In:
Canadian Journal of Physiology and Pharmacology, Canadian Science Publishing, Vol. 63, No. 7 ( 1985-07-01), p. 787-797
Abstract:
Coronary sinus pressure (P cs ) elevation shifts the diastolic coronary pressure–flow relation (PFR) of the entire left ventricular myocardium to a higher pressure intercept. This finding suggests that P cs is one determinant of zero-flow pressure (F zf ) and challenges the existence of a vascular waterfall mechanism in the coronary circulation. To determine whether coronary sinus or tissue pressure is the effective coronary back pressure in different layers of the left ventricular myocardium, the effect of increasing P cs was studied while left ventricular preload was low. PFRs were determined experimentally by graded constriction of the circumflex coronary artery while measuring flow using a flowmeter. Transmural myocardial blood flow distribution was studied (15-μm radioactive spheres) at steady state, during maximal coronary artery vasodilatation at three points on the linear portion of the circumflex PFR both at low and high diastolic P cs (7 ± 3 vs. 22 ± 5 mmHg; p 〈 0.0001) (1 mmHg = 133.322 Pa). In the uninstrumented anterior wall the blood flow measurements were obtained in triplicate at the two P cs levels. From low to high P cs , mean aortic (98 ± 23 mmHg) and left atrial (5 ± 3 mmHg) pressure, percent diastolic time (49 ± 7%), percent left ventricular wall thickening (32 ± 4%), and percent myocardial lactate extraction (15 ± 12%) were not significantly changed. Increasing P cs did not alter the slope of the PFR; however, the P zf , increased in the subepicardial layer (p 〈 0.0001), whereas in the subendocardial layer P zf did not change significantly. Similar slopes and P zf were observed for the PFR of both total myocardial mass and subepicardial region at low and high P cs . Subendocardial: subepicardial blood flow ratios increased for each set of measurements when P cs was elevated (p 〈 0.0001), owing to a reduction of subepicardial blood flow; however, subendocardial blood flow remained unchanged, while starting in the subepicardium toward mid-myocardium blood flow decreased at high P cs . This pattern was similar for the uninstrumented anterior wall as well as in the posterior wall. Thus as P cs increases it becomes the effective coronary back pressure with decreasing magnitude from the subepicardium toward the subendocardium of the left ventricle. Assuming that elevating P cs results in transmural elevation in coronary venous pressure, these findings support the hypothesis of a differential intramyocardial waterfall mechanism with greater subendo- than subepi- cardial tissue pressure.
Type of Medium:
Online Resource
ISSN:
0008-4212
,
1205-7541
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
1985
detail.hit.zdb_id:
127527-6
detail.hit.zdb_id:
2004356-9
