Coronary microcirculation during halothane, enflurane, isoflurane, and adenosine in dogs

Evaluate the Correlation between the TIMI Frame Count, IMR, and CFR in Coronary Microvascular Disease

Objective

To evaluate the correlation between the TIMI frame count, IMR, and CFR in coronary microvascular disease (slow flow phenomenon).

Methods

TFC and IMR were recorded in the nitroglycerin and ATP administration states, and the relationship between TFC, IMR, and CFR in specific states was analyzed.

Results

A total of 41 patients with baseline TFC >25 frames on coronary angiography were enrolled, and nitroglycerin reduced TFC by 50% from baseline in 24 (58.54%) patients; 16 of the remaining 17 patients were able to achieve a 50% reduction in TFC by further intracoronary ATP injection. 10 patients were further tested for IMR, and the results showed significant correlations between baseline TFC and IMR (r = 0.775, P=0.008), TFC and IMR after nitroglycerin (r = 0.875, P=0.001), and the minimal TFC and IMR that could be obtained with nitroglycerin or ATP administration (r = 0.890, P=0.001). There was also a significant correlation between the proportional improvement in TFC and CFR before and after nitroglycerin injection (r = 0.685, P=0.029). In addition, we observed a lower IMR measured after nitroglycerin than after ATP in three patients, suggesting that CMD may be dominated by NO-sensitive vascular such as prearterioles and that an extensive analysis of the target site of CMD may be achieved by stepwise drug administration.

Conclusion

Induction of TFC in different states by a stepwise drug approach may serve as a potential primary screening method for coronary microcirculatory dysfunction, thereby reducing the need for further IMR or CFR testing.

Comparison of adenosine, isoflurane, and desflurane on myocardial tissue oxygen pressure during coronary artery constriction in dogs

OBJECTIVE

To compare adenosine-, isoflurane-, or desflurane-induced hypotension with and without left anterior descending (LAD) coronary artery constriction for the effects on myocardial tissue oxygen pressure (PmO(2)) in dogs.

DESIGN

Prospective, randomized, nonblinded.

SETTING

University teaching hospital.

PARTICIPANTS

Male nonpurpose-bred dogs (n = 18).

INTERVENTIONS

Dogs were anesthetized with 1.5% isoflurane (n = 12) or 8% desflurane (n = 6). A flow probe and balloon occluder were placed on the LAD artery. A probe that measured myocardial oxygen pressure was inserted into the middle myocardium in the LAD region. Myocardial oxygen consumption (MVO(2)) was calculated as LAD flow x arterial minus coronary sinus oxygen content.

MEASURES AND MAIN RESULTS

Measures were made during hypotension produced by adenosine infusion, 2.8% isoflurane, or 14% desflurane with and without LAD constriction to decrease blood flow 30%. Without LAD artery constriction, adenosine infusion increased LAD flow 90% and MVO(2) 70%, 2.8% isoflurane produced no change in MVO(2), and 14% desflurane decreased MVO(2) 25%, but no treatment changed PmO(2). LAD artery constriction decreased PmO(2) 50% by itself. Adenosine infusion during LAD constriction decreased tissue oxygen pressure an additional 60%, 2.8% isoflurane produced no change, and 14% desflurane increased PmO(2) 100%.

CONCLUSION

There was an inverse relationship between the effect of adenosine, 2.8% isoflurane, and 14% desflurane on MVO(2) and PmO(2) during ischemia. This is consistent with reports that increasing oxygen demand worsens myocardial ischemia.

