Abstract

To assess the relations between coronary perfusion pressure, blood flow, and the diastolic pressure-segment length relation in the conscious animal, circumflex pressure was incrementally decreased in 10 resting, chronically instrumented dogs by a hydraulic occluding cuff while monitoring left ventricular pressure and regional segment length (with piezoelectric crystals) in the circumflex and left anterior descending territories. In five dogs, regional blood flow was measured by microsphere injections at selected circumflex pressures. The diastolic portion of the pressure-segment length curve was unchanged when decrements in circumflex pressure were within the autoregulatory range, that is, unassociated with changes in blood flow or systolic function. Further decrements in circumflex pressure, which decreased blood flow and regional segment shortening (both p less than 0.05), caused a progressive downward and rightward shift of the pressure-segment length curve (p less than 0.05). The rate of relaxation, as measured by tau (the time constant of pressure decay during isovolumic relaxation, which is calculated assuming either a fixed or a variable asymptote) and peak negative dP/dt, decreased slightly during reductions in circumflex pressure within the autoregulatory range and greatly at lower pressure (all p less than 0.05). Thus, in the conscious animal, reductions in coronary perfusion pressure within the autoregulatory range do not affect the diastolic pressure-segment length curve but cause modest decreases in the rate of isovolumic relaxation. Further reductions in coronary perfusion pressure, below the limits of blood flow autoregulation, cause an increased extent of relaxation with a marked downward shift of the diastolic pressure-segment length curve as well as a large decrease in the rate of relaxation.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.