Niven, Alexander S.

BACKGROUND: Methacholine challenge testing (MCT) is a common bronchoprovocation technique used to assess airway hyper-responsiveness. We previously demonstrated that the addition of a viral filter to the nebulizer exhalation limb substantially reduced expelled particles during MCT. Our aim was to evaluate whether this modification affects the delivered dose of methacholine. METHODS: A mechanical ventilator was connected to a lung simulator with breathing frequency 15 breaths/min, tidal volume 500 mL, inspiratory-expiratory ratio 1:1, with a sinusoidal waveform. We compared methacholine dose delivery using the Hudson Micro Mist or AeroEclipse II BAN nebulizers powered by either a dry gas source or a compressor system. A filter placed in line between the nebulizer and test lung was weighed before and after 1 min of nebulized methacholine delivery. Mean inhaled mass was measured with and without a viral filter on the exhalation limb. Dose delivery was calculated by multiplying the mean inhaled mass by the respirable fraction (particles < 5 μm) and inhalation time. Unpaired t test was used to compare methacholine dose delivery with and without viral filter placement. RESULTS: The addition of a viral filter did not significantly affect methacholine dose delivery across all devices tested. Using a 50-psi dry gas source, dose delivered with or without a viral filter did not differ with the Hudson (422.3 μg vs 282.0 μg, P = .11) or the AeroEclipse nebulizer (563.0 μg vs 657.6 μg, P = .59). Using the compressor, dose delivered with and without a viral filter did not differ with the Hudson (974.0 μg vs 868.0 μg, P = .03) or the AeroEclipse nebulizer (818.0 μg vs 628.5 μg, P = .42). CONCLUSIONS: The addition of a viral filter to the nebulizer exhalation limb did not affect methacholine dose during bronchoprovocation testing. Routine use of a viral filter should be considered to improve pulmonary function technician safety and infection control measures during the ongoing COVID-19 pandemic.

Abstract Background A patent foramen ovale (PFO) is a persistent embryonic defect in the interatrial septum. Platypnoea-orthodeoxia syndrome is characterized by positional hypoxaemia that is most commonly due to right-to-left shunting through a PFO. Dynamic right-to-left shunting through a PFO can also exacerbate positional hypoxaemia without platypnea-orthodeoxia syndrome. Case summary A 78-year-old woman with hyperthyroidism and paroxysmal atrial fibrillation (AF) presented with positional hypoxaemia exacerbated by supine positioning. Diagnostic testing revealed intermittent right-to-left shunting through a PFO triggered by worsening atrial functional tricuspid regurgitation and elevated right atrial pressures. Diuresis, rate control, and thyroidectomy initially led to resolution of positional hypoxaemia, but recurrent AF episodes triggered right-to-left shunting with recurrent desaturation. Left atrial and cavo-tricuspid isthmus ablation led to restoration of normal sinus rhythm and resolution of positional hypoxaemia without PFO closure. Discussion The clinical presentation of intermittent intracardiac right-to-left shunting can mimic decompensated heart failure with pulmonary oedema. Persistent hypoxaemia out of proportion to the degree of pulmonary oedema and minimally responsive to supplemental O2 should raise suspicion for right-to-left shunt aetiology. Positional arterial blood gases can facilitate the diagnostic evaluation of refractory hypoxaemia in cases of suspected shunting. Diagnostic imaging for PFO detection includes both transthoracic and transesophageal echocardiography with Valsalva manoeuver and agitated saline injection. Closure of a PFO for management of arterial deoxygenation syndromes should not be performed before treating other causes of arterial deoxygenation and optimizing factors that may exacerbate shunting across the PFO.

