Cardiac Catheterization in Mice to Measure the Pressure Volume Relationship: Investigating the Bowditch Effect

Summary

This article describes the measurement of murine left ventricular function via pressure/volume analysis at different heart rates.

Abstract

Animal models that mimic human cardiac disorders have been created to test potential therapeutic strategies. A key component to evaluating these strategies is to examine their effects on heart function. There are several techniques to measure in vivo cardiac mechanics (e.g., echocardiography, pressure/volume relations, etc.). Compared to echocardiography, real-time left ventricular (LV) pressure/volume analysis via catheterization is more precise and insightful in assessing LV function. Additionally, LV pressure/volume analysis provides the ability to instantaneously record changes during manipulations of contractility (e.g., β-adrenergic stimulation) and pathological insults (e.g., ischemia/reperfusion injury). In addition to the maximum (+dP/dt) and minimum (-dP/dt) rate of pressure change in the LV, an accurate assessment of LV function via several load-independent indexes (e.g., end systolic pressure volume relationship and preload recruitable stroke work) can be attained. Heart rate has a significant effect on LV contractility such that an increase in the heart rate is the primary mechanism to increase cardiac output (i.e., Bowditch effect). Thus, when comparing hemodynamics between experimental groups, it is necessary to have similar heart rates. Furthermore, a hallmark of many cardiomyopathy models is a decrease in contractile reserve (i.e., decreased Bowditch effect). Consequently, vital information can be obtained by determining the effects of increasing heart rate on contractility. Our and others data has demonstrated that the neuronal nitric oxide synthase (NOS1) knockout mouse has decreased contractility. Here we describe the procedure of measuring LV pressure/volume with increasing heart rates using the NOS1 knockout mouse model.

Introduction

The purpose of the heart is to pump blood throughout the body to meet the metabolic demands of the organism. Since these demands are constantly fluctuating (e.g., during exercise), the heart must adapt (i.e., increase cardiac output). The heart has devised numerous pathways to accomplish this feat. The prime manner the heart achieves this is via an increase in heart rate (i.e., Bowditch effect)¹. That is, as one’s heart rate increases, this results in an increase in contractility and an increase in cardiac output. Thus, heart function is exceedingly dependent upon heart rate. Unfortunately, heart disease (e.g., myoc....

Protocol

NOTE: This animal protocol was approved by the Institutional Animal Care and Use Committee (IACUC) at The Ohio State University. This procedure can be used on any mouse in which the inner diameter of the carotid artery is large enough to insert the catheter. Use mice that are above 16 g (older than ~2 months).

1. Preparing Mouse for Catheterization

1. Seal all surgical instruments and supplies in a sterilization pouch. Sterilize the pouch in an autoclave machine. Maintain a sterile field throughout the procedure and wear sterile gloves.
2. Anesthetize mice with ketamine (55 mg/kg) plus xylazine (15 mg/kg) by intraperitoneal ....

Results

The proper insertion of the catheter into the left ventricle is an important step to attain appropriate pressure and volume values. Shown in Figure 1, using LabChart Pro 7, is the changing of the pressure waveform (shape and values) as the catheter goes from the artery into the ventricle.

After proper insertion of the catheter into the left ventricle, the pressure (P) and volume (V) values obtained will then be used to generate the PV loops (shown in Figure 2).......

Discussion

A critical step for this technique to obtain a reliable measure of contractility is proper catheter placement into the LV. If the catheter is not placed correctly, when the LV contracts the walls may contact the catheter resulting in very high, and not physiological, pressure values causing irregular shaped PV loops. If needed, the catheter can be rotated to achieve the correct placement. Another key step for this technique is to make sure the mouse received proper anesthesia. If the mouse is over anesthetized, this will.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Xlyzine 100 mg/ml	Ana Sed	4821
Katamin 50 mg/ml	Ketalar	310006
Heparin	APP Pharmaceuticals	6003922
4-0 silk thread	Surgical specialties	SP102
6-0 silk thread	Surgical specialties	MBKF270
Forceps	Fine Science Tools	11251-10
Curve forceps	Fine Science Tools	11274-20
Scissors	Fine Science Tools	14090-09
Vascular clamp	Fine Science Tools	18555-03
Microscope	World precision instruments	PZM-3
Pressure catheter	Millar instruments	SPR-839
Pressure and volume system	Millar instruments	MPVS-300
PowerLab4/35	AD instruments	N12128
LabchartPro 7	AD instruments
Temperature controller	CWE	TC-1000
Stimulator	Grass	SD-5
Sterile glove	Micro-Touch	1305018821
Hair remover lotion	Nair
Betadine surgical scrub	Veterinary	NDC 6761815401
Alcohol	Decon Laboratories	2801
Bovie cautery	Bovie	AA29
1 ml Syringe (26 G needle)	BD	8017299