We have used a 2.2 MHz continuous-wave Doppler blood velocity meter (Bach-Simpson BVM 202) to measure ascending aortic blood velocity and acceleration, and have obtained from the velocity signal a noninvasive measure of stroke volume and cardiac output by combining the Doppler technique with M-mode echocardiography. In two separate studies we have systematically altered the loading conditions of the heart with lower body pressure; and the inotropic state of the heart with dobutamine (5 micrograms . kg-1 . min-1), and documented the changes in mean velocity (MV), maximum acceleration (MA), stroke volume (SV), cardiac output (CO) and left ventricular end-diastolic dimension (EDD) (M-mode echocardiography). Application of lower body pressure to subjects in a 30 degrees head-up tilt position caused a systematic increase in preload, as shown by a 9% increase in EDD, which raised SV by a maximum of 33% (p less than or equal to 0.001) and CO by 32% (p less than or equal to 0.01), thus showing a classical Starling response; whilst there was relatively little increase in MA. Conversely, infusion of dobutamine, an inotropic agent, caused a 29.2% increase in MA (p less than or equal to 0.01) with minimal increase in SV. Thus, the ability to measure ascending aortic blood velocity allows noninvasive monitoring of changes in both inotropic state and Starling function, with considerable ease and rapidity.

SUMMARY Three weeks after myocardial infarction in 50 patients the effect of the infusion of a graded dose of dobutamine was compared with that of symptom limited treadmill exercise testing. The following variables were measured: blood pressure, heart rate, ST segment changes, Doppler aortic blood flow, and cross sectional echocardiographic dimensions. The heart rate and double product increased more -during exercise than during dobutamine infusion, while maximum acceleration in the ascending aorta increased more during dobutamine infusion than during exercise. Significant ST depression was recorded in 22 Patients and methods PATIENTSExercise and dobutamine stress tests were performed three weeks after acute myocardial infarction in fifty patients (mean (SD) age 56 (5), range 35-69). Nine (18%) of the patients were women. The diagnosis of acute myocardial infarction was based on at least two of three criteria: (a) a history of chest pain suggestive of myocardial ischaemia persisting for at least 30 minutes; (b) evolution ofnew pathological Q waves or persistent ST-T wave changes suggestive of non-Q wave infarction; (c) a rise in the concentrations of aspartate transaminase, hydroxybutyrate dehydrogenase, or creatine kinase to at least twice the upper limits of the reference ranges. The resting electrocardiogram showed anterior infarction in 16 patients, inferior in 22, lateral in four, true posterior in two, and non-Q wave infarction in six. Three (6%) patients had a history of a previous myocardial infarction. Patients with bundle branch block or nonischaemic valvar heart disease were excluded.Patients were randomly selected for the study before the exercise test and their written consent was obtained. 521

We have studied the haemodynamic effects of the application of the medical anti-shock trouser (MAST) in 10 healthy subjects in the semi-upright position in order to simulate mild hypovolaemia. Left ventricular end diastolic dimension (EDD) was measured by M-mode echocardiography and cardiac output (CO) by the Doppler ultrasound technique. Forearm blood flow (FBF) was measured by plethysmography and blood pressure (BP) by the standard cuff technique. Systematic increases in MAST pressure of up to 80 mm Hg were applied. EDD increased to a maximum of 9.3% (p less than or equal to 0.01) which was associated with a maximum increase in CO of 31.7% (p less than or equal to 0.05). FBF increased by a maximum of 54.2% (p less than or equal to 0.001) whilst BP increased by a maximum of 12% (p less than or equal to 0.001). These results demonstrate that the application of the MAST is an effective means of transferring blood to the central circulation by compression of the capacitance vessels resulting in significant increases in cardiac output and tissue perfusion. At high pressures there was evidence of compression of resistance vessels, which may be useful in reducing blood loss. The ease and rapidity with which his suit can be applied suggests that it may be useful in the short term treatment of hypovolaemia.

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