Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent episodes of partial or complete upper-airway obstruction during sleep. Although cardiac autonomic impairment is involved in the development of cardiovascular disease in OSAS, the mechanism underlying this derangement is rather unknown. It can be assessed by a recently introduced analysis of the heart rate turbulence (HRT). The aim of the paper is to describe the effects of pathological respiratory pattern on HRT in OSAS. HRT has been assessed by turbulence onset (TO) and turbulence slope (TS) indexes in 20 polysomnographic recordings of severe OSAS patients, and separately calculated during both normal (NR) and obstructive apnea (OA) respiratory pattern. Results showed that, although there is an overall depressed HRT for both indexes, while the TO during OA phases is not significantly different from those of NR epochs, the TS during OA phases is very significantly higher than in NR phases. This novel finding shows a previously unknown paradoxical increase of TS during OA episodes, followed by a marked decrease during subsequent NR phases, where OSAS patient show higher sympathetic tone. Such deeper understanding of the integrated autonomic response in different OSAS pathophysiological conditions could be useful to address an overall cardiorespiratory assessment and treatment in sleep-related breathing disorders.