Chronic Cardiac Output measurements in unrestrained rats: Surgical description

Measurement of systemic blood flow and cardiac output in awake but restrained rats has previously been possible via complicated tether and electrical commutator systems that are no longer widely available. A new, fully implantable telemetry system with modified transit‐time volume flow probes, allows ascending aorta flow (cardiac output minus coronary flow) measurements in unrestrained rats over extended periods of time. A surgical protocol (adapted from Thomas L. Smith, PhD. Dept. of Orthopaedic Surgery, Wake Forest Baptist Health) was developed for the chronic implantation of the flow probe around the rat ascending aorta, with subcutaneous tunneling of the flowprobe cable to the implant site and securing of the telemetry unit in the abdominal cavity. Animals may be deeply anesthetized with 5% isoflurane and directly intubated transpharyngeally to avoid use of long lasting injectable anesthetics. The pectoral muscles are bisected to expose the transversus costarium crossing the 3rd intercostal space (surgical approach to the aorta) to insert on the 4th rib. The thoracic cavity is opened ~ 3 mm lateral to the sternum to avoid the internal mammary artery and extended dorsally ~ 1 cm. The 3rd intercostal space is expanded with a lacrimal sac retractor to permit reflection of the lung and thymus allowing exposure of the superior vena cava and ascending aorta. A 5 mm section of the aorta is isolated from the vena cava and pulmonary artery and sutures are placed around the aorta. The flow probe is placed in midsternal position and sutures are used to position the aorta into the probe lumen. The intercostal space is closed with 3 sutures and the probe cable secured with the telemetry implant located in the abdomen. The chest is evacuated and surgical incisions are closed. This technique permits long term internal battery or inductively powered assessment of cardiac output along with ECG and/or arterial pressure measurements. This is particularly important for vascular resistance determinations and also other applications that require simultaneous measurements of flow, pressure and ECG in small animals. Telemetry data from rat at day 6 post implantation. Telemetry data from rat at day 6 post implantation. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.