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The respiratory system controls the minute volume element of the equation. The respiratory system primarily consists of the lungs and the airway that provides a pathway for the air to reach the lungs. Normal respiratory function consists of a negative pressure system in which the diaphragm pulls down while the rib cage expands and draws air into the lungs. Normal bellows function and diaphragmatic function are essential to the normal mechanical process of breathing. In the lungs are the alveoli, the tiny sacs that store oxygen and contain the capillaries where respiratory gasses (oxygen and carbon dioxide) are exchanged. The vast majority of the inspired oxygen (95%) is stored in the alveoli of the lungs, and the other 5% is freely circulating in the plasma.
Normal resting minute volume is ~4-8 L per minute for a human adult. Minute volume is the result of two factors; respiratory rate and tidal volume. It is important to understand the relationship between the two and how they affect each other. If a patient is breathing too fast, they are not taking the adequate time to completely fill the lungs with air. Better stated, they cannot take in adequate tidal volume if they are breathing too fast. Breathing too slowly can allow for adequate tidal volume, however, the demand for oxygen will soon overload the available supply if the patient does not take in an adequate supply of oxygen at a regular interval. Adequate tidal volume ensures that there is an adequate supply of oxygen available for circulation to the organ tissues.
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