title: Direct observation of epicardial coronary capillary hemodynamics during reactive hyperemia and during adenosine administration by intravital video microscopy.
abstract: Using high-resolution intravital charge-coupled device video microscopy, we visualized the epicardial capillary network of the beating canine heart in vivo to elucidate its functional role under control conditions, during reactive hyperemia (RH), and during intracoronary adenosine administration. The pencil-lens video-microscope probe was placed over capillaries fed by the left anterior descending artery in atrioventricular-blocked hearts of open-chest, anesthetized dogs paced at 60-90 beats/min (n = 17). In individual capillaries under control conditions, red blood cell flow was predominant during systole or diastole, indicating that the watershed between diastolic arterial and systolic venous flows is located within the capillaries. Capillary flow increased during RH and reached a peak flow velocity (2.1 +/- 0.6 mm/s), twice as high as control (1.2 +/- 0.5 mm/s), with enhancement of intercapillary cross-connection flow and enlargement of diameter (by 17%). With adenosine, capillary flow velocity significantly increased (1.8 +/- 0.7 mm/s). However, the increase in volumetric capillary flow with adenosine estimated from red blood cell velocity and diameter was less than the increase in arterial flow, whereas that during RH was nearly equivalent to the increase in arterial flow. There was a time lag of approximately 1.5 s for refilling of capillaries during RH, indicating their function as capacitance vessels. In conclusion, the coronary capillary network functions as 1) the major watershed between diastolic-dominant arterial and systolic-dominant venous flows, 2) a capacitor, and 3) a significant local flow amplifier and homogenizer of blood supply during RH, but with adenosine the increase in capillary flow velocity was less than the increase in arterial flow.
authors.affiliation: Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine and Dentistry, Japan. kkiyooka@cc.okayama-u.ac.jp <kkiyooka@cc.okayama-u.ac.jp>
authors.forename: Takahiko
authors.initials: T
authors.lastname: Kiyooka
authors.forename: Osamu
authors.initials: O
authors.lastname: Hiramatsu
authors.forename: Fumiyuki
authors.initials: F
authors.lastname: Shigeto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakamoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tachibana
authors.forename: Toyotaka
authors.initials: T
authors.lastname: Yada
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ogasawara
authors.forename: Masahito
authors.initials: M
authors.lastname: Kajiya
authors.forename: Taro
authors.initials: T
authors.lastname: Morimoto
authors.forename: Yuki
authors.initials: Y
authors.lastname: Morizane
authors.forename: Satoshi
authors.initials: S
authors.lastname: Mohri
authors.forename: Juichiro
authors.initials: J
authors.lastname: Shimizu
authors.forename: Tohru
authors.initials: T
authors.lastname: Ohe
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Kajiya
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002196:Capillaries / Q000187:drug effects / Q000502:physiology; D003326:Coronary Circulation / Q000187:drug effects* / Q000502:physiology*; D004285:Dogs; D005260:Female; D006940:Hyperemia / Q000503:physiopathology*; D008297:Male; D018715:Microscopy, Video / Q000295:instrumentation / Q000379:methods*; D010496:Pericardium
chemical_list: D000241:Adenosine