The Contractile Response of the Thoracic Aorta to Vasoactive Substances

"At the OR, the patient will be sedated and have a transoesophageal echo (TEE) catether inserted, which is part of standard clinical care. When a patient becomes hypotensive and the attending anesthesiologist decides to infuse any of the following drugs (phenylephrine, ephedrine, norepinephrine, nitroprusside, or nicardipine), before infusion, the anesthesiolgist will acquire with TEE 10 beats of the thoracic ascending and descending aorta respectively. This is defined as one measurement. Five minutes after infusion the same measurement is repeated. A maximum of 10 measurements (5 before and 5 after infusion of a drug) per patient will be performed.~We want to explicitly mention that for study purposes the surgery or anesthesia will never be prolonged or modified, nor will any drugs be give for study purposes."