Barnas G M, Green M D, Mackenzie C F, Fletcher S J, Campbell D N, Runcie C, Broderick G E
Anesthesiology Research Laboratories, University of Maryland School of Medicine, Baltimore 21201.
Anesthesiology. 1993 Feb;78(2):251-9. doi: 10.1097/00000542-199302000-00007.
Little is known about the extent to which changes in postures in clinical situations affect respiratory mechanics, even in humans with healthy respiratory systems. This study tested the hypothesis that posture has only small effects on overall respiratory system mechanics in healthy subjects, despite changes in parts of the respiratory system in some postures.
Measurements were made of airway flow, airway and esophageal pressures, and rib cage and abdominal volume displacements (with inductance plethysmography) of awake, healthy subjects, relaxed at functional residual capacity, during external forcing at 0.2 Hz with a tidal volume of 8-10 ml/kg. From these measurements, discrete Fourier transform was used to calculate elastances (E) and resistances (R) of the total respiratory system, lungs, total chest wall, and compartments of the chest wall (rib cage, diaphragm-abdomen, and belly wall). Measurements were made while the subjects were in nine different postures: in six of these, the torso was straight; in three, the torso was bent or twisted.
Although changes in mechanics of parts of the respiratory system were evident in certain postures, overall respiratory mechanics were not greatly affected by posture. Changing from sitting to supine decreased E and R of the diaphragm-abdomen about 50% (P < .05), but total chest wall E and R changed only slightly. Lung E increased 24% (P < .05), but total respiratory E did not change (P < .05). Lung and total respiratory R increased 40-50% (P < .05) with this same change in posture. As long as the torso was straight, however, changes in orientation of 30 degrees from the horizontal or a shift to lateral posture resulted in only minor changes in the variables measured. Postures in which the torso was twisted or bent increased E of the total chest wall 20-30% compared to supine (P < .05), due to increases in E of one or more compartments. Respiratory system E also increased, at most 14%. Although lung R decreased 30-45% (P < .05) in these postures compared to supine with a straight torso, chest wall and total respiratory R generally were unchanged.
Changes in respiratory system mechanics over a wide range of postures that may be encountered clinically are relatively small in healthy awake subjects due to adaptability of total chest wall mechanical behavior.
即使在呼吸系统健康的人群中，临床情况下姿势变化对呼吸力学的影响程度也鲜为人知。本研究检验了一个假设，即尽管某些姿势下呼吸系统的部分结构会发生变化，但姿势对健康受试者整体呼吸系统力学的影响很小。
对清醒、健康的受试者在功能残气量下放松状态时进行测量，测量气道流量、气道和食管压力以及胸廓和腹部容积位移（使用感应体积描记法），在0.2Hz频率下以8 - 10ml/kg的潮气量进行外部强迫通气。通过这些测量，使用离散傅里叶变换来计算整个呼吸系统、肺、整个胸壁以及胸壁各部分（胸廓、膈肌 - 腹部和腹壁）的弹性（E）和阻力（R）。在受试者处于九种不同姿势时进行测量：其中六种姿势下，躯干是直的；三种姿势下，躯干是弯曲或扭转的。
尽管在某些姿势下呼吸系统部分结构的力学变化很明显，但整体呼吸力学受姿势的影响不大。从坐姿变为仰卧位时，膈肌 - 腹部的E和R降低约50%（P <.05），但整个胸壁的E和R变化很小。肺的E增加24%（P <.05），但整个呼吸系统的E没有变化（P <.05）。随着相同的姿势变化，肺和整个呼吸系统的R增加40 - 50%（P <.05）。然而，只要躯干是直的，与水平方向成30度的方向变化或向侧卧位的转变只会导致所测量变量的微小变化。与仰卧位相比，躯干扭转或弯曲的姿势会使整个胸壁的E增加20 - 30%（P <.05）），这是由于一个或多个部分的E增加所致。呼吸系统的E也会增加，最多增加14%。尽管与躯干挺直的仰卧位相比，在这些姿势下肺的R降低30 - 45%（P <.05），但胸壁和整个呼吸系统的R通常没有变化。
由于整个胸壁力学行为的适应性，在临床可能遇到的广泛姿势范围内，健康清醒受试者的呼吸系统力学变化相对较小。
