Respiration: definition, mechanism.
Pulmonary & Alveolar Ventilation. Pulmonary volumes and capacities.
Dead space: physiological & anatomical,
Lung function test: name & significance.
Respiration: definition, mechanism.
Pulmonary & Alveolar Ventilation. Pulmonary volumes and capacities.
Dead space: physiological & anatomical,
Lung function test: name & significance.
Respiration: Respiration is a physiological process of inhaling and exhaling air between the lungs and the atmosphere.
Mechanism of Respiration:
The lungs can expand and contract in two main ways-
1) Downward and upward movement of the diaphragm increases and decreases the vertical diameter of the thoracic cavity.
Elevation and depression of the ribs by intercostal muscles increase and decrease the anteroposterior diameter of the thoracic cavity.
2) Pressure changes in the alveoli and pleural cavity.
Procedure of Respiration (1)
Inspiration: (Active process because muscles contract during this phase)
Diaphragm contracts and moves downward
↓
External intercostal muscles contract
↓
Thoracic volume increases
↓
Pressure inside alveoli becomes negative
↓
Air flows into the lungs
Expiration (Passive process because muscles relax during this phase)
Diaphragm and intercostal muscles relax
↓
Thoracic cavity returns to normal size
↓
Elastic recoil of lungs helps push air out
↓
Pressure inside lungs becomes slightly positive
↓
Air flows out of the lungs
Pulmonary Ventilation: The amount of new air taken into or out of the lungs in each minute.
(Respiratory rate × Tidal Volume)
Alveolar Ventilation: The rate at which new air reaches the alveoli and adjacent gas exchange area in each minute.
Respiratory rate × (Tidal volume - Dead space volume)
Pulmonary Volumes: Pulmonary volumes refer to the different volumes of air moved in and out of the lungs.
Tidal Volume (TV): Air inspired or expired with each normal breath. Normal Value: ~500 mL
Inspiratory Reserve Volume (IRV): Extra volume of air inspired forcefully after a normal inspiration. Normal Value: ~3000 mL
Expiratory Reserve Volume (ERV): Extra volume of air expired forcefully after a normal expiration. Normal Value: ~1100 mL
Residual Volume (RV): Air remaining in lungs after forceful expiration. Normal Value: ~1200 mL
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Pulmonary Capacities: Pulmonary capacities are the sum of two or more pulmonary volumes
Inspiratory Capacity (IC = TV + IRV): Maximum amount of air that can be inspired after normal expiration. Normal Value: ~3500 mL
Functional Residual Capacity (FRC = ERV + RV): Air remaining in lungs after normal expiration. Normal Value: ~2300 mL
Vital Capacity (VC = (IRV + ERV + TV): Maximum amount of air expelled after a full inspiration. Normal Value: ~4600 mL
Total Lung Capacity (TLC): Total volume of air in lungs after a maximal inspiration. Normal Value: ~5800 mL
Dead space: Dead space refers to the portion of the respiratory system where no gas exchange occurs
Anatomical: The volume of air present in the conducting zone of the respiratory tract, which does not participate in gas exchange. Nose, pharynx, larynx, trachea, bronchi, terminal bronchioles.... It is about 150ml for an adult. Measured by Fowler's method.
Physiological: The total volume of air in the respiratory system that does not participate in gas exchange, including both anatomical dead space and alveolar dead space. Measured by Bohr's method.
Definition: Lung function tests are the tests that are used to assess the functional status of the lungs in both physiological and pathological conditions.
Spirometry: It is a lung function test to measure the lung volumes and capacities using an instrument called a spirometer.
Main Parameters Measured by Spirometry: TV → IRV → ERV ; VC → IC → FVC → FEV₁ → FEV₁/FVC
RV – Residual Volume (not measured by spirometry). RV measured via Helium Dilution Method, Nitrogen Washout Method, Body Plethysmography (most accurate)