Intraspecific scaling of arterial blood pressure in the Burmese python

Abstract

Interspecific allometric analyses indicate that mean arterial blood pressure (MAP) increases with body mass of snakes and mammals. In snakes, MAP increases in proportion to the increased distance between the heart and the head, when the heart-head vertical distance is expressed as ρgh (where ρ is the density of blood, g is acceleration due to gravity and h is the vertical distance above the heart), and the rise in MAP is associated with a larger heart to normalize wall stress in the ventricular wall. Based on measurements of MAP in Burmese pythons ranging from 0.9 to 3.7 m in length (0.20-27 kg), we demonstrate that although MAP increases with body mass, the rise in MAP is merely half of that predicted by heart-head distance. Scaling relationships within individual species, therefore, may not be accurately predicted by existing interspecific analyses.

What makes the heart of Boa constrictor (Squamata: Boidae) beat faster?

“…A negative relationship between heart rate and body mass had been previously reported in reptiles, and more specifically snakes (SEYMOUR 1987, LILLYWHITE et al 1999, ENOK et al 2014). Seymour's results are restricted to Australian snakes and were obtained from a small sample size (only 13 individuals in nine different species).…”

“…Even though most modern studies have used another method to measure heart rate, which includes a surgically inserted catheter filled with heparinized saline connected to a pressure transducer (WANG et al 2001, ENOK et al 2014, we have found that our method produces similar results (see discussions below for more details). Furthermore, digital palpation is easier to perform, cheaper, and safer for the subjects.…”

“…Seymour's results are restricted to Australian snakes and were obtained from a small sample size (only 13 individuals in nine different species). The heart rate of Burmese pythons, Python bivittatus Kuhl, 1820, is negatively related with body size (ENOK et al 2014), but the HR values obtained for this species are lower than for B. constrictor. This may be due to differences in mass between the two species.…”

“…Metabolic rates influence heart rate and other physiological responses. Large vertebrates have slower heart rate when compared with smaller ones (LILLYWHITE et al 1999, SCHMIDT-NIELSEN 2002, a pattern that has been confirmed for some Australian snakes (SEYMOUR 1987) and Burmese pythons (ENOK et al 2014). In one study conducted on snake embryos (DU et al 2013) the heart rate was higher in small species than in larger ones.…”

“…In one study conducted on snake embryos (DU et al 2013) the heart rate was higher in small species than in larger ones. However, general laws governing cardiovascular functions and body size may have exceptions, and for this reason it is important to evaluate whether or not they apply to different species (ENOK et al 2014). This is particularly true for snakes, a group for which the relationship between heart rate and body size remains relatively unexplored.…”