Separating the contributions of vascular anatomy and blood viscosity to peripheral resistance and the physiological impl
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ORIGINAL PAPER
Separating the contributions of vascular anatomy and blood viscosity to peripheral resistance and the physiological implications of interspecific resistance variation in amphibians Zachary F. Kohl • Michael S. Hedrick Stanley S. Hillman
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Received: 3 October 2012 / Revised: 24 April 2013 / Accepted: 30 April 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Amphibian pulmonary and systemic vascular circuits are arranged in parallel, with potentially important consequences for resistance (R) to blood flow. The contribution of the parallel anatomic arrangement to total vascular R (RT), independent of blood viscosity, is unknown. We measured pulmonary (RP) and systemic (RS) vascular R with an in situ Ringer’s solution perfusion technique using anesthetized anuran and urodele species to determine: (1) relative contributions of vascular anatomy and blood viscosity to RT; (2) distensibility index (%D flow kPa-1) of the pulmonary and systemic vascular circuits; and (3) interspecific correlates of variation in these parameters with red blood cell size, cardiac power output, and aerobic capacities. RP was lower than RS in anurans, while RP of the urodeles was greater than RS and significantly greater than anuran RP. Anuran RT was lowest and did not vary interspecifically, whereas urodele RT was significantly greater than anuran, and varied interspecifically. Pulmonary and systemic circuit distensibility differences may explain cardiac shunt patterns in toads with changes in cardiac output from rest to activity. When blood viscosity was taken into account, vascular resistance accounted for about 25 % of RT while blood viscosity accounted for the remaining 75 %. Owing to lower RT, terrestrial anuran species required lower cardiac power
Communicated by I. D. Hume. Z. F. Kohl (&) M. S. Hedrick Department of Biological Sciences, University of North Texas, 1155 Union Circle #305220, Denton, TX 76203-5017, USA e-mail: [email protected] Z. F. Kohl S. S. Hillman Department of Biology, Portland State University, Portland, OR 97207-0751, USA
outputs when moving fluid through their vasculature compared to aquatic species. These results indicate that physical characteristics of the vasculature can account for interspecific differences in cardiovascular physiology and suggest a co-evolution of cardiac and vascular anatomy among amphibians. Keywords Amphibian Shunt Lung evolution Resistance Viscosity Cardiovascular Abbreviations RP Pulmonary resistance RS Systemic resistance RG Gill resistance RT Total resistance RBC Red blood cell VO2max Maximal rate of O2 consumption Pi Input pressure RFR Relative flow rate Qmax Maximal blood flow rate RVM Relative ventricle mass
Introduction In closed circulatory systems, the addition of fluid to the arterial circuit taken from the venous circuit creates a pressure difference proportional to the compliances (D volume/D pressure) of the arterial and venous vasculatures. This pressure difference represents the driving force for fluid movement that is opposed by
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