Preliminary “in vivo” study on peripheral venous pressure (PVP) in the equine finger in static and quasi-static movements and “foot pump” mechanism.

There is a marked interest in the mechanism and function of the finger and the hoof of the horse, but there is a lack in the literature of "in vivo" investigation of the behavior of the Peripheral Venous Pressure (PVP) in the finger and the local effect of the mechanism of the "foot pump". Two theories explain this mechanism:1)the blood is withdrawn thanks to the dilation or "elaterio" of the posterior foot region (Strasser 2001); 2)the hoof squeezes the blood during the load phase (Pollit 1996). Aim of the Study The aim of this "in vivo" preliminary work is to study the PVP in the horse foot in static and quasi-static conditions in order to investigate the effect of the mechanism of "foot pump" on the local peripheral circulation. The mechanism of the "foot pump" has been evaluated by the PVP changes in relation to the different loads on the front legs during different moviments (static and quasistatic). Materials and methods The surveys were conducted on the forelimb in "clinically healthy" horses: 7 competitive (4 shod and 3 unshod) and 3 non-competitive never shod horses. The lateral digital vein was canulated under local anesthesia and PVP measuremed after 120 min in order to exclude possible influences on the vascular tone. Local PVP was electronically evaluated with the horse’s forelimbs in static and quasi-static conditions: a)four Feet Standing, on the ground (4FS-g), examined foot lifted and loaded; b)four Feet Standing, both forelimbs on the podoblocks (4FS-p) examined foot lifted and loaded; c)standing, controlateral forelimb lifted and loaded (3FS-g); d)standing, both forelimbs on the podoblocks, controlateral forelimb lifted and loaded (3FS-p); e)standing, forelimb on the podoblocks, controlateral forelimb lifted and loaded (3FS-p); e)standing, forelimb on the podoblocks, controlateral forelimb lifted and palmar angle variation on the examined foot (-15°/0°/+15°) (3FS-a), f)four Feet Standing, head and neck turned laterally (4FS-1). The statistical analysis is performed by analysis of variance with ANOVA and t student. Result No differences in baseline values of PVP were observed between right and left limb of the same horse. Shod and unshod horses in standing position showed a significant difference (p<0,05) in PVP, independently from their competitive activity. Significant local PVP variations were recorded in the examined leg when loaded after lifting (p<0.05), both when evaluated on the ground or on the podoblock. When the examined foot was lifted (4FS-g), a significant reduction in PVP was recorded (-18,31±3.02 mmHg) after loaded. Lifting the contralateral leg in 3FS-g condition, the PVP value showed a rapid slight increase followed by a significant reduction (-11±3.4 mmHg) and a slow return to baseline. Comparing the two results, the difference is statistically significant (p<0.05). A similar variation was observed in conditions 4FS-p and 3FS-p.The lifting of one forelimb causes a concomitant involvement of the contralateral leg: the influence of this active quasi-static condition, as in 3FS-g and 3FS-p, in the horse foot may be attributed to the isometric muscular contraction rather then to the different distribution of the weight. This evidence supports the theory that attributes the "blood pumping" action to the phalangeal flexion-extension since there is a concurrent muscular action on the local vascular system and on the corium microcirculation (Pollit 1996). The study was communicated to Italian Ministry of Health 24 January 2014. Pollitt CC 1996 Eq Vet J 28,38-46. Strasser H 2001