Tuesday, January 22, 2008

What is it about your cough?

A cough reflex is actually an attempt by the body to clear excess secretions, mucous, inhaled irritants, toxins and foreign materials from the airways. It is a natural expulsive defence mechanism of the body that protects the respiratory sytem by clearing it voluntarily or involuntarily. Thus, cough should not be stopped or held back.

The sequence of events in a cough reflex:

Inhalation to a high lung volume -> closure of the glottis -> contraction of the expiratory muscles (generating high positive intrathoracic pressure) -> opening of the glottis -> high velocity expulsion of air through the airways -> continued contraction of the expiratory muscles.

The diagram below shows the 4 stages in a cough reflex.

It is noteworthy to bare in mind that any conditions such as those causing weakness of the expiratory muscles, vocal cord pathology or tracheostomies causes impairment in the ability of the body to clear their airways effectively.

An occasional cough is normal as it helps clear foreign substances and secretions from the lungs and helps prevent infections.

Based on the type of we can generally classify cough into:

1.Dry cough - cough that does not bring up any sputum during expulsion
2.Productive cough - cough that brings up sputum or mucus during expulsion

Based on the duration of the cough it is generally accepted that a cough that lasts more than 3 weeks can be considered as chronic cough, although there are some quarters who feel that not every prolonged cough that last more than 3 weeks can be considered as chronic. I will not dig any deeper into it's technicalities in this post (Google it!). Let's try to see the possible causes of chronic cough as there has been a rise in such cases in our primary health care centers.

Among the common causes of chronic cough:

1. Postnasal drip caused by chronic rhinitis and sinusitis

Glands in your nose and throat produce a quart or two of mucus, which cleans and moisturizes our nasal passages. Normally, we swallow the fluid without knowing it, but in rhinitis, the cells lining the nasal passages becomes inflammed and swollen. It then start producing mucus in extensive amounts. The excess mucus then accumulates behind the nose and descend down the throat. This is called postnasal drip and can cause irritation and inflammation that triggers your cough reflex.

Patients with cough due to this condition will typically have frequent clearing of their throat during the day, will complain of cough when talking for prolonged periods of time or when laughing, and will often have worse cough when they first lie down at night.

If the postnasal drip is chronic, your cough is likely to become chronic, too. Though postnasal drip is often obvious, it's possible to have the condition without ever having symptoms.

Sinuses are air filled spaces situated in our skull. The main sinuses are :
Frontal sinus in the forehead, Ethmoid sinus between our eyes, Maxillary sinus in our cheek bones and Sphenoid sinus at the back of the nose.

Sinusitis, similar to rhinitis, is a condition where the cells lining the sinus gets inflammed, swollen and starts producing excessive mucus, which in turn descends down behind the throat, leading to post nasal drip.

There is also a condition called rhino sinusitis which is the combination of both the conditions above.

Common triggers of rhinitis sinusitis:

  • Inhaled irritants such as dust, smog, smoke.

  • Food allergies. Common food that causes allergy are nuts, eggs, wheat, milk and dairy products, soy products, seeds, sea food with shell, etc.

  • Illnesses; Such as flu, colds, bronchitis, ear infections, tonsillitis and asthma

N.B: In asthma, not only does the excess mucus lead to an asthma attack, but it also causes a sufferer to start breathing through the mouth taking in non-filtered, non humidified and cold air. This in turn can trigger and worsens the asthma attack.

2. Asthma

This is a common cause of chronic cough in adults and in children. The cough commonly occurs with wheezing and shortness of breath. The absence of wheezing on the other hand does not mean that the person is not having an asthma attack. There is a type of asthma, sometimes referred to as cough variant asthma, where cough is the only symptom. An asthma-related cough may be seasonal or caused by an upper respiratory tract infection, or exposure to cold air, chemicals or fragrances.

3. Gastroesophageal reflux disease (GERD)

Here there is a back flow of the stomach acid upwards along the esophagus that constantly causes irritation in the esophagus, throat and even the lungs that leads to chronic coughing, heartburn and sour taste behind the tongue. There is also cough that is caused by asymptomatic GERD.

