One key aspect of cardiovascular function analyzed by pharmacology studies is total peripheral resistance (TPR) also known as systemic vascular resistance (SVR). Vascular resistance is influenced by vasoconstriction and vasodilation, blood volume, heart rate and contractility. Many therapeutic agents used to treat hypertension, heart failure and angina function as vasodilators to reduce vascular resistance. Vasoconstrictors increase vascular resistance and are used for treating hypotension, hemorrhage and shock.
Total peripheral resistance is calculated from the mean arterial pressure (MAP), central venous pressure (CVP) and cardiac output (CO) as described below:
TPR = (MAP-CVP)/CO
Central venous pressure is often ignored since it is very small compared to the mean arterial pressure. Making the relationship:
TPR = MAP/CO
Transonic® Perivascular flow probes are ideal for measuring cardiac output by measuring the volume flow through the aorta. COnfidence flow probes® are designed specifically for cardiac output measurements in large animals. Solid-state Pressure Catheters measure MAP and/or CVP with great accuracy. Pressure and flow can both be measured with EndoGear® telemetry for long term studies without tethering. For translational studies in medium to large animals, LabCOstatus calculates cardiac output, cardiac index and systemic vascular resistance index amongst other parameters using ultrasound dilution through arterial and central venous catheter lines.
Regional Vascular Resistance
Pharmacological agents do not necessarily impact all vascular beds equally, making regional vascular resistance a parameter of interest in some studies. Measuring blood flow into the organ or region of interest (RBF) combined with MAP is the most common method for determining regional vascular resistance (RVR).
RVR = MAP/ RBF
Transonic Perivascular flow probes can be placed on vessels as small as 0.3 mm in diameter for blood flow measurements to most organs or regions.