Cardioinhibitory-vasodepressor response to head-up tilt without hypoxaemia or myocardial ischaemia.
We evaluated whether hypoxaemia and/or myocardial ischaemia are of importance for development of the bradycardic hypotensive phase (cardioinhibitory-vasodepressor syncope) of central hypovolaemia. Arterial blood gas variables and a twelve-lead electrocardiogram (ECG) were followed during head-up tilt in seven men. During tilt, before presyncopal symptoms appeared, mean arterial pressure (MAP) increased (from 67 +/- 7 to 78 +/- 6 mmHg) (mean +/- SE) as did heart rate (HR) (61 +/- 4 to 99 +/- 8 beats min-1) and total peripheral resistance (TPR) (11 +/- 1 to 17 +/- 1 mmHg min l-1) (P < 0.01), while cardiac output (5.9 +/- 0.5 to 4.6 +/- 0.6 l min-1) and central venous pressure (CVP) (4.2 +/- 0.4 to 1.3 +/- 0.7 mmHg) decreased (P < 0.01). After 40 +/- 7 min of head-up tilt presyncopal symptoms appeared together with a decrease in MAP to 48 +/- 7 mmHg, HR to 71 +/- 11 beats min-1 and TPR to 9 +/- 2 mmHg min l-1 (P < 0.01). Arterial oxygen tension was not changed and there was no ST-segment depression of the ECG. The results indicate that during central hypovolaemia decreases in HR and TPR are elicited during normoxaemia and without electrocardiographic signs of myocardial ischaemia.
Matzen
S
S
Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark.
Secher
N H
NH
D000328:Adult; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D001808:Blood Vessels / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology; D002307:Cardiography, Impedance; D002496:Central Venous Pressure / Q000502:physiology; D004562:Electrocardiography; D006257:Head / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D017202:Myocardial Ischemia / Q000503:physiopathology*; D011187:Posture; D014655:Vascular Resistance / Q000502:physiology