高気圧環境下の換気動態に関する研究
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概要
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The maximum voluntary ventilation (MVV) has been measured up till now as the only index of the ventilatory dynamics under high atmospheric pressures, as the MVV is known to decrease with the increase of the density in accordance with the formula: MVV=1/√<density> (S. Miles). As referred in several reports, the said formula has been confirmed as valid to the MVV observed under hyperbaric environment. However, there still remain some problems to be solved in the measurement of the MVV itself, such as the breathing mechanics involved. It is uncertain that the MVV reflects clearly the ventilatory dynamics under high pressures. This paper shows some experimental studies to determine the best indicator which faithfully expresses the ventilatory dynamics under the hyperbaric environment. The pressure-flow relatioship of the air flow in a simulated breathing by a sine wave pump, satisafied under various ambient pressures is expressed by the Rohrer's equation: P=K_1V-K_2V^2 (P: driving pressure, V: air flow, and K_1 & K_2: parameters concerning the physical properties of the gas mixture), being a nonlinear relation. It was obvious that the parameter K_2, concerned with the gas density, increased proportionally to the increase of the depth. The K_2 value tended to increase with the increase of the turbulance in ventilation. The viscous resistance (viscance) value △P/V followed straight lines in respect to the increase of atmospheric pressure and the gradient became larger with the increase of the air flow. Viscance value nearly doubled at 4 Ata compared with those at 1 Ata. MVV in 14 subjects, having approximately the same ventilatory functions, decreased with the increase of the ambient perssure. The observed MVV under high perssures showed decreases by 40.3% and 53.4% at 4 and 6 Ata respectively against the MVV value at 1 Ata, and %MVV were 61.8% and 50.3% respectively, while their observed %MVV at 1 Ata were 105%. This means that the ventilatory dynamics capacity become in almost half of the 1 Ata values. The measured FEV_<1.0> or one minute value of "vital capacity through effort" under increasing ambient pressures did not coinside with the predicted velues. And the decrease of the rate of FMF_<25-75>% or intermediate flow-rate through maximum effort at 1 to 6 Ata was very significant, i.e. 46.5% and 59.6% at 4 and 6 Ata respectively. As a result of this study, the following formula was obtained: Y=2.0689X-<0.4452> (Y: measured FMF, X: ambient pressure). The FMF values thus obtained could well represent the pressure-flow relationship of the air flow in the simulates breating under various ambient pressures. Accordingly, the FMF value reflects the ventilatory dynamics faithfully under hyperbaric environments. This fact depends on the "effort independent" during the measurement, because hyperbaric effects of the ventilation are only reflected in the increase of viscous resistance of the air-way. On the contrary, the MVV under hyperbaric environments is influenced by the respiratory muscles, elastance and inertance during one cycle of ventilation. consequently, at MVV measurement, certain errors may be introduced to the measured values. Therefore, mean decrease rate of the MVV does not agree with the calculated value from the Mile's formula, being smaller than those obtained by other authors, and FEV_<1.0> values obtained at hyperbaric environments do not also reflect the hyperbaric effect.
- 社団法人日本産業衛生学会の論文
- 1969-09-20