Right-to-left shunt has modest effects on C02 delivery to the gut during digestion, but compromises oxygen delivery

TY - JOUR

T1 - Right-to-left shunt has modest effects on C02 delivery to the gut during digestion, but compromises oxygen delivery

AU - Nielsen, Christian Lind Malte

AU - Malte, Hans

AU - Reinholdt, Lærke

AU - Findsen, Anders

AU - Hicks, James W.

AU - Wang, Tobias

PY - 2017/2/15

Y1 - 2017/2/15

N2 - By virtue of their cardiovascular anatomy, reptiles and amphibians can shunt blood away from the pulmonaryor systemic circuits, but the functional role of this characteristic trait remains unclear. It has been suggested that right-to-left (R-L) shunt (recirculation of systemic blood within the body) fuels the gastric mucosa with acidified and CO2-rich blood to facilitate gastric acid secretion during digestion. However, in addition to elevating PCO2, R-L shunt also reduces arterial O2 levels and would compromise O2 delivery during the increased metabolic state of digestion. Conversely, arterial PCO2 can also be elevated by lowering ventilation relative to metabolism (i.e. reducing the air convection requirement, ACR). Based on a mathematical analysis of the relative roles of ACR and R-L shunt on O2 and CO2 levels, we predict that ventilatory modifications are much more effective for gastric CO2 supply with only modest effects on O2 delivery. Conversely, elevating CO2 levels by means of R-L shunt would come at a cost of significant reductions in O2 levels. The different effects of altering ACR and R-L shunt on O2 and CO2 levels are explained by the differences in the effective blood capacitance coefficients.

AB - By virtue of their cardiovascular anatomy, reptiles and amphibians can shunt blood away from the pulmonaryor systemic circuits, but the functional role of this characteristic trait remains unclear. It has been suggested that right-to-left (R-L) shunt (recirculation of systemic blood within the body) fuels the gastric mucosa with acidified and CO2-rich blood to facilitate gastric acid secretion during digestion. However, in addition to elevating PCO2, R-L shunt also reduces arterial O2 levels and would compromise O2 delivery during the increased metabolic state of digestion. Conversely, arterial PCO2 can also be elevated by lowering ventilation relative to metabolism (i.e. reducing the air convection requirement, ACR). Based on a mathematical analysis of the relative roles of ACR and R-L shunt on O2 and CO2 levels, we predict that ventilatory modifications are much more effective for gastric CO2 supply with only modest effects on O2 delivery. Conversely, elevating CO2 levels by means of R-L shunt would come at a cost of significant reductions in O2 levels. The different effects of altering ACR and R-L shunt on O2 and CO2 levels are explained by the differences in the effective blood capacitance coefficients.

KW - Gas exchange

KW - Heart

KW - Mathematical model

KW - Reptile

KW - Shunting

UR - http://www.scopus.com/inward/record.url?scp=85013350090&partnerID=8YFLogxK

U2 - 10.1242/jeb.149625

DO - 10.1242/jeb.149625

M3 - Journal article

C2 - 27980124

SN - 0022-0949

VL - 220

SP - 531

EP - 536

JO - Journal of Experimental Biology

JF - Journal of Experimental Biology

IS - 4

ER -