Effects of basal anaesthesia on cardiac function

Olfactory receptor 78 modulates renin but not baseline blood pressure

Olfactory receptor 78 (Olfr78) is a G protein-coupled receptor (GPCR) that is expressed in the juxtaglomerular apparatus (JGA) of the kidney as well as the peripheral vasculature, and is activated by gut microbial metabolites. We previously reported that Olfr78 plays a role in renin secretion in isolated glomeruli, and that Olfr78 knockout (KO) mice have lower plasma renin activity. We also noted that in anesthetized mice, Olfr78KO appeared to be hypotensive. In this study, we used radiotelemetry to determine the role of Olfr78 in chronic blood pressure regulation. We found that the blood pressure of Olfr78KO mice is not significantly different than that of their WT counterparts at baseline, or on high- or low-salt diets. However, Olfr78KO mice have depressed heart rates on high-salt diets. We also report that Olfr78KO mice have lower renin protein levels associated with glomeruli. Finally, we developed a mouse where Olfr78 was selectively knocked out in the JGA, which phenocopied the lower renin association findings. In sum, these experiments suggest that Olfr78 modulates renin, but does not play an active role in blood pressure regulation at baseline, and is more likely activated by high levels of short chain fatty acids or hypotensive events. This study provides important context to our knowledge of Olfr78 in BP regulation.

Molecular and Integrative Physiological Effects of Isoflurane Anesthesia: The Paradigm of Cardiovascular Studies in Rodents using Magnetic Resonance Imaging

To-this-date, the exact molecular, cellular, and integrative physiological mechanisms of anesthesia remain largely unknown. Published evidence indicates that anesthetic effects are multifocal and occur in a time-dependent and coordinated manner, mediated via central, local, and peripheral pathways. Their effects can be modulated by a range of variables, and their elicited end-effect on the integrative physiological response is highly variable. This review summarizes the major cellular and molecular sites of anesthetic action with a focus on the paradigm of isoflurane (ISO) - the most commonly used anesthetic nowadays - and its use in prolonged in vivo rodent studies using imaging modalities, such as magnetic resonance imaging (MRI). It also presents established evidence for normal ranges of global and regional physiological cardiac function under ISO, proposes optimal, practical methodologies relevant to the use of anesthetic protocols for MRI and outlines the beneficial effects of nitrous oxide supplementation.

Analyzing left ventricular function in mice with Doppler echocardiography

Mice are widely used in heart failure research. Accurate evaluation of cardiac structure and function is key to modern cardiovascular research. Doppler echocardiography is a simple, reproducible, and non-invasive method, which allows a longitudinal study of these small animals. Besides common parameters such as left ventricular chamber size, mass, and function, new emerging echo tools are of great interest for small animal imaging. In this review, we describe the technical issues linked to murine cardiovascular anatomy and physiology and the most current echo parameters that can be used.

[Echocardiography in mouse]

Assessing cardiac phenotype requires invasive or noninvasive techniques in mouse. Echocardiography is a noninvasive technique for evaluating cardiac function. The purpose of this paper is to underline echocardiography modalities and new tools Doppler applications like tissue Doppler imaging.

Reproducibility of transthoracic echocardiography in small animals using clinical equipment

OBJECTIVE

Transthoracic echocardiography has been employed to assess left ventricular dimensions and function in small animals. The aim of this study was to identify the limits of transthoracic echocardiography in a commonly used Wistar rat model by assessing intraobserver variability, interobserver variability, and day-to-day variability of examinations implying registrations and measurements.

METHODS

Twenty male adult Wistar rats (body weight 496+/-52 g) were examined under volatile isoflurane anesthesia (heart rate 302+/-26 bpm) by transthoracic echocardiography (Sonos 7500; Philips) with a 15 MHz-transducer. For calculation of intraobserver variability, examinations were repeated by the same examiner and for interobserver variability, examinations were performed independently by two investigators. For day-to-day variability, examinations were repeated 14 days later. Left ventricular diameters and areas were analyzed in parasternal short axis and in a modified parasternal long axis. Fractional shortening, area shortening, ejection fraction, stroke volume, and cardiac output were calculated.

RESULTS

Left ventricular end-diastolic diameter was 8.9+/-0.6 mm, fractional shortening 39.0+/-5.3%, area shortening 59.6+/-6.1%, ejection fraction 83.3+/-5.1%, stroke volume 0.24+/-0.06 ml, and cardiac output 72.9+/-20.6 ml/min. Intraobserver variability of left ventricular end-diastolic diameter, fractional shortening, area shortening, and ejection fraction was less than 10%, increasing to 19% for stroke volume and cardiac output. Interobserver variability of left ventricular end-diastolic diameter, fractional shortening, area shortening, ejection fraction was less than 13%, increasing to 23% for stroke volume and 25% for cardiac output. Day-to-day variability of left ventricular end-diastolic diameter, area shortening, ejection fraction was less than 11% whereas for stroke volume it was 21% and for cardiac output it was 22%. F-ratio test comparing investigated variabilities did not reveal significant differences.

CONCLUSIONS

M-mode and two-dimensional echocardiography in large rats by clinically common high-end ultrasound systems can be assessed reliably. Parameters of global left ventricular performance like stroke volume and cardiac output could not be assessed with similar reliability.

OPTIMIZING DOSAGE OF KETAMINE AND XYLAZINE IN MURINE ECHOCARDIOGRAPHY

1. Ketamine and xylazine (KX) mixture is the most commonly used anaesthetic drug during echocardiography in mice to induce sedation and immobility. Nevertheless, the doses of KX reported in the literature vary substantially with associated significant difference in cardiac function. To explore the optimal KX dosage and observation time for murine echocardiography, we compared the effects of various KX combinations on echocardiographic measurement. 2. Mice were anaesthetized with ketamine (50 or 100 mg/kg) and xylazine (0-10 mg/kg). Echocardiography was performed 5, 10, 20 and 40 min after induction of anaesthesia. Also, cardiac function was assessed in mice with and without pressure-overload induced left ventricle (LV) hypertrophy and dysfunction, either under anaesthesia with KX or whilst conscious. 3. Ketamine at 100 mg/kg alone or together with xylazine at 0.1 mg/kg was associated with a high and stable heart rate (HR), a high fractional shortening (FS) and produced the least effect on LV inner dimension at end of diastole (LVIDd). Ketamine and xylazine at 100 and 10 mg/kg, respectively, produced a lower and stable FS, but with a low and unstable HR. All other combinations resulted in depressed and unstable cardiac function during this period. 4. The dose-dependent suppression of FS by xylazine was counteracted partly by ketamine. 5. Although in the chronic pressure-overload model LV hypertrophy can be detected accurately in both the anaesthetized or conscious state, systolic dysfunction was masked partially by higher doses of xylazine (2.5 or 10 mg/kg) combined with ketamine at 100 mg/kg. 6. With KX anaesthesia, both the dose of xylazine and the anaesthetic duration are critical in achieving an ideal condition for murine echocardiography. Ketamine at 100 mg/kg alone produces acceptable anaesthesia, stable cardiac function with a minimal depressant effect and is therefore recommended if single-dose anaesthetic is to be used.

Impact of Anesthesia on Echocardiographic Evaluation of Systolic and Diastolic Function in Rats

BACKGROUND

Echocardiography is used on rats but general anesthesia is usually necessary to be able to obtain a good quality echocardiogram. Each type of anesthetic agent has specific impacts on hemodynamics and, therefore, may affect differentially the echocardiographic measurements.

OBJECTIVES

We sought to compare the echocardiograms of normal rats and rats with chronic aortic regurgitation under anesthesia using ketamine-xylazine or isoflurane.

METHODS

Animals underwent an echocardiogram with both drugs sequentially. Echocardiographic measurements were compared.

RESULTS

Mitral diastolic Doppler measurements (early diastolic filling wave [E] and late atrial diastolic filling wave [A] velocities) were significantly affected by the type of anesthesia in the normal group but not left ventricular dimensions or ejection fraction. Left ventricular dimensions were affected by the type of anesthesia in the aortic regurgitation group and diastolic Doppler flow.

CONCLUSION

The anesthetic agent has significant specific impacts on many echocardiographic measurements. Investigators working with rat models should be aware of those potential effects.

Measurement of cardiac function in conscious rats

The goal of this study was to establish that 1. blood velocity profile in the rat aorta is parabolic, and 2. measure of left ventricular thickening fraction can be used in rats. Spontaneously hypertensive and normotensive Wistar Kyoto rats were instrumented with a 20-MHz pulsed Doppler flow probe around the thoracic aorta and a 20-MHz pulsed Doppler thickening probe on the left ventricle. Doppler frequency shifts were measured throughout the entire aorta diameter, and individual blood velocity profiles were constructed. It was demonstrated that blood velocity in the ascending aorta of rats is laminar; therefore, cardiac output can be measured using the pulsed Doppler method. In Wistar Kyoto rats, left ventricular thickening fraction was 24 +/- 1% and 25 +/- 1%, 2 and 3 weeks following surgery. In spontaneously hypertensive rats, left ventricular thickening fraction was 22 +/- 2%. Halothane depressed left ventricular thickening fraction, whereas isoproterenol increased left ventricular thickening fraction in conscious rats. Thus, pulsed Doppler technique is a valuable tool for evaluating cardiovascular function in conscious rats.

Echocardiographic assessment of cardiac function in conscious and anesthetized mice

Using a high-frequency linear transducer (15L8), we studied 1) the feasibility of performing echocardiography in nonanesthetized mice compared with mice given pentobarbital sodium (Pento) or a mixture of ketamine and xylazine and 2) the feasibility of echocardiographic evaluation of left ventricular (LV) hypertrophy, dilatation, and function in mice with two-kidney, one-clip hypertension or myocardial infarction (MI). Heart rate (HR) in awake mice was 658 +/- 9 beats/min; Pento and ketamine plus xylazine reduced HR to 377 +/- 11 and 293 +/- 19 beats/min, respectively, associated with a significant decrease in shortening fraction (SF), ejection fraction (EF), and cardiac output (CO) and an increase in LV end-diastolic (LVEDD) and end-systolic dimensions (LVESD). Mice with 4 wk of two-kidney, one-clip hypertension had increased LV mass (15.62 +/- 0. 62 vs. 22.17 +/- 1.79 mg) without altered LV dimensions, SF, EF, or CO. Mice studied 4 wk post-MI exhibited obvious LV dilatation and systolic dysfunction, as evidenced by increased LVEDD and LVESD and decreased SF, EF, and CO. Our findings clearly show the adverse impact of anesthesia on basal cardiac function and the difficulty in interpreting data obtained from anesthetized mice. We believe this is the first study to demonstrate the feasibility of using echocardiography to assess cardiovascular function in the nonanesthetized mouse.

Effects of methoxyflurane anesthesia on the pharmacokinetics of 125I-IAZA in Sprague-Dawley rats

Effects of methoxyflurane anesthesia on the pharmacokinetics of intravenous 125I-IAZA in rats are reported. No significant differences in t(1/2alpha), t(1/2beta), V(SS), and ClTB for total radioactivity (125I-IAZA and metabolites) were observed between the anesthetized (Group 1, n = 4) and nonanesthetized (Group 2, n = 3) animals. For 125I-IAZA, ClTB increased from 646 +/- 52 mL/h/kg to 2250 +/- 351 mL/h/kg and t(1/2beta) decreased from 97.7 +/- 17.5 min to 35.6 +/- 5.4 min, for Groups 1 and 2, respectively. There were no differences in V(SS) or t(1/2alpha) between the two groups. These findings support literature reports of anesthetic effects on xenobiotic pharmacokinetics, and indicate a need for caution in the evaluation of preclinical imaging studies in which animals are immobilized with anesthetics.

Comparison between acute hypoxia-induced and mechanically-induced pulmonary artery hypertension on the hemodynamics, myocardial contractility and regional blood flow in dogs

Two groups of eight anesthetized dogs with pulmonary artery hypertension (PAH) were compared. PAH was induced by submitting one group (HP) to hypoxia (FiO2 range: 6-10%) and the other group (ME) to microemboli through glass microbead injection into the pulmonary circulation. Hypoxia-induced PAH was moderate (PAP: +65%; PVR: +152%) contrasting with marked PAH after microbead injection (PAP: +190%; PVR: +389%). For similar effects on left ventricular contractility (LV dP/dt max and segmental myocardial shortening), heart rate and systemic vascular resistance, left ventricular end-diastolic pressure showed significant differences between the two groups (HP group: +75%, ME group: -9%), and so did left ventricular end-diastolic length (HP: +9%, ME: -11%). Thus, contrary to the injection of microbeads, hypoxia did not give rise to any pulmonary barrier, and consequently the changes in cardiac output (HP: +19%, ME: -15%) and hepatic blood flow (HP: +383%, ME: -77%) were significantly different. Hypoxia, and not microbead injection, was responsible for systemic hypertension (MAP: +34% and -4%, respectively). The microbead model resulted in a significantly higher PVR/SVR ratio compared to the hypoxic model (HP: 0.14, ME: 0.41). Hypoxia increased left and right myocardial blood flows whereas microbead injection affected only right ventricular blood flow, leading to significantly different RV/LV endocardial perfusion ratios (HP: +10%, ME: +98%). We conclude that microbead-induced PAH is more appropriate than hypoxia-induced PAH for hemodynamic and pharmacological studies.

Is pentobarbital appropriate for basal anesthesia in the working rat heart model?

In the present study we have examined the effects of the general anesthetic agents for the excision of the heart on the hemodynamic function of the ischemic perfused heart. Animals were divided into three groups. In one group rats were anesthetized with sodium pentobarbital intraperitoneally. Animals of the second and third groups were anesthetized with inhalation anesthetics, sevoflurane and isoflurane, respectively. The hearts were then rapidly excised and perfused by a working heart model. After control perfusion, whole-heart ischemia was induced by one-way aortic valve for 15 min followed by reperfusion for 30 min. During preischemic control period, cardiac output (CO) and left ventricular dP/dT maximum (LV dP/dT max) in the isoflurane group were significantly higher than those in the pentobarbital group. During reperfusion, CO and LV dP/dT max in the isoflurane and sevoflurane groups recovered more rapidly than those in the pentobarbital group. Although there were no significant differences in myocardial ATP and glycogen levels among the groups, myocardial lactate in the pentobarbital group was significantly higher than those in the sevoflurane and isoflurane groups. These results suggest that intraperitoneal pentobarbital anesthesia, administered prior to heart excision, may affect the performance of the ischemic perfused heart thereafter. Therefore, we would suggest that isolation of hearts by means of inhalation anesthesia is better than by means of pentobarbital in the working rat heart.

Intraoperative complications in patients receiving amiodarone: characteristics and risk factors

This article reviews amiodarone's adverse cardiovascular properties, concentrating on those in surgical patients, and evaluates several potential risk factors. Amiodarone has negative inotropic and chronotropic properties as well as peripheral vasodilating properties that may manifest as bradycardia, reduced cardiac output, and hypotension. These reactions are clinically important during surgery, because of resistance to pharmacologic resuscitation and an increased mortality rate. Potential risk factors include ventricular dysfunction, rapid infusion rate, hypocalcemia, cardiopulmonary bypass, general anesthesia, concurrent negative inotropic or chronotropic drugs, and an elevated serum amiodarone or desethylamiodarone concentration. The following measures may decrease the risk of intraoperative adverse reactions in amiodarone-treated patients. The serum calcium concentration should be at the physiologic level and the serum amiodarone and digoxin concentrations should be in the therapeutic range. Negative inotropic and chronotropic agents should be discontinued when possible. A temporary cardiac pacemaker may prevent intraoperative hypotension due to bradycardia. Amiodarone may be discontinued before surgery to minimize the risk of intraoperative complications, but this decision should balance the potential for amiodarone-associated intraoperative complications against the risk of arrhythmia recurrence and the delay of surgery.