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Thoracic Medicine

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Sleep Medicine

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Sleep apnoea may make it hard for you to remember simple things, such as where you parked your car or left your house keys, a small study suggests.

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Researchers believe that disrupted circadian clocks are the reason that shift workers experience higher incidences of type 2 diabetes, obesity and cancer. The body's primary circadian clock, which regulates sleep and eating, is in the brain. But other body tissues also have circadian clocks, including the liver, which regulates blood glucose levels.

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In recent research is has been found that disruption to rapid eye-movement (REM) sleep caused by sleep apnoea, may affect an individual’s capacity to form new spatial memories.

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Office workers with more light exposure at work had longer sleep duration, better sleep quality, more physical activity and better quality of life compared to office workers with less light exposure in the workplace.

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Can you be sleep deprived without knowing it? Sleep is not always prioritised however the implications can be devastating. Even one night sleep deprived can be impacting your body on a variety of different levels; physically and psychologically. The only way to know if you are getting consolidated sleep is to monitor with specialised equipment what is happening when you are asleep.

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In what may be the largest study of sleep problems among individuals with multiple sclerosis (MS), researchers at UC Davis have found that widely undiagnosed sleep disorders may be at the root of the most common and disabling symptom of the disease: fatigue. Study paticipant reports of sleep disorder frequency, sleep patterns and complaints of excessive daytime sleepiness suggest that sleep problems may be a hidden epidemic in the MS population.

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Asthma and Diving

What is Asthma?

Asthma is a disease characterized by narrowing of the airways, specifically bronchi, in response to a variety of stimuli (See Image 1.0: Bronchi). It is not a fixed response and a patient can have a sudden worsening in lung function called an “attack.” An asthma attack can be triggered by pollen and other so-called “allergens” such as cold air, irritants in the atmosphere, colds or flu.

Why Diving Affects Asthmabronchi

The bronchial narrowing in asthma has two effects: one is to decrease the amount of air that can be moved in and out of the lungs. This can reduce exercise capacity — especially for a diver, who already has reduced breathing capacity due to the external resistance of his breathing apparatus and the increased internal resistance due to higher breathing gas density at depth. Secondly, reduced airway caliber could cause trapping of gas in the lung during ascent. If trapped gas expands at a rate greater than it can be exhaled through the narrowed airways lung rupture can result, causing arterial gas embolism or pneumothorax (collapsed lung).

Another related concern with asthma and diving has been the increased propensity of airways in asthmatics to narrow when exposed to the conditions implicit in diving: inhalation of cold, dry air and/or sea water (the latter by losing the mouthpiece or from a leaky regulator). Dr. Mark Harries from the British Medical Olympic Center has pointed out that asthmatics who dive are at risk from exercise limitation, not just peripheral gas-trapping. While exercising on land it is easy enough to stop, rest and catch one’s breath; this may not be possible underwater.

Are people with asthma allowed to dive?

It is recommended that asthmatics maintain a relationship with their specialist for maintenence of their condition during their diving careers.

There is a high prevalence of asthma in the Australian and New Zealand population. Strenuous exercise is frequently required of the diver, and there are many opportunities for accidental aspiration of sea water to occur. Inhaling dry air from a tank or fine aerosols of hyperosmolar saline through a faulty valve are stimuli also encountered by the diver. In the last decade there has been a nationwide effort to improve education of doctors and patients about asthma and its treatment through advertising campaigns. Inhaled corticosteroids are more available and more widely used than they were 10 years ago. Lung function tests are more commonly requested and the testing apparatus used in laboratories is more sophisticated, permitting measurements of flow at low lung volumes.

It is now clear that bronchial hyperresponsiveness (BHR) to hyperpnea of dry air, an absolute contraindication for SCUBA diving, can be associated with normal values for resting spirometry. Currently most laboratories provide a choice of bronchial provocation tests. The role of the bronchial provocation test in the assessment of the diver or intending diver should be to identify those persons who would be at risk from acute airway narrowing during the activities associated with diving. Those who have demonstrable BHR should be told that they may be at increased risk of pulmonary barotraumas and the details of the possible consequences of this should be explained.

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Some people aren’t even aware they have active asthma

The following questions were asked to people wishing to begin a diving course prior to completing a bronchial provocation test.  Subsequently these people were confirmed to have asthma.

How would you describe your asthma over the past 3 months? 
10 percent of  answered 'None at all'.

Does exercise trigger your asthma? 
17.4 percent of  answered 'No'.asthmadiving

In the last 3 months have you used a bronchodilator? 
28 percent answered 'No'.

How many days in the last 2 weeks have you had morning wheeze or chest tightness? 
21.6 percent answered 'None'

The Mannitol Challenge

The Mannitol challenge is a type of bronchial provocation test.  Mannitol is a naturally occurring sugar alcohol which is a stable compound with few side-effects.  Following inhalation, Mannitol is deposited on the airway surface which causes an increase in osmolarity of the airway surface liquid. Water then moves out of the epithelial cells in an attempt to restore balance, causing the epithelial cells to shrink. As the cells attempt to regain their volume, intracellular calcium rises, which is thought to trigger the release of inflammatory mediators such as histamines, prostaglandins and leukotrienes. In sensitive individuals the release of these mediators causes the bronchial smooth muscle to contract and the airways to narrow. This is measured by a fall in FEV1 (Forced Expiratory Volume in one second).

Additional Sources of Reference

Click on any of the links below for more information regarding Asthma and Diving.
South Pacific Underwater Journal
The British Sub Aqua Club
Divers Alert Network
Asthma Australia

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