A Physical Analog to Assess Surgical Face Mask Air Flow Resistance During Tidal Ventilation.

A large variety of disposable face masks have been produced since the onset of the COVID-19 pandemic. Decreased resistance to inspiration improves adherence to the use of the mask; the so called breathability is usually estimated by the measurement of air flow across a section of the tissue under a given pressure difference. We hypothesized that the mask pressure-flow relationship studied in conditions that mimic tidal breathing could allow a more comprehensive characterization of airflow resistance, a major determinant of mask comfort. A physical analog was made of a plaster cast dummy head connected through a pneumotachograph to a series of bellows inflated/deflated by a respirator. Pressure was measured at the mock airway opening over which the mask was carefully secured. The precision of the measurement equipment was quantified using two estimates of measurement error: repeatability coefficient (RC) and within-mask coefficient of variation (CVwm). The airflow resistance of 10 surgical masks was tested on 4 different days. Resistance means did not differ significantly among four repeated measures (0.34 hPa.s.L-1; 0.37 hPa.s.L-1; 0.37 hPa.s.L-1; and 0.37 hPa.s.L-1; p = 0.08), the estimated RC was 0.08 hPa.s.L-1 [95%CI: 0.06-0.10 hPa.s.L-1], and CVwm was 8.7% [95%CI: 1.5-12.2%]. Multiple comparisons suggest the presence of a learning effect by which the operator reduced the error over the course of repetitive resistance measurements. Measurement precision improved considerably when the first set of measures was not taken into account [RC ~ 0.05 hPa.s.L-1 (95%CI: 0.03-0.06 hPa.s.L-1); CVwm~4.5% (95%CI: 1.9-6.1%)]. The testing of the face mask resistance (R) appears simple and highly repeatable in conditions that resemble tidal breathing, once operator training was assured. The procedure adds further to the current standard assessment of breathability and allows estimating the maximal added respiratory load, about 10-20% of the respiratory resistance reported in heathy adult subjects.

A Calibration Device to Compare Body Plethysmographs Among Pediatric Lung Function Laboratories.

Multi-center studies in specific airway resistance have shown significant inter laboratory variability. Comparison of plethysmographic equipment using a lung model easily transportable from one site to another should be of help to international normative studies. A resistor made of parallel capillary tubes - insuring adequate linearity within 1 L/sec - was connected to a glass bottle. Thermal time constants were measured while the bottle was empty and while stuffed with steel wool. In the latter, isothermal condition was estimated to occur only at very low frequency (around 0.01 Hz) and gas compression was polytropic up to 0.6 Hz. With the empty analog, adiabatic gas compression was estimated to occur at frequencies ≥0.2 Hz, and more accurate volume estimation was obtained. The empty analog volume and specific resistance measured in a body plethysmograph on different days indicated within 5% accuracy as well as intersession repeatability. It is concluded that a physical analog built out of simple material provides accurate measurements of specific resistance. The apparatus should be of help to compare plethysmographic equipments from different laboratories.

An inexpensive, MRI compatible device to measure tidal volume from chest-wall circumference.

Mouthpieces and masks change breathing, and distract the subject. Accepted non-invasive methods avoid this problem, inductive plethysmographs and respiratory magnetometers, but are expensive and unusable in magnetic resonance imaging (MRI) scanners. Because changes in ventilation affect arterial gases, and thus cerebral blood flow, measurement of breathing is desirable during many functional MRI studies. Using an old principle, we constructed an inexpensive, non-invasive device unaffected by magnetic fields. We adapted a simple calibration method to reduce error and make the method accessible to more users. 'Pneumobelts' consist of flexible corrugated silicon tubes worn around the rib cage (RC) and the abdomen (AB). Changes in RC and AB are determined from pressure changes within the 'pneumobelts'. Estimates of tidal volume are generated from the sum of the RC and AB changes. We empirically determined the appropriate RC weighting as 1.3:1 (RC:AB). Volume estimation was tested (n = 9) in different body positions and during different breathing maneuvers. The weighted sum of the two signals gave an accurate estimate of tidal volume with tidal volumes less than 1200 ml (mean error = 6-7%). Breaths over 1900 ml produced larger errors (mean error = 11-16%). Our results are generalizable to any linear circumference measuring device.

Gerador de pressäo para a determinaçäo da impedância mecânica de pacientes ventilados artificialmente / Pressure generator for determination of mechanical impedance of the artficialy ventilated patients

Para se determinar a impedância mecânica de pacientes intubados e ventilados artificialmente em UTI, o gerador de pressão senoidal deverá ser capaz de suportar pressões produzidas pelo ventilador, e gerar pressões de amplitudes de 2 a 4 hPa pico a pico. Para a implementação do gerador uma simulação numérica foi realizada tendo como objetivo encontrar a melhor montagem que satisfizesse as condições para tal aplicação. O gerador implemantado foi testado em um sistema RIC.

To determine the mechanical impedance of the intubated and artificialy ventilated patients in Intensive Carte Unit (ICU), the sinusoidal pressure generator must be capable of supporting the pressure generated by the ventilator and to generate a pressure amplitude from 2 to 4 hPa peak to peak. To make the generator assembly, a numerical simulation has been realized, to obtain the best assembly which could satisfy the requirements for such application. The implemented generator has been tested in RIC model system.