RESPIRATION-SYNCHRONOUS FLUCTUATIONS IN STROKE VOLUME, HEART-RATE ANDARTERIAL-PRESSURE IN HUMANS

1. Simultaneous recordings of beat-to-beat left cardiac stroke volume (SV, pulsed ultrasound Doppler), mean arterial pressure (MAP) and hear t rate (HR) were obtained in ten healthy young adults during spontaneo us respiration at supine rest, before and after cholinergic blockade b y atropine (0.035 mg kg-1). 2. Respiration-synchronous fluctuations in SV, HR, cardiac output (CO) and MAP were quantified by spectral analy sis of the recordings of each of these variables. 3. Before atropine a dministration, respiration-synchronous fluctuations in HR and SV were prominent. The changes in HR and SV were inversely related and variati on in SV was the main source of respiratory variability in CO. Respira tion-synchronous fluctuations in MAP were mainly caused by variations in CO. 4. After cholinergic blockade, respiratory HR variations were e liminated, whereas the respiratory fluctuations in SV persisted. The f luctuations in CO and MAP increased. In this situation, mechanically i nduced variations in SV were not counteracted by inverse HR fluctuatio ns and the influence on CO thus increased. 5. The main source of respi ratory fluctuations in MAP in supine humans is thus variation in SV, w hile inverse, vagally mediated HR variations tend to reduce the fluctu ations in CO and MAP.