At a Sept. 5 campaign rally in Cleveland,video lucah ismail izzani Hillary Clinton struggled to speak through her hacking, mucus-filled cough. On a plane with reporters that evening, the Democratic presidential nominee cut herself short, coughing fitfully down the aisle as she clutched a cup of water.

Then on Sunday, Clinton left early from a 9/11 commemoration ceremony in New York, complaining of feeling "overheated." Her doctor later released a statement confirming that the former U.S. secretary of state had pneumonia.

SEE ALSO: Clinton's doctor says she's 'healthy and fit to serve'

Pundits and detractors had speculated for days about the cause of Clinton's poorly-concealed illness.

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The answer, it turns out, was likely contained the cough itself.

Different types of coughs -- such as wet, dry or whooping -- carry important clues about the underlying illness, physicians say. Those sound markers can help inform a doctor's diagnosis, along with a physical exam and possibly an x-ray.

Hillary Clinton is interrupted by coughing spasm during a speech in New York, Feb. 16, 2016. Credit: Andy Katz/Pacific Press/LightRocket via Getty Images

Scientists and health care entrepreneurs are developing technologies that could record the sound of a person's cough, or their lungs, and diagnose a patient on the spot.

"Sounds in general carry very complex information. If adequately decomposed, they could be very useful [in diagnosis]," Dr. William Checkley, an expert on lung disease and professor at the Johns Hopkins Bloomberg School of Public Health, told Mashable.

The true value of these nascent tools, however, won't be their ability to decode the croaks of presidential candidates.

Instead, the devices could help people in rural or impoverished areas where trained physicians are few and far between. With an early diagnosis, families could respond quickly to respiratory illnesses that, left untreated, can kill millions of people a year.

Pneumonia, for instance, is the No. 1 infectious cause of death in children worldwide, according to the World Health Organization. The respiratory disease killed more than 920,000 children under 5 years old in 2015, even though many cases of pneumonia can be easily treated with antibiotics.

The new technologies could also help those people who do have access to quality medical care, but don't bother to visit the doctor, perhaps in the hopes that their cough will disappear on its own.

"People don't seek treatment for what turns out to be serious conditions. But we all know that the sooner you can be diagnosed with an illness, the better the outcome, in terms of recovery," said Brian Leedman, the co-founder and executive director of ResApp Health, an Australian health care company.

Cough-tunes

ResApp is developing a smartphone application that can record the sound of your cough, run the data through an algorithm and produce a diagnosis on the spot. The company expects to run its first U.S. clinical trial this fall.

"There is information contained in the sound of your cough -- signatures that are specific to a particular illness," Leedman told Mashableby phone from Perth, where the health care firm is based.

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Udantha Abeyratne, ResApp's chief technical adviser and a professor at the University of Queensland, first developed the cough-analyzing technology.

Abeyratne won a $100,000 grant from the Bill and Melinda Gates Foundation in 2009 to equip mobile phones and mp3 players with microphones that could record cough and sleep sounds, with the goal of helping to diagnose pneumonia in developing countries.

Researchers worked with 91 hospitalized children in Indonesia to test the technology, and then compared their results with clinical diagnoses made by pediatric physicians. The program identified pneumonia cases with over 90 percent sensitivity, meaning it identified most patients who actually had pneumonia, according to a 2013 study.

Leedman's firm acquired the technology in 2015 and raised $4 million to fund clinical trials in Australia. After testing and refining the algorithm on about 1,500 adults and children, Leedman said the technology is nearly 100 percent accurate in diagnosing pneumonia and asthma.

A pneumonia-stricken child in Dhaka, Bangladesh, Jan. 24, 2016. Credit: Zakir Hossain Chowdhury / Barcroft Media via Getty Images

ResApp raised another $12.5 million to fund its push into the U.S. market. The company is now preparing for clinical trials throughout the United States, starting with Massachusetts General Hospital in Boston.

Leedman said ResApp is primarily focused on entering the global telemedicine market, which promises to replace some doctor's visits with internet calls and web chats.

With ResApp, patients could download an app and cough a few times into their smartphones; the doctor would instantly receive the data, remotely issue a diagnosis and call in a prescription to the patient's local pharmacy.

The technology would fill what Leedman called a glaring gap in internet-driven health care.

"What can a doctor do to you in a telehealth call if you have a respiratory problem? They can't pull out their stethoscope," he said.

Listen to your lungs

Dr. Checkley, the lung disease expert at Johns Hopkins, said the method of analyzing cough sounds “is something that needs to be validated.” A better method for diagnosing respiratory illnesses may be analyzing the sound of a person's lungs, not their coughs, he added.

The physician spoke by phone from Puno, Peru, a city that sits at 12,500 feet above sea level on the shore of Lake Titicaca. Dr. Checkley leads a research field site in the Peruvian city, and he is helping to developing cost-effective tools for treating childhood pneumonia.

Original image has been replaced. Credit: Mashable

One device could record sounds from the lungs -- similar to how a typical stethoscope works, except the audio is run through an algorithm that interprets the sound and makes a diagnosis.

"It goes directly to the source, and you listen to different sounds all throughout the lungs," Dr. Checkley said. "That might be harder to do with one cough source, rather than multiple sounds from multiple areas in the lungs."

The team is developing a prototype of the lung-listening device and will soon begin field testing in Peru to fine tune the algorithm. A grant from Johns Hopkins Whiting School of Engineering will fund those early tests.

Dr. Checkley said the team hopes the device will cost around $300 to $500. While the device will work on any person, the researchers specifically hope it will help improve diagnoses for children ages 5 and under.

The team is also developing a cost-effective ultrasound tool to help physicians treat patients in the field.

Still, he added from Puno, "there's a lot of work that still needs to be done to understand how these devices can add to the repertoire of diagnostics."