Dissection of carotid sinus hypersensitivity: the timing of vagal and vasodepressor effects and the effect of body position
Résumé
Background We assessed the timing of vagal and sympathetic factors that mediate hypotension during carotid sinus massage (CSM) in patients with carotid sinus hypersensitivity. We hypothesised that a fall in cardiac output would precede vasodepression, and that vasodepression would be exaggerated by head-up tilt. Methods and results We performed pulse contour analyses on blood pressure recordings during CSM in syncope patients during supine rest and head-up tilt. In a subset we simultaneously recorded muscle sympathetic nerve activity supine. During supine rest, systolic blood pressure decreased from 150±7 mmHg to 107±7 mmHg (p<.001) and heart rate from 64±2 to 39±3 beats/minute (p<.01). Cardiac output decreased with heart rate to nadir (66± 6% of baseline), 3.1±0,4 s after onset of bradycardia. By contrast, total peripheral resistance reached nadir (77±3% of baseline) after 11±1 s. During head-up-tilt, systolic blood pressure fell from 149±10 mmHg to 90±11 mmHg and heart rate decreased from 73±4 to 60±7 beats/minute. Compared to supine rest, cardiac output nadir was lower (60±8 vs 83±4%, p<0.05), whereas total peripheral resistance nadir was similar (81±6 vs 80±3%). The time to nadir from onset of bradycardia did not differ from supine rest. At the onset of bradycardia there was an immediate withdrawal of muscle-sympathetic nerve activity while total peripheral resistance decay occurred much later (6-8 s). Conclusion The hemodynamic changes following CSM have a distinct temporal pattern that is characterised by an initial fall in cardiac output (driven by heart rate), followed by a later fall in total peripheral resistance even though sympathetic withdrawal is immediate. This pattern is independent of body position.
Domaines
Médecine humaine et pathologie
Origine : Fichiers produits par l'(les) auteur(s)