Snake constriction rapidly induces circulatory arrest in rats

Abstract

As legless predators, snakes are unique in their ability to immobilize and kill their prey through the process of constriction, and yet how this pressure incapacitates and ultimately kills the prey remains unknown. In this study, we examined the cardiovascular function of anesthetized rats before, during and after being constricted by boas (Boa constrictor) to examine the effect of constriction on the prey's circulatory function. The results demonstrate that within 6 s of being constricted, peripheral arterial blood pressure (PBP) at the femoral artery dropped to 1/2 of baseline values while central venous pressure (CVP) increased 6-fold from baseline during the same time. Electrocardiographic recordings from the anesthetized rat's heart revealed profound bradycardia as heart rate (f H ) dropped to nearly half of baseline within 60 s of being constricted, and QRS duration nearly doubled over the same time period. By the end of constriction (mean 6.5±1 min), rat PBP dropped 2.9-fold, f H dropped 3.9-fold, systemic perfusion pressure (SPP=PBP−CVP) dropped 5.7-fold, and 91% of rats (10 of 11) had evidence of cardiac electrical dysfunction. Blood drawn immediately after constriction revealed that, relative to baseline, rats were hyperkalemic (serum potassium levels nearly doubled) and acidotic (blood pH dropped from 7.4 to 7.0). These results are the first to document the physiological response of prey to constriction and support the hypothesis that snake constriction induces rapid prey death due to circulatory arrest.

The big squeeze: scaling of constriction pressure in two of the world's largest snakes, Python reticulatus and P. molurus bivittatus

“…Later, Moon and Mehta (2007) tested snakes of different species and sizes, and inferred that low pressures may cause suffocation, moderate pressures may cause circulatory arrest, and extremely high pressures may cause spinal injury. Boback et al (2015) nicely extended this earlier work by directly measuring circulatory function in rats during constriction; they showed that a constriction pressure of 20 kPa can severely impede cardiac and circulatory function in rats. In the prey, heart rate decreased, cardiac electrical activity became abnormal, and blood pressure increased ca.…”

“…When fighter pilots experience negative gravitational accelerations (G-forces), they incur a rush of blood to the brain that causes rapid loss of consciousness (Balldin, 2002). Constriction pressures above the venous blood pressure of the prey will impede blood flow and oxygen delivery to tissues (reviewed by Moon and Mehta, 2007;Boback et al, 2015). Constriction pressures dramatically higher than the prey's blood pressure could force blood away from the site of constriction and into the extremities, including the head and brain.…”

“…Pressure-wave impacts occur over milliseconds, whereas snakes constrict for orders of magnitude longer. Based on our current knowledge of how pressure affects tissues, it is likely that high constriction pressures are capable of interfering with, or completely disabling, both circulatory and neural function (Toth et al, 1997;Moon, 2000;Moon and Mehta, 2007;Courtney and Courtney, 2009;Boback et al, 2015). The world's largest snakes are capable of quickly incapacitating large and potentially dangerous prey by causing multiple kinds of injuries.…”

“…In the prey, heart rate decreased, cardiac electrical activity became abnormal, and blood pressure increased ca. sixfold in the vena cava near the heart and decreased by half peripherally in the femoral artery, all indicating that constriction can induce circulatory arrest (Boback et al, 2015). However, to our knowledge, no previous work has tested the effects of constriction pressure on neural tissue, one of the most immediately important tissue systems in the prey.…”

The king of snakes: performance and morphology of intraguild predators (Lampropeltis) and their prey (Pantherophis)

“…Although both morphology and physiology are important, behavior can determine the ways in which morphological elements and physiological capacities are used (Hertz et al, 1982). For snakes that use constriction behavior, predation performance can be evaluated by measuring peak constriction pressure (Moon, 2000;Moon and Mehta, 2007;Boback et al, 2015;Penning et al, 2015;Penning and Dartez, 2016). Constriction pressure is a biologically important measure of performance (Moon and Mehta, 2007) because it can determine the time needed to subdue the prey and reduces the chances of prey escaping or causing injury to the snake.…”