title: Dynamics of the RR-interval versus blood pressure relationship at exercise onset in humans.
abstract: OBJECTIVE
  The dynamics of the postulated phenomenon of exercise baroreflex resetting is poorly understood, but can be investigated using closed-loop procedures. To shed light on some mechanisms and temporal relationships participating in the resetting process, we studied the time course of the relationship between the R-R interval (RRi) and arterial pressure with a closed-loop approach.
  
  
  METHODS
  On ten young volunteers at rest and during light exercise in supine and upright position, we continuously determined, on single-beat basis, RRi (electrocardiography), and arterial pressure (non-invasive finger pressure cuff). From pulse pressure profiles, we determined cardiac output (CO) by Modelflow, computed mean arterial pressure (MAP), and calculated total peripheral resistance (TPR).
  
  
  RESULTS
  At exercise start, RRi was lower than in quiet rest. As exercise started, MAP fell to a minimum (MAPm) of 72.8 ± 9.6 mmHg upright and 73.9 ± 6.2 supine, while RRi dropped. The initial RRi versus MAP relationship was linear, with flatter slope than resting baroreflex sensitivity, in both postures. TPR fell and CO increased. After MAPm, RRi and MAP varied in opposite direction toward exercise steady state, with further CO increase.
  
  
  CONCLUSIONS
  These results suggest that, initially, the MAP fall was corrected by a RRi reduction along a baroreflex curve, with lower sensitivity than at rest, but eventually in the same pressure range as at rest. After attainment of MAPm, a second phase started, where the postulated baroreflex resetting might have occurred. In conclusion, the change in baroreflex sensitivity and the resetting process are distinct phenomena, under different control systems.
authors.affiliation: Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.|Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bringard
authors.affiliation: Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland.|Division of Respiratory and Critical Care Physiology and Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson St, Torrance, CA, 90502, USA.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Adami
authors.affiliation: Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Viale Europa 11, 25123, Brescia, Italy.
authors.forename: Nazzareno
authors.initials: N
authors.lastname: Fagoni
authors.affiliation: Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.|Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland.
authors.forename: Timothée
authors.initials: T
authors.lastname: Fontolliet
authors.affiliation: Service de Pneumologie, Programme Hypertension Pulmonaire, Département des Spécialités de Médecine, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Lador
authors.affiliation: Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland.|Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Moia
authors.affiliation: Dipartimento di Scienze Neurologiche, Biomediche e del Movimento, Università di Verona, Via Felice Casorati 43, 37131, Verona, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Tam
authors.affiliation: Département d'Anesthésiologie, Pharmacologie et Soins Intensifs, Hôpitaux Universitaires de Genève, 4 rue Gabrielle-Perret-Gentil, CH-1211, Genève 4, Switzerland. Guido.Ferretti@unige.ch.|Département des Neurosciences Fondamentales, Université de Genève, 1 rue Michel Servet, CH-1211, Genève 4, Switzerland. Guido.Ferretti@unige.ch.|Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, Viale Europa 11, 25123, Brescia, Italy. Guido.Ferretti@unige.ch.
authors.forename: Guido
authors.identifier: http://orcid.org/0000-0001-7592-0416
authors.initials: G
authors.lastname: Ferretti
mesh_terms: D000328:Adult; D017704:Baroreflex; D001794:Blood Pressure; D002302:Cardiac Output; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011187:Posture
keywords: Baroreflex resetting; Baroreflex sensitivity; Exercise transients; Heart rate; Mean arterial pressure; Peripheral resistance