TACHYCARDIA AND CORONARY BLOOD-FLOW - NONINVASIVE ESTIMATION DURING VALSALVA MANEUVER AND EXERCISE

Simultaneous changes in cycle length and coronary blood flow were stud ied during Valsalva manoeuvre and supine cycloergometer exercise test in 10 male patients (mean age 48+/-12 years) who had successfully unde rgone myocardial revascularization by surgical anastomosis of the left internal mammary artery on the left anterior descending coronary arte ry. Blood velocity curves in the left internal mammary artery were obt ained by a non-invasive continuous-wave Doppler probe at rest, in the last phase of the expiratory effort of the Valsalva manoeuvre and at t he maximum load attained during the exercise test. Mean arterial press ure by sphygmomanometer, and cardiac cycle length on the basis of Dopp ler recording were measured. Mean blood velocity, the length of the bl ood column entering the coronary bed at each cycle (cardiac cycle time s mean velocity), an index of blood cell acceleration (the ratio of me an velocity to cardiac cycle), and an index of coronary resistance (th e ratio of mean pressure to mean velocity), were calculated. For appro ximately the same change in cycle length, coronary resistance decrease d in exercise, with an increased mean velocity, but increased in Valsa lva, with no changes tn mean velocity. The length of the blood column entering the coronary bed at each cycle was unchanged in exercise, wit h a marked increase in the acceleration index, while it decreased in V alsalva. Therefore, we hypothesize that tachycardia has a limiting eff ect on sympathetic coronary constriction in Valsalva when cardiac exte rnal work is decreased, and an additional vasodilatory effect on coron ary bed in exercise when external work is increased.