Airway Mechanics

Formula for Raw ([blank_start]Mouth[blank_end] Pressure - [blank_start]Alveolar[blank_end] Pressure) / [blank_start]Flow[blank_end]

Airway resistance: Difference in pressure between the [blank_start]mouth[blank_end] and the [blank_start]alveoli[blank_end], related to gas [blank_start]flow[blank_end] at the mouth. Typical value [blank_start].6[blank_end] - [blank_start]2.4[blank_end] cmH2O / L/sec Measured by body pleth: Pt pants gently with open shutter at a rate of [blank_start]1.5[blank_end] - [blank_start]2.5[blank_end] breaths per second. This creates an 2 shaped curve on screen that plots flow against box pressure. Shutter closes and second curve is produced that plots mouth pressure against box pressure. Raw is calculated from these 2 graphs.

Normal Raw Values Nose, mouth, upper airway: [blank_start]50[blank_end]% Trachea, Bronchi: [blank_start]30[blank_end]% Small Airways: [blank_start]20[blank_end]%

Airway Conductance ([blank_start]Gaw[blank_end]) Flow per unit of [blank_start]pressure[blank_end] change in L/sec/cmH2O Reciprical of Raw: 1/[blank_start]Raw[blank_end] [blank_start]Specific[blank_end] conductance is the same but is measured by liter of [blank_start]lung[blank_end] volume: (1/Raw)/[blank_start]TLC[blank_end] or [blank_start]FRC[blank_end] Normal Value: .[blank_start]42[blank_end] - [blank_start]1.67[blank_end] L/sec/cmH20 More appropriate than Raw for small airway disease

Compliance Volume Change per unit of Pressure change CLT = Lungs and [blank_start]Thorax[blank_end] = [blank_start].2[blank_end] L/cmH2O CL = [blank_start]Lungs[blank_end] Only = [blank_start].2[blank_end] L/cmH2O CT = [blank_start]Thorax[blank_end] only = [blank_start].1[blank_end] L/cmH2O In vented patients record plateau pressure at different lung volumes.

Compliance: [blank_start]Esophogeal[blank_end] Balloon Technique Catheter with inflatable [blank_start]balloon[blank_end] is marked [blank_start]50[blank_end] cm from the tip. Balloon is inserted through the nose and swallowed into [blank_start]stomach[blank_end]. In the stomach pressure swings [blank_start]positive[blank_end] on inspiration and [blank_start]negative[blank_end] on expiration after 1 ml of air is injected. Balloon is retracted into [blank_start]esophagus[blank_end] and the pressure swings [blank_start]reverse[blank_end]. Catheter is [blank_start]35[blank_end] - [blank_start]45[blank_end] cm from the nose. Air is evacuated from the balloon, then [blank_start].5[blank_end] ml is injected. Pt inspires to [blank_start]TLC[blank_end] before taking any measurements to standardize. Have pt inspire again - pressure and volume measurements are taking at zero flow. Lung compliance is taken from slope of P-V [blank_start]curve[blank_end] over segment from FRC to [blank_start]FRC[blank_end] +.5L At FRC balloon pressure should equal [blank_start]-5[blank_end] cmhO Max elastic [blank_start]recoil[blank_end] pressure is the most [blank_start]negative[blank_end] pressure at TLC Static lung compliance is the difference of [blank_start]esophageal[blank_end] pressure and mouth [blank_start]pressure[blank_end].

Static Lung Compliance Change in lung [blank_start]volume[blank_end] per unit change in transpulmonary [blank_start]pressure[blank_end] measured over the straight portion of P-V curve between FRC and FRC + [blank_start].5L[blank_end] Δ[blank_start]V[blank_end] / Δ[blank_start]Pst[blank_end] Normal Value = [blank_start].2[blank_end] L/cmH2O

Abnormal Compliance CL is [blank_start]decreased[blank_end] in [blank_start]restrictive[blank_end] disease like pneumonia, atelectasis, pulm fibrosis CL is [blank_start]increased[blank_end] in emphysema because of loss of [blank_start]elasticity[blank_end] CT is [blank_start]decreased[blank_end] with chest wall deformities and obesity.

Maximum Static Recoil Pressure Most [blank_start]negative[blank_end] pressure obtained at TLC Normal value is [blank_start]24.4[blank_end] - [blank_start]34.5[blank_end] cmH2O

CoEffecient of Retraction COR is used to express the maximal static recoil [blank_start]pressure[blank_end] of the lung relative to the lung [blank_start]volume[blank_end] (TLC) COR = (Pst at [blank_start]TLC[blank_end]) / [blank_start]TLC[blank_end] Normal Value = [blank_start]4[blank_end]-[blank_start]8[blank_end] cmH2O/L