Reduction in Chest CT Severity and Improved Hospital Outcomes in SARS-CoV-2 Omicron Compared with Delta Variant Infection

Background The SARS-Cov-2 Omicron variant demonstrates rapid spread but reduced disease severity. Studies evaluating lung imaging findings of Omicron infection versus non-Omicron infection remain lacking. Purpose To compare the Omicron variant with the SARS-CoV-2 Delta variant according to their chest CT radiologic pattern, biochemical parameters, clinical severity, and hospital outcomes after adjusting for vaccination status. Materials and Methods This retrospective study included hospitalized adult patients with reverse transcriptase-polymerase chain reaction test results positive for SARS-CoV-2, with CT pulmonary angiography performed within 7 days of admission between December 1, 2021, and January 14, 2022. Multiple readers performed blinded radiologic analyses that included RSNA CT classification, chest CT severity score (CTSS) (range, 0 [least severe] to 25 [most severe]), and CT imaging features, including bronchial wall thickening. Results A total of 106 patients (Delta group, n = 66; Omicron group, n = 40) were evaluated (overall mean age, 58 years ± 18 [SD]; 58 men). In the Omicron group, 37% of CT pulmonary angiograms (15 of 40 patients) were categorized as normal compared with 15% (10 of 66 patients) of angiograms in the Delta group (P = .016). A generalized linear model was used to control for confounding variables, including vaccination status, and Omicron infection was associated with a CTSS that was 7.2 points lower than that associated with Delta infection (β = -7.2; 95% CI: -9.9, -4.5; P < .001). Bronchial wall thickening was more common with Omicron infection than with Delta infection (odds ratio [OR], 2.4; 95% CI: 1.01, 5.92; P = .04). A booster shot was associated with a protective effect for chest infection (median CTSS, 5; IQR, 0-11) when compared with unvaccinated individuals (median CTSS, 11; IQR, 7.5-14.0) (P = .03). The Delta variant was associated with a higher OR of severe disease (OR, 4.6; 95% CI: 1.2, 26; P = .01) and admission to a critical care unit (OR, 7.0; 95% CI: 1.5, 66; P = .004) when compared with the Omicron variant. Conclusion The SARS-CoV-2 Omicron variant was associated with fewer and less severe changes on chest CT images compared with the Delta variant. Patients with Omicron infection had greater frequency of bronchial wall thickening but less severe disease and improved hospital outcomes when compared with patients with Delta infection. © RSNA, 2022 Online supplemental material is available for this article.

Improved COVID-19 outcomes in a large non-invasive respiratory support cohort despite emergence of the alpha variant

Introduction

Respiratory high-dependency units (rHDUs) are used to manage respiratory failure in COVID-19 outside of the intensive care unit (ICU). The alpha variant of COVID-19 has been linked to increased rates of mortality and admission to ICU; however, its impact on a rHDU population is not known. We aimed to compare rHDU outcomes between the two main UK waves of COVID-19 infection and evaluate the impact of the alpha variant on second wave outcomes.

Methods

We conducted a single-centre, retrospective analysis of all patients with a diagnosis of COVID-19 admitted to the rHDU of our teaching hospital for respiratory support during the first and second main UK waves.

Results

In total, 348 patients were admitted to rHDU. In the second wave, mortality (26.7% s vs 50.7% first wave, χ²=14.7, df=1, p=0.0001) and intubation rates in those eligible (24.3% s vs 58.8% first wave, χ²=17.3, df=2, p=0.0002) were improved compared with the first wave. In the second wave, the alpha variant had no effect on mortality (OR 1.18, 95% CI 0.60 to 2.32, p=0.64). Continuous positive airway pressure (CPAP) (89.5%) and awake proning (85.6%) were used in most patients in the second wave.

Discussion

Our single-centre experience shows that rHDU mortality and intubation rates have improved over time in spite of the emergence of the alpha variant. Our data support the use of CPAP and awake proning, although improvements in outcome are likely to be multifactorial.

Longitudinal trajectory of cardiac magnetic resonance and cardiopulmonary exercise testing findings in moderate to severe COVID-19 and association with symptoms

Background

Cardiac magnetic resonance (CMR) and cardiopulmonary exercise testing (CPET) have provided important insights into the prevalence of early cardiopulmonary abnormalities in COVID-19 patients. It is currently unknown whether such abnormalities persist over time and relate to ongoing symptoms.

Purpose

To describe the longitudinal trajectory of cardiopulmonary abnormalities on CMR and CPET in moderate to severe COVID-19 patients and assess their relationship with ongoing symptoms.

