Beat-by-beat analysis of cardiac output and blood pressure responses to short-term barostimulation in different body positions.
Rapid quantification of the human baro-reflex control of heart rate has been achieved on a beat-by-beat basis using a neck-chamber with quick ECG-triggered pressure changes.  Referring to recent findings on heart rate and stroke volume, the present study uses this technique to compare cardiac output as well as blood pressure changes in supine and upright position to investigate feedback effects and to confirm postural reflex modifications not revealed by RR-interval changes. A suction profile starting at +40 mmHg and running 7 steps of pressure decrease down to -65 mmHg was examined in 0 degree and 90 degrees tilting position while beat-by-beat recordings were done of heart rate, stroke volume (impedance-cardiography) and blood pressure (Finapres (tm)) (n=16). The percentual heart rate decrease failed to be significantly different between positions. A suction-induced stroke volume increase led to a cardiac output almost maintained when supine and significantly increased when upright. A decrease in all blood pressure values was found during suction, except for systolic values in upright position which increased. Conclusively, (a) it is confirmed that different inotropy accounts for the seen gravitational effect on the cardiac output not represented by heart rate (b) identical suction levels in different positions lead to different stimuli at the carotid receptor. This interference has to be considered in microgravity studies by beat-by-beat measurement of cardiac output and blood pressure.
Hildebrandt
W
W
Physiologisches Institut, Deutsche Sporthochschule Koln, Germany.
Schutze
H
H
Stegemann
J
J
D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D002307:Cardiography, Impedance; D002346:Carotid Sinus / Q000502:physiology; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology*; D011311:Pressoreceptors / Q000502:physiology*; D016683:Supine Position