Mechanics of Breathing

Intra-alveolar pressure (PA): The pressure within the alveoli
Intra-pleural pressure: The pressure within the pleural cavity
Atmospheric pressure (PB): The pressure exerted by the weight of air in the atmosphere

Boyle’s Law: At a constant temperature, the pressure of a gas decreases as the volume increases and vice versa.
- Inspiration:
- The pressure within the alveoli is lower than atmospheric pressure, allowing air to flow into the lungs.
- Expiration:
- The pressure within the alveoli is higher than atmospheric pressure, forcing air out of the lungs.

Muscle Contraction: The act of inspiration involves the contraction of several muscles which create changes in thoracic volume.
Mechanisms:
- Bucket Handle Movement: Elevation of lateral shafts of the ribs increases thoracic volume.
- Pump Handle Movement: Superior and anterior movement of the sternum also contributes to thoracic volume increase.

Muscles Involved:
- Sternocleidomastoid: Assists in elevating the sternum.
- Pectoralis Minor: Aids in the elevation of the ribs.
- External Intercostal Muscles: Contract to elevate the ribs, increasing thoracic volume.
- Diaphragm: Contracts, increasing vertical diameter of thorax.
Factors Promoting Inspiration:
- Relaxation of expiratory muscles.
- Contraction of chest-elevating muscles.
- Increase in vertical diameter of thorax.
- Increase in anteroposterior and transverse dimensions of the thorax.
- Decrease in intrapleural (intrathoracic) pressure.
- Cohesion of visceral and parietal pleurae.
- Compliance of thorax and lungs allows lung expansion.
- Establishment of a pressure gradient from atmosphere to alveoli as alveolar pressure decreases.

Factors That Promote Expiration:
- Relaxation of inspiratory muscles.
- Contraction of expiratory muscles.
- Decrease in size of the thorax due to muscle relaxation.
- Elastic recoil of lung tissue aids in expiration.
- Increase in intrapleural (intrathoracic) pressure as lungs decrease in size.
- Increase in alveolar pressure leads to pressure gradient going from alveoli to atmosphere.
Muscles Involved:
- Internal Intercostal Muscles: Contract to decrease thoracic volume.
- Diaphragm: Relaxes during expiration.
- Abdominal Muscles: Contract to aid in expelling air.

Spirometry: A method used to measure lung volumes.
Volumes:
- Inspiratory Reserve Volume (IRV): Additional amount of air that can be inhaled after a normal inhalation.
- Tidal Volume (VT): Amount of air inhaled or exhaled during normal breathing.
- Expiratory Reserve Volume (ERV): Additional amount of air that can be exhaled after a normal exhalation.
- Residual Volume (RV): Amount of air remaining in the lungs after a complete exhalation.
- Inspiratory Capacity (IC): Total amount of air that can be inhaled after a normal expiration, calculated as IRV + VT.
- Functional Residual Capacity (FRC): Amount of air left in the lungs after a normal exhalation, calculated as ERV + RV.
- Vital Capacity (VC): Maximum amount of air that can be exhaled after maximum inhalation, calculated as IRV + VT + ERV.
- Total Lung Capacity (TLC): Maximum amount of air contained in lungs, calculated as VC + RV.

Eupnea: Normal breathing pattern.
Hyperventilation: Characterized by rapid and deep respirations.
Hypoventilation: Characterized by slow and shallow respirations.
Apnea: Cessation of respirations.
Cheyne-Stokes Respiration: Alternating periods of apnea and hyperventilation.
Biot's Breathing: Repeated sequences of deep gasps followed by apnea.

Efficient Combination: Each alveolus is well-ventilated with air and well-perfused with blood.
Inefficient Arrangement: If ventilation to an alveolus is obstructed but blood perfusion remains unchanged, it leads to low Po_2 since blood is not being fully oxygenated.
Vasoconstriction Response: In cases of poor ventilation, vasoconstriction of the pulmonary arteriole to the affected alveolus reduces blood perfusion, ensuring more efficient matching between ventilation and perfusion.

Description of hiccup and its sudden involuntary inhalation followed by a closed vocal cords closure which produces a sound.

Chronic Bronchitis: Narrowing of air tubes due to swollen tissues and excessive mucus production. Enlarged submucosal glands are involved.
Asthma: Inflammation of the epithelial lining of the bronchi, smooth muscle constriction, and edema of the respiratory mucosa contribute to airway obstruction.
Emphysema: Characterized by the enlargement and destruction of alveolar walls, leading to damaged lung tissue that cannot be repaired. Hyperinflation and fusion of alveoli into large air spaces occurs, causing significant obstruction.