Lorino H, Harf A, Atlan G, Brault Y, Lorino A M, Laurent D
J Appl Physiol Respir Environ Exerc Physiol. 1980 May;48(5):911-6. doi: 10.1152/jappl.1980.48.5.911.
Plotting a line to the variables obtained during a panting maneuver, i.e. thoracic volume and mouth pressure, is the conventional way of computing plethysmographic thoracic gas volume (TGV). This procedure is reliable if the magnitude of the thoracic volume changes is large compared to the drift on the signal; this is one of the major problems in volumetric plethysmography. We propose replacing the thoracic volume signal (Vt) by its time derivative (Vt) and similarly mouth pressure (Pm) with its time derivative (Pm). Drift is thus ruled out, and the magnitude of Vt is preserved when the subject fails to carry out noticeable changes in thoracic volume during the panting, since even then the speed of these changes in thoracic volume remains high. The use of Vt and Pm appeared to be necessary when a minicomputer was connected to a pressure-compensated flow plethysmograph to obtain an automatic calculation of TGV. A regression-line technique applied to signals obtained during the panting was used to find the slope of the relation and thus TGV. However, this slope can only be predicted with less than 5% error if the correlation coefficient is very high (i.e., above 0.99). The analysis of 121 recordings from patients showed that the mean r was only 0.954 when Vt and Pm were used. It increased to 0.993 with Vt and Pm. For the same recordings the comparison of hand-calculated TGV and computer-derived TGV showed a much better agreement for the Vt-Pm method (standard error of the estimate (SEE) = 0.14 liter) than for the Vt-Pm method (SEE = 0.34 liter). These results emphasize that, in contrast to the manual technique, the computer does not adequately handle even a small drift of the thoracic signal. The proposed time-derivative method is therefore useful for a hand calculation, but essential to a reliable computer determination of thoracic gas volume
将一条线绘制到在呼吸动作期间获得的变量上，即胸廓容积和口腔压力，这是计算体积描记法胸廓气体容积（TGV）的传统方法。如果胸廓容积变化的幅度与信号漂移相比很大，那么这个过程是可靠的；这是体积描记法中的主要问题之一。我们建议用其时间导数（Vt）代替胸廓容积信号（Vt），同样地，用口腔压力（Pm）的时间导数（Pm）代替口腔压力（Pm）。这样就排除了漂移，并且当受试者在呼吸期间胸廓容积没有明显变化时，Vt的大小得以保留，因为即使在那时，这些胸廓容积变化的速度仍然很高。当将小型计算机连接到压力补偿式流量体积描记仪以自动计算TGV时，使用Vt和Pm似乎是必要的。应用于呼吸期间获得的信号的回归线技术用于找到关系的斜率，从而得到TGV。然而，只有当相关系数非常高（即高于0.99）时，这个斜率才能以小于5%的误差进行预测。对121例患者记录的分析表明，使用Vt和Pm时，平均r仅为0.954。使用Vt和Pm时，r增加到0.993。对于相同的记录，手工计算的TGV与计算机得出的TGV的比较表明，Vt - Pm方法（估计标准误差（SEE）= 0.14升）比Vt - Pm方法（SEE = 0.34升）的一致性要好得多。这些结果强调，与手动技术相比，计算机甚至不能很好地处理胸廓信号的小漂移。因此，所提出的时间导数方法对手工计算很有用，但对于可靠地通过计算机确定胸廓气体容积至关重要
