Myogenic response, elasticity and KATP channels : role on the properties and regulation of coronary bypass conduits
The studies presented in this thesis have demonstrated that the phenomenon of the myogenic response plays a pivotal role in the behaviour of vascular smooth muscle of the blood vessels that are used as conduits during coronary surgery, and that many diverse clinical conditions may affect the myogenic properties of these vessels. To that end I have used the tissue organ bath technique to establish the possible relationship between the various clinical conditions suffered by patients undergoing elective isolated coronary bypass surgery. I have found that internal thoracic artery (ITA), radial artery (RA) and long saphenous vein graft (LSVG) have distinctively different internal diameters and myogenic characteristics. The internal diameter and myogenic responses of RA lay almost halfway between ITA and LSVG. Furthermore in these series of experiments I was able to identify various clinical conditions that appear to have a bearing in formulating the myogenic behaviour of the studied vessels. To that end I was able to demonstrate that reduced left ventricular ejection fraction (LV-EF) and history of myocardial infarction(s) may be associated with larger ITA and LSVG internal diameters and discussed ITA myogenic responsiveness, while unstable angina with smaller RA and LSVG (but not ITA) internal diameters. The myogenic responses of ITA may be augmented in obese and diabetic patients and alleviated by diuretics. ACE inhibitors and KATP channel openers appeared to have a weakening effect on the myogenic responses of the RA. Understanding the myogenic properties of coronary bypass conduits and how these properties are affected from the various clinical conditions may be of great importance as it may lead to potential new strategies to prevent perioperative conduit-related complications and long-term graft failure and they deserve further investigation. Furthermore, these studies have confirmed that the way the elastic properties of the blood vessels are modified by disease states has an impact on the longevity of the conduits and therefore to the outcome of surgery. Accordingly, I was able to demonstrate that Left coronary artery Main Stem (LMS) disease is associated with significantly reduced vascular elasticity when compared to non-LMS coronary disease and also that patients with ischaemic heart disease and reduced arterial elasticity also exhibit increased venous stiffness, proportionate to the age of the patients.