The COVID-19 pandemic has reshaped the demand for goods and services worldwide. The combination of a public health emergency, economic distress, and misinformation-driven panic have pushed customers and vendors towards the shadow economy. In particular, dark web marketplaces (DWMs), commercial websites accessible via free software, have gained significant popularity. Here, we analyse 851,199 listings extracted from 30 DWMs between January 1, 2020 and November 16, 2020. We identify 788 listings directly related to COVID-19 products and monitor the temporal evolution of product categories including Personal Protective Equipment (PPE), medicines (e.g., hydroxyclorochine), and medical frauds. Finally, we compare trends in their temporal evolution with variations in public attention, as measured by Twitter posts and Wikipedia page visits. We reveal how the online shadow economy has evolved during the COVID-19 pandemic and highlight the importance of a continuous monitoring of DWMs, especially now that real vaccines are available and in short supply. We anticipate our analysis will be of interest both to researchers and public agencies focused on the protection of public health.
Of 60 patients aged 45 to 66 years with aortic valve stenosis, 28 (47 per cent) had angina pectoris. Significant coronary arterial obstruction was shown by selective coronary cineangiography in 14 of them. Systolic pressure gradients across the aortic valve were lower in patients with angina than in those without. In those with angina, systolic gradients were higher in those with normal coronary arteriograms than in those with demonstrable coronary arterial disease. Aortic valve replacement relieved the angina in all patients who had normal coronary arteriograms. When valve replacement was combined with coronary bypass grafting in those with coronary arterial disease, surgical mortality was higher and symptomatic relief less predictable. Incapacitating angina in patients with aortic stenosis was nearly always associated with significant coronary disease. In those with less severe angina it was impossible to predict the state of the coronary arteries. Two patients, who did not have angina and who did not undergo coronary arteriography, died after aortic valve replacement and were found at necropsy to have unsuspected severe coronary disease. We, therefore, suggest that coronary arteriography should be carried out in all patients over the age of 40 years in whom surgery is being considered for aortic stenosis.
The second heart sound is caused by closure of the aortic-and pulmonary valves at the end of ventricular systole. Two components, from the separate closure of the two valves, are usually audible because of slight asynchrony of the two ventricles, aortic closure preceding pulmonary closure in normal subjects (Leatham and Towers, 1951). Potain (1866) observed that the character of the second heart sound altered with respiration. While it might be single during the expiratory phase of continued respiration it became clearly split with inspiration. Such a change in the second sound is found in most normal subjects and is due to prolongation of right ventricular systole during inspiration. This may be explained by the increased filling of the right atrium and ventricle from the great veins which takes place with the inspiratory fall in intra-thoracic pressure. No such change can occur on the left side of the heart since intrathoracic pressure changes affect the pulmonary veins and heart chambers equally. Sometimes a clearly split second heart sound becomes single or more closely split on inspiration (Fig. 1). Such paradoxical behaviour of the second sound with respiration is due to reversal of the normal order of valve closure, pulmonary closure preceding aortic closure (Leatham, 1952). This auscultatory sign may be recognized in the neighbourhood of the pulmonary area and confirmed by phonocardiography. A study has been made of 40 cases in which paradoxical splitting of the second heart sound was recognized on clinical and phonocardiographic examination.Method. The heart sounds were studied in simultaneous recordings taken from the pulmonary and mitral areas. The electrocardiogram and indirect carotid pulse were registered at the same time. High frequency records were used (Leatham, 1952) and measurements were made from the onset of the earliest high-frequency vibration recorded, tracings being made during held expiration. Additional phonocardiograms were made in the fourth or fifth left interspace close to the sternum in many cases to record splitting of the first heart sound, and records were taken during quiet respiration where possible. The aortic component of the second heart sound was identified in the records made at the pulmonary and mitral areas by its coincidence with the dicrotic notch of the carotid pulse (allowance being made for the delay in transmission of the arterial pulse to the carotid vessels). The pulmonary component was readily identified in records made at the pulmonary area but was absent from the mitral area records; it had no constant relation to the dicrotic notch. When splitting of the first heart sound was present the left-and right-sided components were identified where possible. These are probably caused by closure ofthe atrio-ventricular valves (Dock, 1933) and in normal subjects mitral closure is slightly before tricuspid. The tricuspid element is loudest at the left sternal edge in the fourth or fifth space and the mitral element at the apex. Confirmation of mitral closure was ob...
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