Intramyocardial blood volume, perfusion and transit time in response to embolization of different sized microvessels.
OBJECTIVE
To study the role of the coronary microcirculation in response to different-sized microemboli, we measured changes in intramyocardial microvascular blood volume (Bv), perfusion (F) and transit time (TT) and also microvascular patterns of injury.


METHODS
Bv, F and TT were quantitated in 24 pigs at baseline and again 2 min after repeat injections of 10- or 100-microm microspheres at rest or during intracoronary adenosine infusion. The association of Bv and TT was assessed in the microsphere pigs and in nine control pigs. Microvascular injury was studied on gross-pathologic and histologic samples.


RESULTS
At rest, initial injection of 10-microm microspheres led to increases in Bv and F, but progressively decreased with additional injections. In contrast, even small numbers of 100-microm microspheres always led to decreases in Bv and F. Injection of microspheres during adenosine-induced vasodilation always resulted in decreases in peak Bv and F irrespective of their diameters, but microvascular TTs remained unaltered. In control pigs, however, TTs were inversely related to adenosine-induced changes in Bv. Histologically, 100-microm microspheres resulted in patchy distribution of microcirculatory plugging, while 10-microm microspheres induced contiguous hemorrhagic myocardial injury.


CONCLUSIONS
Microsphere-induced changes in intramyocardial Bv and F and the associated pattern of myocardial injury are related to the size of embolized microvessels and the initial perfusion state. Microvascular functional volume reserve mechanisms appear to play a key role accompanying flow- and TT-preservation.
Möhlenkamp
Stefan
S
Department of Physiology and Biophysics, Alfred 2-409, Mayo Clinic and Foundation, Rochester, MN 55905, USA.
Beighley
Patricia E
PE
Pfeifer
Eric A
EA
Behrenbeck
Thomas R
TR
Sheedy
Patrick F
PF
Ritman
Erik L
EL
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001810:Blood Volume / Q000187:drug effects; D003326:Coronary Circulation / Q000187:drug effects; D003327:Coronary Disease / Q000473:pathology / Q000503:physiopathology*; D004617:Embolism / Q000473:pathology / Q000503:physiopathology*; D006439:Hemodynamics; D008297:Male; D008833:Microcirculation; D008863:Microspheres; D009206:Myocardium / Q000473:pathology; D013552:Swine; D014665:Vasodilator Agents / Q000494:pharmacology
D014665:Vasodilator Agents; D000241:Adenosine