Cardiovascular effects of static carotid baroreceptor stimulation during water immersion in humans

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 280; no. 6; pp. H2607 - H2615
• Main Authors: Pump, Bettina, Shiraishi, Makoto, Gabrielsen, Anders, Bie, Peter, Christensen, Niels Juel, Norsk, Peter
• Format: Journal Article
• Language: English
• Published: United States 01.06.2001
• Subjects: Adult; Atrial Function, Left - physiology; Blood Pressure - physiology; Cardiovascular Physiological Phenomena; Carotid Sinus - physiology; Heart Rate - physiology; Humans; Immersion; Male; Neck - physiology; Norepinephrine - blood; Physical Stimulation; Posture - physiology; Pressoreceptors - physiology; Space life sciences; Suction; Supine Position - physiology; Vasopressins - blood
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.2001.280.6.h2607

1  Danish Aerospace Medical Centre of Research, National University Hospital, DK-2200 Copenhagen, Denmark; 2  Division of Neurology, St. Marianna University, Kanagawa, Kawasaki, Japan; 3  Department of Medical Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen; and 4  Department of Internal Medicine and Endocrinology, Herlev Hospital, DK-2730 Herlev, Denmark We hypothesized that the more-pronounced hypotensive and bradycardic effects of an antiorthostatic posture change from seated to supine than water immersion are caused by hydrostatic carotid baroreceptor stimulation. Ten seated healthy males underwent five interventions of 15-min each of 1 ) posture change to supine, 2 ) seated water immersion to the Xiphoid process (WI), 3 ) seated neck suction (NS), 4 ) WI with simultaneous neck suction ( 22 mmHg) adjusted to simulate the carotid hydrostatic pressure increase during supine (WI + NS), and 5 ) seated control. Left atrial diameter increased similarly during supine, WI + NS, and WI and was unchanged during control and NS. Mean arterial pressure (MAP) decreased the most during supine (7 ± 1 mmHg, P  < 0.05) and less during WI + NS (4 ± 1 mmHg) and NS (3 ± 1 mmHg). The decrease in heart rate (HR) by 13 ± 1 beats/min ( P  < 0.05) and the increase in arterial pulse pressure (PP) by 17 ± 4 mmHg ( P  < 0.05) during supine was more pronounced ( P  < 0.05) than during WI + NS (10 ± 2 beats/min and 7 ± 2 mmHg, respectively) and WI (8 ± 2 beats/min and 6 ±   1 mmHg, respectively, P  < 0.05). Plasma vasopressin decreased only during supine and WI, and plasma norepinephrine, in addition, decreased during WI + NS ( P  < 0.05). In conclusion, WI + NS is not sufficient to decrease MAP and HR to a similar extent as a 15-min seated to supine posture change. We suggest that not only static carotid baroreceptor stimulation but also the increase in PP combined with low-pressure receptor stimulation is a possible mechanism for the more-pronounced decrease in MAP and HR during the posture change. antidiuretic hormone; blood pressure; lower body negative pressure