Sleep Research Laboratory, Toronto Rehabilitation Institute, ON, Canada.
J Clin Monit Comput. 2011 Oct;25(5):285-94. doi: 10.1007/s10877-011-9307-z. Epub 2011 Sep 29.
To test the ability of a microphone recording system, located distal to the respiratory outflow tract, to track the timing of the inspiratory and expiratory phases of breathing in awake healthy subjects.
Fifteen subjects participated. Breath sounds were recorded using a microphone embedded in a face frame in a fixed location in relation to the nostrils and mouth, while simultaneously recording respiratory movements by respiratory inductance plethysmography (RIP). Subjects were studied while supine and were instructed to breathe normally for 2 min: through their noses only (nasal breathing), during the first min, and through their mouths only (oral breathing) during the second min. Five subjects (test group) were chosen randomly to extract features from their acoustic data. Ten breaths (5 nasal and 5 oral breaths) from each subject were studied. Inspiratory and expiratory segments of breath sounds were determined and extracted from the acoustic data by comparing it to the RIP trace. Subsequently, the frequency spectrum of each phase was then determined. Spectral variables derived from the 5 test subjects were applied prospectively to detect breathing phases in the remaining 10 subjects (validation group).
Test group data showed that the mean of all inspiratory spectra peaked between 30 and 270 Hz, flattened between 300 and 1,100 Hz, and peaked again with a center frequency of 1,400 Hz. The expiratory spectra peaked between 30 and 180 Hz and its power dropped off exponentially after that. Accordingly, the bands ratio (BR) of frequency magnitudes between 500 and 2500 Hz to frequency magnitudes between 0 and 500 Hz was chosen as a feature to distinguish between breathing phases. BR for the mean inspiratory spectrum was 2.27 and for the mean expiratory spectrum was 0.15. The route of breathing did not affect the BR ratio within the same phase. When this BR was applied to 436 breathing phases in the validation group, 424 (97%) were correctly identified (Kappa = 0.96, P < 0.001) indicating strong agreement between the acoustic method and the RIP.
Frequency spectra of breathing sounds recorded from a face-frame, reliably identified the inspiratory and expiratory phases of breathing. This technique may have various applications for respiratory monitoring and analysis.
测试位于呼吸流出道远端的麦克风录音系统在清醒健康受试者中跟踪呼吸吸气和呼气阶段时间的能力。
15 名受试者参与了研究。呼吸音通过嵌入在与鼻孔和嘴固定位置的面框中的麦克风记录，同时通过呼吸感应体积描记法（RIP）同时记录呼吸运动。受试者仰卧位，指导他们正常呼吸 2 分钟：第 1 分钟通过鼻子（鼻呼吸），第 2 分钟仅通过嘴（口呼吸）。随机选择 5 名受试者（测试组）从其声学数据中提取特征。对每位受试者的 10 次呼吸（5 次鼻呼吸和 5 次口呼吸）进行了研究。通过将呼吸音的声学数据与 RIP 迹线进行比较，确定并提取呼吸音的吸气和呼气段。随后，确定每个阶段的频谱。从 5 名测试受试者中得出的频谱变量被前瞻性地应用于检测剩余 10 名受试者（验证组）的呼吸阶段。
测试组数据显示，所有吸气谱的平均值在 30 至 270 Hz 之间达到峰值，在 300 至 1100 Hz 之间变平，在中心频率为 1400 Hz 处再次达到峰值。呼气谱在 30 至 180 Hz 之间达到峰值，之后其功率呈指数下降。因此，选择 500 至 2500 Hz 与 0 至 500 Hz 之间的频率幅度的频带比（BR）作为区分呼吸阶段的特征。平均吸气谱的 BR 为 2.27，平均呼气谱的 BR 为 0.15。在同一阶段，呼吸途径不会影响 BR 比值。当将此 BR 应用于验证组的 436 个呼吸阶段时，424 个（97%）被正确识别（Kappa=0.96，P<0.001），表明声学方法和 RIP 之间具有很强的一致性。
从面框记录的呼吸音频谱可靠地识别了呼吸的吸气和呼气阶段。该技术可能在呼吸监测和分析方面有多种应用。
