Ventilation & Perfusion PDF

VENTILATION & PERFUSION Prepared by: Nuraini Che Aziz VENTILATION (V) Refers to the movement of air into and out of the lungs. Rate at which air enters or leaves the lungs. Ensures oxygen (O₂) delivery to the alveoli and the removal of carbon dioxide (CO₂) from the bo...

VENTILATION & PERFUSION Prepared by: Nuraini Che Aziz VENTILATION (V) Refers to the movement of air into and out of the lungs. Rate at which air enters or leaves the lungs. Ensures oxygen (O₂) delivery to the alveoli and the removal of carbon dioxide (CO₂) from the body. Two types of ventilation: 1. Pulmonary Ventilation 2. Alveolar Ventilation 1. Pulmonary Ventilation Definition: The process of moving air in and out of respiratory tract in a given minute of time during quiet breathing. Also called minute ventilation or respiratory minute volume (RMV). Pulmonary ventilation is a cyclic process, by which fresh air enters the lungs and an equal volume of air leaves the lungs. Calculation for Pulmonary Ventilation Normal value of pulmonary ventilation is 6 L/minute. It is a product of tidal volume (TV) and the rate of respiration (RR). It is calculated by formula: Pulmonary Ventilation = Tidal volume x Respiratory rate (cycles of breath) = 500 ml x 12/min = 6000 ml/min 2. ALVEOLAR VENTILATION Definition: Amount of air utilized for gaseous exchange every minute. Alveolar ventilation is different from pulmonary ventilation. Pulmonary ventilation – 6L of air moves in and out of respiratory tract every minute. But the whole volume of air is not fully utilized for gas exchange. Alveolar ventilation – volume of air subjected to gas exchange. Air trapped in the respiratory passage (dead space) does not take part in gas exchange. Calculation for Alveolar Ventilation Normal value of alveolar ventilation is 4200 ml (4.2 L)/min. It is calculated by formula: Alveolar Ventilation = (Tidal volume – dead space) x Respiratory rate = (500 – 150) ml x 12/min = 4200 ml (4.2 L)/min DEAD SPACE Part of respiratory tract, where gas exchange does not take place. Air present in dead space is called dead space air. Types of dead space: 1. Anatomical dead space 2. Physiological dead space Anatomical Dead Space Extends from nose up to terminal bronchiole. Includes nose, pharynx, trachea, bronchi and branches of bronchi up to terminal bronchioles. These structures serve only as the passage for air movement. Gas exchange does not take place in these structures Physiological Dead Space Includes anatomical dead space plus two additional volumes. Additional volume: 1. Air in the alveoli that are not functioning. In some respiratory diseases, alveoli do not function due to dysfunction or destruction of the alveolar membrane. 2. Air in the alveoli that do not receive adequate blood flow. Gas exchange do not take place during inadequate blood supply. These two additional volume = wasted ventilation. Normal Value of Dead Space Normal volume of dead space = 150 ml. Under normal conditions, physiological dead space is equal to anatomical dead space. All alveoli are functioning and all alveoli receive adequate blood flow in normal conditions. Physiological dead space increases during respiratory diseases, which affect the pulmonary blood flow or the alveoli. PERFUSION (Q) Refers to the flow of blood through the pulmonary capillaries. Enables the transport of oxygen from alveoli to tissues and the return of CO₂ to the lungs for exhalation. Maintained by the pulmonary circulation, a low- pressure, high-volume system. VENTILATION – PERFUSION RATIO Ventilation-perfusion ratio is the ratio of alveolar ventilation and amount of blood that perfuse the alveoli. a measure of the relationship between the amount of air entering the alveoli (V) and the amount of blood flowing through the capillaries surrounding the alveoli in the lungs (Q). Expressed as VA/Q VA = alveolar ventilation Q = blood flow (perfusion) Normal Value & Calculation (Ventilation-Perfusion Ratio) Normal value = 0.84 Alveolar ventilation is calculated by the formula:  SIGNIFICANCE OF VENTILATION-PERFUSION RATIO Ventilation-perfusion ratio signifies the gas exchange. It is affected if there is any change in alveolar ventilation or blood flow. Ventilation without perfusion = dead space (wasted air) Perfusion without ventilation = shunt (wasted blood) Thank you