CONTRIBUTIONS OF TIDAL LUNG-INFLATION TO HUMAN R-R INTERVAL AND ARTERIAL-PRESSURE FLUCTUATIONS

We studied the effects of mechanical lung inflation on respiratory fre quency R-R interval and arterial pressure fluctuations in nine healthy young adults undergoing elective orthopedic surgery. We conducted thi s research to define the contribution of pulmonary and thoracic stretc h receptor input to respiratory sinus arrhythmia. We compared fast Fou rier transform spectral power during three modes of ventilation: (1) s pontaneous, frequency-controlled (0.25 Hz) breathing, (2) intermittent positive pressure ventilation (0.25 Hz, with a tidal volume of 8 ml/k g) and (3) high frequency jet ventilation (5.0 Hz, 2.5 kg/cm(2)), afte r sedation and vecuronium paralysis. Mean R-R intervals, arterial pres sures and arterial blood gas levels were comparable during all three b reathing conditions. Respiratory frequency systolic pressure spectral power was comparable during spontaneous breathing and conventional mec hanical ventilation, but was significantly reduced during high frequen cy jet ventilation (P < 0.05). Respiratory frequency R-R interval spec tral power (used as an index of respiratory sinus arrhythmia) declined dramatically with sedation and muscle paralysis (P < 0.05), but was g reater during conventional mechanical, than high frequency jet ventila tion (P < 0.05). These results suggest that although phasic inputs fro m pulmonary and thoracic stretch receptors make a statistically signif icant contribution to respiratory sinus arrhythmia, that contribution is small. (C) 1998 Elsevier Science B.V.