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Functioning and Features of Ventilators, Oxygen Concentrators, Oxygen Cylinders, and Cryogenic Tanks.

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Characteristics of Respiration

The respiratory system manages two tasks,

  1. Inhaling: Taking in the air from the atmosphere which consists of 21% Oxygen.
  2. Exhaling: Expelling harmful gases (carbon dioxide) from our body.

Two organs are crucial for the proper functioning of the system:

  1. Diaphragm: Muscles below the chest that assist lungs to expand.
  2. Lungs: consist of millions of micro sacs(alveoli) where the exchange of oxygen and carbon dioxide takes place between air and blood.

When diaphragm contract and pull itself down it allows lungs to expand which results in the air running into lungs; inhalation. Contrary when the diaphragm is relaxed it squeezes the lungs and the air is exhaled out. Hence inhaling air requires an effort by muscles to move the diaphragm from its relaxed position.

Complications in The Respiration

  1. The patient is able to inhale and exhale air properly but infection in the lungs blocks the gas transfer at some points by which oxygen level decreases in the blood.
  2. The lungs of the patient are clean but the diaphragm is injured or weak hence inhale and exhale of air is not achieved properly.
  3. In case of infection initially patient may able to inhale and exhale air properly. Later on due to blockage oxygen level decreases and it affects the working efficiency of vital organs like the brain and heart. This directly affects the movement of the diaphragm and will lead to both the above complications

Ventilators:

Ventilators are mechanical equipment that carries out the easy passage of pure air or oxygen through the lungs and expel carbon dioxide out of the lungs. Typically the machine creates pressure for one second which inflates the lungs with pure air, then pauses for roughly three seconds to allow the patient to exhale. This cycle is repeated for as long as the machine is in use. sometimes the machine is set to work automatically when the patient stops breathing for few seconds.

Ventilators are broadly categorized as Positive pressure ventilators and Negative pressure ventilators based on the type of air pressure created for the patient so that he can breathe easily.

Positive pressure ventilator:

A positive pressure ventilator exerts high pressure into the lungs by directly feeding pure air through nostrils. this pressure allows the lungs to expand and the diaphragm doesn't need to put in the effort. When high pressure of the ventilator is turned off for a couple of seconds air is exhaled automatically from the lungs.

Invasive ventilation and non-invasive ventilation are terms given to procedures by which positive pressure is applied into the lungs of the patient.

Negative pressure ventilator:

A negative pressure ventilator needs bulkier apparatus than a positive pressure ventilator, but this keeps the patient's head and mouth free for movements and other oral activities.

The body of the patient below the neck is encased into a wooden or metal box, only the head is out of the box. Negative pressure is applied into the box (air is sucked out from the box). Negative pressure leads to expansion of the chest and lungs, which causes a decrease in pressure of lung cavities and initiates the flow of ambient air into the lungs through the mouth.

Two Types of Ventilation by Positive Pressure Ventilator

Invasive Ventilation

A process is termed invasive when pressurized air or concentrated oxygen is fed directly into the lungs through a tube. 'Directly into the lungs' means; the tube is inserted through the mouth or nose to the trachea and air/oxygen is directly released into the tracheal tube.

Non-invasive ventilation

When a mask or helmet is installed on the face of the patient and pure air or oxygen is given through it with pressure is known as non-invasive ventilation. Because intubation (a tube through the mouth into the windpipe) is not required in this process it is known as non-invasive.

Oxygen Production and Storage

Production or Distillation of Oxygen

Ambient air (atmospheric pure air) consists of 78% Nitrogen, 21% Oxygen and 1% of Argon and Carbon dioxide, and a negligible amount of other gases. Industries separate these components by the distillation process. The air is collected, purified by different filters, compressed, and then cooled down. This cooled air is now free from minute particles, moisture, hydrocarbons, and carbon dioxide. Still, it is a mixture of Nitrogen, Oxygen, and argon.

The mixture of Nitrogen, Oxygen, and Argon needs to be separated by the distillation process. Before it could be distilled in the tower, the mixture needs to be converted into liquid form. The mixture of compressed air is cooled down to around -183 °C. This is the temperature where oxygen becomes liquid while Nitrogen and Argon remain in gaseous form, as they both have lower boiling points. Production and processing of any material at these extreme temperatures is known as cryogenic.

Compressed Oxygen Gas Cylinders, GOX (Gaseous Oxygen)

Oxygen gas cylinder contains oxygen in very compressed form, these portable gas cylinders are common in hospitals and clinics. Unused cylinders may have gas compressed at about 2000 psi or 135 atmospheric pressure. Often capacity of these cylinders is marked in liters, that doesn't mean that these cylinders hold liquid oxygen! Liters either mention the volume of the cylinder or the volume of the oxygen when released in 1 atmospheric pressure. The actual quantity of oxygen in the cylinder always depends on the pressure, and volume of the cylinder, it is a little complicated process to calculate.

Cryogenic Oxygen Tanks, LOX (Liquid Oxygen)

Storing Oxygen in liquid form needs a temperature below -183°C (cryogenic storage) hence very special tanks are required for the purpose. These tanks consist of two different layers of metallic cover. The inner metallic vessel holds the liquid oxygen below -183°C while the outer metallic body functions as a protecting cover. Between both metallic body is a vacuum which insulates the inner vessel from outer temperatures.

The inner vessel needs to be kept at -185°C so obviously, the cooling system has to be attached to the tank to keep the temperature constant. Extra apparatus to handling extreme temperature and maintaining specific temperature makes the tank bulkier and more complicated compared to compressed gas cylinders. Cryogenic tanks are available in multiple forms;

  1. Small portable units for homes and offices.
  2. Large fixed tanks outside hospitals and institutions.
  3. Cylindrical tanks installed over trucks/lorry.

It should be noted that 1 L of liquid Oxygen = 860 L of gaseous Oxygen. It is worth separating and storing oxygen in Cryogenic form but it is more convenient to handle it in gas cylinders in hospitals and clinics.

Oxygen Concentrator

Oxygen concentrators are types of equipment that take in ambient air, purify it from pollutants, and deliver concentrated oxygen to the patient. Electrical fans suck in the air from the surroundings and pass it through several different materials which filter out the pollutant (particles, carbon dioxide, and moisture) from the air. Filtered air largely consists of only three elements Nitrogen, Argon, and Oxygen, henceforth a special material is used that concentrates oxygen, zeolite.

Zeolite is a microporous crystalline material, it allows molecules of a substance to pass through it based on the size, shape, and polarity of the molecule. Lithium type and sodium type zeolite are most commonly used in oxygen concentrators. Molecules that couldn't pass through the material are adsorbed in zeolite's sieves.

Oxygen molecules are comparatively smaller than nitrogen and argon molecules. When the air is forced through the zeolite, oxygen readily passes through it. Nitrogen and argon couldn't make it through and get deposited in the sieves of the material. The air which comes out from another side of the zeolite is more concentrated in oxygen, around 40% to 90% oxygen depending upon the type of zeolite used. Gradually when all the sieves are occupied by nitrogen and argon zeolite is activated again through the reverse process.

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