Version August 2025
| The diving environment |
| Diving is an arduous underwater activity in which environmental conditions affect bodily structure and function. |
| For every 10 meters descent in sea water, ambient pressure increases by 100 kPa, equivalent to 1 atmosphere (1 bar). The volume of a given mass of gas changes inversely in proportion to pressure. The gas in bodily cavities such as the lungs, sinuses, middle ear and intestine is therefore subject to compression during descent and expansion during ascent. This may lead to tissue damage. |
| Partial pressure of gases increases in direct proportion to the increase in ambient pressure. Greater quantities of inert gas, mainly nitrogen, therefore dissolve in tissues at depth and come out of solution on ascent. |
| The density of inhaled gas increases with pressure, restricting breathing. |
| Immersion displaces blood from the periphery into the thorax, reducing lung volume. |
| Work of breathing increases due to a combination of increased gas density, increased hydrostatic pressure, and altered respiratory mechanics. |
| The underwater breathing apparatus adds dead space and increases resistance to breathing. |
| During diving, carbon dioxide retention may result from the above listed effects on the body. |
| Potential risks of diving |
| General risks: panic, hypothermia, physical trauma, and drowning. |
| Equipment/technique problems: hypoxia, hyperoxia, or poisoning by inappropriate gas mixtures or contaminant gases may result from equipment malfunction or poor dive planning. A malfunctioning respiratory regulator may result in aspiration. |
| Barotrauma: is caused by compression or expansion of gas filled spaces during descent or ascent, respectively. Compression of the lungs during descent may lead to alveolar exudation and haemorrhage. Expansion of the lungs during ascent may cause lung rupture leading to pneumothorax, pneumomediastinum, and arterial gas embolism. |
| Decompression illness: may occur when gas, which has dissolved in tissues while at depth, comes out of solution as bubbles. Clinical manifestations vary, the most severe being cardiorespiratory and neurological. |
| Loss of buoyancy control: is a cause of many accidents, usually when it leads to rapid uncontrolled ascent. |
| It is also essential to consider comorbidities such as diabetes and epilepsy which may influence capability for diving but are outside the scope of this document. |
| The physician should bear the following general concepts in mind when assessing respiratory fitness to dive: |
| The subject may be required to swim in strong currents. |
| The subject may be required to rescue a companion (dive buddy) in the event of an emergency. |
| The diving environment is associated with a risk of lung rupture. |
| The gas breathed by the diver may be very cold. |
| Buoyancy control is essential and requires training, experience, and use of appropriate equipment. |
| The following recommendations are therefore made. |
| Assessment of respiratory fitness to dive |
| In the history, particular attention should be paid to current respiratory symptoms, previous history of lung disease including childhood history, previous trauma to the chest, and previous episodes of pneumothorax. |
| Respiratory system examination should be performed. |
| Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and peak expiratory flow rate (PEF) should be measured. FEV1 and PEF should normally be greater than 80% of predicted and the FEV1/FVC ratio greater than 70 percent. |
| Routine chest radiography is not considered necessary in asymptomatic subjects with no significant respiratory history and normal examination findings. However, all professional divers, including recreational divers, who plan to work as instructors are recommended by the Health and Safety Executive to undergo chest radiography. |
| Chest radiography is appropriate if there is a previous history of any significant respiratory illness - for example, pleurisy, pneumonia, recurrent respiratory infections, sarcoidosis, chest surgery or trauma, pneumothorax - and those with current respiratory symptoms and/or abnormal examination findings. |
| Routine measurement of the expiratory flow-volume loop, exercise testing, or bronchial provocation testing are not considered necessary although these tests may be useful in specific cases. |
| Thoracic CT scanning, which has greater sensitivity than standard chest radiography to detect lung structural abnormality, may be useful in specific areas. |
