airway resistance

同

RAW

WordNet

1. untempered and unrefined; "raw talent"; "raw beauty"
2. informal terms for nakedness; "in the raw"; "in the altogether"; "in his birthday suit" (同)altogether, birthday_suit
3. lacking training or experience; "the new men were eager to fight"; "raw recruits" (同)new
4. used of wood and furniture; "raw wood" (同)unsanded
5. brutally unfair or harsh; "received raw treatment from his friends"; "a raw deal"
6. having the surface exposed and painful; "a raw wound"
7. not processed or refined; "raw sewage"
8. not treated with heat to prepare it for eating
9. any mechanical force that tends to retard or oppose motion
10. the capacity of an organism to defend itself against harmful environmental agents; "these trees are widely planted because of their resistance to salt and smog"
11. the action of opposing something that you disapprove or disagree with; "he encountered a general feeling of resistance from many citizens"; "despite opposition from the newspapers he went ahead" (同)opposition
12. (psychiatry) an unwillingness to bring repressed feelings into conscious awareness
13. group action in opposition to those in power
14. the military action of resisting the enemys advance; "the enemy offered little resistance"
15. the degree of unresponsiveness of a disease-causing microorganism to antibiotics or other drugs (as in penicillin-resistant bacteria)

PrepTutorEJDIC

1. (食物が)『生の』,『料理されていない』 / (物が)『原料のままの』,加工されていない / (皮膚が)『赤むけの』,傷口のあいた;(…で)赤むけの《+『with』+『名』》 / (人が)経験のない,未熟な;(…に)不慣れの《+『to』+『名』》 / 湿気があって寒い / 《話》ひどい
2. 〈U〉〈C〉(…に)『抵抗』(『反抗』)『すること』;(…を)『こらえること』《+『to』(『against』)+『名』(do『ing』)》 / 〈U〉(病気などに対する)『抵抗力』《+『against』(『to』)+『名』》 / 〈U〉〈C〉(またresistance movement)(権力・圧制に対する)抵抗運動,レジスタンス / 〈U〉(空気の)抵抗;(電気の)抵抗
3. 〈C〉航空路 / 〈C〉(鉱山などの)通風路 / 《複数形》航空会社

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/06/29 09:40:03」(JST)

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[Wiki en表示]

In respiratory physiology, airway resistance is the resistance of the respiratory tract to airflow during inspiration and expiration. Airway resistance can be measured using body plethysmography.

Definition

Analogously to Ohm's Law:

$R_{AW}={\frac {{\Delta }P}{\dot {V}}}$

Where:

${\Delta P}=P_{ATM}-P_{A}$

So:

$R_{AW}={\frac {P_{\mathrm {ATM} }-P_{\mathrm {A} }}{\dot {V}}}$

Where:

• $R_{AW}$ = Airway Resistance
• ${\Delta }P$ = Pressure Difference driving airflow
• $P_{ATM}$ = Atmospheric Pressure
• $P_{A}$ = Alveolar Pressure
• ${\dot {V}}$ = Volumetric Airflow (not minute ventilation which confusingly maybe represented by the same symbol)

N.B. P_A and ${\dot {V}}$ change constantly during the respiratory cycle.

Determinants of airway resistance

There are several important determinants of airway resistance including:

• The diameter of the airways
• Whether airflow is laminar or turbulent

Hagen–Poiseuille equation

In fluid dynamics, the Hagen–Poiseuille equation is a physical law that gives the pressure drop in a fluid flowing through a long cylindrical pipe. The assumptions of the equation are that the flow is laminar viscous and incompressible and the flow is through a constant circular cross-section that is substantially longer than its diameter. The equation is also known as the Hagen–Poiseuille law, Poiseuille law and Poiseuille equation.

${\Delta P}={\frac {8\eta l{\dot {V}}}{\pi r^{4}}}$

Where:

• $\Delta P$ = Pressure difference between the ends of the pipe
• $l$ = Length of pipe
• $\eta$ = the dynamic viscosity
• ${\dot {V}}$ = the volumetric flow rate (Q is usually used in fluid dynamics, however in respiratory physiology it denotes cardiac output)
• $r$ = the radius of the pipe

Dividing both sides by ${\dot {V}}$ and given the above definition shows:-

$R={\frac {8\eta l}{\pi r^{4}}}$

While the assumptions of the Hagen–Poiseuille equation are not strictly true of the respiratory tract it serves to show that, because of the fourth power, relatively small changes in the radius of the airways causes large changes in airway resistance.

