Abstract
The Frank–Starling relationship is a fundamental concept in cardiovascular physiology, relating change in cardiac filling to its output. Historically, this relationship has been measured by physiologists and clinicians using invasive monitoring tools, relating right atrial pressure (Pra) to stroke volume (SV) because the Pra-SV slope has therapeutic implications. For example, a critically ill patient with a flattened Pra-SV slope may have low Pra yet fail to increase SV following additional cardiac filling (e.g., intravenous fluids). Provocative maneuvers such as the passive leg raise (PLR) have been proposed to identify these “fluid non-responders”; however, simultaneously measuring cardiac filling and output via non-invasive methods like ultrasound is cumbersome during a PLR. In this Hypothesis and Theory submission, we suggest that a wearable Doppler ultrasound can infer the Pra-SV relationship by simultaneously capturing jugular venous and carotid arterial Doppler in real time. We propose that this method would confirm that low cardiac filling may associate with poor response to additional volume. Additionally, simultaneous assessment of venous filling and arterial output could help interpret and compare provocative maneuvers like the PLR because change in cardiac filling can be confirmed. If our hypothesis is confirmed with future investigation, wearable monitors capable of monitoring both variables of the Frank–Starling relation could be helpful in the ICU and other less acute patient settings.
Highlights
When receiving more blood from peripheral tissues, cardiac myocytes elongate and contract with greater force—ensuring that the heart ejects what it receives [1]; this fundamental attribute is known as the Frank–Starling mechanism
Intravenous fluid in the intensive care unit (ICU) is associated with adverse events [11] and that targeted administration of intravenous fluids improves patient-centered outcomes [9, 12], delivering fluid therapy in the ICU based on functional hemodynamic monitoring (FHM) has become standard-ofcare [13,14,15]
In this Hypothesis and Theory, we describe the physiological rationale and provide early proof-of-concept, feasibility data suggesting that simultaneous venous and arterial Doppler should be used to infer the slope of the Frank–Starling curve
Summary
When receiving more blood from peripheral tissues, cardiac myocytes elongate and contract with greater force—ensuring that the heart ejects what it receives [1]; this fundamental attribute is known as the Frank–Starling mechanism. Given that arterial Doppler ultrasound tracks SV [18, 19] and venous Doppler qualitatively changes in response to increased right atrial pressure [2, 3], we hypothesize that a wireless, wearable Doppler ultrasound simultaneously insonating the common carotid artery and internal jugular vein will demonstrate the Frank–Starling relationship in real time. In this manner, hands-free ultrasound can identify patients with low cardiac filling pressure who are, volume “unresponsive” and determine if provocative maneuvers like the PLR augment cardiac filling. From the wearable Doppler, the patient was inferred to have a relatively low SV/ Pra
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