Background: COVID-19 reveals new manifestations not only in the acute phase but also in the long term. The latter is what has been termed as ‘post acute sequelae of SARS-CoV-2 infection’ (PASC) — or “long COVID”— with dyspnea as one of its hallmarks. Cardiopulmonary stress testing (CPET) is increasingly being used to better evaluate such patients. Objective: To compare CPET findings of long COVID patients versus non-COVID patients with undifferentiated dyspnea on exertion seen at Mayo Clinic. Methods: A cohort study was carried out using Mayo Clinic’s exercise testing database. The study group included 77 PASC patients confirmed by a positive antigen or PCR test with no prior history of heart or lung disease. PASC patients were compared to 766 non-COVID patients with unspecified dyspnea without known diagnosis of cardiac or pulmonary disease. ANOVA according to the general linear model and Pearson’s Chi square were used for the bivariate analysis of the quantitative and categorical variables, respectively. Analyses were controlled for age, sex, and beta blocker use as appropriate. Both HR and SBP at rest and peak exercise were significantly different between groups, although the absolute differences were small. Results: Compared with the control group, the post-COVID patients were younger (mean age 47 SD ±14.9 years versus 50.5 SD ±10.1 years) and more likely to be female (70.1% (54 of 77) vs 57.6% (441 of 766)). Although there were many significant differences in the CPET results, the most outstanding were a lower FAC (73 SD ±19.4% vs 85.2 SD ±20.8%) and peak VO2 (22 SD ±6.4 ml/kg/min vs 25.8 SD ±7.37 ml/kg/min) in the study group (p<.0001). Also, CNS changes during CPET were reported at higher rates (19.5% (15 of 77) vs 11.4% (87 of 766)) while dyspnea at lower rates (55.8% (43 of 77) vs 65.7% (503 of 766)) in post-COVID patients (p=0.02). When adjusting for age and sex, weight was significantly higher in the study group (p=0.03) although the absolute difference was modest and BMI remained not significant. PFTs did not suggest any pulmonary abnormalities. Conclusions: We identified a high rate of severe exercise limitation among long COVID patients. Young women may be at higher risk for these complications. Pre-exercise PFTs and absence of objective respiratory limitation during CPET argue against a primary pulmonary cause of the observed limitations, though evaluation of cardiac, autonomic, and muscular impairment is pending. Further studies are warranted to untangle the physiologic abnormalities responsible for these observations.

BACKGROUND: Methacholine bronchoprovocation or challenge testing (MCT) is commonly performed to assess airway hyper-responsiveness in the setting of suspected asthma. Nebulization is an aerosol-generating procedure, but little is known about the risks of MCT in the context of the ongoing coronavirus disease 2019 (COVID-19) pandemic. We aimed to quantify and characterize aerosol generation during MCT by using different delivery methods and to assess the impact of adding a viral filter. METHODS: Seven healthy subjects performed simulated MCT in a near particle-free laboratory space with 4 different nebulizers and with a dosimeter. Two devices continuously sampled the ambient air during the procedure, which detected ultrafine particles, from 0.02–1 μm, and particles of sizes 0.3, 0.5, 1.0, 2.0, 5.0, and 10 µm, respectively. Particle generation was compared among all the devices, with and without viral filter placement. RESULTS: Ultrafine-particle generation during simulated MCT was significant across all the devices. Ultrafine-particle (0.02–1 μm) concentrations decreased 77%–91% with the addition of a viral filter and varied significantly between unfiltered (P < .001) and filtered devices (P < .001). Ultrafine-particle generation was lowest when using the dosimeter with filtered Hudson nebulizer (1,258 ± 1,644 particle/mL). Ultrafine-particle concentrations with the filtered nebulizer devices using a compressor were higher than particle concentrations detected when using the dosimeter: Monaghan (3,472 ± 1,794 particles/mL), PARI (4,403 ± 2,948), Hudson (6,320 ± 1,787) and AirLife (9,523 ± 5,098). CONCLUSIONS: The high particle concentrations generated during MCT pose significant infection control concerns during the COVID-19 pandemic. Particle generation during MCT was significantly reduced by using breath-actuated delivery and a viral filter, which offers an effective mitigation strategy.