1 Dept of Pulmonary Medicine, Critical Care Medicine and Sleep Disorders, Vardhman Mahavir Medical College and Safdarjung Hospital (VMMC&SJH), New Delhi, India.
2 Medical Institute of Sumy State University, Sumy, Ukraine.
3 Military Medical Academy, Sofia, Bulgaria.
4 Sleep and Ventilation Unit, Royal Brompton and Harefield NHS Foundation Trust, London, UK.