Cardiorespiratory coupling is influenced by body position and slow paced 0.1Hz breathing in a state specific manner

Objective: Cardiorespiratory coupling (CRC), a set of cardiac and respiratory rhythms that optimise the body oxygenation and the adaptability of the cardiorespiratory system to the external and internal environment, RRI vagal and sympathetic modulation, quiescence,


Methods:
The ECG (RRI) and respiration signals were simultaneously recorded in 20 healthy human subjects in four conditions.

Subjects
We conducted the study protocol on 20 healthy adult human subjects (13 males, age 34.4±7.4) which was approved by Ethical Committee of Faculty of Medicine, University of Belgrade. Inclusion criteria: absence of any health problems and an age between 20 and 45 years. Exclusion criteria were: subjugation to any therapy (acupuncture, medications, etc); a history of cardiovascular, pulmonar or any other diseases; presence of any health disorders, at the time of the assessment, pathological symptoms during the experimental procedures. For female participants an additional criterium of exclusion was the second part of menstrual cycle .
All participants were advised to refrain from food and drink about 4 hours before the experiment, not to exercise, to be restful and alert.

Study protocol
The study protocol was performed under controlled laboratory conditions at the Laboratory for biosignals, Institute for Biophysics, Faculty of Medicine, University of Belgrade. It was conducted in quiet, refreshing and constant temperature environment (22±1ºC). Experiments were undertaken between 8 and 12 AM 4 . All subjects were subjected to 10 minutes of relaxation in a supine position before recording. There was no restriction imposed on the air flow rate. They were also strictly instructed not to talk during the experimental procedures.The ECG (RRI) and respiration signals were simultaneously recorded in 4 conditions/sessions: supine and standing positions at spontaneous breathing rates,and in supine and standing positions with the slow paced 0.1Hz breathing rates. Session recordings lasted for 20 minutes, with a 5 minute pause between the supine and standing position, in order to meet the criteria for cardiorespiratory complexity analysis 5,6 and to obtain the stabilization of autonomic regulation in each state 4 . The sequence of these four sessions was randomly chosen. Slow breathing with a paced rhythm of 0.1 Hz was dictated by a computer web metronom (www.webmetronome.com). Subjects were trained and instructed for slow breathing regime before the recording sessions.

Data acqusition
ECG and respiration signal acquisition was done by means of Biopac MP100 system (Biopac System, Inc, Santa Barbara, CA, USA;AcqKnowledge 3,91 software). Main ECG lead registration electrodes were attached on the projections of clavicle bones and the grounding on the ancle of the right leg.The belt with resistive strain gauge transducer for continuous recording of breathing was placed slightly above the costal line. Both signals were sampled with 1000 Hz frequency rate. These results support provocative hypothesis that Qpr might be a promising marker of cardiorespiratory ventilation-perfusion efficiency, specifically increased during slow 0.1Hz breathing.
Further research on this hypothesis is necessary.