Vasoconstriction seen in coronary bypass grafts during handgrip in humans

Abstract

In animal studies, sympathetically mediated coronary vasoconstriction has been demonstrated during exercise. Human studies examining coronary artery dynamics during exercise are technically difficult to perform. Recently, noninvasive transthoracic Duplex ultrasound studies demonstrated that 1) patients with left internal mammary artery (LIMA) grafts to the left anterior descending artery can be imaged and 2) the LIMA blood flow patterns are similar to those seen in normal coronary arteries. Accordingly, subjects with LIMA to the left anterior descending artery were studied during handgrip protocols as blood flow velocity in the LIMA was determined. Beat-by-beat analysis of changes in diastolic coronary blood flow velocity (CBV) was performed in six male clinically stable volunteers (60 +/- 2 yr) during two handgrip protocols. Arterial blood pressure (BP) and heart rate (HR) were also measured, and an index of coronary vascular resistance (CVR) was calculated as diastolic BP/CBV. Fatiguing handgrip performed at [40% of maximal voluntary contraction (MVC)] followed by circulatory arrest did not evoke an increase in CVR (P = not significant). In protocol 2, short bouts of handgrip (15 s) led to increases in CVR (18 +/- 3% at 50% MVC and 20 +/- 8% at 70% MVC). BP was also increased during handgrip. Our results reveal that in conscious humans, coronary vasoconstriction occurs within 15 s of onset of static handgrip at intensities at or greater than 50% MVC. These responses are likely to be due to sympathetic vasoconstriction of the coronary circulation.

Transthoracic Doppler echocardiography to noninvasively assess coronary vasoconstrictor and dilator responses in humans

“…In the present report, we noted similar relative (and simultaneous) increases in CVR during handgrip exercise in both the LIMA graft and the LAD within the same individual. These vasoconstrictor responses are consistent with our recent work performed in a similar patient population (15).…”

“…In the subjects that we studied, the LIMA was grafted to the coronary artery to bypass the stenosed coronary artery segments. We found that static handgrip evoked coronary vasoconstriction (15). In the present report, we speculated that vascular responses to static handgrip would be qualitatively similar in the LIMA graft and in the distal native LAD into which the LIMA graft was inserted.…”

“…We have previously shown that the LIMA is relatively easy to interrogate with TTD (15). Moreover, previous reports have indicated that hemodynamics in the LIMA graft are reflective of that of the native coronary artery (9,10).…”

“…A linear-array, highfrequency transducer (7-10 MHz) with a 6-MHz-pulsed Doppler frequency was used for these studies. The LIMA was scanned along the left sternal border in the second or third intercostal space (15), whereas the blood velocity in the LAD was measured along the left midclavicular line in the 4th or 5th intercostal space with the patients lying in the left lateral decubitus position.…”

“…We have recently employed the TTD method to examine left internal mammary artery (LIMA) blood velocity during static handgrip exercise (15). In the subjects that we studied, the LIMA was grafted to the coronary artery to bypass the stenosed coronary artery segments.…”