Effects of heart rate on hemodynamic severity of @entity3979 in the XXXX .

@entity1423 @entity235 @entity450 @entity3979 @entity850
In 14 open-chest mongrel @entity235 , the effects of heart rate on hemodynamic severity of proximal @entity3979 were studied. @entity850 was produced by a circumferential wire snare on left circumflex coronary artery. An intermediate @entity850 was defined by reduction of peak reactive @entity450 response to 200% of control flow, a critical @entity850 by prevention of any reactive @entity450 flow to a 15-s occlusion. Heart rate was increased stepwise from control to 160 and 200 beats/min by left atrial pacing. In intermediate @entity850 , increased pacing rate reduced peripheral coronary pressure distal to the @entity850 from 77 +/- 3 to 73 +/- 4 to 65 +/- 3 mm Hg (p less than 0.05) and increased @entity850 resistance from 0.30 +/- 0.05 to 0.34 +/- 0.05 to 0.35 +/- 0.05 resistance units (p less than 0.05). In critical @entity850 , increased heart rate changed peripheral coronary pressure from 45 +/- 5 to 49 +/- 5 to 48 +/- 5 mm Hg (p less than 0.01) and reduced stenotic resistance from 1.24 +/- 0.19 to 1.08 +/- 0.18 to 1.15 +/- 0.19 resistance units (p less than 0.005). A significant correlation between changes in stenotic resistance and peripheral coronary pressure was obtained (r = -0.71, p less than 0.001). In maximally dilated coronary arteries, a circumferential @entity850 decreased circumflex artery flow to 50%. Increased pacing rate up to nearly 200 beats/min raised peripheral coronary pressure distal to the @entity850 from 51 +/- 4 to 56 +/- 4 mm Hg (p less than 0.005) and changed stenotic resistance from 0.41 +/- 0.13 to 0.30 +/- 0.06 to 0.33 +/- 0.10 resistance units (p less than 0.05). It is assumed that the changes in peripheral coronary pressure alter the luminal area of the @entity850 and hence calculated stenotic resistance. Other possible mechanisms like turbulent streaming, vasomotion or @entity1423 appear to be of minor importance in the present experimental conditions.
