In physiology, dead space is the volume of air inhaled that does not take part in gas exchange, either because it (1) remains in the conduction air path, or (2) achieves an alveoli that is not perfused or perfused. In other words, not every air in every breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, removing the inspiratory part that remains in the conduction air path where there is no gas exchange.
The benefit is a design that seems wasteful for ventilation that includes dead space.
- Carbon dioxide is maintained, making blood and bicarbonate interstices possible.
- The inspired air is brought to body temperature, increasing the affinity of hemoglobin for oxygen, increasing the absorption of O 2 .
- The particulate material is trapped in the mucus lining the conduction air duct, allowing its removal by mucociliary transport.
- The inspired air is moistened, improving the quality of airway mucus.
In humans, about one-third of each breathing breaks have no change in the levels of O 2 and CO 2 . In adults, it is usually in the range of 150 mL.
The dead space can be improved (and better imagined) by breathing through long tubes, like a snorkel. Although one end of the snorkel opens into the air, when the wearer breathes, they inhale a large amount of air remaining in the snorkel from the previous breath. Thus, a snorkel increases one's dead space by adding more "air channels" that do not participate in gas exchange.
Video Dead space (physiology)
Components
The total dead space (also known as physiological dead spaces ) is the amount of anatomical dead space plus alveolar dead space.
Space dead anatomy
The anatomical dead space is part of the airways (such as the mouth and trachea to the bronchioles) that drain the gas into the alveoli. There is no gas exchange in these spaces. In healthy lungs where the alveolar dead space is small, the Fowler method accurately measures the anatomical dead space by nitrogen washing techniques.
The normal value for the volume of dead space (in mL) is approximately lean body mass (in pounds), and averages about one-third of the resting tidal volume (450-500 mL). In the original Fowler study, the anatomical dead chamber was 156 Ã, Â ± 28 mL (n = 45 males) or 26% of their tidal volume. Despite the flexibility of the trachea and the smaller conduction air channel, their overall volume (ie anatomical dead space) is slightly altered with bronchoconstriction or when breathing hard during exercise.
Birds have a disproportionately large anatomical dead space (they have tracheas that are longer and wider than mammals of the same size), reducing airway resistance. This adaptation does not affect gas exchange because birds run through the air through their lungs - they do not breathe in and out like mammals.
Alveolar dead space
The alveolar dead space is the amount of alveol volume that has little or no blood flowing through adjacent pulmonary capillaries, ie, ventilated but non-diffused alveoli, and where, as a result, no gas exchange occurs. The alveolar dead space can be neglected in healthy individuals, but may increase dramatically in some lung diseases due to incompatibility of ventilation-perfusion.
Maps Dead space (physiology)
Calculating dead space
The concentration of carbon dioxide (CO 2 ) in the healthy alveoli is known. This is similar to the concentration in arterial blood since CO 2 quickly balances the entire alveolar-capillary membrane. The amount of CO 2 exhaled from the healthy alveoli will be diluted by air in the airflow and through the air from the bad perfusion alveoli. This dilution factor can be calculated after CO 2 in the exhaled breath is determined (either electronically monitor the exhaled breath or by collecting breath exhaled in the bag of impermeant gas (Douglas bag) and then measuring the mixed gas in the collection bag). Algebraically, this dilution factor will give us physiological dead space as calculated by the Bohr equation:
Alveolar dead space
A different maneuver is used in measuring the anatomical dead space: the test subjects breathe all the way out, inhale deeply from the 0% nitrogen gas mixture (usually 100% oxygen) and then breathe out onto the equipment that measures the volume of nitrogen and gas. This final breath occurs in three phases. The first phase has no nitrogen, and the air entering the lungs is only as far as the airways do. The nitrogen concentration then increases rapidly during the short second phase and finally reaches the plateau, the third phase. The anatomic dead space is equal to the volume exhaled during the first phase plus half that is exhaled during the second phase. (The Bohr equation is used to justify the inclusion of a second half-phase in this calculation.)
Dead space and ventilated patient
The depth and frequency of our breathing is determined by the chemoreceptors and brain stem, modified by a number of subjective sensations. When ventilated, the patient breathes with the rate and tidal volume determined by the machine. Due to the dead space, taking a deeper slower breath (eg ten 500 ml of breath per minute) is more effective than taking short short breaths (eg twenty 250 ml breaths per minute). Although the amount of gas per minute is equal (5 L/min), most of the shallow breath is dead space, and does not allow oxygen to enter the blood.
Mechanical shutdown space
The mechanical dead chamber is a dead space in a device in which the respiratory gas must flow in both directions as the user pulls in and out, increasing the respiratory effort required to obtain the amount of usable air or the same breathing gas, and risking the accumulation of carbon dioxide from shallow breath. This applies an external extension of the physiological dead space.
This can be reduced by:
- Use a separate inlet and exhaust with a one-way valve placed in the funnel. This limits the dead space between the non-return valve and the user's mouth and/or nose. The additional dead space can be minimized by keeping the volume of external dead space as small as possible, but this should not greatly improve breathing work.
- With a full face mask or a helmet request:
- Keep the volume small, or
- Has a small internal orinasal mask inside the main mask, which separates the external respiratory tract from the inside of another mask.
- In some models the funnel-filled face mask as used on the dive regulator is installed, which has the same functionality as the orinasal mask, but can further reduce the volume of external dead space, at the cost of forcing the mouth-swing.
- In treatment, this is corrected by a ventilator installation check that determines the volume of dead space in the ventilator circuit.
Smaller volume around the mouth increases speech distortion. This can make communication more difficult.
The free-flow dive helicopter avoids dead space problems by supplying far more air than can be used by divers, making the entire inside of the helmet effectively breathe fresh air at significantly higher gas usage charges in open circuit systems.
See also
- Bohr equation
- Christian Bohr
- Respiratory system
References
Further reading
Arend Bouhuys. 1964. "Deep breathing room." at the Handbook of Physiology. Part 3: Respiration. Vol 1. Wallace O. Fenn and Hermann Rahn (eds). Washington: American Physiological Society.
John B. West. 2011. Respiratory Physiology: The Essentials. Lippincott Williams & amp; Wilkins; The ninth edition. ISBN 978-1609136406.
External links
- Dead Space on the Johns Hopkins School of Medicine Interactive Breathing Physiology website.
- mechanical ventilation tutorial in critical care tutorial Patric Neligan
Source of the article : Wikipedia
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