Insights into the evaporation characteristics of saliva droplets and aerosols: Levitation experiments and numerical modeling

Understanding the transmission phenomena of SARS-CoV-2 by virus-laden droplets and aerosols is of paramount importance for controlling the current COVID-19 pandemic. Detailed information about the lifetime and kinematics of airborne droplets of different size is relevant in order to evaluate hygiene measures like wearing masks but also social distancing and ventilation concepts for indoor environments. However, the evaporation process of expiratory droplets and aerosols is not fully understood. Consequently, the main objective of this study is to present evaporation characteristics of saliva droplets. An acoustic levitator is utilized in conjunction with microscopic imaging for recording the temporal evolution of the evaporation of saliva droplets under well-defined ambient conditions. Following the evaporation of the water content, a saliva droplet reaches a final size, which remains stable in the timescale of hours. By investigating numerous droplets of different size, it was found that the final droplet diameter correlates well to 20 % of the initial diameter. This correlation is independent of the ambient conditions for a temperature range from 20  °C to 29  °C and a relative humidity from 6 % to up to 65 %. The experimentally obtained evaporation characteristics are implemented into a numerical model, which is based on one-dimensional droplet kinematics and a rapid mixing evaporation model. By taking into account the evaporation-falling curve as presented by Wells, the significance of the experimental results for predicting the lifetime of saliva droplets and aerosols is demonstrated. The numerical predictions may be used to determine the impact of the droplet size and the ambient conditions on the transmission risks of infectious diseases like COVID-19.

Non-contact heart rate monitoring utilizing camera photoplethysmography in the neonatal intensive care unit - a pilot study

BACKGROUND

Presently the heart rate is monitored in the Neonatal Intensive Care Unit with contact sensors: electrocardiogram or pulse oximetry. These techniques can cause injuries and infections, particularly in very premature infants with fragile skin. Camera based plethysmography was recently demonstrated in adults as a contactless method to determine heart rate.

AIM

To investigate the feasibility of this technique for NICU patients and identify challenging conditions.

STUDY DESIGN AND PARTICIPANTS

Video recordings using only ambient light were made of 19 infants at two NICUs in California and The Netherlands. Heart rate can be derived from these recordings because each cardiovascular pulse wave induces minute pulsatile skin color changes, invisible to the eye but measurable with a camera.

RESULTS

In all infants the heart beat induced photoplethysmographic signal was strong enough to be measured. Low ambient light level and infant motion prevented successful measurement from time to time.

CONCLUSIONS

Contactless heart rate monitoring by means of a camera using ambient light was demonstrated for the first time in the NICU population and appears feasible. Better hardware and improved algorithms are required to increase robustness.

An objective assessment of laparoscopic antireflux surgery

BACKGROUND

Complicated gastroesophageal reflux disease (GERD) requires long-term medical therapy, which in some instances is incompletely effective or poorly tolerated. Additionally, there is concern about the consequences of prolonged acid suppression therapy. Surgical correction of GERD has been a therapeutic option for decades. With the advent of video-assisted laparoscopic surgery, antireflux surgery has had a resurgence in popularity.

PATIENTS AND METHODS

Between October 1992 and June 1995, 20 patients who underwent laparoscopic antireflux surgery were completely studied preoperatively and 3 months postoperatively with 24-hour pH monitoring and esophageal manometry. Follow-up averaged 18 months. The indication for surgery was medically refractory disease in 75%, intolerance to medication in 10%, and concern regarding the consequences of long-term medical therapy in 15%. Two thirds of these patients had complicated GERD.

RESULTS

Operative time averaged 4 hours. There was no conversion to an open procedure. There was no mortality. Two patients had recurrent reflux, for a failure rate of 10%. Overall, postoperative reflux episodes and percent of time pH was less than 4 dropped significantly. Lower esophageal sphincter function showed a statistically significant increase in mean postoperative resting pressure and residual sphincter pressure during swallowing. There was no change in motility postoperatively.

CONCLUSIONS

Laparoscopic antireflux surgery is a safe, effective, therapeutic alternative in the management of gastroesophageal reflux disease.

Familial transmission of a deletion of chromosome 21 derived from a translocation between chromosome 21 and an inverted chromosome 22

Chromosome analysis of a newborn boy with Down syndrome resulted in the identification of a family with an unusual derivative chromosome 22. The child has 46 chromosomes, including two chromosomes 21, one normal chromosome 22, and a derivative chromosome 22. Giemsa banding and fluorescent in situ hybridization (FISH) studies show that the derivative chromosome is chromosome 22 with evidence of both paracentric and pericentric inversions, joined to the long arm of chromosome 21 from 21q21.2 to qter. The rearrangement results in partial trisomy 21 extending from 21q21.2 to 21q terminus in the patient. The child's mother, brother, maternal aunt, and maternal grandmother are all carriers of the derivative chromosome. All have 45 chromosomes, with one normal chromosome 21, one normal chromosome 22, and the derivative chromosome 22. The rearrangement results in the absence of the short arm, the centromere, and the proximal long arm of chromosome 21 (del 21pter-21q21.2) in carriers. Carriers of the derivative chromosome in this family have normal physical appearance, mild learning disabilities and poor social adjustment.

Familial Pallister-Hall syndrome: case report and hormonal evaluation

Pallister-Hall syndrome is a usually lethal dysplasia/malformation syndrome characterized by hypothalamic hamartoblastoma, hypopituitarism, postaxial polydactyly, craniofacial malformations, imperforate anus, and other malformations. We report a familial case in a male infant and his female sib fetus, suggesting autosomal recessive inheritance, or germinal mosaicism for an autosomal dominant mutation, or a segregating submicroscopic chromosome abnormality. Detailed endocrine evaluation on the surviving infant revealed documented pituitary function, pituitary deficit, and hypothalamic deficiency. We suggest that hypothalamic dysfunction contributes to the hypopituitarism seen in Pallister-Hall syndrome.

Cheyne-Stokes respiration in congestive heart failure

Cheyne-Stokes respiration is an abnormal breathing pattern which commonly occurs in patients with decompensated congestive heart failure and neurologic diseases, in whom periods of tachypnea and hyperpnea alternate with periods of apnea. In the majority of these patients, the ventilatory patterns may not be recognized, and the clinical features are generally dominated by the underlying disease process. Cheyne-Stokes respiration may, however, have profound effects on the cardiopulmonary system, causing oxygen desaturation, cardiac arrhythmias, and changes in mental status. Treatment of Cheyne-Stokes respiration in congestive heart failure with supplemental oxygen or nasal continuous positive airway pressure, in addition to conventional therapy, may improve the overall cardiac function and perhaps the patient's prognosis.

Immunofluorescence and electron microscopic findings in a congenital arrector pili hamartoma

A congenital arrector pili hamartoma is a neoplasm that presents as multiple or solitary dermal nodules in a dermatomal distribution. To elucidate and clarify its histogenesis, a lesion derived from a 3-year-old boy was studied by light microscopy, indirect immunofluorescence, using antibodies against basal lamina constituents and against interstitial matrix components, and electron microscopy. In addition, a rabbit antibody specific for bovine smooth-muscle myosin was used. The antibodies against the basal lamina components and fibronectin all showed an intense perimysial fluorescence that ensheathed and surrounded individual leiomyocytes. Anti-smooth-muscle myosin exhibited intense cytoplasmic fluorescence. Furthermore, electron microscopy showed fusiform cells with abundant myofilaments, dense bodies, and pericellular basal lamina as seen in smooth muscle. These studies suggest the probable origin of this hamartoma from pili arrector muscle and could be used as an adjunct in histopathological diagnosis.