Reflux of acid to the posterior pharynx may cause inflammation and edema of the vocal cords. In some cases, patients will have recurrent aspiration with a consequent low-grade chemical pneumonitis (inflammation of the lung tissue) in the lungs.Finally, GERD may lead to cough by provoking bronchospasm (narrowing of the bonchus, the main airway tube). Acid in the esophagus can induce bronchospasm in patients with asthma via reflex mechanism mediated by the vagus nerve.

4. Respiratory tract infection

A respiratory tract infection almost always cause inflammation of the cells that line the airways. This does to a certain extent make it sensitive to irritants, which in turn triggers a cough reflex.

Other not so common causes of chronic cough:

1. Blood pressure drugs

Chronic cough is a notorious side effect of a group of anti-hypertensive drugs (blood pressure drugs) known as Angiotensin-Converting Enzyme (ACE) inhibitors. This side effect is more apparent among the Asian population and can begin from within a week to even more than six months after starting therapy.

2. Chronic bronchitis

This is long-standing inflammation of the major airways (bronchial tubes) which can cause congestion, breathlessness, wheezing and a cough. This can be caused by infection or in chronic smokers who's airways have been damaged.

3. Bronchiectasis

This is a serious, chronic lung condition in which abnormal widening of your bronchus affects their ability to clear mucus from your lungs. Signs and symptoms include a cough that may bring up discolored sputum or blood, shortness of breath and fatigue. In bronchiectasis, areas of the bronchial wall are destroyed and become chronically inflamed, ciliated cells are damaged or destroyed, and secretions (mucus) accumulate. Also, the bronchial wall becomes less elastic—the affected airways become wider and flabby and may develop outpouchings or sacs that resemble tiny balloons.

The most common cause of this condition is severe respiratory infections. Also can be caused by immune deficiency disorders, hereditary disorders (such as cystic fibrosis), mechanical factors (such as bronchial obstruction caused by an inhaled object, a lung tumor, or other disorders) and from inhaling toxic substances that injure the bronchi, such as noxious fumes, gases, smoke (including tobacco smoke), and injurious dust (silica, coal dust).

4. Lung cancer

This is relatively uncommon. Only a small percentage of people with a chronic cough have lung cancer, and most are current or former smokers. If you smoke now, smoked at one time or your sputum contains blood, see your doctor.

Medical myths

I received this via email update today. Thought it would make an interesting read:

Medical Myths

by Rachel C Vreeman, fellow in children’s health services research1, Aaron E Carroll, assistant professor of paediatrics2 1 Children’s Health Services Research, Indiana University School of Medicine, Indianapolis, IN, USA, 2 Regenstrief Institute, Indianapolis, IN, USA Correspondence to:R C Vreeman

Sometimes even doctors are duped, say Rachel C Vreeman and Aaron E Carroll. Physicians understand that practicing good medicine requires the constant acquisition of new knowledge, though they often assume their existing medical beliefs do not need re-examination. These medical myths are a light hearted reminder that we can be wrong and need to question what other falsehoods we unwittingly propagate as we practice medicine. We generated a list of common medical or medicine related beliefs espoused by physicians and the general public, based on statements we had heard, endorsed on multiple occasions and thought were true or might be true. We selected seven for critical review:

