Pulmonary Pathophysiology

Histology of the lung

• Respiratory epithelium

• Connective tissue fibers, and cartilage:

support and maintain open air way

• Alveolar cells (type I and type II)

Capillary lumen

Type I pneumocyte Type I

pneumocyte

Type IIpneumocyte

Endothelium

Alveolar space

Normal Lung

Function of the lung

• Gas exchange

• Protection against infection by alveolar macrophages

• Surfactant secretion: allow expansion of alveoli with air

Lung function tests

• Tidal volume (TV): it is the amount of gas

inhaled or exhaled with each resting breath.

• Residual volume (RV): it is the amount of gas

remaining in the lungs at the end of maximum

exhalation.

• Vital capacity (VC): it is the total amount of

gas that can exhaled following maximum

inhalation.

• Total lung capacity (TLC): it is the amount of

gas in the lung at the end of maximum

inhalation.

TLC = RV+ VC

Reduction of Pulmonary Function

• Inadequate blood flow to the lungs:

hypoperfusion

• Inadequate air flow to the alveoli:

hypoventilation

Noso-comial infections

• Factors that reduce airflow also compromise

particle clearance and predispose to infection.

• High rate of pneumonia in hospital patients due

in large part to impaired ventilation and

clearance.

• Restricted lung movement and ventilation

may arise due to:

• Positioning

• Constricting bandages

• Central nervous system depression

• Coma

Signs and Symptoms of Pulmonary

Disease

1- Dyspnea: subjective sensation of uncomfortable

breathing, feeling “short of breath”

• Ranges from mild discomfort after exertion to

extreme difficulty breathing at rest.

• Usually caused by diffuse and extensive rather

than focal pulmonary disease.

Causes of Dyspnea :

– Airway obstruction

–Greater force needed to provide adequate

ventilation

–Wheezing sound due to air being forced

through airways narrowed due to constriction

or fluid accumulation

– Decreased compliance of lung tissue

Signs of dyspnea:

• Flaring nostrils

• Use of accessory muscles in breathing

• Retraction (pulling back) of intercostal spaces

2- Cough

• Attempt to clear the lower respiratory

passages by forceful expulsion of air

• Most common when fluid accumulates in

lower airways

Causes of Cough:

• Inflammation of lung tissue

• Increased secretion in response to mucosal irritation

• Inhalation of irritants

• Intrinsic source of mucosal disruption – such as tumor

invasion of bronchial wall

• Excessive blood hydrostatic pressure in pulmonary

capillaries

– Pulmonary edema – excess fluid passes into airways

• When cough can raise fluid into pharynx, the

cough is described as a productive cough, and

the fluid is sputum.

– Production of bloody sputum is called hemoptysis

• Not threatening, but can indicate a serious

pulmonary disease

–Tuberculosis, lung abscess, cancer, pulmonary

infarction.

• If sputum is purulent------- infection of lung or airway is

indicated.

• Cough that does not produce sputum is called a dry, or

nonproductive cough.

• Acute cough is one that resolves in 2-3 weeks from onset

of illness or treatment of underlying condition.

• Acute cough caused by upper respiratory tract (URT)

infections, allergic rhinitis, acute bronchitis, pneumonia,

congestive heart failure, pulmonary embolus, or

aspiration.

• A chronic cough is one that persists for more than

3 weeks.

• In nonsmokers, almost always due to postnasal

drainage syndrome, asthma, or gastroesophageal

reflux disease

• In smokers, chronic bronchitis is the most

common cause, although lung cancer should be

considered.

3- Cyanosis

• When blood contains a large amount of unoxygenated

hemoglobin, it has a dark red-blue color which gives skin a

characteristic bluish appearance.

• Most cases arise as a result of peripheral vasoconstriction –

result is reduced blood flow, which allows hemoglobin to give

up more of its oxygen to tissues- peripheral cyanosis.

• Best seen in nail beds

• Due to cold environment, anxiety, etc.

• Central cyanosis can be due to :

– Abnormalities of the respiratory membrane

– Mismatch between air flow and blood flow

– Expressed as a ratio of change in ventilation (V) to

perfusion (Q) : V/Q ratio

• Pulmonary thromboembolus ---- reduced blood

flow

• Airway obstruction ---- reduced ventilation

• In persons with dark skin can be seen in the whites of the

eyes and mucous membranes.

• Lack of cyanosis does not mean oxygenation is normal!!

• In adults not evident until severe hypoxemia is

present

• Clinically observable when reduced hemoglobin

levels reach 5 g/ dl.

