没看懂，脉搏血氧仪

Pulse Oximetry

Saturation may be measured photometrically in vivo as well as in vitro. Light at two different wavelengths is either transmitted through a finger or an ear lobe or else is reflected from the skin, usually on the forehead. The usual wavelengths used are 660 nm, where there is a large difference between the oxyhaemoglobin and deoxyhaemoglobin spectra (Fig. 10.19), and 940 nm, close to the isosbestic point.With the original techniques, most of the blood that was visualized was venous or capillary rather than arterial, and the result depended on a brisk cutaneous blood flow to minimize the arterial/venous oxygen difference. The older techniques have now been completely replaced by pulse oximeters, which relate the optical densities at the two wavelengths to the pulse wave detected by the same sensor.The signal between the pulse waves is subtracted from the signal at the height of the pulse wave; the difference is because of the inflowing arterial blood reflecting the saturation of the arterial blood.

脉搏血氧仪

无论体内还是体外，都可用光度法测量饱和度。两种不同波长的光要么通过手指或耳垂透射，要么从皮肤反射（通常是前额）。通常使用氧合血红蛋白和脱氧血红蛋白吸收度差异较大的660nm和接近等吸收点的940nm的波长（图10.19）。在最初的测量技术中，大多数测量的不是动脉血而是静脉或毛细血管血，为最大限度地测量动脉血而非静脉血，测量的是皮肤快速血流的氧饱和度。脉搏血氧仪现已完全取代旧技术，它将两个波长处的光密度与同一传感器检测到的脉冲波相关联。脉搏波间的信号已减去了脉搏波最高度点信号，差值就反映了流入的动脉血。

两个地方没看懂