Volatility continued to be the main narrative in the stock market this week, with the S&P 500 falling 4.6%. Tech stocks continue to see outsize losses, with the tech-heavy Nasdaq Composite falling 4.9% during the week. That performance brings the Nasdaq's total declines since Oct. 1 to 13.3%.

But there were some interesting company-specific stories during the week as well. Namely, Apple (NASDAQ:AAPL) launched its electrocardiogram (ECG) app, DocuSign (NASDAQ:DOCU) saw its growth accelerate, and Facebook (NASDAQ:FB) boosted its share-repurchase program.

Here's a look at each of these stories.

Apple Watch Series 4

Apple Watch Series 4. Image source: Apple.

Apple

When tech giant Apple announced its Apple Watch Series 4 in September, one of the main features the tech giant showed off was an app that used the device's electric heart-rate sensor to administer an FDA-approved ECG. But the app wasn't available yet.

On Thursday, Apple's ECG app for the Apple Watch Series 4 was finally released in a software update.

"Starting today, the ECG app on Apple Watch Series 4 marks the first direct-to-consumer product that enables customers to take an electrocardiogram right from their wrist," Apple said in a press release on Thursday, "capturing heart rhythm in a moment when they experience symptoms like a rapid or skipped heart beat and helping to provide critical data to physicians."

DocuSign

When e-signature and cloud-based document company DocuSign went public this spring, investors had high expectations. Software-as-a-service companies are all the rage recently, as investors consider these companies to have scalable business models and excellent growth prospects.

DocuSign hasn't disappointed. In fact, when DocuSign reported its fiscal third-quarter results this week, the company revealed an acceleration in its revenue growth rate. Revenue rose 37% year over year, above the company's second-quarter revenue growth rate of 33%. 

Even when excluding revenue from the company's recent acquisition of cloud-based document and contract management company SpringCM, the company's year-over-year top-line growth was still 34%. 

Facebook

In 2017, social network Facebook authorized $15 billion to buy back its own shares. But with the stock falling nearly 40% since a high this summer, management wants to be opportunistic. In a Dec. 6 SEC filing, the company said its board of directors approved a $9 billion increase to its $15 billion share-repurchase authorization. 

Facebook has been buying its stock back at an accelerated rate as shares have fallen. During the company's third quarter, the social network bought back about $4.3 billion worth of its own stock, up from $3.2 billion in Q2. Given Facebook's authorization for $9 billion more in share repurchases and the stock's further decline since Q3 ended, it wouldn't be surprising if Facebook buys back significantly more stock in Q4.

Daniel Sparks owns shares of Apple. The Motley Fool owns shares of and recommends Apple and Facebook. The Motley Fool has the following options: long January 2020 $150 calls on Apple and short January 2020 $155 calls on Apple. The Motley Fool recommends DocuSign. The Motley Fool has a disclosure policy.