Combined Effects of Masking and Distance on Aerosol Exposure Potential.

OBJECTIVE: To quantify the efficacy of masking and "social distancing" on the transmission of airborne particles from a phantom aerosol source (simulating an infected individual) to a nearby target (simulating a healthy bystander) in a well-controlled setting. METHODS: An aerosol was created using monodisperse polystyrene latex beads in place of infectious respiratory secretions. Detection was by aerodynamic particle spectrometry. Both reusable cloth masks and disposable paper masks were studied. Transmission was simulated indoors during a 3-minute interval to eliminate the effect of variable ventilation rate on aerosol exposure. The study commenced on September 16, 2020, and concluded on December 15, 2020. RESULTS: Compared with a baseline of 1-foot separation with no masks employed, particle count was reduced by 84% at 3 feet of separation and 97% at 6 feet. A modest decrease in particle count was observed when only the receiver was masked. The most substantial exposure reduction occurred when the aerosol source was masked (or both parties were masked). When both the source and target were masked, particle count was reduced by more than 99.5% of baseline, regardless of separation distance or which type of mask was employed. CONCLUSION: These results support the principle of layered protection to mitigate transmission of SARS-CoV-2, the virus causing COVID-19, and other respiratory viruses and emphasize the importance of controlling the spread of aerosol at its source. The combination of masking and distancing reduced the exposure to exhaled particulates more than any individual measure. Combined measures remain the most effective way to combat the spread of respiratory infection.

Vibrometry: a novel noninvasive application of ultrasonographic physics to estimate wall stress in native aneurysms.

Our objective was to test vibrometry as a means to measure changes in aneurysm sac pressure in an in vitro aneurysm model. Explanted porcine abdominal aortas and nitrile rubber tubes were used to model an aneurysm sac. An ultrasound beam was used to vibrate the surface of the aneurysm model. The motion generated on the surface was detected either by reflected laser light or by a second ultrasound probe. This was recorded at different aneurysm pressures. The phase of the propagating wave was measured to assess changes in velocity and to see if there was a correlation with aneurysm pressure. The cumulative phase shift detected by laser or Doppler correlated well with increasing hydrostatic pressure in both the rubber and the porcine aorta model. The square of the mean pressure correlated well with the cumulative phase shift when dynamic pressure was generated by a pump. However, the pulse pressure was poorly correlated with the cumulative phase shift. Noninvasive measurement of changes in aortic aneurysm sac tension is feasible in an in vitro setting using the concept of vibrometry. This could potentially be used to noninvasively detect wall stress in native aneurysms and endotension after endovascular aneurysm repair (EVAR) and to predict the risk of rupture.

Noninvasive measurement of aortic aneurysm sac tension with vibrometry.

OBJECTIVE: Currently, the risk of aneurysm sac rupture after endovascular abdominal aortic aneurysm repair (EVAR) is estimated by using a group of anatomic variables. Available techniques for pressure monitoring include either direct measurement using catheter-based techniques or indirect measurement requiring implantation of a pressure sensor during aneurysm repair. None of these methods is without limitations. Radiation pressure, such as that generated by a modulated ultrasound (US) beam, can induce surface vibration at a distance. The velocity of the resulting surface waves depends on the tensile stress of the vibrated surface. By measuring the change in wave velocity, it is possible to detect the change in tensile stress and calculate the pressure through the vibrated surface. We tested this concept in an in vitro aneurysm model. METHODS: Rubber tubes and explanted porcine abdominal aortas were used to model an aneurysm sac. The surface of the model was vibrated with an amplitude-modulated US beam. The resulting motion was detected either by reflected laser light or by Doppler US. The phase of the propagating wave was measured to assess changes in velocity with different pressures. RESULTS: Increasing hydrostatic pressure in the rubber model correlated well with the cumulative phase shift (R(2) = 0.96-0.99; P < .0001). By using a pump to generate dynamic pressure (between 110 and 200 mm Hg), the cumulative phase shift correlated well with the square of the mean pressure (R(2) = 0.92; P < .0001); however, the correlation with pulse pressure was poor (24-36 mm Hg; r = 0.38; P < .02). In the porcine in vitro aortic sac model, the cumulative phase shift detected with both laser (r = 0.94-0.99; P < .0001) and Doppler (r = 0.96-0.99; P < .0001) correlated well with the aneurysm pressure. CONCLUSIONS: Application of vibrometry for noninvasive measurement of aortic aneurysm sac tension is feasible in an in vitro setting. The concept of vibrometry may be used to detect endotension noninvasively after EVAR. Vibrometry may also be used to estimate wall stress in native aneurysms, and it may predict the risk of aneurysm rupture. CLINICAL RELEVANCE: Vibrometry may offer a technique for completely noninvasive monitoring of aneurysm sac pressure after EVAR. Vibrometry is based on the following principles: radiation pressure, such as that generated by modulated US, can induce surface vibration at a distance; by measuring the change in wave velocity of vibration, it is possible to detect changes in tensile stress and calculate the pressure through the vibrated surface. We tested this concept in an in vitro model and found that application of vibrometry for noninvasive measurement of aortic aneurysm sac tension is feasible. Vibrometry may also be used to estimate wall stress in native aneurysms.