A recent Respiratory Medicine digest,
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Study Type: Commentary/narrative review

Key Question: What is the pathobiological basis, clinical significance, and trial utility of airway mucus plugs in asthma and COPD?

Key Findings:

• Mucus plug burden, quantified via CT-based scoring (e.g., bronchopulmonary segment mucus plug score), correlates with increased exacerbations, accelerated spirometric decline in both asthma and COPD, and excess mortality in COPD
• Biologic therapies in asthma trials have demonstrated measurable reductions in mucus plug burden alongside spirometric improvement, supporting mucus plugging as a treatable trait
• Quantitative imaging methods for mucus plug scoring are under active development but lack standardisation

Clinical Relevance: CT-quantified mucus plug burden may offer UK respiratory clinicians a phenotyping and treatment-monitoring tool, particularly when considering biologic therapy eligibility and response in severe asthma and COPD.

Limitations: As a narrative review, no primary data are presented and evidence synthesis is not systematic.

Study Type: Retrospective cohort study (registry-based)

Key Question: Does each additional prior exacerbation incrementally increase future exacerbation risk in bronchiectasis, and is this consistent across aetiologies and regions?

Key Findings:

• Future exacerbation risk rose progressively with each prior exacerbation: IRR 1.45 (1 prior), 1.84 (2), 2.50 (3), and 3.56 (≥4), with no plateau identifying a clear threshold.
• One prior severe (hospitalised) exacerbation was strongly associated with future severe exacerbations (IRR 3.96, 95% CI 3.71–4.22).
• The frequent exacerbator phenotype was consistent across all aetiologies and geographic regions within the 30-country EMBARC cohort (n=19,324).

Clinical Relevance: The established ≥3 exacerbations/year threshold may be overly simplistic; UK clinicians should consider even 1–2 prior exacerbations as clinically significant when stratifying risk and targeting preventive treatment.

Limitations: Observational registry design precludes causal inference, and exacerbation ascertainment may vary across contributing centres.

Study Type: Retrospective cohort study (high-plex spatial proteomics)

Key Question: Do EGFR and KRAS mutations differentially shape the spatial immune architecture of the NSCLC tumour microenvironment, and does this influence prognosis?

Key Findings:

• EGFR- and KRAS-mutant tumours showed higher tumour cell density with reduced cytotoxic T cell, dendritic cell, and granulocyte infiltration compared to wild-type tumours across 197 samples (>2 million cells)
• EGFR-mutant tumours were specifically enriched for M2-like tumour-associated macrophages with closer spatial clustering; KRAS-mutant tumours showed increased T-regulatory cells and TAMs in proximity to tumour cells
• Spatial immune metrics (cellular neighbourhoods, nearest-neighbour distances, proximity profiling) independently correlated with survival on Cox proportional hazards modelling

Clinical Relevance: This provides a mechanistic basis for immunotherapy resistance in EGFR/KRAS-mutant NSCLC — a common clinical dilemma — and suggests spatially-defined immune phenotypes could refine patient selection for immunotherapy.

Limitations: Retrospective design limits causal inference and generalisability across treatment-diverse real-world populations.

Study Type: Prospective cohort study (COPDGene registry)

Key Question: Does occupational exposure to dust and/or fumes predict future respiratory, cardiovascular, and other clinical outcomes in smokers?

Key Findings:

• Combined dust-and-fumes exposure (34.4% of participants) was associated with significantly more respiratory exacerbations (aRR 1.38, 95% CI 1.26–1.52) versus unexposed individuals over up to 15 years
• The same group had higher odds of ASCVD (aOR 1.35, 95% CI 1.17–1.56) and pneumonia (aOR 1.39, 95% CI 1.19–1.63)
• Dust-only or fumes-only exposures were not independently highlighted as significant; cancer and venous thromboembolism showed no significant association

Clinical Relevance: Occupational history taking in UK respiratory clinics should be prioritised, as combined dust-and-fumes exposure represents a modifiable risk factor influencing exacerbation burden and cardiovascular outcomes, with implications for COPD management and occupational health referral pathways.

Limitations: Occupational exposure was self-reported at a single baseline timepoint, introducing potential misclassification and recall bias.