Methods

Fifty-eight previously hospitalised COVID-19 patients and 30 age, sex, body mass index, comorbidity-matched controls underwent CMR, CPET and a symptom-based questionnaire at 2–3 months (2–3m). Repeat assessments (including gas transfer) were performed in 46 patients at 6 months (6m).

Results

During admission, 1/3rd of patients needed ventilation or intensive care (Table 1) and three (5%) had a raised troponin.

On CMR, patients had preserved left (LV) and right ventricular (RV) volumes and function at 2–3m from infection. By 6m, LV function did not change but RV end diastolic volume decreased (mean difference −4.3 mls/m2, p=0.005) and RV function increased (mean difference +3.2%, p&lt;0.001, Fig. 1A).

Patients had higher native T1 (a marker of fibroinflammation) at 2–3m compared to controls (Table 1, Fig. 1B), which normalised by 6m. Extracellular volume was normal and improved by 6m. Native T2, a marker of myocardial oedema, did not differ between patients and controls on serial CMR. At 2–3m, late gadolinium enhancement (LGE) was higher in patients (p=0.023) but became comparable to controls by 6m (p=0.62). Six (12%) patients had LGE in a myocarditis pattern and one (2%) had myocardial infarction. None had active myocarditis using the Modified Lake Louise Criteria.

Lung imaging (T2-weighted) revealed parenchymal abnormalities in 2/3rds of patients at 2–3 and 6 months. The extent of abnormalities improved on serial imaging (Table 1). Gas transfer (DLco) was worse in those with lung abnormalities (77% vs 91% of predicted, p=0.009).

CPET revealed reduced peak oxygen consumption (pVO2) in patients at 2–3m, which normalised by 6m (80.5% to 93.3% of predicted, p=0.001) (Table 1, Fig. 1C). At 2–3m, 49% of patients had submaximal tests (respiratory exchange ratio &lt;1.1), reducing to 25% by 6m (p=0.057). VE/VCO2 slope, a marker of lung efficiency, was abnormal in patients but improved on serial CPET (Table 1, Fig. 1D).

Cardiac symptoms (chest pain, dyspnoea, palpitations, dizziness or syncope) were present in 83% of patients at 2–3m, reducing to 52% by 6m (p&lt;0.001). There was no significant association between CMR or CPET parameters and persistent cardiac symptoms at 6m (Fig. 1E).

Conclusions

Cardiopulmonary parameters (on CMR and CPET) improved in moderate-severe COVID-19 patients from 2–3 to 6 months post infection. Despite this, patients continued to experience cardiac symptoms which had no relationship with measured parameters.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): 1. NIHR Oxford and Oxford Health Biomedical Research Centre, Oxford British Heart Foundation (BHF) Centre of Research Excellence (RE/18/3/34214), United Kingdom Research Innovation and Wellcome Trust2. Medical Research Council and Department of Health and Social Care/National Institute for Health Research Grant (MR/V027859/1) ISRCTN number 10980107 Table 1Figure 1

Successful awake proning is associated with improved clinical outcomes in patients with COVID-19: single-centre high-dependency unit experience

The SARS-CoV-2 can lead to severe illness with COVID-19. Outcomes of patients requiring mechanical ventilation are poor. Awake proning in COVID-19 improves oxygenation, but on data clinical outcomes is limited. This single-centre retrospective study aimed to assess whether successful awake proning of patients with COVID-19, requiring respiratory support (continuous positive airways pressure (CPAP) or high-flow nasal oxygen (HFNO)) on a respiratory high-dependency unit (HDU), is associated with improved outcomes. HDU care included awake proning by respiratory physiotherapists. Of 565 patients admitted with COVID-19, 71 (12.6%) were managed on the respiratory HDU, with 48 of these (67.6%) requiring respiratory support. Patients managed with CPAP alone 22/48 (45.8%) were significantly less likely to die than patients who required transfer onto HFNO 26/48 (54.2%): CPAP mortality 36.4%; HFNO mortality 69.2%, (p=0.023); however, multivariate analysis demonstrated that increasing age and the inability to awake prone were the only independent predictors of COVID-19 mortality. The mortality of patients with COVID-19 requiring respiratory support is considerable. Data from our cohort managed on HDU show that CPAP and awake proning are possible in a selected population of COVID-19, and may be useful. Further prospective studies are required.

Mutation of the von Hippel-Lindau gene alters human cardiopulmonary physiology

Intracellular responses to hypoxia are coordinated by the von Hippel-Lindau--hypoxia-inducible factor (VHL-HIF) transcriptional system. This study investigated the potential role of the VHL-HIF pathway in human systems-level physiology. Patients diagnosed with Chuvash polycythaemia, a rare disorder in which VHL signalling is specifically impaired, were studied during acute hypoxia and hypercapnia. Subjects breathed through a mouthpiece and ventilation was measured while pulmonary vascular tone was assessed echocardiographically. The patients were found to have elevated basal ventilation and pulmonary vascular tone, and ventilatory, pulmonary vasoconstrictive and heart rate responses to acute hypoxia were greatly increased, as were heart rate responses to hypercapnia. The patients also had abnormal pulmonary function on spirometry. This study's findings demonstrate that the VHL-HIF signalling pathway, which is so central to intracellular oxygen sensing, also regulates the organ systems upon which cellular oxygen delivery ultimately depends.

