L4 Ventilation Perfusion Matching and Dead Space Notes PDF

L4 Ventilation perfusion matching and dead space Dead space Factor affecting the volume of dead space Definition: The volume of air in the respiratory passages that does not undergo 1.Sympathetic stimulation gases exchange with the blood. → bronchodilation → increase the volume of dead space. Dead s...

L4 Ventilation perfusion matching and dead space Dead space Factor affecting the volume of dead space Definition: The volume of air in the respiratory passages that does not undergo 1.Sympathetic stimulation gases exchange with the blood. → bronchodilation → increase the volume of dead space. Dead space= 150ml 2.Parasympathetic stimulation What is the relationship of dead space and → bronchoconstriction→ decrease the volume of dead space. conducting zone??? Types of Dead Space Importance of dead space 1-Anatomical dead space 1.Warm , moist, and filter the inspired air. air present in conducting zone (from nose to terminal bronchiole) where gaseous exchange does not take part. 2.It causes the difference in composition between the alveolar air and expired air. 2- Alveolar dead space Presents in non-functional alveoli-of poor blood supply Dead Space 3- Physiological dead space Anatomical dead space + alveolar dead space Normally , there is no alveolar dead space because all alveoli are functioning 3.Regulates the resistance to air flow. 4.It is responsible for the difference between pulmonary ventilation and alveolar ventilation So, Anatomical dead space = Physiological dead space Alveolar ventilation Pulmonary ventilation Definition: It is the volume of air reaching the alveoli per minute. Alveolar ventilation = Tidal volume - Dead space x Respiratory rate Definition: It is the volume of air breathed in or out in one minute. Pulmonary ventilation = Tidal volume x Respiratory rate = 500 ml x 12 = 6L /min during rest Pulmonary ventilation= Minute ventilation= Minute respiratory volume Which is important pulmonary ventilation or alveolar ventilation? Alveolar ventilation. It is an indicator of gas exchange = 500 ml - 150 = 350 = 4.2 L /min during rest. x x 12 12 Factor affecting alveolar ventilation 1.Rate and depth of breathing: shallow rapid breathing → decrease alveolar ventilation 2.Volume of the dead space: increased dead space → decrease alveolar ventilation In case of hypoxia (decrease O2), the alveolar ventilation is decrease while pulmonary ventilation is normal as in 1- Shallow rapid breathing 2- Increased alveolar dead space Pulmonary Perfusion Pulmonary perfusion is the flow of blood through pulmonary capillaries. Inside the lung there are 3 zone (In standing position) 1. Zone 1: No blood flow because alveolar pressure > pulmonary capillary pressure. 2. Zone 2: Intermittent blood flow, The blood flow occurs only in systolic blood pressure. 3. Zone 3: Continuous blood flow, The blood flow occurs during the cardiac cycle (during systolic blood pressure Zone 1 blood flow occurs only under abnormal conditions. 1- Increased intra-alveolar pressure (Alveolar inflammation and alveolar edema). and diastolic blood pressure) 2- Marked decrease in blood flow Normally, Lung contains only Zone 2 and 3 Zone 3 right-side heart failure At Apex of the lung: little blood flow At base of the lung: five times increase in the blood flow. as in sever blood loss or Ventilation Perfusion Ratio (VA/Q) Alveolar ventilation VA = 4 L/min. Pulmonary perfusion Q = cardiac output = 5 L/min. So, Ventilation Perfusion Ratio(VA/Q) = 4/5= 0.8. However, the ventilation and the perfusion are not equal throughout the lung in standing position. In the Figure: Ventilation is decrease from Base (Bottom) to the apex (Top) of the lung. Perfusion is Markedly decrease from base to the apex of the lung At the apex of the lung: At the apex of the lung , there is much more ventilation than perfusion. Ventilation > perfusion. VA/Q = 3 At the base of the lung, there is much more perfusion than ventilation. Average VA/Q = 0.8 At the base of the lung: Perfusion > ventilation. VA/Q = 0.6 Causes of Pathological Ventilation Perfusion Ratio (VA/Q) High V/Q ratio: Pulmonary thrombi or emboli→ less perfusion → decreased gas exchange. Emphysema → high ventilation→ decreased gas exchange. For health lung , the body needs adequate ventilation and perfusion in order to maintain adequate gas exchange Low V/Q ratio: Bronchial asthma →less ventilation → decreased gas exchange. Lung scintigraphy, or ventilation-perfusion (V/Q) scan, is one of the commonly performed studies in nuclear medicine. A V/Q scan consists of two portions, the V or ventilation portion and the Q or perfusion portion.(Derenoncourt et al., 2021) Uses: 1. pulmonary embolism. 2. Emphysema