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Biomedical subjects

S Sehati

Publications and source records attributed to S Sehati.

4 recordsLinked to original sources
PubMed2001

Effect of changes in lung volume on acoustic transmission through the human respiratory system.

The variation of acoustic attenuation with lung density was determined in experimental studies on seven healthy human volunteers, using a change of lung volume as a means of varying lung density. White noise between 50 and 680 Hz was introduced into the mouth and the transmitted signals were recorded with four microphones on the posterior chest wall (left/right, top/base) at 24, 40, 60 and 80% of total lung capacity. The change in lung volume had a frequency-dependent effect on acoustic attenuation in all subjects. A frequency between 177 and 243 Hz was identified, where altering the lung volume between 24 and 80% of total lung capacity induced a change in attenuation of only 1.0 (+/-0.5) to 2.7 (+/-1.8) dB, while at a frequency of 364-436 Hz marked variations in attenuation 8.9 (+/-2.0) to 21.5 (+/-4.8) dB occurred with similar lung volume changes.

Acoustics↗
PubMed2000

Sound transmission between 50 and 600 Hz in excised pig lungs filled with air and helium.

This study measured transit time (TT) and attenuation of sound transmitted through six pairs of excised pig lungs. Single-frequency sounds (50-600 Hz) were applied to the tracheal lumen, and the transmitted signals were monitored on the tracheal and lung surface using microphones. The effect of varying intrapulmonary pressure (Pip) between 5 and 25 cmH(2)O on TT and sound attenuation was studied using both air and helium (He) to inflate the lungs. From 50 to approximately 200 Hz, TT decreased from 4.5 ms at 50 Hz to 1 ms at 200 Hz (at 25 cmH(2)O). Between approximately 200 and 600 Hz, TT was relatively constant (1.1 ms at upper and 1.5 ms at lower sites). Gas density had very little effect on TT (air-to-He ratio of approximately 1.2 at upper sites and approximately 1 at lower sites at 25 cmH(2)O). Pip had marked effects (depending on gas and site) on TT between 50 and 200 Hz but no effect at higher frequencies. Attenuation was frequency dependent between 50 and 600 Hz, varying between -10 and -35 dB with air and -2 and -28 dB with He. Pip also had strong influence on attenuation, with a maximum sensitivity of 1.14 (air) and 0.64 dB/cmH(2)O (He) at 200 Hz. At 25 cmH(2)O and 200 Hz, attenuation with air was about three times higher than with He. This suggests that sound transmission through lungs may not be dominated by parenchyma but by the airways. The linear relationship between increasing Pip and increasing attenuation, which was found to be between 50 and approximately 100 Hz, was inverted above approximately 100 Hz. We suggest that this change is due to the transition of the parenchymal model from open to closed cell. These results indicate that acoustic propagation characteristics are a function of the density of the transmission media and, hence, may be used to locate collapsed lung tissue noninvasively.

Acoustics↗
PubMed1989

Monitoring of end-tidal carbon dioxide partial pressure during high frequency jet ventilation.

A new method has been developed to measure end-tidal carbon dioxide partial pressure (PECO2) during high frequency jet ventilation (HFJV). A digital flow controller incorporated in a computerized high frequency jet ventilator was used to deliver either a single deep breath or a series of three deep breaths. On user request, HFJV was interrupted and the deep breaths delivered, after which HFJV was resumed. Using a mathematical model, we were able to predict accurately the pressures to which the lungs would be inflated during deep breaths. The effect of varying the deep breath pressure (Pdb) on the ratio of end-tidal PCO2 to arterial (PCO2 (PECO2:PaCO2) was studied in three dogs. In all the dogs, within an optimum Pdb range of 5-10 cm H2O, PECO2 during the first deep breath was found to be similar (+/- 0.2 kPa) to the PaCO2 immediately before the onset of deep breaths. Deep breaths delivered above or below the optimum Pdb range resulted in a decrease in the ratio PECO2:PaCO2. The frequency of jet ventilation (12-200 b.p.m.) before the onset of the deep breaths did not affect PECO2:PaCO2.

Anesthesia, Intravenous↗