An individual small airway has much greater resistance than a large airway, however there are many more small airways than large ones. Therefore, resistance is greatest at the bronchi of intermediate size, in between the fourth and eighth bifurcation.

Laminar flow versus turbulent flow

Where air is flowing in a laminar manner it has less resistance than when it is flowing in a turbulent manner. If flow becomes turbulent, and the pressure difference is increased to maintain flow, this response itself increases resistance. This means that a large increase in pressure difference is required to maintain flow if it becomes turbulent.

Whether flow is laminar or turbulent is complicated, however generally flow within a pipe will be laminar as long as the Reynolds number is less than 2300.

$Re={{\rho {\mathrm {v} }d} \over \mu }$

where:

• $Re$ is the Reynolds number
• $d$ is the diameter of the pipe.
• ${\mathbf {\mathrm {v} }}$ is the mean velocity.
• ${\mu }$ is the dynamic viscosity.
• ${\rho }\,$ is the density.

This shows that larger airways are more prone to turbulent flow than smaller airways. In cases of upper airway obstruction the development of turbulent flow is a very important mechanism of increased airway resistance, this can be treated by administering Heliox which is much less dense than air and consequently more conductive to laminar flow.

Changes in airway resistance

Airway resistance is not constant. As shown above airway resistance is markedly affected by changes in the diameter of the airways, therefore diseases affecting the respiratory tract can increase airway resistance. Airway resistance can change over time, for example, in asthma during an attack the airways constrict causing an increase in airway resistance. Airway resistance can also vary between inspiration and expiration, for example, in emphysema there is destruction of the elastic tissue of the lungs which help hold the small airways open, therefore during expiration, particularly forced expiration, these airways may collapse causing increased airway resistance.

Derived parameters

Airway conductance (G_AW)

This is simply the mathematical inverse of airway resistance.

$G_{AW}={\frac {1}{R_{AW}}}$

Specific airway resistance (sR_aw)

$sR_{AW}={R_{AW}}{V}$

Where V is the lung volume at which R_AW was measured.

Also called volumic airway resistance. Due to the elastic nature of the tissue that supports the small airways airway resistance changes with lung volume. It is not practically possible to measure airway resistance at a set absolute lung volume, therefore specific airway resistance attempts to correct for differences in lung volume at which different measurements of airway resistance were made.

Specific airway resistance is often measured at FRC, in which case:

$sR_{AW}={R_{AW}}\times {FRC}$

Specific airway conductance (sG_aw)

$sG_{AW}={\frac {G_{AW}}{V}}={\frac {1}{R_{AW}V}}={\frac {1}{sR_{AW}}}$

Where V is the lung volume at which G_AW was measured.

Also called volumic airway conductance. Similarly to specific airway resistance, specific airway conductance attempts to correct for differences in lung volume.

Specific airway conductance is often measured at FRC, in which case:

$sG_{AW}={\frac {G_{AW}}{FRC}}$

See also

• turbulent flow
• laminar flow
• Reynolds number
• Upper airway resistance syndrome (UARS)

References

External links

• Overview at med.jhmi.edu
• Calculator at medstudents.com.br

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Related Links

• Airway resistanceとは - goo Wikipedia (ウィキペディア)

Airway resistance is a concept in respiratory physiology that describes the resistance of the respiratory tract to airflow during inspiration and expiration. Airway resistance can be measured using body plethysmography.

• Airway resistance | definition of airway resistance by Medical ...

resistance [re-zis´tans] 1. opposition, or counteracting force, as opposition of a conductor to passage of electricity or other energy or substance. ... Designed for light to moderate snorers, and for those that have difficulty with nasal airway resistance ...

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★リンクテーブル★

リンク元	「気道抵抗」「raw」
関連記事	「airway」「resistance」

「気道抵抗」

　　[★]

英

airway resistance

-単位：cmH2O/l

• 正常な成人：1.5 cmH2O/l (PT.353)

• 末梢の細気管支では気道抵抗に関与しない (標準麻酔学 第2版 p.11)

気体の移動は拡散に依存するため。

• 気道抵抗は10分岐までの細気管支により生じている (標準麻酔学 第2版 p.11)

英

airway resistance

同

Raw

英

airway resistance

「raw」

　　[★]

• adj.

• 生の、未加工の

関

uncooked、unprocessed

同

airway resistance

　 　 　 　 　 　 　 　 　

「airway」

　　[★] 気道 respiratory tract

　

「resistance」

　　[★]