1. People should drink at least eight glasses of water a day:

We used Medline and Google to search for evidence to support or refute each of these claims. Because "proving a negative" can be challenging, we noted instances in which there was no evidence to support the claim people should drink at least eight glasses of water a day. The advice to drink at least eight glasses of water a day can be found throughout the popular press. One origin may be a 1945 recommendation that stated: A suitable allowance of water for adults is 2.5 litres daily in most instances. An ordinary standard for diverse persons is 1 millilitre for each calorie of food. Most of this quantity is contained in prepared foods. If the last, crucial sentence is ignored, the statement could be interpreted as instruction to drink eight glasses of water a day. Another endorsement may have come from a prominent nutritionist, Frederick Stare, who once recommended, without references, the consumption "around 6 to 8 glasses per 24 hours," which could be "in the form of coffee, tea, milk, soft drinks, beer, etc". The complete lack of evidence supporting the recommendation to drink six to eight glasses of water a day is exhaustively catalogued in an invited review by Heinz Valtin in the American Journal of Physiology. Furthermore, existing studies suggest that adequate fluid intake is usually met through typical daily consumption of juice, milk, and even caffeinated drinks. In contrast, drinking excess amounts of water can be dangerous, resulting in water intoxication, hyponatraemia, and even death.

2. We use only 10% of our brain:

The belief that we use only 10% of our brains has persisted for over a century, despite dramatic advances in neuroscience. In another extensive expert literature review, Barry Beyerstein provides a detailed account of the origins of this myth and the evidence disputing it. Some sources attribute this claim to Albert Einstein, but no such reference or statement by Einstein has ever been recorded. This myth arose as early as 1907, propagated by multiple sources advocating the power of self improvement and tapping into each person’s unrealised latent abilities. Evidence from studies of brain damage, brain imaging, localisation of function, microstructural analysis and metabolic studies show that people use much more than 10% of their brains. Studies of patients with brain injury suggest that damage to almost any area of the brain has specific and lasting effects on mental, vegetative, and behavioural capabilities. Numerous types of brain imaging studies show that no area of the brain is completely silent or inactive. The many functions of the brain are highly localised, with different tasks allocated to different anatomical regions. Detailed probing of the brain has failed to identify the "non-functioning" 90%. Even micro-level localisation, isolating the response of single neurones, reveals no gaps or inactive areas. Metabolic studies, tracking differential rates of cellular metabolism within the brain, reveal no dormant areas.

3. Hair and fingernails continue to grow after death:

Morbid information about the body captures the imagination and reinforces medical mythology. In All Quiet on the Western Front, the author describes a friend’s fingernails growing in corkscrews after the burial. Johnny Carson even perpetuated this myth with his joke, "For three days after death hair and fingernails continue to grow, but phone calls taper off." To quote the expert opinion of forensic anthropologist William Maples, "It is a powerful, disturbing image, but it is pure moonshine. No such thing occurs." This myth does have a basis in a biological phenomenon that can occur after death. As Maples and numerous dermatologists explain, dehydration of the body after death and drying or desiccation may lead to retraction of the skin around the hair or nails. The skin’s retraction can create an appearance of increased length or of greater prominence because of the optical illusion created by contrasting the shrunken soft tissues with the nails or hair. The actual growth of hair and nails, however, requires a complex hormonal regulation not sustained after death.

4. Shaving hair causes it to grow back faster, darker, or coarser:

Another common belief is that shaving hair off will cause it to grow back in a darker or coarser form or to grow back faster. It is often reinforced by popular media sources and perhaps by people contemplating the quick appearance of stubble on their own body. Strong scientific evidence disproves these claims. As early as 1928, a clinical trial showed that shaving had no effect on hair growth. More recent studies confirm that shaving does not affect the thickness or rate of hair regrowth. In addition, shaving removes the dead portion of hair, not the living section lying below the skin’s surface, so it is unlikely to affect the rate or type of growth. Shaved hair lacks the finer taper seen at the ends of unshaven hair, giving an impression of coarseness. Similarly, the new hair has not yet been lightened by the sun or other chemical exposures, resulting in an appearance that seems darker than existing hair.

