:
- Ventricular Preload:
  - The degree of myocardial fiber stretch before contraction (end-diastole).
  - Greater stretch generally leads to greater contractility.
  - Ventricular preload is reflected in the ventricular end-diastolic volume (VEDV) or ventricular end-diastolic pressure (VEDP).
  - Increased VEDP correlates with increased cardiac output.
  - The Frank-Starling law describes the relationship between VEDP and cardiac output.
  - Decreased ventricular compliance leads to VEDP exceeding VEDV.
- Ventricular Afterload:
  - The force against which the ventricles must work to pump blood.
  - Determined by:
    - Total cross-sectional area of the vascular space.
    - Volume and viscosity of the ejected blood.
  - Pulmonary Vascular Resistance (PVR):
    - Calculated as (Mean Pulmonary Artery Pressure (MPAP) - Mean Left Atrial Pressure (MLAP)) / Cardiac Output x 80.
    - Normal range: 20-120 dynes.
  - Systemic Vascular Resistance (SVR):
    - Calculated as (Mean Arterial Pressure (MAP) - Mean Right Atrial Pressure (MRAP)) / Cardiac Output x 80.
    - Normal range: 800-1500 dynes.
  - Arterial systolic pressure is a good indicator of ventricular afterload.
- Myocardial Contractility:
  - Force generated by the myocardium.
  - Increased contractility (positive inotropism) leads to increased cardiac output.
  - Clinical indicators:
    - Blood pressure: Increased blood pressure indicates increased cardiac output.
    - Skin temperature: Increased cardiac output leads to warmer skin temperature and a pink appearance.

Vascular Resistance

Resistance (R) = Blood Pressure (BP) / Cardiac Output (CO).
Increased resistance leads to increased blood pressure and increased afterload.
Factors influencing pulmonary vascular resistance:
- Active mechanisms
- Passive mechanisms

Active Mechanisms

Abnormal Blood Gases:
- Hypoxia:
  - The partial pressure of oxygen in the alveoli (PAO2) controls this response.
  - Blood flow is redirected away from hypoxic lung regions to areas with higher PAO2.
  - Chronic hypoxia can lead to pulmonary hypertension and cor pulmonale.
- Hypercapnia and Acidosis:
  - Pulmonary vascular resistance increases in response to hypercapnia.
  - This effect is more related to pH (hydrogen ion concentration) than to carbon dioxide itself.
Pharmacologic Stimulation:
- Vasoconstriction:
  - Epinephrine (alpha and beta receptors)
  - Norepinephrine (alpha receptors, primarily arteries)
  - Dobutamine (beta receptors, heart, lungs, skeletal muscles)
  - Dopamine (beta receptors)
  - Phenylephrine (alpha receptors, decongestant)
- Vasodilation:
  - Oxygen
  - Isoproterenol
  - Aminophylline
  - Calcium-blocking agents
Pathologic Conditions:
- Vessel blockage or obstruction (thrombus)
- Vessel wall diseases (sclerosis)
- Vessel destruction (emphysema)
- Vessel compression (pneumothorax)

Passive Mechanisms

In response to mechanical changes:
- Pulmonary Artery Pressure (PAP) changes:
  - Increased PAP leads to decreased pulmonary vascular resistance.
  - High PAP creates high distending intraluminal pressure, increasing the total cross-sectional area of vessels.
  - This induces:
    - Recruitment: Opening of previously closed vessels.
    - Distension: Stretching or widening of previously open vessels.
    - Both mechanisms have limits.
- Left Atrial Pressure (LA) changes:
  - Increased LA pressure leads to decreased pulmonary vascular resistance.
- Lung Volume changes:
  - Varies depending on the location of the vessel.
    - Alveolar vessels:
      - Thin-walled, making them susceptible to changes in pleural pressure.
      - As the lungs inflate, resistance offered by alveolar vessels progressively increases.
      - During positive pressure ventilation, transmural pressure can become negative, restricting blood flow.
    - Extraalveolar vessels:
      - Thicker-walled.
      - As the lungs inflate, transmural pressure increases, causing vessel distension.
- Blood Volume changes:
- Blood Viscosity changes:

Summary of Lung Volume Changes

Low lung volumes:
- Extraalveolar vessels narrow, increasing vascular resistance.
- Alveolar vessels widen, decreasing vascular resistance.

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Description

This quiz covers the distribution of pulmonary blood flow across different zones in the lungs. It explores the concepts of gravity dependency and pressure differences that influence blood flow, particularly in zones 1, 2, and 3. Test your understanding of how these factors interact in normal and pathological conditions.