The impact of muscle strength on exercise capacity and symptoms.

The capacity to exercise is a major contributor to functional limitation and is accompanied by increased morbidity and mortality. What are the most important physiological contributors to exercise capacity? Cross-sectional data from consecutive patients referred to the McMaster University Medical Centre exercise laboratory for incremental cardiopulmonary exercise testing from 1988 to 2012 were analysed. Exercise capacity was determined by maximal power output (MPO) in kpm·min-1. The contributions of quadriceps strength (maximal peak force in kg using maximal dynamic voluntary contractions against hydraulic resistance), inspiratory muscle strength (determined using maximal inspiratory pressure (MIP)), maximal breathing capacity (MBC) and gas exchange (carbon monoxide transfer coefficient (K CO)) were determined using regression coefficients in a multiple linear regression model. Dyspnoea and leg fatigue were measured using the modified Borg scale. Contributors to dyspnoea and leg fatigue were assessed using nonlinear regression. A total of 36 389 patients were included (60% male, mean±sd age 53±18 years). Mean±sd MPO, quadriceps strength and MIP achieved were 792±333 kpm·min-1, 46±18 kg and 75±31 cmH2O, respectively. MIP and quadriceps strength accounted for over half the variation in MPO (R2=0.57). Quadriceps strength was a stronger predictor of MPO (standardised regression coefficient, ß±se 0.37±0.005) than MBC (ß±se 0.16±0.005) and K CO (ß±se 0.16±0.004), when adjusted for age, sex, height and weight. The effort required to cycle and breathe at any given power intensified systematically as both respiratory and peripheral muscle strength declined. Muscle weakness causes exercise intolerance and should be routinely assessed in patients presenting with fatigue and dyspnoea, and those with functional limitation both in the presence or absence of disease.

Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: A systematic review and meta-analysis of randomized trials.

BACKGROUND: Respiratory protective devices are critical in protecting against infection in healthcare workers at high risk of novel 2019 coronavirus disease (COVID-19); however, recommendations are conflicting and epidemiological data on their relative effectiveness against COVID-19 are limited. PURPOSE: To compare medical masks to N95 respirators in preventing laboratory-confirmed viral infection and respiratory illness including coronavirus specifically in healthcare workers. DATA SOURCES: MEDLINE, Embase, and CENTRAL from January 1, 2014, to March 9, 2020. Update of published search conducted from January 1, 1990, to December 9, 2014. STUDY SELECTION: Randomized controlled trials (RCTs) comparing the protective effect of medical masks to N95 respirators in healthcare workers. DATA EXTRACTION: Reviewer pair independently screened, extracted data, and assessed risk of bias and the certainty of the evidence. DATA SYNTHESIS: Four RCTs were meta-analyzed adjusting for clustering. Compared with N95 respirators; the use of medical masks did not increase laboratory-confirmed viral (including coronaviruses) respiratory infection (OR 1.06; 95% CI 0.90-1.25; I2  = 0%; low certainty in the evidence) or clinical respiratory illness (OR 1.49; 95% CI: 0.98-2.28; I2  = 78%; very low certainty in the evidence). Only one trial evaluated coronaviruses separately and found no difference between the two groups (P = .49). LIMITATIONS: Indirectness and imprecision of available evidence. CONCLUSIONS: Low certainty evidence suggests that medical masks and N95 respirators offer similar protection against viral respiratory infection including coronavirus in healthcare workers during non-aerosol-generating care. Preservation of N95 respirators for high-risk, aerosol-generating procedures in this pandemic should be considered when in short supply.