A Technique of Forced Expiratory Noise Time Evaluation Provides Distinguishing Human Pulmonary Ventilation Dynamics During Long-Term Head-Down and Head-Up Tilt Bed Rest Tests Simulating Micro and Lunar Gravity.

Anatoly E Kostiv,Vladimir P Katuntsev,Svetlana N Shin,Viktor M Baranov,Irina A Pochekutova,Veronika V Malaeva,Vladimir I Korenbaum

doi:10.3389/fphys.2018.01255

Abstract

Estimating the effect of microgravity/hypogravity on pulmonary ventilation function remains topical. Recently developed acoustic techniques based on the evaluation of the forced expiratory noise time (FETa) were hypothesized to be a promising tool for this aim. The aim of the protocol is to study the effect of two different modalities of bed rest space simulations (microgravity and lunar gravity) on FETa and spirometric indices. The FETa in the frequency band of 200–2000 Hz, recorded above human trachea, was evaluated. The 21st-day exposure to 6 degree head-down tilt (HDT) bed rest, simulating microgravity, and 9.6 degree head-up tilt (HUT) bed rest with head-zero tilt (HZT) rest intervals (HUT + HZT), simulating lunar gravity, in statistically identical subgroups of five and six healthy male volunteers, was studied. In the course of HDT bed rest, a significant elongation of FETa was found in relation to background measurements in “sitting” position (p = 0.016). The effect corresponded to a significant decrease of basic spirometric indices (p < 0.02). Moreover, FETa provided reliable discrimination of HDT and HUT + HZT bed rest tests (p = 0.018), while spirometric indices did not (p > 0.05). Based on previously found correlations (Korenbaum and Pochekutova, 2008; Malaeva et al., 2017), a FETa elongation in response to HDT bed rest was attributed to an increase of aerodynamic resistance of the respiratory tract. The technique seems promising to monitor human pulmonary ventilation dynamics in long-term space missions; however, new studies are welcome to verify it in real spaceflight.

Highlights

It is well known that in microgravity, a redistribution of body fluids to the cranial direction takes place
There were no significant differences in age, anthropometric data, as well as in acoustic and spirometric parameters between subgroups involved in the head-down tilt (HDT) and the head-up tilt (HUT) + head-zero tilt (HZT) bed rest tests 2 days before starting hypokinesia (Table 1)
According to our study in the group of 11 healthy volunteers, a statistically significant decrease of spirometric indices volume capacity (VC), FEV1, FEV1/forced VC (FVC), and maximal midexpiratory flow (MMEF) is found on the third day of exposure to the 6 degree HDT bed rest in comparison with background values taken in the “sitting” position 2 days before starting the HDT

Summary

Introduction

It is well known that in microgravity, a redistribution of body fluids to the cranial direction takes place. Blood moves from the lower extremities to the abdominal cavity and thorax (Gazenko et al, 1997; Prisk, 2000) increasing a blood filling of lungs (Grigor’ev and Egorov, 1988; West et al, 1997). The diaphragm forms a more convex shape limiting lung volumes. These structural and functional changes caused by gravity discharge may result in alterations of pulmonary ventilation and gas exchange (West et al, 1997; Prisk, 2000; Prisk et al, 2002; Baranov, 2011; Watenpaugh, 2016). The problem of estimating the effect of microgravity/hypogravity on pulmonary ventilation remains topical

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