Basic Pulmonary Anatomy and Physiology

 

In good health the human respiratory system functions with precision and adaptability, accepting oxygen and emitting carbon dioxide via immaculate feedback loops, a safe haven in multifarious environments.  

 

In the periphery of the lungs, miniscule alveoli, the "grapes" of the respiratory tree, receive inspired air.  In these tiny sacs oxygen molecules flow across alveolar epithelial cells into the pulmonary interstitium, a potential space composed of   supportive connective tissue-the "skeleton" of the lung.  Oxygen enters alveolar capillaries' red corpuscles, and is pumped by the heart to the body's organs.^{See  URL 1}

  

Pathophysiology of Interstitial Lung Disease

 

Obliged to inhale atmospheric gases for survival, humans risk air-borne attacks on the pulmonary interstitium by smoke, dust, pollen, viruses, bacteria, fungi, and other ethereal pathogens. 

 

The middle layer of the lung is also vulnerable to blood-borne assault, by autoantibodies, deranged T-cells, circulating drugs like amiodarone, nitrofurantoin, NSAIDs, and anti-neoplastic agents.

 

Inhalation of tobacco combustion products causes significant lung disease and respiratory mortality in the USA.  Cigarette smoking affects the airways, causing lung cancer, asthma, and chronic obstructive pulmonary disease (COPD).  

 

In the alveoli it destroys epithelial cells, reducing oxygen-absorbing surface area, producing emphysema, a factor in the progression of COPD.  Cigarette smoking induces various types of interstitial pneumonitis. 

 

Invasion of the lung by foreign matter provokes an immunological counterattack, creating a battlefield-inflammation, bashing intruders, burning innocent bystanders. 

 

2400 years ago Hippocrates described and treated phlegm-in Greek, "inflammation."   he postulated four vital humors-blood, black bile, yellow bile, and phlegm-which, if kept in balance, promoted good physical and psychiatric health. 

 

In the first century Celsus recorded four classic signs of inflammation: calor, rubor, dolor, and turgor (heat or fever, redness, pain, and swelling).  He phlebotomized patients with signs of inflammation, to remove excess amounts of blood seen in the fever and ruddy complexion.

 

Interstial Lung Disease

 

The suffix "itis" indicates "inflammation in medical terminology.  Interstitial pneumonitis is identified microscopically as an inflammatory infiltrate composed of fibrocytes, lymphocytes, and macrophages filling the pulmonary interstitium^{See URL 2} 

 

Interstitial Lung Disease (ILD) is a spectrum of pulmonary diseases sharing certain features yet each phylogenetically unique.  Elucidation of the etiology and pathophysiology of these disorders remains problematic. 

 

Discovered in 1965, pulmonary diseases of the interstitium have undergone intensive research and attempts at classification, often leading to the confirmation of the label idiopathic (in essence "I don't know what it is.").

 

Table 1. Interstitial Lung Diseases Associated with Cigarette Smoking

 

Disease	People Affected	% Smokers	Treatment	Outlook
IPF	Men over 60	More than 60%	Lung transplant	50-70% die within 5 yrs.
DIP	Men 40-50	More than 90%	Quit tobacco, corticosteroids	<10% die within 5 yrs.
RB-ILD	People 40-50	More than 90%	Quit tobacco, corticosteroids	Death is rare from this disease
PLCH	Whites 20-40	> 99%	Quit tobacco, + corticosteroids, immunosuppressives, lung transplant	75% 5-yr survival

 

IPF = Idiopathic Pulmonary Fibrosis; DIP = Desquamative Interstitial Pneumonia; RB-ILD = Respiratory Bronchiolitis associated Interstitial Lung Disease; PLCH = Pulmonary Langerhans' Cell HistiocytosisHH.  Other ILDs are associated with lower smoking rates.

 

As seen in Table 1, some ILDs respond favorably to smoking cessation. Those of unknown etiology, such as AIP (Acute Interstitial Pneumonia) are resistant to treatment.  AIP afflicts men and women equally at ages > 40.

 

ILDs result from toxic effects of ionizing radiation prescribed therapeutically for malignant neoplasms in or near a lung.  Rays penetrating body layers traumatize living matter in vulnerable, radiolucent lungs.

 

An immunological attack on "self," found in "collagen vascular" disease states, can  cause interstitial pneumonitis.  Rheumatoid arthritis alone or with methotrexate  is etiologic in some interstitial pneumonias, also witnessed in systemic lupus erythematosus (SLE), scleroderma, dermatomyositis,  ankylosing spondylitis, and other autoimmune disorders.

 

Idiopathic Pulmonary Fibrosis

 

Five million worldwide and 200,000 people alive in the USA today suffer from the most common ILD, idiopathic pulmonary fibrosis (IPF).  In previous decades and sometimes now it is called usual interstitial pneumonia (UIP).^[1] 

 

IPF has no known cause and no curative treatment.  Appropriate candidates may respond initially to transplantation of a single lung, but 5-year survival is low.

