Respiration: Ventilation (V), Perfusion (Q) And VQ Relationship Flashcards
Definition of ventilation
Process by which air moves in and out of lung
Definition of perfusion
Process by which deoxygenated blood passes through the lung and becomes oxygenated
Major determinant of normal gas exchange and thus the level of PO2 and PCO2 in blood in the relationship between and perfusion
Relationship is called V/Q ratio
What is the relationship ventilation and perfusion
V/Q ratio
What is compliance
Compliance refers to how much effort is required to stretch the lungs and chest wall
What is high compliance
Means that the lungs and chest wall expand easily
Decreased compliance is a common feature in pulmonary conditions
1) scarring in lung tissue (tuberculosis)
2) lung filled with fluid (edema)
3) deficiency in surfactant production
4) destruction of elastic fibres (emphysema)
What is resistance
Resistance refers to any narrowing or obstruction of the airway that may reduce airflow
Large diameter airways have decreased resistance
Increased resistance is a common feature in pulmonary conditions such as
1) asthma
2) COPD due to obstruction or collapse of airways
What is anatomical dead space
Volume of gas during each breath that fills the conducting airways
What is a physiological dead space
Total volume of gas in each breath that does not participate in gas exchange eg alveoli that are perfused but not ventilated
What are the two blood supplies to the lungs
- pulmonary circulation
- bronchial circulation
What is the pulmonary circulation
Brings deoxygenated blood from heart to lung and oxygenated blood from lung to heart
What is bronchial circulation
Brings oxygenated blood to lung parenchyma
Describe the difference between the systemic circulation and the pulmonary circulation
Pulmonary circulation is a low pressure and low resistance system - influenced by gravity more than the systemic circulation is
What is the V/Q ratio
The ratio of ventilation to blood flow
What is the average V/Q relationship for the lung
0.8-1.2 - varies greatly
What is the perfect V/Q ratio in single alveolus
V/Q = 1
Describe anatomical shunts
Most anatomical shunts occur within the heart - blood from the right atrium or ventricle crosses septum to left atrium or ventricle - right to left shunt
What can shunts result in
Varying degrees of hypoxemia
What is atelectasis
Obstruction of ventilation due to mucus plugs, airway oedema, foreign bodies, tumours in airways
What is COPD
A condition in which airflow is obstructed
Encompasses emphysema and chronic bronchitis
Long term smoking most frequent cause
What is emphysema
Structures in alveoli over inflated, lungs loose elasticity therefore they can’t expand and take in air, patients can inhale but exhalation is difficult due to decreased elastic recoil
What is chronic bronchitis
Inflammation of bronchi causing mucous production and excesssive swelling, shortness in breath with mild exertion
What is pulmonary fibrosis
A type of interstital lung disease, scarring and thickening of tissue, decreased elasticity, decreased gas exchange
What is a healthy lung volume
70% of lung volume expired in 1 second
Why is there regional differences in ventilation and perfusion
Largely due to gravity
If the alveolar sack is completely blocked by a shunt what will be the V/Q value
V/Q=0
What is atrial hypoxemia
Arterial PO2 < 80mmHg
What is hypoxia
When insufficient O2 to carry out metabolic functions - when arterial PO2 < 60mmHg
What is hypercapnia
Increase in arterial PCO2> 40mmHg
What is hypocapnia
Decrease in Arterial PCO2 < 35mmHg