5. Reading in dim light ruins your eyesight:

The fearful idea that reading in dim light could ruin one’s eyesight probably has its origins in the physiological experience of eye strain. Suboptimal lighting can create a sensation of having difficulty in focusing. It also decreases the rate of blinking and leads to discomfort from drying, particularly in conditions of voluntary squinting. The important counterpoint is that these effects do not persist. The majority consensus in ophthalmology, as outlined in a collection of educational material for patients, is that reading in dim light does not damage your eyes. Although it can cause eye strain with multiple temporary negative effects, it is unlikely to cause a permanent change on the function or structure of the eyes. Even in patients with Sjögren’s syndrome (an autoimmune disease that features inflammation in certain glands of the body), decreased functional visual acuity associated with strained reading improves when they stop reading. One review article on myopia concludes that increased use of one’s eyes, such as reading in dim light or holding books too close to the face, could result in impaired ocular growth and refractive error. The primary evidence cited was epidemiological evidence of the increased prevalence of myopia and the high incidence of myopia in people with more academic experience. The author notes that this hypothesis is just beginning to "gain scientific credence." In the past reading conditions involved even less light, relying on candles or lanterns, so increased rates of myopia over the past several centuries does not necessarily support that dim reading conditions are to blame. In contrast to that review, hundreds of online expert opinions conclude that reading in low light does not hurt your eyes.

6. Eating turkey makes people especially drowsy:

The presence of tryptophan in turkey may be the most commonly known fact pertaining to amino acids and food. Scientific evidence shows that tryptophan is involved in sleep and mood control and can cause drowsiness. L-tryptophan has been marketed as a sleep aid. The myth is the idea that consuming turkey (and the tryptophan it contains) might particularly predispose someone to sleepiness. Actually, turkey does not contain an exceptional amount of tryptophan. Turkey, chicken, and minced beef contain nearly equivalent amounts of tryptophan (about 350 mg per 115 g), while other common sources of protein, such as pork or cheese, contain more tryptophan per gram than turkey. Any effects of the tryptophan in turkey are probably minimised by consuming it in combination with other food, which would limit its absorption according to expert opinion. In fact, consuming supplemental tryptophan on an empty stomach is recommended to aid absorption. Other physiological mechanisms explain drowsiness after meals. Any large solid meal (such as turkey, sausages, stuffing, and assorted vegetables followed by Christmas pudding and brandy butter) can induce sleepiness because blood flow and oxygenation to the brain decreases, and meals either high in protein or carbohydrate may cause drowsiness. Accompanying wine may also play a role.

7. Mobile phones create considerable electromagnetic interference in hospitals:

In a search by http://imageb.epocrates.com/mailbot/links?EdID=35935713&LinkID=17467 we could not find any cases of death caused by the use of a mobile phone in a hospital or medical facility. Less serious incidents, including false alarms on monitors, malfunctions in infusion pumps, and incorrect readings on cardiac monitors, have occasionally been reported. Although no references or dates are given, one government website published an anecdote in 2002 describing how use of a mobile phone in an intensive care unit resulted in an unintended bolus of adrenaline (epinephrine) from an infusion pump. After publication of a journal article citing more than 100 reports of suspected electromagnetic interference with medical devices before 1993, the Wall Street Journal published a front page article highlighting this danger. Since that time, many hospitals banned the use of mobile phones, perpetuating the belief. Despite the concerns, there is little evidence. In the United Kingdom, early studies showed that mobile phones interfered with only 4% of devices and only at a distance of <1>


Despite their popularity, all of these medical beliefs range from unproved to untrue. Although this was not a systematic review of either the breadth of medical myths or of all available evidence related to each myth, the search methods produced a large number of references. While some of these myths simply do not have evidence to confirm them, others have been studied and proved wrong. Physicians would do well to understand the evidence supporting their medical decision making. They should at least recognise when their practice is based on tradition, anecdote, or art. While belief in the described myths is unlikely to cause harm, recommending medical treatment for which there is little evidence certainly can. Speaking from a position of authority, as physicians do, requires constant evaluation of the validity of our knowledge.

Summary points

Even physicians sometimes believe medical myths contradicted by scientific evidence. The prevalence and endorsement of simple medical myths point to the need to continue to question what other falsehoods physicians endorse. Examining why we believe myths and using evidence to dispel false beliefs can move us closer to evidence based practice.

Source: http://www.epocrates.com/