Isautier, Jennifer

ABSTRACT Introduction Measurement of the work of breathing (Wb) during exercise provides useful insights into the energetics and mechanics of the respiratory muscles across a wide range of minute ventilations. The methods and analytical procedures used to calculate the Wb during exercise have yet to be critically appraised in the literature. Purpose The aim of this systematic review was to evaluate the quality of methods used to measure the Wb during exercise in the available literature. Methods We conducted an extensive search of three databases for studies that measured the Wb during exercise in adult humans. Data were extracted on participant characteristics, flow/volume and pressure devices, esophageal pressure (P oes ) catheters, and methods of Wb analysis. Results A total of 120 articles were included. Flow/volume sensors used were primarily pneumotachographs ( n = 85, 70.8%), whereas the most common pressure transducer was of the variable reluctance type ( n = 63, 52.5%). Esophageal pressure was frequently obtained via balloon-tipped catheters ( n = 114, 95.0%). Few studies mentioned calibration, frequency responses, and dynamic compensation of their measurement devices. The most popular method of measuring the Wb was pressure–volume integration ( n = 51, 42.5%), followed by the modified Campbell ( n = 28, 23.3%) and Dean & Visscher diagrams ( n = 26, 21.7%). Over one-third of studies did not report the methods used to process their pressure–volume data, and the majority (60.8%) of studies used the incorrect Wb units and/or failed to discuss the limitations of their Wb measurements. Conclusions The findings of this systematic review highlight the need for the development of a standardized approach for measuring Wb, which is informative, practical, and accessible for future researchers.

There are growing concerns that the COVID-19 pandemic has facilitated a sedentary shift in our physical activity habits. A reduction in physical activity during the pandemic may be secondary to restrictive policies implemented at the government-level, typically those policies which limit interpersonal contact; for example, physical/social distancing. It is without question that social distancing is a necessary measure to mitigate community transmission of the novel virus; however, these policies often limit the public’s opportunities to engage in physical activity. The strictest enforcement of social distancing occurs during an authority-mandated ‘lockdown’ (also known as a ‘shelter-in-place’ or ‘stay-at-home’ order). This Viewpoint focuses on the current evidence demonstrating that physical activity declines during a COVID-19 ‘lockdown’. We highlight the point that most of the available evidence stems from investigations using non-validated, self-reported measures of physical activity and discuss the caveats therewith. This Viewpoint explores whether current evidence reflects an ‘actual’ or rather a ‘perceived’ reduction in physical activity, and raises the question of whether this distinction matters in the end.

Background Previous studies have demonstrated that the near‐infrared spectroscopy venous occlusion technique (NIRS‐VOT) provides a valid assessment of regional forearm muscle blood flow; however, day‐to‐day reproducibility of hemodynamic variables derived from the NIRS‐VOT remains to be determined, particularly across the range of physiological blood flows observed during handgrip exercise. Purpose The purpose of this study was to evaluate the day‐to‐day reproducibility of forearm hemodynamics assessed via the NIRS‐VOT. Methods Near‐infrared spectroscopy (NIRS) data were obtained from the flexor digitorum superficialis muscle on the right arm of 14 young, healthy adults (age: 27 ± 6 yrs; BMI: 24.6 ± 2.8 kg·m −2 ). The NIRS‐VOT was performed via rapid inflation of a pneumatic cuff placed on the upper arm for approximately 10 s. The NIRS‐VOT was performed at rest, and immediately after a 15 s isometric handgrip contraction at 20%, 40% and 60% of the subject’s maximum voluntary contraction. Measurements were repeated 3–5 times. Participants returned to the laboratory for a second visit on a separate day, and repeated the same number of measurements. Forearm blood flow (FBF), and blood pressure were measured on a beat‐by‐beat basis, and forearm vascular conductance (FVC) was calculated. FBF and FVC were subsequently compared for day‐to‐day reproducibility. Results FBF and FVC significantly increased with the intensity of handgrip exercise ( P < 0.05); however, these measures of forearm hemodynamics were not significantly different ( P >0.05) between Day 1 and Day 2 at each exercise‐intensity (Table ). Conclusion The findings of the present study indicate that the NIRS‐VOT provides a reliable assessment of regional forearm muscle hemodynamics across a physiological range of blood flows incurred by isometric handgrip exercise. Support or Funding Information MJJ is funded by the NIH (R‐35‐HL139854) and the Mayo Foundation. CCW is supported by the NIH training grant (5T32DK007352‐39), JRS is supported by AHA (18POST3990251), and TJC is funded by AFAR Postdoctoral Transition Award (DIAMOND18161). FBF and FVC on experimental days Day 1 Day 2 P ‐value FBF , mL · min − 1 · 100mL − 1 (tissue) Rest 2.0 ± 0.5 0.8 ± 0.2 0.001 20% MVC 14.4 ± 2.65 15.4 ± 2.4 0.679 40% MVC 26.0 ± 5.19 28.0 ± 4.3 0.606 60% MVC 39.4 ± 6.39 47.4 ± 7.7 0.858 FVC , mL · min − 1 · 100 mmHg − 1 Rest 170 ± 47.3 72 ± 16.4 0.001 20% MVC 1297 ± 227.8 1454 ± 209.6 0.380 40% MVC 2496 ± 492.8 2656 ± 434.0 0.912 60% MVC 3820 ± 659.1 4542 ± 744.7 0.535 MVC , kg 49.4 ± 3.0 47.9 ± 2.6 0.721 Abbreviations: FBF, forearm blood flow; FVC, forearm vascular conductance; MVC, maximal voluntary contraction. Values are presented as means ± SE. P values indicate comparison between days 1 and 2.

The purpose of this report was to 1) detail the construction of a low-cost device that provides a “reference” flow waveform for pneumotachograph (PNT) calibration, i.e., the “syringe potentiometer” (SP), and to compare the 2) accuracy and 3) practical performance of “calibration curves” obtained with the SP device to other more established methods of PNT calibration, i.e., the weighted averaging (WA) and polynomial least-squares (PolyLS) methods. Volume and flow waveforms obtained via the SP device were validated against a motion capture system and were deemed accurate surrogates of actual syringe volume and flows. The SP device was used to construct a calibration curve of a PNT by dividing the flow waveform of the SP by the analog output of the PNT amplifier. A total of 187 inspiratory and 187 expiratory strokes were collected. When the entire data set of expiratory strokes was used, the SP, WA, and PolyLS methods together demonstrated acceptable volume and flow errors as per American Thoracic Society/European Respiratory Society recommendations (less than ±3.5% and less than ±5.0% errors, respectively). The “practical” performance of each method was assessed with a nested subsampling procedure, whereby volume and flow errors were evaluated as the number of strokes was increased (in blocks of 5 strokes). To this end, the SP method demonstrated practical performance superior to that of the WA and PolyLS approaches, whereby acceptable volume and flow errors were achieved after only 5 calibration strokes; the WA and PolyLS methods required 15 and 20 strokes, respectively, to achieve the same level of volume and flow accuracy.NEW & NOTEWORTHY This report describes the construction and validation of a low-cost device for the purposes of pneumotachograph (PNT) calibration: the “syringe potentiometer” (SP). Calibration of a PNT with the SP device yielded acceptable volume and flow errors (<3.5% and 5%, respectively) across a wide range of flows (<0.5 to 15 L/s). The SP device offered superior “practical performance” over other established PNT calibration methods, whereby acceptable volume and flow errors were achieved after only five calibration strokes.