Comparison of ultrasound-assessed diaphragmatic performance and respiratory strength between healthy volunteers and patients with long COVID: an observational case-control study

• Grant number: 23/13815-4
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: December 01, 2023
• End date: November 30, 2025
• Field of knowledge: Health Sciences - Medicine - Medical Clinics
• Principal Investigator: Carlos Roberto Ribeiro de Carvalho
• Grantee: Pauliane Vieira Santana
• Host Institution: Faculdade de Medicina (FM). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/01769-5 - Late assessment of physical, psychological and cognitive effects in a cohort of patients surviving COVID-19 hospitalization at a tertiary university hospital: a multidisciplinary approach, AP.TEM

Abstract

Introduction: A variable proportion of COVID-19 patients evolve with varied and persistentsymptoms, a condition usually referred to as "long COVID". Dyspnea and fatigue are the mostcommon persistent symptoms in long COVID, and the underlying pathophysiological mechanisms ofthese symptoms may involve impairment of the inspiratory muscles. Although there is evidence ofrespiratory muscle dysfunction in the acute phase of COVID-19, there are gaps in thecharacterization of inspiratory muscle function during long COVID, mainly due to the difficulty indetermining diaphragm function with gold standard techniques. Thoracic ultrasound (TUS) is avalidated test for assessing the diaphragm and parasternal muscles. UST can be a complementarytool to inspiratory force measurements, through volitional and non-volitional methods, forrespiratory muscle assessment.Objectives: The primary objective of the study is to compare diaphragm performance, UST, andrespiratory muscle strength in patients with long COVID-19 with healthy individuals matched forgender and age. Our secondary objective will be to correlate the respiratory muscle function ofpatients with long COVID with the severity of Covid 19 viral pneumonia, dyspnea, fatigue andrespiratory strength.Hypothesis: Our primary hypothesis is that long COVID patients with symptoms of dyspnea andfatigue have inspiratory and expiratory muscle dysfunction when compared to healthy volunteers.Our secondary hypothesis is that in patients with long Covid, respiratory muscle dysfunctioncorrelates with: the severity of Covid-19 viral pneumonia, dyspnea, fatigue, and inspiratory andexpiratory strength.Methods: This will be an observational, cross-sectional, case-control study with prospectivelycollected data. 33 patients previously hospitalized with COVID-19 who report persistent respiratorysymptoms (dyspnea) or fatigue during outpatient follow-up will be included. In addition, 33 healthyvolunteers matched by gender and age will be included. Dyspnea will be quantified using theMedical Research Council (MRC) and Borg scales. Fatigue will be quantified using the Fatigue ImpactScale (FIS). The severity of Covid viral pneumonia at the time of hospitalization in the group ofpatients with long Covid will be recorded by length of hospital stay, need for ICU admission, needfor invasive and non-invasive mechanical ventilation. Respiratory muscle strength will be assessedby volitional measures [maximal inspiratory pressure (PiMax) and maximal expiratory pressure(PeMax) and nasal inspiratory sniffing pressure (SNIP)] and non-volitional measures [mouthpressure after phrenic nerve magnetic stimulation (Pmo,Tw)] . The function of the diaphragm andthe parasternal intercostal muscle will be explored using thoracic ultrasound (TUS). UST willevaluate the diaphragm to determine its excursion, thickness, transverse thickening (thickeningfraction) and longitudinal thickening ("diaphragmatic strain"), as well as assessing contraction andrelaxation speeds. UST will evaluate the parasternal intercostal muscle to determine its thicknessand transverse thickening (thickening fraction).