Independent effects of heart–head distance and caudal blood pooling on blood pressure regulation in aquatic and terrestrial snakes

Abstract

SUMMARY Changes in orientation in a gravitational field markedly alter the patterns of blood pressure and flow in animals, especially tall or long ones such as giraffes or snakes. Vertical orientation tends to reduce blood flow and pressure in the head for two major reasons. First, the increased vertical blood column above the heart creates a gravitational hydrostatic pressure against which the heart must work. Second, expansion of dependent vessels in the lower extremities causes blood pooling and reduces return of venous blood to the heart, thereby lowering flow and pressure. For most animals, it is difficult to separate these two effects, but snakes offer the possibility of bending the animal in the region of the heart and manipulating the two ends of the body independently. We studied baroregulatory responses in terrestrial pythons (Liasis fuscus) and aquatic file snakes (Acrochordus arafurae) by tilting only the front or rear parts and then the whole animal. Changes in head blood pressure during partial tilts added up to the change during full tilt. The vertical distance to the head had twice as much influence on head blood pressure than did blood pooling in the pythons and four times as much in file snakes. This accounts for the cephalad location of the heart in terrestrial species compared with aquatic ones.

Autonomic control of heart rate during orthostasis and the importance of orthostatic-tachycardia in the snake Python molurus

“…Based on the methodology of Seymour and Arndt (2004), the inclination protocol consisted of tilting the serpents to the desired angle within ~5 s, maintaining the tilt for 1 min, and bringing them back to the horizontal position for at least 5 min. It is important to emphasize that it was not possible to continue the inclination for over 1 min or even to perform it in an angle above 60°, because under these conditions, the animals tried to move excessively and prevented data collection.…”

Understanding the Vital Signs: BP, HR, RR, TEMP, SaO2 … and SV

“…This observation also accounts for the cephalad location of the heart in terrestrial snakes as compared with aquatic snakes…. else terrestrial snakes would faint when they tried to climb a tree [4]. FYI: Birds have a higher BP than humans.…”

Intraspecific scaling of arterial blood pressure in the Burmese python

“…The cardiovascular system of long-bodied animals, such as snakes, is particularly affected by gravity, and terrestrial and arboreal species are endowed with effective physiological mechanisms and structural adaptations that prevent pooling of blood in the lower body parts and maintain cardiac filling when body position is altered (Lillywhite, 1987;Lillywhite, 2005;Lillywhite and Donald, 1994;Lillywhite and Gallagher, 1985;Seymour and Arndt, 2004;Lillywhite et al, 2012). An interspecific comparison of 16 individuals belonging to nine different species of terrestrial snakes revealed a significant rise in MAP with body length, such that MAP increased proportionally to the distance between the heart and the head when expressed as the rise in gravitational pressure (ρgh) (Seymour, 1987).…”