Exercise‐induced pulmonary perfusion redistribution in heaves

Abstract

SummaryThis study aimed to compare exercise-induced pulmonary perfusion redistribution in healthy vs. 'heavey' horses using scintigraphy, a minimally invasive technique. Six healthy (A) and 5 'heavey' horses in remission (B I ) and during clinical signs of disease (B II ) were investigated. Dimensions of the exercising pulmonary perfusion (Q E ) images were expressed in percent of the resting perfusion (Q R ) images. Computed Q E to Q R ratios (Q E /Q R ) images enabled the definition of the region more perfused at exercise than at rest (R 1 ).In all groups, exercise induced a major enlargement of the Q image but a larger increase of the lung height was found in 'heavey' horses. Compared to A, 'heavey' horses showed a larger R 1 region with a significantly higher Q E /Q R . Location of R 1 pointed out the dorsal lung region as a major site of pulmonary perfusion redistribution for all groups.This work demonstrated (1) the feasibility of using scintigraphy for studying exercise-induced pulmonary perfusion redistribution; (2) perfusion redistribution to the dorsal lung with exercise and (3) an intensified redistribution in 'heavey' horses, either clinically affected or not.

Respiratory diseases and their effects on respiratory function and exercise capacity

“…They showed that the caudodorsal region of the thorax experienced larger pressure oscillations than other regions, and post mortem and histopathological studies have demonstrated that EIPH occurs precisely in that region . Ventilation heterogeneity is also accompanied by regional variations in perfusion . During exercise, blood flow increases primarily in the dorsal‐caudal region of the lung .…”

The effects of pulse‐delivered inhaled nitric oxide on arterial oxygenation, ventilation‐perfusion distribution and plasma endothelin‐1 concentration in laterally recumbent isoflurane‐anaesthetized horses

“…; Harmegnies et al. ). However, there is evidence that this does indeed occur as blood flow was shunted to the nondependent lung in anaesthetized laterally‐recumbent horses (Stolk ).…”

“…This is also most likely the mechanism in the horse, although this is still unproven and somewhat in question since success of this therapy would require overcoming gravitational effects caused by the large vertical lung gradient in an adult horse. Although normal pulmonary blood flow distribution in the horse is only partially gravity-dependent, the fact that the shunt occurs in the dependent lung means that blood redistributed from the shunt would have to more against gravity (Dobson et al 1985;Bernard et al 1996;Hlastala et al 1996;Erickson et al 1999;Harmegnies et al 2002). However, there is evidence that this does indeed occur as blood flow was shunted to the nondependent lung in anaesthetized laterally-recumbent horses (Stolk 1982).…”

Lower airway function

“…It must be pointed out that perfusion heterogeneity is greater in horses suffering from recurrent airway obstruction than in healthy horses. 44 Vascular diameter is modulated by smooth muscles that respond to vasoactive compounds. A wide range of mediators can modulate vascular smooth muscle tone, and among these epinephrine, norepinephrine, dopamine, prostaglandin and endothelin, 45 which is notably potent, are vasoconstrictors, and isoproterenol, bradykinin, histamine, nitric oxide and acetylcholine produce vasodilatation.…”