Comparative Effects of Hypoxia on Respiratory and Cardiac Function in Reptiles

Respiratory responses to short term hypoxia in the snapping turtle, Chelydra serpentina

“…Heart rate increases 2.2-fold in agreement with earlier studies (Boyer, 1966). An increase in the cardiac output and/or a decrease in the R-L shunt determines an increase in the pulmonary blood flow (Burggren et al, 1977;Crossley et al, 1998).…”

“…ing (Vitalis and Milsom, 1986b) and is subjected to vagal control from pulmonary stretch receptors (Milsom, 1990). On the basis of the values for oxygen uptake previously reported (Boyer, 1966), and our data for ventilation volume, pulmonary oxygen extraction can be estimated to increase from 0.19 in normoxia to 0.39 at 5% O 2 . Similar increases in extraction have been observed in Trachemys scripta (Jackson, 1973), and are probably common in all turtles.…”

“…Snapping turtles exposed to different degrees of hypoxia displayed the typical increase in total ventilation previously reported in other chelonian species when inspired oxygen tensions dropped below a certain threshold (Boyer, 1966;Jackson, 1973;Benchetrit et al, 1977;Burggren et al, 1977;Glass et al, 1978Vitalis and Milsom, 1986a), which in snapping turtles appears to be between 5 and 10 kPa O 2 .…”

“…The preferential modulation of ventilation frequency in determining total expired volume in turtles is thought to be an adaptive strategy to minimize the cost of breath- a V : A , alveolar ventilation; P 50 , oxygen tension at half-saturation; Q : sys , systemic blood flow; Q : pul , pulmonary blood flow; Pa O 2 , arterial oxygen tension. Constants utilized in the model analysis: Hill coefficient= 1.75 (this study); blood oxygen carrying capacity=3.98 mmol l −1 (this study); lung diffusion deficit= 10 mmHg (Wang and Hicks, 1996); tidal volume = 30.6 ml BTPS kg −1 (this study); lung anatomical dead space =0.7 ml BTPS kg −1 (Vitalis and Milsom, 1986a) and rate of oxygen uptake= 0.25 ml min −1 kg −1 (Boyer, 1966). Alveolar ventilation and shunt flow were obtained by calculation.…”

“…In snapping turtles (Chelydra serpentina), oxygen uptake is maintained relatively constant even when the inspired oxygen fraction is as low as 2%, which is partly achieved via cardiorespiratory adjustments (Boyer, 1966). However, it is at present not known whether the well-known ability of this and other turtle species to withstand hypoxia (Ultsch, 1985) could also be due to adjustments at the molecular level, altering blood oxygen binding properties, as known for other vertebrates.…”