主動式呼氣閥的開發與測試

Development and Testing of an Active Exhalation Valve

使用呼吸防護具時，佩戴者對於呼吸阻力的感受，是影響舒適度的重要指標之一。當呼吸阻力越大，除了必須更用力呼吸之外，也讓密合度的要求更具挑戰。實務上，唯有在兼具密合與舒適時，才能長時間且正確地使用呼吸防護具。近年來，以動力淨氣式呼吸防護具（Powered Air-Purifying Respirator, PAPR）取代無動力式呼吸防護具，作為第一線醫護人員的配備越來越受到關注。相較之下，雖然PAPR的吸氣阻力較低，但由於佩戴者須克服送風機的壓力才能呼出氣體，因此反而會有較高的呼氣阻力。本研究探討一主動式呼氣閥的開發與測試，並藉此來降低PAPR的呼氣阻力，減少佩戴時的不適感。
本研究針對一款市售的定流率型PAPR進行改造與測試。首先，設計並製作一款由傳統呼氣閥、微型直流電磁鐵和邏輯電路板所構成的主動式呼氣閥。然後，使用壓力計和直讀式微粒計數器，分別測量PAPR改造前、後，面體內的靜壓值和粒子濃度。
結果證實主動式呼氣閥可以在不影響PAPR原本的防護係數之下，顯著降低面體內呼氣時的靜壓值。以PAPR的供氣流率約70 L/min的條件為例，當潮氣容積為0.5 L、呼吸頻率為12 breath/min時，PAPR面體內的最大靜壓值在主動式呼氣閥的作用之下，可以從原本的17 mmH2O下降至約6 mmH2O。本研究所開發的主動式呼氣閥，可以顯著改善佩戴固定流率式PAPR時，因呼吸阻力所造成的不舒適性。

The resistance that the wearer feels when breathing is one of the most important as¬pects of comfort when wearing a respirator. The higher the resistance, the harder the user has to breathe and more challenging to get a good seal on the face. It’s only when a tight-fit¬ting respirator fits well and is comfortable that it remains worn throughout the day. Re¬cently, using PAPRs as an alternative to non-powered respirators for front-line healthcare workers has received increasing attention. With the help of the blower unit, a traditional PAPR has much lower inhalation resistance than one operated under a non-powered mode. Conversely, the exhalation resistance would be more significant because the wearer should combat the blower to exhale. Therefore, this article presents the development and testing of an active exhalation valve. The main objective is to reduce the wearer's discomfort by reducing the air resistance during exhalation without compromising the protection provided by traditional PAPRs.
In this study, a commercially available constant flow rate PAPR was modified and test¬ed. First, the active exhalation valve, which was made of a traditional exhalation valve, a miniature DC electromagnet, and a logic circuit board, was designed and fabricated. Then, under the simulated breathing conditions, the static pressure value and particle concentra¬tion in the facepiece of the PAPR equipped with the active exhalation valve and the original one were measured using a digital pressure sensor and a direct-reading particle counter, re¬spectively.
The active exhalation valve significantly reduced the static pressure during exhalation in the facepiece without affecting the original protection factor provided by the PAPR. Tak¬ing the condition that the supply airflow rate of PAPR was about 70 L/min as an example, when the tidal volume was 0.5 L, and the breathing frequency was 12 breaths/min, the max¬imum static pressure in the facepiece of the PAPR can reduce from the original 17 mmH2O to about 6 mmH2O under the action of the active exhalation valve. The active exhalation valve developed by our research can significantly improve the discomfort caused by breath¬ing resistance when wearing a constant flow rate PAPR.