Relating Noninvasive Cardiac Output and Total Peripheral Resistance Estimates to Physical Activity in an Ambulatory Setting

The prevalence and cost of heart disease indicate the need for better methods of detecting, diagnosing and treating this pervasive problem. Appropriate monitoring outside of the hospital can potentially lead to earlier diagnosis and reduced costs. We use electrocardiogram (ECG) and continuous arterial blood pressure (ABP) data collected in an ambulatory setting to examine two important cardiovascular quantities, namely cardiac output (CO) and total peripheral resistance (TPR), over a range of physical activities. CO and TPR can be estimated from heart rate, pulse pressure and mean arterial blood pressure, which in turn are directly obtained from the ECG and ABP signals. More specifically, we employ a wearable cardiac and motion monitor designed by colleagues at MIT to simultaneously record ECG and 3-axis acceleration to onboard memory. The acceleration data is used to generate an estimate of physical activity at each time point. Additionally, we use a Portapres continuous blood pressure monitor to concurrently record the ABP waveform. We present representative results from data collected in a controlled ambulatory setting. Heart rate, mean ABP, CO and TPR responses to physical activity are generally consistent with what might be expected from cardiovascular physiology. The longer-term challenge is to correlate the dynamic behavior of these quantities with the state of cardiac health.