title: Intravascular pressure profiles in elephant seals: hypotheses on the caval sphincter, extradural vein and venous return to the heart.
abstract: In order to evaluate hemodynamics in the complex vascular system of phocid seals, intravascular pressure profiles were measured during periods of rest-associated apnea in young elephant seals (Mirounga angustirostris). There were no significant differences between apneic and eupneic mean arterial pressures. During apnea, venous pressure profiles (pulmonary artery, thoracic portion of the vena cava (thoracic vena cava), extradural vein, and hepatic sinus) demonstrated only minor, transient fluctuations. During eupnea, all venous pressure profiles were dominated by respiratory fluctuations. During inspiration, pressures in the thoracic vena cava and extradural vein decreased -9 to -21 mm Hg, and -9 to -17 mm Hg, respectively. In contrast, hepatic sinus pressure increased 2-6 mm Hg during inspiration. Nearly constant hepatic sinus and intrathoracic vascular pressure profiles during the breath-hold period are consistent with incomplete constriction of the caval sphincter during these rest-associated apneas. During eupnea, negative inspiratory intravascular pressures in the chest ("the respiratory pump") should augment venous return via both the venae cavae and the extradural vein. It is hypothesized that, in addition to the venae cavae, the prominent para-caval venous system of phocid seals (i.e., the extradural vein) is necessary to allow adequate venous return for maintenance of high cardiac outputs and blood pressure during eupnea.
authors.affiliation: Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0204, USA. pponganis@ucsd.edu
authors.forename: P J
authors.initials: PJ
authors.lastname: Ponganis
authors.forename: T Knower
authors.initials: TK
authors.lastname: Stockard
authors.forename: D H
authors.initials: DH
authors.lastname: Levenson
authors.forename: L
authors.initials: L
authors.lastname: Berg
authors.forename: E A
authors.initials: EA
authors.lastname: Baranov
mesh_terms: D000818:Animals; D001049:Apnea / Q000503:physiopathology; D001158:Arteries / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D008955:Models, Cardiovascular; D012039:Regional Blood Flow / Q000502:physiology; D046048:Seals, Earless / Q000502:physiology*; D014680:Veins / Q000502:physiology*