Separating the direct effect of hypoxia from the indirect effect of changes in cardiac output on the maximum pressure difference across the tricuspid valve in healthy humans

In healthy humans, changes in cardiac output are commonly accommodated with minimal change in pulmonary artery pressure. Conversely, exposure to hypoxia is associated with substantial increases in pulmonary artery pressure. In this study we used non-invasive measurement of an index of pulmonary artery pressure, the maximum systolic pressure difference across the tricuspid valve (DeltaPmax), to examine the pulmonary vascular response to changes in blood flow during both air breathing and hypoxia. We used Doppler echocardiography in 33 resting healthy humans breathing air over 6-24 h to measure spontaneous diurnal variations in DeltaPmax and cardiac output. Cardiac output varied by up to approximately 2.5 l/min; DeltaPmax varied little with cardiac output [0.61+/-0.74 (SD) mmHg min l(-1)]. Eight of the volunteers were also exposed to eucapnic hypoxia (end-tidal PO2 = 50 mmHg) for 8 h. In this group DeltaPmax rose progressively from 21 mmHg to 37 mmHg over 8 h. By comparing diurnal variations in DeltaPmax during air breathing with changes in DeltaPmax during hypoxia in the same eight individuals, we concluded that only approximately 5% of the changes in DeltaPmax during hypoxia could be attributed to concurrent changes in cardiac output. The low sensitivity of DeltaPmax to changes in cardiac output makes it a useful index of hypoxic pulmonary vasoconstriction in healthy humans.

Human pulmonary vascular responses to hypoxia and hypercapnia

The ability of alveolar gas composition to influence pulmonary vascular tone has been appreciated for over 50 years. In particular, it has been proposed that both O2 and CO2 could play a role in the matching of perfusion to ventilation within the lung, improving the overall efficiency of gas exchange. A wide variety of experimental approaches has been used to investigate pulmonary vascular effects of the respiratory gases in a range of mammalian species. In this article, we review experiments performed in healthy humans, identify particular difficulties in the interpretation of such experiments, and discuss possible approaches to future study.

Release by hypoxia of a soluble vasoconstrictor from rabbit small pulmonary arteries

BACKGROUND

Soluble pulmonary vasoconstrictors released in response to hypoxia have been reported in pig and rat preparations, but not in rabbit preparations.

METHODS

We used myography to evaluate the contribution of a soluble factor to constriction in rabbit small pulmonary arteries (external diameter 300-475 microm) exposed to 45 min hypoxia (PO(2)=9 mm Hg).

RESULTS

Hypoxia produced gradually intensifying constriction. Return to euoxia (PO(2)=145 mm Hg) for 30 min relaxed only approximately 30% of the constriction, whereas elution of the myograph bath yielded full relaxation. Reapplication of the eluent gradually restored the constriction to its pre-elution level over a 30-min period.

CONCLUSIONS

In this closed system, a soluble factor contributes substantially to hypoxic pulmonary vasoconstriction.

Human pulmonary vascular response to 4 h of hypercapnia and hypocapnia measured using Doppler echocardiography

Hypercapnia has been shown in animal experiments to induce pulmonary hypertension. This study measured the sensitivity and time course of the human pulmonary vascular response to sustained (4 h) hypercapnia and hypocapnia. Twelve volunteers undertook three protocols: 1) 4-h euoxic (end-tidal Po(2) = 100 Torr) hypercapnia (end-tidal Pco(2) was 10 Torr above normal), followed by 2 h of recovery with euoxic eucapnia; 2) 4-h euoxic hypocapnia (end-tidal Pco(2) was 10 Torr below normal) followed by 2 h of recovery; and 3) 6-h air breathing (control). Pulmonary vascular resistance was assessed at 0.5- to 1-h intervals by using Doppler echocardiography via the maximum tricuspid pressure gradient during systole. Results show progressive changes in pressure gradient over 1-2 h after the onset or offset of the stimuli, and sensitivities of 0.6 to 1 Torr change in pressure gradient per Torr change in end-tidal Pco(2). The human pulmonary circulatory response to changes in Pco(2) has a slower time course and greater sensitivity than is commonly assumed. Vascular tone in the normal pulmonary circulation is substantial.