Wavelet entropy of Doppler ultrasound blood velocity flow waveforms distinguishes nitric oxide-modulated states

Wavelet entropy assesses the degree of order or disorder in signals and presents this complex information in a simple metric. Relative wavelet entropy assesses the similarity between the spectral distributions of two signals, again in a simple metric. Wavelet entropy is therefore potentially a very attractive tool for waveform analysis. The ability of this method to track the effects of pharmacologic modulation of vascular function on Doppler blood velocity waveforms was assessed. Waveforms were captured from ophthalmic arteries of 10 healthy subjects at baseline, after the administration of glyceryl trinitrate (GTN) and after two doses of N(G)-nitro-L-arginine-methyl ester (L-NAME) to produce vasodilation and vasoconstriction, respectively. Wavelet entropy had a tendency to decrease from baseline in response to GTN, but significantly increased after the administration of L-NAME (mean: 1.60 ± 0.07 after 0.25 mg/kg and 1.72 ± 0.13 after 0.5 mg/kg vs. 1.50 ± 0.10 at baseline, p < 0.05). Relative wavelet entropy had a spectral distribution from increasing doses of L-NAME comparable to baseline, 0.07 ± 0.04 and 0.08 ± 0.03, respectively, whereas GTN had the most dissimilar spectral distribution compared with baseline (0.17 ± 0.08, p = 0.002). Wavelet entropy can detect subtle changes in Doppler blood velocity waveform structure in response to nitric-oxide-mediated changes in arteriolar smooth muscle tone.

Ultrasound imaging in teaching cardiac physiology

This laboratory session provides hands-on experience for students to visualize the beating human heart with ultrasound imaging. Simple views are obtained from which students can directly measure important cardiac dimensions in systole and diastole. This allows students to derive, from first principles, important measures of cardiac function, such as stroke volume, ejection fraction, and cardiac output. By repeating the measurements from a subject after a brief exercise period, an increase in stroke volume and ejection fraction are easily demonstrable, potentially with or without an increase in left ventricular end-diastolic volume (which indicates preload). Thus, factors that affect cardiac performance can readily be discussed. This activity may be performed as a practical demonstration and visualized using an overhead projector or networked computers, concentrating on using the ultrasound images to teach basic physiological principles. This has proved to be highly popular with students, who reported a significant improvement in their understanding of Frank-Starling's law of the heart with ultrasound imaging.

Ultrasound in undergraduate medical education: A systematic and critical review

Introduction: Point-of-care ultrasound (POCUS) use in clinical care is growing rapidly, and advocates have recently proposed the integration of ultrasound into undergraduate medical education (UME). The evidentiary basis for this integration has not been evaluated critically or systematically. In this study, we conducted a critical and systematic review framed by the rationales enumerated by advocates of ultrasound in UME in academic publications.

Methods: This research was conducted in two phases. First, the dominant discursive rationales for the integration of ultrasound in UME were identified using techniques from Foucauldian critical discourse analysis (CDA) from an archive of 403 academic publications. We then sought empirical evidence in support of theses rationales, using a critical synthesis methodology also adapted from CDA.

Results: We identified four dominant discursive rationales, with different levels of evidentiary support. Ultrasound was not demonstrated to improve students’ understanding of anatomy. The benefit of ultrasound in teaching physical examination was inconsistent,and rests on minimal evidence. With POCUS, students’ diagnostic accuracy was improved for certain pathologies, but findings were inconsistent for others. Finally, the rationale that ultrasound training in UME will improve quality of patient care was difficult to evaluate.

Discussion: Our analysis has shown that the frequently repeated rationales for the integration of ultrasound in UME are not supported by a sufficient base of empirical research. The repetition of these dominant discursive rationales in academic publications legitimizes them and may preclude further primary research. Since the value of clinical ultrasound use by medical students remains unproven, educators must consider whether the associated financial and temporal costs are justified or whether more research is required.