Mediastinal emphysema is a medical condition characterized by the presence of air or gas within the mediastinum, which is the central compartment of the thorax that contains the heart, esophagus, trachea, bronchi, thymus gland, and other associated structures.

In mediastinal emphysema, the air accumulates in the mediastinal tissues and spaces, leading to their abnormal distention or swelling. This condition can result from various causes, including:

* Pulmonary trauma or barotrauma (e.g., mechanical ventilation, scuba diving)
* Infections that cause gas-forming organisms (e.g., pneumomediastinum)
* Air leakage from the lungs or airways (e.g., bronchial rupture, esophageal perforation)
* Certain medical procedures (e.g., mediastinoscopy, tracheostomy)

Mediastinal emphysema can cause symptoms such as chest pain, cough, difficulty breathing, and swallowing problems. In severe cases, it may lead to life-threatening complications, including tension pneumothorax or mediastinitis. Treatment depends on the underlying cause and severity of the condition.

Subcutaneous emphysema is a medical condition where air or gas collects in the subcutaneous tissue, which lies beneath the skin and above the muscle layer. This tissue covers the entire body, but the collection of air usually occurs in the chest wall, neck, or face. The accumulation of air can cause swelling, crepitus (a crackling or crunching sound when touched), and tightness in the affected area. Subcutaneous emphysema is often associated with underlying conditions such as trauma, pulmonary disease, or certain medical procedures that result in air leaks from the lungs or other structures into the subcutaneous tissue. It can be a serious condition if left untreated, as it may lead to complications like mediastinal emphysema or tension pneumothorax. Immediate medical attention is necessary for proper diagnosis and treatment.

Pulmonary emphysema is a chronic respiratory disease characterized by abnormal, permanent enlargement of the airspaces distal to the terminal bronchioles, accompanied by destruction of their walls and without obvious fibrosis. This results in loss of elastic recoil, which leads to trappling of air within the lungs and difficulty exhaling. It is often caused by cigarette smoking or long-term exposure to harmful pollutants. The disease is part of a group of conditions known as chronic obstructive pulmonary disease (COPD), which also includes chronic bronchitis.

Emphysema is a chronic respiratory disease characterized by abnormal, permanent enlargement of the airspaces called alveoli in the lungs, accompanied by destruction of their walls. This results in loss of elasticity and decreased gas exchange efficiency, causing shortness of breath and coughing. It is often caused by smoking or exposure to harmful pollutants. The damage to the lungs is irreversible, but quitting smoking and using medications can help alleviate symptoms and slow disease progression.

Barotrauma is a type of injury that occurs when there is a difference in pressure between the external environment and the internal body, leading to damage to body tissues. It commonly affects gas-filled spaces in the body, such as the lungs, middle ear, or sinuses.

In medical terms, barotrauma refers to the damage caused by changes in pressure that occur rapidly, such as during scuba diving, flying in an airplane, or receiving treatment in a hyperbaric chamber. These rapid changes in pressure can cause the gas-filled spaces in the body to expand or contract, leading to injury.

For example, during descent while scuba diving, the pressure outside the body increases, and if the diver does not equalize the pressure in their middle ear by swallowing or yawning, the increased pressure can cause the eardrum to rupture, resulting in barotrauma. Similarly, rapid ascent while flying can cause the air in the lungs to expand, leading to lung overexpansion injuries such as pneumothorax or arterial gas embolism.

Prevention of barotrauma involves equalizing pressure in the affected body spaces during changes in pressure and avoiding diving or flying with respiratory infections or other conditions that may increase the risk of injury. Treatment of barotrauma depends on the severity and location of the injury and may include pain management, antibiotics, surgery, or hyperbaric oxygen therapy.

Hydrostatic pressure is the pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. In medical terms, hydrostatic pressure is often discussed in relation to body fluids and tissues. For example, the hydrostatic pressure in the capillaries (tiny blood vessels) is the force that drives the fluid out of the blood vessels and into the surrounding tissues. This helps to maintain the balance of fluids in the body. Additionally, abnormal increases in hydrostatic pressure can contribute to the development of edema (swelling) in the tissues.

Atmospheric pressure, also known as barometric pressure, is the force per unit area exerted by the Earth's atmosphere on objects. It is measured in units of force per unit area, such as pascals (Pa), pounds per square inch (psi), or, more commonly, millimeters of mercury (mmHg).

Standard atmospheric pressure at sea level is defined as 101,325 Pa (14.7 psi) or 760 mmHg (29.92 inches of mercury). Atmospheric pressure decreases with increasing altitude, as the weight of the air above becomes less. This decrease in pressure can affect various bodily functions, such as respiration and digestion, and may require adaptation for individuals living at high altitudes. Changes in atmospheric pressure can also be used to predict weather patterns, as low pressure systems are often associated with stormy or inclement weather.

An encyclopedia is a comprehensive reference work containing articles on various topics, usually arranged in alphabetical order. In the context of medicine, a medical encyclopedia is a collection of articles that provide information about a wide range of medical topics, including diseases and conditions, treatments, tests, procedures, and anatomy and physiology. Medical encyclopedias may be published in print or electronic formats and are often used as a starting point for researching medical topics. They can provide reliable and accurate information on medical subjects, making them useful resources for healthcare professionals, students, and patients alike. Some well-known examples of medical encyclopedias include the Merck Manual and the Stedman's Medical Dictionary.

In medical terms, pressure is defined as the force applied per unit area on an object or body surface. It is often measured in millimeters of mercury (mmHg) in clinical settings. For example, blood pressure is the force exerted by circulating blood on the walls of the arteries and is recorded as two numbers: systolic pressure (when the heart beats and pushes blood out) and diastolic pressure (when the heart rests between beats).

Pressure can also refer to the pressure exerted on a wound or incision to help control bleeding, or the pressure inside the skull or spinal canal. High or low pressure in different body systems can indicate various medical conditions and require appropriate treatment.

The term "diving" is generally not used in the context of medical definitions. However, when referring to diving in relation to a medical or physiological context, it usually refers to the act of submerging the body underwater, typically for activities such as swimming, snorkeling, or scuba diving.

In a medical or physiological sense, diving can have specific effects on the human body due to changes in pressure, temperature, and exposure to water. Some of these effects include:

* Changes in lung volume and gas exchange due to increased ambient pressure at depth.
* Decompression sickness (DCS) or nitrogen narcosis, which can occur when dissolved gases form bubbles in the body during ascent from a dive.
* Hypothermia, which can occur if the water is cold and the diver is not adequately insulated.
* Barotrauma, which can occur due to pressure differences between the middle ear or sinuses and the surrounding environment.
* Other medical conditions such as seizures or heart problems can also be exacerbated by diving.

It's important for divers to undergo proper training and certification, follow safe diving practices, and monitor their health before and after dives to minimize the risks associated with diving.

Blood pressure is the force exerted by circulating blood on the walls of the blood vessels. It is measured in millimeters of mercury (mmHg) and is given as two figures:

1. Systolic pressure: This is the pressure when the heart pushes blood out into the arteries.
2. Diastolic pressure: This is the pressure when the heart rests between beats, allowing it to fill with blood.

Normal blood pressure for adults is typically around 120/80 mmHg, although this can vary slightly depending on age, sex, and other factors. High blood pressure (hypertension) is generally considered to be a reading of 130/80 mmHg or higher, while low blood pressure (hypotension) is usually defined as a reading below 90/60 mmHg. It's important to note that blood pressure can fluctuate throughout the day and may be affected by factors such as stress, physical activity, and medication use.