title: Ventilatory baroreflex sensitivity in humans is not modulated by chemoreflex activation.
abstract: Increasing arterial blood pressure (AP) decreases ventilation, whereas decreasing AP increases ventilation in experimental animals. To determine whether a "ventilatory baroreflex" exists in humans, we studied 12 healthy subjects aged 18-26 yr. Subjects underwent baroreflex unloading and reloading using intravenous bolus sodium nitroprusside (SNP) followed by phenylephrine ("Oxford maneuver") during the following "gas conditions:" room air, hypoxia (10% oxygen)-eucapnia, and 30% oxygen-hypercapnia to 55-60 Torr. Mean AP (MAP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), expiratory minute ventilation (V(E)), respiratory rate (RR), and tidal volume were measured. After achieving a stable baseline for gas conditions, we performed the Oxford maneuver. V(E) increased from 8.8 ± 1.3 l/min in room air to 14.6 ± 0.8 l/min during hypoxia and to 20.1 ± 2.4 l/min during hypercapnia, primarily by increasing tidal volume. V(E) doubled during SNP. CO increased from 4.9 ± .3 l/min in room air to 6.1 ± .6 l/min during hypoxia and 6.4 ± .4 l/min during hypercapnia with decreased TPR. HR increased for hypoxia and hypercapnia. Sigmoidal ventilatory baroreflex curves of V(E) versus MAP were prepared for each subject and each gas condition. Averaged curves for a given gas condition were obtained by averaging fits over all subjects. There were no significant differences in the average fitted slopes for different gas conditions, although the operating point varied with gas conditions. We conclude that rapid baroreflex unloading during the Oxford maneuver is a potent ventilatory stimulus in healthy volunteers. Tidal volume is primarily increased. Ventilatory baroreflex sensitivity is unaffected by chemoreflex activation, although the operating point is shifted with hypoxia and hypercapnia.
authors.affiliation: Department of Pediatrics, New York Medical College, Valhalla, USA. Julian_Stewart@NYMC.edu
authors.forename: Julian M
authors.initials: JM
authors.lastname: Stewart
authors.forename: Eileen
authors.initials: E
authors.lastname: Rivera
authors.forename: Debbie A
authors.initials: DA
authors.lastname: Clarke
authors.forename: Ila L
authors.initials: IL
authors.lastname: Baugham
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Ocon
authors.forename: Indu
authors.initials: I
authors.lastname: Taneja
authors.forename: Courtney
authors.initials: C
authors.lastname: Terilli
authors.forename: Marvin S
authors.initials: MS
authors.lastname: Medow
mesh_terms: D000293:Adolescent; D000328:Adult; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D015992:Body Mass Index; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000188:drug therapy / Q000503:physiopathology; D018496:Hyperoxia / Q000188:drug therapy / Q000503:physiopathology; D000860:Hypoxia / Q000188:drug therapy / Q000503:physiopathology; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D055815:Young Adult
chemical_list: D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine