Particle Size Analysis in Aerosol-Generating Dental Procedures Using Laser Diffraction Technique

The global outbreak of coronavirus disease 2019 (COVID-19) has raised concerns about the risk of airborne infection during dental treatment. Aerosol-generating dental procedures (AGDP) produce droplets and aerosols, but the details of the risks of COVID-19 transmission in AGDP are not well-understood. By discriminating between droplets and aerosols, we devised a method to measure particle size using laser diffraction analysis and evaluated aerosols generated from dental devices for providing a basis for proper infection control procedures. The droplets and aerosols generated from dental devices were characterized by multimodal properties and a wide range of droplet sizes, with the majority of droplets larger than 50 μm. AGDP emitted few aerosols smaller than 5 μm, which are of concern for pulmonary infections due to airborne transmission. In addition, the use of extraoral suction was found to prevent the spread of aerosols from high-speed dental engines. This study suggests that the risk of aerosol infections is considerably limited in regular dental practice and that current standard precautions, such as mainly focusing on protection against droplet and contact infections, are sufficient. While several cases of airborne transmission of COVID-19 in general clinics and emergency hospitals have been reported, cluster outbreaks in dental clinics have not yet been reported, which may indicate that AGDP does not pose a significant threat in contributing to the spread of SARS-CoV-2.

Microarray analysis of macrophage response to infection with Streptococcus oralis reveals the immunosuppressive effect of hydrogen peroxide

Oral streptococci including mitis group streptococci are commensal residents and are also the first to colonize the oral cavity. However, various species of these oral streptococci have the potential to invade the host and occasionally lead to severe infectious disease such as cardiovascular diseases. Oral streptococci have close interactions with the host immune system including macrophages at the oral mucosal surface. One notable common trait of oral streptococcus including Streptococcus oralis (S. oralis) is the production of hydrogen peroxide (H₂O₂). Using a comprehensive microarray approach, we sought to understand the innate immune response profiling affected by H₂O₂ production from oral streptococci. We compared the gene expression patterns of macrophages infected with S. oralis wild type (WT) and streptococcal pyruvate oxidase knockout (SpxB-KO), a strain that does not produce H₂O₂. We found that H₂O₂ from S. oralis suppressed proinflammatory gene expression such as TNF-α, that is induced in response to infection, and activated the cellular stress genes such as Egr-1 in response to oxidative stress. A comparative gene ontology analysis of S. oralis WT and SpxB-KO strains revealed that during infection, down regulated genes were closely related to the processes involved in the host defense reaction and up regulated genes were related with the cellular stress responses. Using qPCR analysis, we also confirmed the same pattern of expression changes such as TNF-α, IL-6 and Egr-1. Furthermore, supernatant from SpxB-KO could not suppress the expression of TNF-α in macrophages stimulated with LPS. These findings suggested that H₂O₂ production from S. oralis leads to the suppression of inflammatory responses and NF-κB signaling pathways in macrophages as well as the induction of the oxidative stress response. We concluded that streptococcal H₂O₂ production has the beneficial effects of modulating the innate immune response, thereby stabilizing streptococcal colonization at the mucosal surface and even in the bloodstream leading to cardiovascular disease after invasion, in addition to the commensal role to compete other bacterial species as initial colonizer at oral cavity.

Electrophysiological abnormalities of the atrial muscle in patients with sinus node dysfunction without tachyarrhythmias

The duration and the number of fragmented deflections of the right atrial electrograms were assessed and quantitatively measured in 74 patients who underwent endocardial catheter mapping during sinus rhythm. The bipolar electrograms were recorded at 12 sites in the right atrium. An abnormal atrial electrogram was defined as a duration of 100 ms or longer, and/or 8 or more fragmented deflections, according to our previous criteria. The patients were divided into two groups. The control group consisted of 41 age-matched patients with normal sinus node function and without paroxysmal atrial fibrillation. The study group comprised 33 patients with sinus node dysfunction but without tachyarrhythmias. Abnormal atrial electrograms were observed in 8 (19.5%) control patients, and in 16 (48.5%) sinus node dysfunction patients; p < 0.02. The total number of abnormal electrograms was 14 (2.89%) of 483 atrial electrograms in controls, and 36 (9.38%) of 384 in the study group; p < 0.0002. The mean duration (75.6 +/- 17) and the mean number of fragmented deflections (4.1 +/- 2) of the total atrial electrograms in the sinus node dysfunction group was significantly greater than that in controls (70.9 +/- 11 and 3.6 +/- 1, respectively); p < 0.01. The mean number of abnormal electrograms per patient in the study group (1.06 +/- 1.8) was significantly higher than that in the control group (0.3 +/- 0.8); p < 0.05. These data suggest that: (1) there is a significantly greater electrophysiological abnormality of the atrial muscle in patients with sinus node dysfunction but without paroxysmal atrial fibrillation than in age-matched controls, and (2) not only the sinus node but also the atrial muscle is electrophysiologically altered in patients with sinus node dysfunction but without tachyarrhythmias.

The influence of advancing age on the electrophysiological changes of the atrial muscle induced by programmed atrial stimulation

The influence of advancing age on the electrophysiological changes of the atrial muscle induced by programmed atrial stimulation, such as fragmented atrial activity (FAA), interatrial conduction delay (ICD), and repetitive atrial firing (RAF), was investigated in 42 patients with neither documented episodes of paroxysmal atrial fibrillation nor sick sinus syndrome. The induction rates of FAA, ICD, and RAF were not affected by age. The zones of FAA, ICD and RAF, did not show any correlation with age. However, the longest coupling interval giving rise to FAA (longest CI-FAA) or ICD (longest CI-ICD) showed a significant correlation with age (longest CI-FAA; r = 0.428, p less than 0.01, longest CI-ICD; r = 0.398, p less than 0.01). Although the longest coupling interval giving rise to RAF did not show a direct correlation with age (r = 0.267), it was significantly longer in patients over 60 years of age than in those under 60 (p less than 0.05). These results suggest that aging affects the electrophysiological properties of the atrial muscle, which can help to explain why atrial fibrillation is seem more frequently in the elderly.

Electrophysiological abnormalities of the atrial muscle in patients with manifest Wolff-Parkinson-White syndrome associated with paroxysmal atrial fibrillation

We investigated the electrophysiological properties of the atrial muscle in 33 patients with manifest Wolff-Parkinson-White syndrome. Group I consisted of 13 patients with paroxysmal atrial fibrillation and group II consisted of 20 patients without paroxysmal atrial fibrillation. The anterograde and retrograde effective refractory periods of the accessory pathway and the inducibility of atrioventricular reciprocating tachycardia were not significantly different between the two groups. Endocardial electrograms, obtained by right atrial catheter mapping, were recorded during sinus rhythm from 12 sites of the right atrium in 12 of the 13 group I patients and in all group II patients. An abnormal atrial electrogram was defined as 100 msec or longer in duration, and/or the occurrence of eight or more deflections. Ten (83%) of the 12 group I patients had abnormal atrial electrograms, while only two (10%) of the 20 group II patients had abnormal atrial electrograms, and the difference was significant (P less than 0.01). Thirty-six (26%) of the total 139 electrograms obtained from 12 group I patients and two (1%) of the total 199 electrograms obtained from 20 group II patients fulfilled the criteria for an abnormal atrial electrogram, and the difference was significant (P less than 0.01). The fragmented atrial activity zone, interatrial conduction delay zone, and repetitive atrial firing zone obtained by right atrial extrastimulation were significantly wider in group I than in group II, respectively. It was concluded that electrical abnormalities of the atrial muscle may play an important role in the occurrence of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome.

Conduction properties of the antegrade fast and slow AV nodal pathways associated with AV nodal reentrant tachycardia

To elucidate differences in conduction properties among the normal atrioventricular (AV) node and the antegrade fast and slow dual AV nodal pathways (DAVNPW), AV nodal conduction curves were analyzed quantitatively in 38 patients. Eighteen patients had antegrade DAVNPW with AV nodal reentrant tachycardia (AVNRT) (dual pathways group) and the remaining 20 had smooth AV nodal conduction curves, without evidence of AV nodal dysfunction (control group). The effective refractory period (ERP) of the antegrade fast pathway was longer than that of the normal AV node (at both basic cycle lengths of 700 and 500 msec, p less than 0.01). Although the atrial premature beats were delayed by a longer ERP in the fast pathway, there was no significant difference in the degree of prolongation of AV nodal conduction time related to shortening of the coupling interval (i.e., ratio of A2H2 increment to A1A2 decrement) between these two pathways. On the other hand, the ERP of the antegrade slow pathway was similar to that of the normal AV node. The degree of prolongation of AV nodal conduction time (relative to the shortening of the coupling interval) was greater in the antegrade slow pathway than in the normal AV node. In conclusion, these findings suggest that in DAVNPW with AVNRT: (1) the antegrade fast pathway is similar to the AV node and its conduction properties are unlikely to be better than those of the normal AV node and (2) the antegrade slow pathway has quantitatively poorer conduction properties than the normal AV node, since it has a greater degree of decremental conduction.

Prolonged and fractionated right atrial electrograms during sinus rhythm in patients with paroxysmal atrial fibrillation and sick sinus node syndrome

Intraatrial catheter mapping of the right atrium was performed during sinus rhythm in 92 patients: Group I = 43 control patients without paroxysmal atrial fibrillation or sick sinus node syndrome; Group II = 31 patients with paroxysmal atrial fibrillation but without sick sinus node syndrome; and Group III = 18 patients with both paroxysmal atrial fibrillation and sick sinus node syndrome. Atrial electrograms were recorded at 12 sites in the right atrium. The duration and number of fragmented deflections of the atrial electrograms were quantitatively measured. The mean duration and number of fragmented deflections of the 516 atrial electrograms in Group I were 74 +/- 11 ms and 3.9 +/- 1.3, respectively. The criteria for an abnormal atrial electrogram were defined as a duration of greater than or equal to 100 ms or eight or more fragmented deflections, or both. Abnormal atrial electrograms were observed in 10 patients (23.3%) in Group I, 21 patients (67.7%) in Group II and 15 patients (83.3%) in Group III (Group II versus Group I, p less than 0.001; Group III versus Group I, p less than 0.001). The mean number of abnormal electrograms per patient with an abnormal electrogram was 1.3 +/- 0.7 in Group I, 2.5 +/- 1.9 in Group II and 3.5 +/- 2.5 in Group III (Group I versus Group II, p less than 0.01; Group II versus Group III, p less than 0.05). A prolonged and fractionated atrial electrogram characteristic of paroxysmal atrial fibrillation can be closely related to the vulnerability of the atrial muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of a fatal atrial fibrillation in patients with asymptomatic Wolff-Parkinson-White pattern

Paroxysmal atrial fibrillation (PAF) in patients with manifest WPW syndrome can be a life-threatening arrhythmia by deterioration into ventricular fibrillation. In patients with asymptomatic WPW pattern, the first PAF may lead to ventricular fibrillation or sudden death. Therefore, the purpose of this study was to predict a fatal PAF in patients with asymptomatic WPW pattern. The patient population was divided into two groups: (1) 145 patients with manifest WPW syndrome, excluding intermittent ones (32 with an episode of PAF, 49 with AV reciprocating tachycardia alone, and 64 without any episode of paroxysmal tachyarrhythmia), and (2) mixed group of patients with and without WPW syndrome (36 with an episode of PAF and 66 without PAF). The results were as follows: (1) (a) out of 32 patients with WPW syndrome and PAF, 8 patients were observed to have both the shortest preexcited R-R interval of less than 200 msec during PAF and the shortest antegrade effective refractory period of the accessory pathway (ERP-AP) of less than 250 msec, 7 of whom had dizziness or syncope during PAF and 2 died suddenly during the follow-up period; (b) 21 (32.8%) out of 64 patients with asymptomatic WPW pattern showed the shortest antegrade ERP-AP less than 250 msec; (2) patients with PAF had a higher tendency to develop repetitive atrial firing (RAF), as well as fragmented atrial activity (FAA), which were induced using programmed atrial stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic properties of atrial muscle in paroxysmal atrial fibrillation

The electrophysiologic properties of atrial muscle were studied by programmed atrial stimulation in 42 patients with paroxysmal atrial fibrillation (PAF) and in 53 control patients without PAF. Single premature atrial stimulation was given at the right atrial appendage following 8 basic stimuli with a basic cycle length of 500 ms. Repetitive atrial firing (RAF) was defined as the occurrence of 2 or more successive premature atrial activations following single premature atrial stimulation. Fragmented atrial activity (FAA) was defined as an increase by more than 75% of the duration of the atrial electrogram in response to a single premature stimulation. Interatrial conduction delay was defined as an increase of the conduction time by more than 50 ms in response to a single premature stimulation. RAF was induced in 26 of 42 patients (61.9%) with PAF and in 14 of 53 control patients (26.4%). FAA and interatrial conduction delay were elicited in 69.0 and 80.9% of patients with PAF and in 34.0 and 56.6% of control patients, respectively. In 16 patients with PAF in whom RAF was not induced, FAA developed in 11 patients (68.8%). In 88.1% of 42 patients with PAF and in 41.5% of 53 controls, RAF or FAA, or both, were elicited by atrial premature stimulation. It is concluded that the incidence of RAF and FAA were significantly higher in patients with PAF than in the control group, and the induction of RAF or FAA, or both, was closely related to the vulnerability of the atrial muscle to atrial fibrillation.