Effects of modest anemia on systemic and coronary circulation of septic sheep

Although a lower transfusion trigger is generally recommended, little evidence is available about the physiological mechanisms of mild anemia in diseases with an imbalance between O2 supply and O2 demand such as sepsis. This study was undertaken to describe the systemic and coronary metabolic O2 reserve in an awake sheep model of hyperdynamic sepsis comparing two different hemoglobin levels. Twenty-four hours after sheep were rendered septic by cecal ligation and perforation (CLP), blood transfusion (n = 7, hemoglobin = 120 g/l) and isovolemic hemodilution (n = 8, hemoglobin = 70 g/l), respectively, were performed. Another 24 h later, we measured hemodynamics, organ blood flows, and systemic and myocardial O2 metabolism variables at baseline and through four stages of progressive hypoxia. Maximum coronary blood flow was 766.3 +/- 87.4 ml. min(-1). 100 g(-1) in hemodiluted sheep group versus 422.7 +/- 53.7 ml. min(-1). 100 g(-1) in the transfused sheep (P < 0.01). Myocardial O2 extraction was higher in the transfusion group (P = 0.03) throughout the whole hypoxia trial. In the hemodilution group, coronary blood flow increased more per increase in myocardial O(2) uptake than in transfused sheep (P < 0.01). This was accompanied by a lower left ventricular epicardial-to-endocardial flow ratio in hemodiluted sheep (1.13 +/- 0.07) than in transfused sheep (1.34 +/- 0.02, P < 0.05). We conclude that the lower coronary blood flow and greater myocardial O2 extraction in transfused septic sheep preserves transmyocardial O2 metabolism better in comparison to hemodiluted sheep.

[Effects of anesthetic agents on arterial reactivity]

OBJECTIVE

To review the effects of halogenated and intravenous anaesthetics on arterial vasoreactivity.

DATA SOURCE

Articles were obtained from a MEDLINE review (search terms: 'vascular smooth muscle, endothelium' used separately or associated with following anaesthetic agents: 'halothane, isoflurane, enflurane, desflurane, sevoflurane, thiopentone, propofol, ketamine, etomidate'. Other sources included review articles and textbooks.

STUDY SELECTION AND DATA EXTRACTION

All experimental studies published since 1975 were analysed and pertinent data extracted.

DATA SYNTHESIS

Within the vascular wall, arterial vasoreactivity involves the endothelium and the vascular smooth muscle. In vivo, arterial vasoreactivity is regulated by neuronal, hormonal, and metabolic factors. In vitro, the direct action of anaesthetic agents on the vessel can be studied in the absence of such factors. In vitro studies with arterial rings have shown that inhalational anaesthetics directly decrease endothelium-independent contraction induced by various pharmacological agents. This direct effect of anaesthetics results from a decrease in intracellular calcium, mainly caused by an inhibition of transsarcoplasmic calcium influx. Volatile anaesthetics decrease endothelium-dependent vasorelaxation at a site(s) within the nitric oxide (NO) signalling pathway, located downstream from the NO-related receptors and upstream from guanylyl cyclase. They may also decrease endothelium-independent vasorelaxation by inhibiting NO activation of guanylate cyclase. Intravenous anaesthetics, such as propofol, barbiturates, ketamine and etomidate also decrease vasoconstriction by various degrees. Propofol is the most potent inhibitor of vasoconstriction and thiopental the least one. All these IV anaesthetics have been shown to inhibit in some circumstances both endothelium-dependent and -independent vasorelaxation. Further studies are required to enable a better understanding of the mechanism and the site of action of these vascular effects of anaesthetics. For example, the investigation of the effects of anaesthetic agents on vascular reactivity in diseases associated with endothelial dysfunction may indirectly provide insight into the role of endothelium.

Sevoflurane preserves endocardial blood flow during coronary ligation in dogs: comparison with adenosine

BACKGROUND

Sevoflurane has been reported to attenuate ischaemia-induced changes of myocardial metabolism, but the mechanism is still unclear. We examined the effect of sevoflurane on regional myocardial blood flow (RMBF) in the ischaemic area and compared the flow with that in the presence of adenosine.

METHOD

Twenty-seven mongrel dogs were anaesthetized with fentanyl infused at the rate of 1 microgram.kg-1.min-1 throughout the experiment. Then they were divided into 4 groups; 0, 1, 2 MAC sevoflurane groups and adenosine group. Adenosine was infused into the left ventricle at a rate of 14.5 mg.kg-1.h-1. The left anterior descending coronary artery (LAD) was ligated for 3 min. RMBF in the endo- and epicardial layers were measured using coloured microspheres.

