Blood flow is equivalent to cardiac output ( ∼ 5 L/min).In healthy individuals the resistance is low and the compliance is high.P L at rium = left atrial pressure ( pulmonary capillary wedge pressure).P pulm ar tery = pulmonary artery pressure.Pulmonary vascular resistance ( PVR): the resistance offered by the pulmonary circulatory system that must be overcome to create blood flow.Mean pulmonary arterial pressure ( mPAP): normal 10–14 mmHg.Use full-body plethysmography or a gas dilution test. Residual volume cannot be measured by spirometry. Volume of air that remains in the lungs after the exhalation of a norm al TV.Maximum volume of air that can be exhaled after the inspiration of a normal TV.Maximum volume of air that can still be forcibly exhaled after the exhalation of a normal TV.Maximum volume of air that can be inhaled after the exhalation of a normal TV.Maximum volume of air that can still be forcibly inhaled following the inhalation of a normal TV.Volume of air that is inhaled and exhaled in a normal breath at rest.Volume of air that remains in the lungs after a maximal exhalation.Difference in lung volume between maximal exhalation and maximal inhalation.Volume of air in the lungs after maxim al inhalation.V D is greater than anatomic dead space in diseases with a V/Q mismatch (e.g., pulmonary embolism ). Volume of gas that reaches the alveoli each minute.In a healthy lung, V D equals the anatomic dead space (normal value: approx.Bohr equation determines the physiologic dead space: V D = V T x ( PaCO 2 - PeCO 2)/( PaCO 2).Alveolar dead space : the sum of the volumes of alveoli that do not participate in gas exchange (mainly apex of the lungs ) These alveoli are ventilated but not perfused.Anatomic dead space : the volume of air in the conducting zone, e.g., mouth, trachea ( approx.V D is the sum of the anatomic dead space and the alveolar dead space.Physiologic dead space (V D): volume of inspired air that does not participate in gas exchang e.Volume of air that a person breathes per minute.Tidal volume ( V T): the volume of air that is inspired or expired in a single breath.Respiratory rate (RR): number of breaths per minute.See “ Chest wall dynamics” for details.Intrathoracic pressure becomes positive to expel the air ( passive elastic recoil of the lungs).passive elastic recoil of the lungs) but expiratory muscles (e.g., intercostal muscles, subcostal muscles) can assist. Expiration is primarily a passive process (i.e.Air reaches the respiratory zone of the respiratory tree (site of gas exchange): respiratory bronchioles → alveolar ducts → alveoli.Intrathoracic pressure becomes even more negative to fill the lungs with air.Inspiratory muscles (mainly external intercostal muscles and the diaphragm) elevate the ribs and sternum and increase the intrathoracic volume.Inspiration of air into the conducting zone of the respiratory tree ( anatomic dead space): nose → pharynx → larynx → trachea → bronchi → bronchioles → terminal bronchioles. Definition: movement of air through the respiratory tract into (inspiration) and out of (expiration) the respiratory zone ( lungs) to facilitate gas exchange (O 2 and CO 2).Inspiration is an active process driven by the respiratory musculature while expiration is passive at rest, driven by the elastic properties of lung tissue. Central regulation of respiration is provided by the respiratory center located in the reticular formation of the medulla oblongata and pons. CO 2 diffuses into the alveoli and is exhaled. In the capillaries, oxygen binds to hemoglobin in erythrocytes or dissolves into the plasma (oxygenation). The gases diffuse across the barrier following pressure gradients. Gas exchange occurs via simple diffusion across the blood-air barrier. Diseases that affect the perfusion (e.g., pulmonary embolism) or ventilation (e.g., foreign body aspiration) can cause a V/Q mismatch. The Euler-Liljestrand mechanism regulates the perfusion of nonventilated alveoli: if a lung section is perfused but not ventilated, there will be a drop in the oxygen concentration in the blood, resulting in hypoxic vasoconstriction. The ventilation-perfusion ratio is higher in the apex of the lung than at its base. Perfusion of the pulmonary capillaries is closely regulated to match ventilation in order to maximize gas exchange. The physiologic dead space is the volume of inspired air that does not participate in gas exchange. Ventilation is the movement of air through the respiratory tract into (inspiration) and out of (expiration) the respiratory zone ( lungs). The main function of the respiratory system is gas exchange (O 2 and CO 2).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |