Measurement of Left Ventricular Performance in Mice Mouse Physiology Core Department of Molecular and Cellular Physiology University of Cincinnati College of Medicine Scientific Director: John N. Lorenz, Ph.D.

1) Measurement of LV pressure and dP/dt in the closed-chest mouse using a high-fidelity Millar pressure transducer

Experimental set-up for evaluating left ventricular pressure (Millar) and systemic arterial pressure (COBE) in a mouse. Data are processed and recorded using a PowerLab system from ADInstruments

Close-up view of a high-fidelity Millar catheter the tip diameter is about 0.5 mm. The pressure-sensing surface is shown at the tip of the catheter

Sample tracing of left ventricular pressure and femoral artery pressure in a mouse. Arrow shows the point where the Millar catheter crosses the aortic valve and enters the ventricle. The inset show stability of the recording over time.

Sample results of ventricular performance showing incremental enhancement of baseline contractility (as evidenced by the lower dP/dt tracing) in heterozygous and homozygous phospholamban-deficient mice. This model provide a clear demonstration of the sensitivity of this approach

Summary data showing the effect of β-adrenergic stimulation in wild type, and phospholamban-deficient mice.

2) Force frequency analysis using an intra- cardiac, bipolar pacing electrode

Bipolar pacing electrode – about 0.3 mm diameter - shown in comparison to the Millar transducer. Electrode is introduced via the right jugular vein, and advance to the right atrium. Pacing is accomplished using a Grass stimulator.

Left: Sample tracings of LV pressure and dP/dt before and during electrical capture of the SA nodal rhythm. Bottom tracings show heart rate increasing from 400 – 500 when the stimulating pulses are initiated; an immediate increase in dP/dt is evident. Right: Summary of the force frequency relationship in closed–chest mice.

3) Pressure-Volume analysis in the closed chest mouse: Impedance measurements.

Combination Millar Pressure-Volume catheter (~0.5mm diameter). Flanking the central pressure transducer (circle) are a pair of excitation electrodes (red arrows), which apply a constant oscillating current, and a pair of signal electrodes (blue arrows) to sense volume-dependent changes in voltage.

Original recording of LV pressure (top, green tracing) and LV volume (bottom, blue tracing).

Recording of femoral blood pressure (red) LV pressure (green) and LV volume (blue) under steady state conditions and during a momentary increase in afterload. Afterload was increased by inflating a small balloon positioned in the descending aorta (aortic constriction, AC).

Inset shows the resulting family of pressure-volume loops during aortic constriction-induced elevation of afterload (shown in the highlighted section of the main recording). The end-systolic pressure volume relation is indicated.

Sample pressure-volume loops obtained from a wild type mouse under baseline conditions (blue) and during β–adrenergic stimulation with dobutamine (red).

3) Two-dimensional, M-mode echocardiography and pulse-Doppler flow analysis the intact mouse.

Two-dimensional image of the mouse heat showing clearly defined borders of the left ventricular chamber. The aortic out-flow tract can also be seen.

M-Mode image (“ice-pick view”) of LV contraction. Entire span of the image is one second of recording, showing six consecutive ventricular contractions along a one-dimensional, short-axis view.

Pulse-Doppler recording of aortic outflow (one second recording). By convention, movement away from the transducer (during systole) results in a negative deflection.

Pulse-Doppler recording of mitral inflow during diastole (one second recording). The end-diastolic atrial contraction is clearly represented. By convention, movement toward the transducer results in a positive deflection.

4) Measurement of cardiac output by thermal dilution.

Temperature Probe 0.23 mm OD Arterial pressure Venous Infusion Cold saline Bolus 10-20ul Carotid catheter / Y-connector Set Set-up for measurement of thermal dilution measurement of cardiac output. Cold saline is injected into the flow of blood leaving the left ventricle via a catheter introduced in the right carotid artery. The resulting “temperature-dilution” curve is monitored via a temperature probe positioned in the abdominal aorta via the femoral artery. In contrast to the conventional approach, this configuration avoids the substantial loss of indicator (ie temperature) that would occur if the cold saline were injected into the right atrium, necessitating transit through the pulmonary circulation.

Sample recording of a thermal dilution curve – the injected bolus of cold saline passes the temparature probe, there is a transient decrease in temparature that is proportional to cardiac output.

Original tracing of three consecutive thermal dilution curves (15-20 seconds apart). Upper tracing is blood pressure and shows the artifactual increase that occurs during injection of the salin bolus. Lower tracing shows the resulting transient decrease in temperature. The range of the measurements is less than 10%.

Results of an experiment in which cardiac output was measured by thermal dilution (yellow) and total peripheral resistance derived from CO and MAP. Three measurements (indicated by the blue symbols) were taken under each of the conditions shown (baseline, isoproterenol infusion, saline volume expansion and hemorrhage).