Study Type: Clinical Practice Guideline (ATS; GRADE methodology, informed by systematic reviews and network meta-analyses)

Key Question: Which noninvasive respiratory support strategy — HFNC, NIV, or CPAP — is optimal across acute hypoxemic and hypercapnic respiratory failure, pre-intubation preoxygenation, and post-extubation support?

Key Findings:

• Acute hypoxaemic failure: strong recommendation for HFNC; conditional recommendation for NIV/CPAP — both primarily based on reduced intubation rates
• Acute hypercapnic failure: strong recommendation for NIV (mortality and intubation benefit); HFNC conditionally acceptable only in milder hypercapnia (pH >7.25) with close monitoring
• Preoxygenation: strong recommendation for HFNC or NIV to reduce peri-intubation hypoxaemia; post-extubation: HFNC for low-risk, NIV for high-risk patients to reduce re-intubation

Clinical Relevance: Provides directly applicable, GRADE-rated guidance to standardise NIRS use across UK ICUs and respiratory units where practice remains variable.

Limitations: Recommendations may not fully account for NHS resource constraints or differences in institutional NIV/HFNC capacity.

Study Type: Retrospective cohort study

Key Question: Does nocturnal respiratory effort, measured by oesophageal pressure (PES), independently predict long-term all-cause mortality in patients investigated for OSA?

Key Findings:

• In 16,083 patients followed for a median of 15 years, 9.3% died; median PES of 12.8 cmH₂O correlated with mortality across quartiles
• After adjustment for age, sex, BMI, comorbidities, AHI, and oxygen saturation, 3rd quartile PES remained independently associated with mortality (HR 1.21; 95% CI 1.03–1.43)
• Greater time spent at higher negative PES thresholds was dose-dependently associated with increased mortality risk, independent of conventional OSA metrics

Clinical Relevance: AHI alone may underestimate OSA-related cardiovascular risk; incorporating respiratory effort monitoring could refine prognostication for patients under investigation in UK sleep services.

Limitations: Oesophageal pressure monitoring is invasive and not routinely used in NHS sleep laboratories, limiting immediate clinical translation.

Study Type: Prospective registry-based cohort study with unsupervised machine learning analysis (latent class analysis)

Key Question: Can data-driven phenotyping via latent class analysis improve risk stratification and predict PAH-targeted therapy responses in adults with PAH-CHD?

Key Findings:

• LCA identified four clinically distinct phenogroups within both post- and pre-tricuspid shunt populations, with 2–3-fold mortality differences between best and worst-prognosis groups over 10 years
• In post-tricuspid shunts, a "hyperkinetic" phenogroup uniquely benefited from combination PAH therapy (interaction p=0.026)
• In pre-tricuspid shunts, an older male comorbidity-predominant group showed significantly higher mortality and attenuated treatment response (interaction p=0.037) despite mild haemodynamics

Clinical Relevance: For UK PAH centres managing complex CHD-PAH, this supports moving beyond anatomical classification toward phenotype-guided treatment decisions, potentially informing combination therapy initiation criteria.

Limitations: Single-country registry data from China limits direct generalisability to UK/European PAH-CHD populations with differing demographics and treatment pathways.

Study Type: Commentary / expert practice guidance ("How I Do It" format)

Key Question: Can prostacyclin therapy be safely de-escalated in PAH patients receiving sotatercept, and how should clinicians approach this decision?

Key Findings:

• Conventional monitoring tools (WHO functional class, 6MWD, BNP/NT-proBNP, composite risk scores) lack sufficient granularity to guide de-escalation in higher-functioning patients on sotatercept
• CPET is proposed as a complementary stress-based assessment of cardiopulmonary reserve and RV-pulmonary vascular coupling to improve decision confidence
• A structured, CPET-integrated decision framework is proposed for individualised, shared decision-making around prostacyclin de-escalation

Clinical Relevance: As sotatercept enters UK PAH practice, clinicians will increasingly face requests to rationalise burdensome prostacyclin regimens; this article offers a practical framework where no established protocol currently exists.

Limitations: No original outcome data presented; guidance is expert opinion illustrated by a single case, limiting generalisability pending prospective evidence.