393 PERIODIC BREATHING: WHAT HAPPENS IN THE MUSCLE?


 Periodic breathing (PB) is a recognized sign of poor prognosis in heart failure (HF). It is defined as a cyclic fluctuation of minute ventilation, and oxygen uptake (V̇O2) and carbon dioxide elimination (V̇CO2) at the lungs. It is unknow whether PB influences O2 availability in the cardiac, respiratory and locomotor muscles. To evaluate whether O2 availability at the muscles was affected by PB, we measured at rest, continuously and simultaneously, ventilation, ventilatory gas exchange, arterial hemoglobin O2 saturation and oxygenated/deoxygenated haemoglobin (O2Hb/HHb) content over the quadriceps by near infra-red spectroscopy (NIRS) in a patient with severe HF due to a dilated cardiomyopathy with severe biventricular dysfunction with PB at rest. NIRS application in clinical medicine started after the observation that biological tissues are quite transparent to light in the near infrared spectrum (i.e.700-1,300 nm), the second critical element that enables the use of NIRS is the oxygenation-dependent light absorbing characteristics of haemoglobin (Hb): by applying different light impulse wavelengths, the relative changes in O2Hb and HHb concentration in skeletal muscle can be monitored.
 The left panel shows cyclic fluctuation of ventilation, V̇O2, V̇CO2, PetO2 and PetCO2 patterns, which are partially out of phase between each other and respiratory exchange ratio pattern, and haemoglobin O2 saturation shows a cyclic pattern (95-90%). The cycle length of ventilation was 110 ± 6 s with an amplitude of 28.9 ± 5.1 l/min. NIRS (upper right panel) shows a directionally opposite fluctuation of O2Hb and HHb with a cycle length similar to that observed with ventilation. The average fluctuation on 6 consecutive cycles was 2.95% ± 0.27 (p<0.0001) and 2.73% ± 0.27 (p<0.0001) for O2Hb and HHb respectively. Total Hb was not significantly affected by PB in the muscle, 0.22%±0.38 (p=ns). The present study is the first recording of periodic oscillations of O2 saturated and desaturated Hb concentration at the muscular level at rest in a patient with severe HF and PB: we speculate that the cyclic ventilatory pattern is responsible for a cycling of ventilation and perfusion coupling in the lung. This so-called ventilation/perfusion mismatch induces cyclic fluctuation of blood flow to perfused but unventilated or poorly ventilated (shunt and low V̇A/Q) lung zones and to unperfused or poorly perfused (high V̇A/Q and dead space) ventilated lung zones.