Use of a Wearable Biosensor to Study Heart Rate Variability in Chronic Obstructive Pulmonary Disease and Its Relationship to Disease Severity oleh Seon-Cheol Park, Narongkorn Saiphoklang, Donghyun Jung, David Gomez, Jonathan E. Phillips, Brett A. Dolezal, Donald P. Tashkin, Igor Barjaktarevic, Christopher B. Cooper