Cardiorespiratory interactions during periodic breathing in awake chronic heart failure patients

We applied spectral techniques to the analysis of cardiorespiratory signals [instantaneous lung volume (ILV), instantaneous tidal volume (ITV), arteri al O-2 saturation (Sa(o2)) at the ear, heart rate (HR), systolic (SAP), and diastolic (DAP) arterial pressure] during nonapneic periodic breathing (PB ) in 29 awake chronic heart failure (CHF) patients and estimated the timing relationships between respiratory and slow cardiovascular (<0.04 Hz) oscil lations. Our aim was 1) to elucidate major mechanisms involved in cardiores piratory interactions during PB and 2) to test the hypothesis of a central vasomotor origin of PB. All cardiovascular signals were characterized by a dominant (greater than or equal to 84% of total power) oscillation at the f requency of PB (mean +/- SE: 0.022 +/- 0.0008 Hz), highly coherent (greater than or equal to 0.89), and delayed with respect to ITV (ITV-HR, 2.4 +/- 0 .72 s; ITV-SAP, 6.7 +/- 0.65 s; ITV-DAP, 3.2 +/- 0.61 s; P < 0.01). Sa(o2) was highly coherent with (coherence function = 0.96 +/- 0.009) and almost o pposite in phase to ITV. These findings demonstrate the existence of a gene ralized cardiorespiratory rhythm led by the ventilatory oscillation and sug gest that 1) the cyclic increase in inspiratory drive and cardiopulmonary r eflexes and 2) mechanical effects of PB-induced changes in intrathoracic pr essure are the more likely sources of the HR and blood pressure oscillation s, respectively. The timing relationship between ITV and blood pressure sig nals excludes the possibility that PB represents the effect of a central va somotor rhythm.