Abstract
We recently found (Aliverti, JApplPhysiol, 2010) that during quiet breathing (QB) at rest a small quantity of blood is shifted from the splanchnic vascular bed to the extremities by increasing abdominal pressure (Pab) with diaphragmatic descent. To study if and how blood is displaced to/from the thorax also during exercise, when abdominal muscles contribute to generate Pab variations, in 11 healthy subjects (8M, 3F, 25±7yrs, 70±11kg, 1.78±0.1m) changes in body volume (Vb) and trunk volume (Vtr) were measured simultaneously by whole body and optoelectronic plethysmography, respectively. The volume of blood shifts between the thorax and extremities (Vbs) was obtained as ΔVtr-ΔVb during QB at rest and 3 different types of submaximal constant exercise (ankle flexion against a resistance): spontaneous (SE), rib cage (RCE, voluntary emphasized inspiratory rib cage breathing) and abdominal (ABE, voluntary active abdominal expiration breathing) exercise.
At rest, within breath tidal Vbs averaged 126±94ml. During SE, RCE and ABE it averaged 338±108ml, 420±260ml, 457±207ml, respectively(p<0.001 vs rest). During SE and RCE blood was displaced from the extremities into the thorax (190±313 and 584±508ml, respectively), while during ABE it was displaced from the thorax to the extremities (223±166ml). Oxygen consumption was 3.5±0.5, 17.5±3, 14.9±3 and 14.4±3ml/Kg*min-1, respectively during rest, SE, RCE and ABE.
Our results suggest that even during low levels of exercise significant blood shifts occur from the thorax to the extremities and viceversa. The direction and amount of blood displacement depend on the relative predominance of the action of diaphragm, rib cage and abdominal muscles.
- © 2013 ERS