RESULTS

Sevoflurane decreased both systolic and diastolic blood pressures and LV dp/dt max. Adenosine increased heart rate and coronary flow. The endocardial blood flow in 2 MAC sevoflurane was almost the same as that in the 0 MAC group. Adenosine significantly increased the myocardial blood flow. During 3-min ischaemia, endocardial blood flow in the ischaemic area under 2 MAC sevoflurane was essentially the same as those in 0 MAC and adenosine groups, though myocardial work in 2 MAC sevoflurane was lower compared with that of the other groups.

CONCLUSION

Preservation of endocardial blood flow related to the myocardial work during ischaemia occurred during 2 MAC sevoflurane. The decrease in LV dp/dt max induced by 2 MAC sevoflurane is one of the factors responsible for the preservation of the endocardial blood flow during ischaemia.

Effects of halothane, isoflurane and sevoflurane on calcium-related contraction in porcine coronary arteries

BACKGROUND

Volatile anaesthetics have a direct inhibitory effect upon epicardial coronary arterial smooth muscles (1-4). The site and mode of their action at the cellular level need to be clarified, which was the purpose of our study. The present investigation attempted to answer the question in what way volatile anaesthetics influence Ca(2+)-related contraction in isolated porcine epicardial coronary to understand their intracellular mechanism.

METHODS

Isolated helical strips of porcine epicardial coronary artery without endothelium were suspended for isotonic contraction recordings in Krebs-Ringer's solution. 9.4 x 10(-2) MK+, 2.5 x 10(-3) M Ca(2+)-induced shortening of the strips was regarded as the reference value (100%). After incubation in Ca(2+)-free solution with 10(-3) M ethlene glycol bis (beta-aminoethyl ether)-N, N-tetraacetic acid (EGTA) for 60 minutes, the muscle strips were exposed to increasing Ca2+ concentrations (10(-4)-10(-2)) either in the presence or absence of 1.5 or 2.5 minimum alveolar concentration (MAC) halothane, isoflurane or sevoflurane, with 9.4 x 10(-2) M K+ bath solution.

RESULTS

All three drug groups produced apparent biphasic effects with a cumulative increase of Ca2+ concentration compared with control groups. An initial increase at low Ca2+ concentration was followed by a decrease of Ca(2+)-activated contractions. Isoflurane affected Ca(2+)-induced contraction significantly more than halothane and sevoflurane.

CONCLUSIONS

The results imply that volatile anaesthetics influence Ca(2+)-dependent activity of coronary smooth muscle by complex mechanisms, which involve promotion of intracellular Ca2+ release and other mechanisms that alter sensitivity to calcium.

Measurement of absolute epicardial coronary artery flow and flow reserve with breath-hold cine phase-contrast magnetic resonance imaging

BACKGROUND

Noninvasive measurement of absolute coronary arterial flow and coronary flow reserve would be of considerable use in the diagnosis and management of patients with coronary artery disease. Phase-contrast magnetic resonance imaging (MRI) has been used to measure flow in a variety of vessels. The goal of the present study was to determine if MRI measurements of coronary artery flow in a single breath-hold can be used to determine flow reserve and the severity of pericardial stenosis.

METHODS AND RESULTS

In eight mongrel dogs, a closed chest model of partial left anterior descending coronary artery (LAD) occlusion was created. Coronary flows in the left circumflex artery (LCx) and LAD were measured at rest and during adenosine infusion using velocity-encoded, breath-hold MRI and perivascular ultrasound (US) flowmeters. MRI measurements of absolute coronary flow and coronary flow reserve were highly correlated with US (r = .96 and .94, respectively). Flow reserve measured in the constricted LAD was significantly lower than that in the unconstricted LCx by both US (P = .002) and MRI (P = .011).

CONCLUSIONS

MRI measurements of coronary flow and flow reserve were in good agreement with US measurements. In addition, MRI measurements of coronary flow reserve successfully discriminated stenotic from normal vessels. These results indicate that MRI is a useful method for the noninvasive assessment of coronary flow and stenosis.

