In May, a magnitude 7.4 earthquake hit Madoi county, Qinghai province, turning the sparsely populated county seat into a sea of navy blue disaster-relief tents.

Inside a tent pitched near the hospital, Xu Dong, a renowned heart surgeon whose consulting rooms in Beijing are usually fully booked, was providing local ethnic Tibetans with free diagnoses.

To advise older patients who only spoke Tibetan, Xu, director of the cardiac surgery department at Beijing Tiantan Hospital, turned to a younger member of the group who could speak Mandarin.

Scores of patients had gathered outside the tents set up by Xu and his colleagues. They patiently waited their turn in the freezing drizzle that is common during the fleeting summer on the Qinghai-Tibet Plateau, which stands at an altitude of 4,500 to 5,000 meters.

Many said they had received WeChat messages announcing that experienced doctors from the "lower regions" would be arriving.

Some had driven hundreds of kilometers from their rural communities for one-on-one consultations with experts specializing in problems related to the bones, cardiac issues, the digestive system, gynecology and traditional Chinese medicine.

With prescriptions issued by the specialists, the patients could receive free medication donated by a pharmaceutical company.

Xu, 57, was one of 302 medical and health experts from across the nation who had traveled to the Golog Tibetan autonomous prefecture to help remedy a shortage of high-quality medical resources on the oxygen-deficient plateau that is home to many ethnic Tibetans.

The prefecture's Madoi, an elevated area that is promoted as the "source of the Yellow River", is known for its tough working conditions.

A wall on one street bears an encouraging banner that says local residents "may run short of oxygen, but not a hardworking spirit".

Xu and his colleagues were volunteers for China-Hearts, a charity program launched in 2008, the year a devastating quake tore apart Wenchuan, a sleepy town in Sichuan province, killing more than 69,000 people. The tragedy fueled a nationwide fervor for volunteer work.

The visit to Madoi was Xu's 11th trip to the plateau regions that the program had arranged since 2013.

Over the years, he has advised thousands of herders, from Sichuan and Yunnan provinces to the Tibet autonomous region, mostly at rural clinics that are well-equipped but lack highly trained medical professionals.

China-Hearts has arranged about 2,000 surgeries for children with congenital heart problems in these high places, and Xu has been involved in more than 60 of them.

"As a doctor, I feel honored to do at least something to help them," he said.

Traveling with Xu were some big names from China's medical community, including Dong Jiahong, a leading expert on liver treatment, surgery and transplants. Dong's focus was on echinococcosis or hydatid disease, a parasitic illness caused by liver tapeworms that is common among herders who roam China's northwestern regions.

Herders often have cardiovascular conditions, such as chronic high blood pressure and congenital heart disease.

Experts and local health officials attribute this to a number of factors including the high altitude－where the poor oxygen concentration and low temperatures pose a major health risk－and a lack of awareness of management of chronic disease.