Module 4.0 - Diagnostic Concepts of Oxygenation & Ventilation/Pulmonary Function Testing Flashcards
What is Pulmonary Perfusion?
- It is the movement of mixed venous blood through the pulmonary capillary bed for the purpose of gas exchange between the blood and the alveolar bed.
- The pulmonary vascular system is a high volume system with low capillary resistance.
- Lung bases receive a greater percentage of blood flow than do the apices
What is the average pulmonary blood flow?
about 6 liters/minute
What is the normal mean pulmonary arterial pressure?
12-16mmHg
What is ventilation?
- It is the mechanical movement of air into and out of the alveoli for the purpose of gas exchange between the atmosphere and capillary blood.
- Gas flows from higher atmospheric to lower intrapulmonary pressure during inhalation.
What are the two methods by which ventilation is regulated?
- Central Nervous System
- Chemical Regulations (PaCO2)
Describe the CNS regulation of ventilation
- The brain stem centers (medulla and pons) cells fire automatically to trigger inhalation, others fire to halt inhalation and exhalation occurs passively.
- The cerebral cortex allows voluntary control to override brain stem centers in response to chemical stimuli and lung inflation changes.
Describe the chemical regulation of ventilation
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Central chemoreceptors in medulla respond to increased partial pressure of carbon dioxide in arterial blood (PaCO2), hypercapnia, and acidosis through medullary stimuli by increasing ventilator depth and rate.
- ↑PaCO2 = AUTOMATIC ↑ depth & rate of ventilations
- Hypercapnia is the major stimulus to alter ventilation. Peripheral chemoreceptors in aortic and carotid bodies respond to decreased PaO2 by stimulating medullary centers to enhance ventilation.
What happens to patients with chronically high PaCO2’s?
- In these patient’s the hypercapnic ventilatory drive is lost: these patients respond only to changes in PaO2 by stimulation of peripheral receptors to adjust their ventilation.
- Supplemental oxygen should be given carefully to prevent apnea (begin with 1-2 L/minute and assess patient carefully.
- DO NOT withhold oxygen, mechanical ventilation is a backup).
What is oxygenation and what are 2 factors that can affect oxygenation?
- Oxygenation = Is a measure of the amount of oxygen in the blood and the adequacy of the transport of oxygen through the body
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2 Factors =
- ↓ Hgb = ↓ Oxygenation
- ↓ Cardiac Output = ↓ Oxygenation
What is alveolar diffusion?
- This is the exchange of O2 and CO2 across the alveolocapillary membrane.
- Oxygen diffuses down the concentration gradient from higher alveolar pressure (PAO2) to lower pulmonary capillary pressure (PaO2).
- CO2 diffuses at a rate 20 times greater than that of O2 from capillary to the alveolus.
What is the normal difference between alveolar and arterial oxygen in young adults?
Young adults breathing room air: less than 10 mmHg difference
What is the normal difference between alveolar and arterial oxygen in adults >60 years old?
Adults >60 on room air: less than 20 mmHg difference
What is the normal difference between alveolar and arterial oxygen in patients breathing 100% O2?
Patients breathing 100% oxygen: less than 50 mmHg difference
What does “work of breathing” mean?
The amount of effort required to overcome the elastic and resistive properties of the lungs and chest wall.
What is elasticity (elastic recoil)?
- It is the tendency of the lungs to return to their original shape. Lungs try to collapse because of tension between the interstitial elastic fibers and the surface of the alveoli.
- Chest wall attempts to resist inward-moving recoil