Effects of Isoflurane on Coronary Blood Flow Velocity in Young, Old and ApoE−/− Mice Measured by Doppler Ultrasound

Abstract

The commonly used anesthetic agent, isoflurane (ISO), is a potent coronary vasodilator which could potentially be used in the assessment of coronary reserve, but its effects on coronary blood flow in mice are unknown. Coronary reserve is reduced by age, coronary artery disease, and other cardiac pathologies in man, and some of these conditions can now be modeled in mice. Accordingly, we used Doppler ultrasound to measure coronary flow velocity in mice anesthetized at low (1%) and at high (2.5%) levels of ISO to generate baseline (B) and elevated hyperemic (H) and Y and between A and O were significant (P < 0.01), while the differences in hyperemic velocities were not (P > 0.05). H/B was higher in old mice due to decreased baseline flow rather than increased hyperemic flow velocity. In contrast ApoE −/− mice have increased baseline and hyperemic velocities perhaps due to coronary lesions. The differences in baseline velocities between young and old mice could be due to age-related changes in basal metabolism or to differential sensitivity to isoflurane. We conclude that Doppler ultrasound combined with coronary vasodilation via isoflurane could provide a convenient and noninvasive method to estimate coronary reserve in mice, but also that care must be taken when assessing coronary flow in mice under isoflurane anesthesia because of its potent coronary vasodilator properties.

Doppler Estimation of Reduced Coronary Flow Reserve in Mice with Pressure Overload Cardiac Hypertrophy

“…1), we calculated H/B from peak diastolic coronary velocities rather than mean velocities (Hartley et al, 2007). In that study there were no significant increases in the systolic component of coronary velocity after vasodilation.…”

“…1) that peak diastolic coronary velocity (PDV) is similar in mice ranging in age from 6 weeks to 2 years (Hartley et al, 2007). Eberli et al (1989) found in patients that hyperemic coronary volume flow induced by dipyridamole was similar in controls, in patients with aortic stenosis, and in patients following aortic valve repair, but that baseline flows were different.…”

“…Then a 20 MHz Doppler probe was connected, and velocities were measured in the right and left common carotid arteries. After these non-coronary measurements were completed the 20 MHz probe was clamped in a micromanipulator (Model MM3-3, World Precision Instruments, Sarasota, FL, USA) also attached to the procedure board for stability as previously described (Hartley et al, 2007). The clamp on the manipulator gimbal was loosened, and the probe tip was placed on the left chest at the level of the cardiac base and pointed horizontally toward the anterior basal surface of the heart to sense blood flow velocity in the ascending aorta or in the left main coronary artery at a 2.5 mm depth setting.…”

“…After a stable signal was achieved, a two-second sample of the ECG and the raw quadrature Doppler signals was acquired and stored in a computer file for later analysis (Hartley et al, 2002). Then the isoflurane concentration was reduced to 1% to lower coronary flow to a baseline level (Hartley et al, 2007). After 3-5 minutes or when flow became stable at the low level, the sample volume was readjusted if necessary to maximize velocity and signal strength, and another two-seconds of signals were collected and stored.…”

“…We have recently developed a noninvasive method to measure coronary flow velocity in mice using Doppler ultrasound and have shown that isoflurane gas can be used as a convenient coronary vasodilator when the concentration is increased from 1% to 2.5% (Hartley et al, 2007). We used the ratio of hyperemic/baseline (H/B) left main coronary velocity as an index of CFR, and showed that H/B was a function of age and was reduced in 2-year old apolipoprotein-E null (ApoE −/− ) mice when compared to age-matched controls as shown in Fig.…”