A comparison of coronary hemodynamics during isoflurane and sevoflurane anesthesia in dogs

We studied the effects of sevoflurane and isoflurane on coronary hemodynamics in relation to myocardial oxygen supply and demand. Dogs were anesthetized with pentobarbital and fentanyl and received isoflurane or sevoflurane. An electromagnetic flow probe and a pair of piezoelectric crystals were placed on the left circumflex coronary artery (CX) to measure CX flow and diameter. The dogs were randomly assigned to receive isoflurane or sevoflurane at a dose of 0.75 and 1.5 minimum alveolar anesthetic concentration (MAC). The CX diameter decreased in parallel with the decrease in mean arterial pressure during both anesthetics. The CX blood flow decreased in parallel with the decrease in myocardial oxygen consumption (MVo2) during sevoflurane, whereas it did not change in spite of the decrease in MVO2 during isoflurane. The CX vascular resistance decreased significantly during isoflurane but not during sevoflurane. Moreover, the myocardial oxygen extraction ratio (Mo2exr) decreased at 0.75 and 1.5 MAC isoflurane and at 1.5 MAC sevoflurane, and the decrease in Mo2exr was significantly greater during isoflurane than during sevoflurane. The results suggest that sevoflurane is a less potent coronary arteriolar dilator than isoflurane, and that neither sevoflurane or isoflurane has a direct effect on the diameter of large coronary arteries.

Does nitrous oxide affect coronary microcirculation? An intravital microscopic study in the canine heart

The safe use of nitrous oxide, in particular in patients with coronary artery disease, has been questioned. This study was designed to determine whether nitrous oxide directly affects global coronary hemodynamic variables and coronary arteriolar microvessels in the absence of changes of myocardial oxygen consumption. In dogs the effects of nitrous oxide were evaluated during normotension (NT, intravenous [IV] piritramid, nitrogen/oxygen; and NT/N2O, IV piritramid, nitrous oxide/oxygen) and during hypotension (MAP 60 mm Hg) (HT, IV piritramid, halothane, nitrogen/oxygen; and HT/N2O, IV piritramid, halothane, nitrous oxide/oxygen). The diameter of coronary arteriolar microvessels (range, 20-450 microns) was assessed by intravital fluorescence microscopy. Myocardial blood flow was determined by radioactive microspheres. Systemic and coronary hemodynamics, as well as arteriolar microvessel diameters, were comparable between NT and NT/N2O. During HT, nitrous oxide (HT/N2O) affected neither systemic nor coronary hemodynamics. Moreover, there was no obvious difference in the diameters of coronary microvessels between HT and HT/N2O. In conclusion, nitrous oxide, whether at normotensive or hypotensive conditions, neither influences coronary arteriolar tone nor reduces or redistributes myocardial blood flow.

Comparison of the direct effects of sevoflurane, isoflurane and halothane on isolated canine coronary arteries

We have demonstrated previously, using dog epicardial arteries of different sizes, that isoflurane, like adenosine, is preferentially a small coronary artery dilator, whereas halothane, like nitroglycerin, is a large artery dilator. The present study was designed to compare the direct effects of sevoflurane with those of isoflurane and halothane. Proximal large coronary arteries with an outer diameter (o.d.) of 2.5-3.2 mm and distal small arteries of 0.6-0.9 mm o.d. were isolated from dogs and then cut into vascular rings. They were precontracted with KCl (20 mM), and their relaxant responses to anaesthetics were compared relative to the maximal responses induced by papaverine. Sevoflurane, halothane and isoflurane (1-3 human MAC) induced dose-dependent relaxation of these arteries. The relaxant response to sevoflurane did not differ between large and small arteries. However, the relaxant response of the large arteries to halothane (1.5-2.3%) was greater than that of small arteries (P < 0.01) and the response of small arteries to isoflurane (3.5%) was greater than that of large arteries (P < 0.05). In large arteries, the potency of the relaxant effect at equivalent human MAC could be ranked as halothane > or = sevoflurane > isoflurane, and, in small epicardial arteries as isoflurane > sevoflurane >> halothane. We conclude that, unlike isoflurane, sevoflurane is not a preferential dilator of small coronary arteries.