Typical heart rate monitoring in wearable tech, like smart watches or wireless earbuds, relies at least partially on photoplethysmography (PPG), which uses light pulses to measure blood activity. It works generally well, but it has its limitations. Google scientists wrote in a new research blog yesterday that they had tried a different approach, called audioplethysmography (APG), that uses ultrasound to measure heart rate.

可穿戴技术中典型的心率监测，如智能手表或无线耳塞，至少部分依赖于使用光脉冲测量血液活动的光体积描记法（PPG）。它一般工作得很好，但它有其局限性。谷歌科学家昨天在一个新的研究博客中写道，他们尝试了一种不同的方法，称为听力体积描记术（APG），它使用超声波测量心率。

And they did it with off-the-shelf active noise-canceling (ANC) earbuds and a software update.The trick works by bouncing a low-intensity ultrasound signal off the inside of the ear canal and using the tiny microphone that helps make ANC work to detect skin surface perturbations as blood pumps through it.

他们使用现成的主动噪声消除（ANC）耳塞和软件更新来完成。该技巧的工作原理是将低强度超声波信号从耳道内部弹跳出来，并使用小型麦克风帮助ANC检测血液泵通过皮肤表面的扰动。

According to the blog, the technique was “resilient” even given a bad ear seal, differing ear canal size, or darker skin tones. That last one is notable since heart rate accuracy with darker natural skin tones or tattoos has been an ongoing problem with smartwatches and other wearables until now.A gif illustrating audioplethysmography.

据博客报道，即使耳密封不良，耳道大小不同或肤色较深，该技术也具有“弹性”。最后一个值得注意的是，迄今为止，智能手表和其他可穿戴设备一直存在心率准确度和较暗的自然肤色或纹身问题。一个说明听力体积描记法的gif。

Image: GoogleRelatedThere’s a disconnect between health tech and the people it’s supposed to helpGoogle’s researchers also found the ultrasound approach worked fine when music was playing, but said that it had issues in noisy environments and that “the APG signal can sometimes be very noisy and could be heavily disturbed by body motion.” However, they found they could overcome the motion problem by using multiple frequencies and teasing out the most accurate signal among them.In addition to commercially available earbuds, the researchers also used purpose-built prototypes to test the effect of microphone placement.

图片：GoogleRelated健康技术与应该帮助Google的人之间存在脱节Google的研究人员还发现，当音乐播放时，超声波方法效果很好，但表示它在嘈杂的环境中存在问题，“APG信号有时可能非常嘈杂，可能会受到身体运动的严重干扰。”然而，他们发现他们可以通过使用多个频率并梳理其中最准确的信号来克服运动问题。除了市售的耳塞外，研究人员还使用专用原型来测试麦克风放置的效果。

The field study was performed with 153 participants. The researchers said the median error rate for heart.

实地研究由153名参与者进行。研究人员表示心脏的中位错误率。