Ch 13.2A -- Respiratory Mechanics -- VTPP 435

Ch 13.2A -- Respiratory Mechanics -- VTPP 435

3 Pressure Consideratiosn important in Ventilation

1) Atmospheric (barometric) pressure
2) Intra-alveolar Pressure
3) Intrapleural Pressure

Atmospheric (Barometric) Pressure

-pressure exerted by weight of air in atmosphere on objects on Earth's surface

Intra-alveolar Pressure

-pressure within alveoli
-involved with pressure gradient between it and atmosphere

Intrapleural Pressure

-pressure within pleural sac
-does not equilibrate with atmospheric or intra-alveolar pressure
-in a closed sac with no opening so air does not leave
-is sub atmospheric

Transmural Pressure Gradient

-pressure difference across lung wall that stretches lungs to fill thoracic cavity which is larger than unstretched lungs

Pneumothorax

-abnormal condition of air in pleural cavity
-all 3 pressures are equilibrated
-transmural pressure gradient no longer exists
-lung collapses to unstretched size

Inspiratory Muscles

-skeletal muscles whose contraction enlarges thoracic cavity
-causes lung expansion and movement of air into lungs
-Diaphragm and external intercostal muscles

Diaphragm

-major inspiratory muscle
-innervated by Phrenic Nerve
-descends downward when contracts on stimulation from nerve

External Intercostal Muscles

-inspiratory muscles
-contraction elevates ribs thereby enlarging thoracic cavity
-elevates ribs and sternum

Internal Intercostal Muscles

-expiratory muscles
-contraction pulls ribs downward and inward to reduce cavity size
-flattens chest wal

Intercostal Nerves

-activate external intercostal muscles during inspiration

Accessory Inspiratory Muscles

-are in neck
-contraction raises sternum and elevates first 2 ribs to enlarge upper portion of thoracic cavity for a more forceful contraction

Expiratory Muscles

-skeletal muscles
-contraction reduces size of thoracic cavity
-lets lungs recoil to a smaller size

Bronchoconstriction and Bronchodilation

-Constriction brought by Parasympathetic stimulation
-Dilation brought by sympathetic stimulation

Chronic Obstructive Pulmonary Disease (COPD)

-group of lung diseases
-characterized by increased airway resistance due ot narrowing of lower airways
-3 diseases: Chronic Bronchitis, Asthma, Emphysema

Chronic Bronchitis

-long term inflammatory condition of lower respiratory airways
-triggered by frequent exposure to cigarette smoke, polluted air, or allergens
-airways narrow due to prolonged edematous thickening of airway lining and over producing mucus

Asthma

-airway obstruction
-could cause all clogging and narrowing that cuts off all air
-triggers: repeated exposure to allergens, irritants, respiratory infections, vigorous exercise

Asthma Potential Causes

1. thickening of airway walls due to inflammation or histamine induced edema
2. Plugging of airways by excessive mucus secretion
3. Airway hyperresponsiveness with profound constriction of smaller airways triggered by spasm of smooth muscle in walls of airways

Emphysema

-collapse of smaller airways
-breakdown of alveolar walls
-mostly commonly caused by excessive release of protein digestive enzymes and lack of alpha 1-antitrypsin to inhibit trpysin