 

Sixty percent of patients suffering from IPF are smokers or have been significant cigarette smokers earlier in life.  An elegant case-control study by Baumgartner showed the risk of developing IPF in 21 to 40 pack-year smokers was 2.3 times that of nonsmokers, and that of former smokers to be 1.9 times ever nonsmokers.^[2]

 

The Clinical Picture-IPF

 

In common with other ILDs, IPF presents with shortness of breath and a dry cough.  Physical signs include dry, "Velcro"-like râles (crackles) on chest auscultation and clubbing (spongy swelling of fingertips, toenail pulps and nails). ^{See URL 3}

    

Pulmonary function testing reveals restriction (loss of volume).  The carbon monoxide (CO) diffusion capacity is reduced, indicating a hindrance of gas exchange across the alveolar walls from fibrosis and inflammation.

 

The arterial blood gas measurement reveals hypoxemia (reduced arterial blood oxygen tension).

 

Laboratory testing may show AntiNuclear Antibodies, elevated Erythrocyte Sedimentation Rate, Rheumatoid Factor, CRP and other indicators of inflammation.

 

A chest xray often shows "honey-combed" interstitial infiltrates, especially in the lower lobes, and cysts, especially in the upper lobes. 

 

High Resolution Computerized Tomography often defines the disease process.  Dense fibrous tissue encases the lungs' structures, with large cysts. ^{See URL 4}

   

BronchoAlveolar Lavage, performed during a bronchoscopy often returns fluid containing inflammatory cells.  If needed, a transbronchial biopsy for histopathological diagnosis may also be performed during fiberoptic bronchoscopy. 

 

If a larger sample of lung tissue is needed, transthoracoscopy (placing a scope through the rib cage into the pleural space) allows direct visualization and biopsy of the lung and assists in clinicopathologic classification.

 

Treatment of IPF

 

In its early stages, IPF may be asymptomatic or denied, accepted as a "smoker's cough."  It is possible that early stages of IPF are like DIP or RB-ILD, which abort with smoking cessation. 

 

As the disease progresses, oxygen exchange becomes embarrassed, leading to disability and medical consultation.  At the time of initial diagnosis survival is  three to five years or less.

 

Perusal of IPF medical literature concerning treatment renders variable reviews concerning smoking cessation.

 

IPF at any stage will benefit from smoking cessation.  Not the least benefit will be a marked reduction in inhaled CO, raising aerobic power.  In urban environs, cigarette smoking cessation lowers a smoker's blood CO by 7.5 percent or more, attaining the nonsmoking urbanite's level of 1.5%.

 

Conclusion

 

ILD is an evolving classification of linked-unique lung diseases.  Association of varied potential etiologic agents with the ILD spectrum has provided a methodological approach to diagnosis and treatment over past decades. 

 

Where possible, prevention and vigilance reduce morbidity and mortality of ILDs.  Ongoing study of IPF and AIP should prove fruitful in this era of genetic enlightenment and cyberspace.  Today smoking cessation offers hope in the "smoking associated" interstitial pneumonitides.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hypertext URLs

 

[1] http://www.patient.co.uk/health/Idiopathic-Pulmonary-Fibrosis.htm

 

 

[2] http://en.wikipedia.org/wiki/File:Usual_interstitial_pneumonia_(1).JPG

 

[3] http://www.google.com/imgres?imgurl=http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/18127.jpg&imgrefurl=http://www.nlm.nih.gov/medlineplus/ency/imagepages/18127.htm&h=320&w=400&sz=18&tbnid=DDFP8r0QyAQ31M:&tbnh=99&tbnw=124&prev=/images%3Fq%3Dphoto%2Bof%2Bclubbing%2Bof%2Bthe%2Bfingers&usg=__Lt-82FitIKSgN7DrCzilzNzu624=&ei=OtbXSo2IOY7KsAO-ms2ZBg&sa=X&oi=image_result&resnum=1&ct=image&ved=0CA0Q9QEwAA

 

 

[4] http://upload.wikimedia.org/wikipedia/commons/8/81/Pulmon_fibrosis.PNG

 

 

 

References

 

 

[1] Cecil Textbook of Internal Medicine 1979 p. 978.

 

 

[2] Baumgartner, Am J Respir Crit Care Med. 1997 Jan;155(1):242-8.

 

 

 

 

 

Notes: [1] Cecil Textbook of Internal Medicine 1979 p. 978. [2] Baumgartner, Am J Respir Crit Care Med. 1997 Jan;155(1):242-8.

[Watch page ]

EditText of this page (last edited November 16, 2009)