• Severe anemia and carbon monoxide poisoning give

inadequate oxygenation of tissues without cyanosis

• Individuals with polycythemia may have cyanosis

when oxygenation is adequate.

4- Pain

• Originates in pleurae, airways or chest wall

• Inflammation of the parietal pleura causes sharp or

stabbing pain when pleura stretches during inspiration

– Usually localized to an area of the chest wall, where a

pleural friction rub can be heard

– Laughing or coughing makes pain worse

– Common with pulmonary infarction due to embolism

• Inflammation of trachea or bronchi produce a

central chest pain that is pronounced after

coughing

– Must be differentiated from cardiac pain

• High blood pressure in the pulmonary circulation

can cause pain during exercise that often

mistaken for cardiac pain (angina pectoris).

5- Clubbing

• The selective bulbous enlargement of the end of a digit

(finger or toe).

• Usually painless

• Commonly associated with diseases

that cause decreased oxygenation

– Lung cancer

– Cystic fibrosis

– Lung abscess

– Congenital heart disease

Infectious Diseases of

The Lungs

Introduction:

• Daily 10,000 liters of air - filtered..!

• Pneumonia: Inflammation of lung.

• Respiratory tract infections – commonest in medical

practice.

• Enormous morbidity & mortality.

Etiology:

• Decreased general resistance

• Virulent infection - Lobar pneumonia

• Clearing mechanism

– Decreased Cough Reflex

– Injury of the cilia and mucosa

– Low alveolar defense

– Pulmonary edema or congestion

– Obstructions

– Retention of secretions

Types:

• Viral• Bacterial• Mycoplasmal• Fungal

Patterns of infections:

• Airway - Bronchitis, Bronchiectasis

• Parenchyma

– Pneumonia

• Bronchopneumonia

• Lobar pneumonia

– Lung abscess

– Tuberculosis

Pneumonia

• Pathology:

– Alveolar

• Bronchopneumonia (Streptococcus pneumoniae, Haemophilus

influenza, Staphylococcus aureus)

• Lobar (Streptococcus pneumoniae)

– Interstitial (Influenza virus, Mycoplasma pneumoniae)

• Pathogenesis

– Inhalation of air droplets

– Aspiration of infected secretions or objects

– Hematogenous spread

Bronchopneumonia

• Suppurative inflammation of lung tissue caused by

Staph, Strep, Pneumo & H. influenza

• Patchy consolidation – not limited to lobes.

• Usually bilateral

• Lower lobes common, but can occur anywhere

• Complications:

– Abscess

– Empyema

– Dissemination

Broncho-pneumonia

Broncho-pneumonia

Broncho-pneumonia

Bronchopneumonia:

Bronchopneumonia

Lobar Pneumonia:

• Fibrinosuppurative consolidation – whole lobe

• Rare due to antibiotic treatment.

• ~95% - Strep pneumoniae

• The course runs in four stages:

– Congestion.

– Red Hepatization.

– Gray Hepatizaiton.

– Resolution.

Lobar pneumonia

Lobar pneumonia: whole lobe(s) involved

Fixed specimen, grey hepatization

Lobar Pneumonia:

Lobar Pneumonia – Gray hep…

Lung Abscess:• Focal suppuration with necrosis of lung tissue• Organisms commonly cultured:

– Staphylococci– Streptococci– Gram-negative– Anaerobes– Frequent mixed infections

• Mechanism:– Aspiration

– Post pneumonic

– Septic embolism

– Neoplasms

• Productive Cough, fever.

• Clubbing

• Complications: Systemic spread, septicemia.

Lung Abscess:

Abscess formation

Bronchopneumonia - Abscess formation

Lung Abscess:

Pulmonary tuberculosis

• Caused by Mycobacterium tuberculosis.

• Transmitted through inhalation of infected droplets

• Primary

– Single granuloma within parenchyma and hilar

lymph nodes (Ghon complex).

• Infection does not progress (most common).

• Progressive primary pneumonia

• Miliary dissemination (blood stream).

Ghon complex

Pulmonary tuberculosis

• Secondary

– Infection (mostly through reactivation) in a

previously sensitized individual.

– Pathology

• Cavitary fibrocaseous lesions

• Bronchopneumonia

• Miliary TB

Fibrocaseous

Granuloma

Miliary TB

Opportunistic pneumonias

• Infections that affect immunosuppressed patients

• Associated disorders:

– AIDS

– Iatrogenic

• Cancer patients

• Transplant recipients

Usual interstitial pneumonia / idiopathic pulmonary fibrosis

• Progressive fibrosing disorder of unknown cause

• Adults 30 to 50 years old

• Respiratory and heart failure (cor pulmonale) ~ 5 y