Rapid changes in mucociliary transport in the tracheal epithelium caused by unconditioned room air or nebulized hypertonic saline and mannitol are not determined by frequency of beating cilia.

BACKGROUND: Inspired air is heated and humidified in the nose before it reaches lower airways. This mechanism is bypassed during tracheostomy, directly exposing the airways to colder and drier air from the environment, known to negatively affect mucociliary transport; however, little is known about how quickly mucociliary transport deteriorates. This study determines the short-term effect of flowing room air and nebulized hypertonic saline and mannitol on mucociliary transport in the trachea. In an ovine perfused in vitro tracheal model (N = 9) the epithelium was exposed to 25 L/min of flow, heated to lamb body temperature (38 °C) and fully saturated with water vapor as the control, followed by either room air (22 °C and 50% relative humidity) or nebulized solutions of NaCl 7% and mannitol 20% up to 1 min for a short duration, until mucociliary transport had visually changed. Mucus transport velocity (MTV) and cilia beat frequency (CBF) were continuously measured with video-microscopy. RESULTS: Exposing the tracheal epithelium to air heated to body temperature and fully humidified had stable MTV 9.5 ± 1.1 mm/min and CBF 13.4 ± 0.6 Hz. When exposed to flow of room air, MTV slowed down to 0.1 ± 0.1 mm/min in 2.0 ± 0.4 s followed by a decrease in CBF to 6.7 ± 1.9 Hz, after 2.3 ± 0.8 s. Both MTV and CBF recovered to their initial state when heated and humidified air-flow was re-introduced. Exposing the tracheal epithelium to nebulized hypertonic saline and nebulized mannitol for 1 min increased MTV without a subsequent increase in CBF. CONCLUSIONS: This study demonstrates mucociliary transport can deteriorate within seconds of exposing the tracheal epithelium to flowing room air and increase rapidly when exposed to nebulized hypertonic solutions. The reduction in MTV precedes slowing of CBF with room air and MTV increases without a subsequent increase in CBF during the nebulization. Their relationship is non-linear and a minimum CBF of approximately 6 Hz is required for MTV > 0, while MTV can reach 10.9 mm/min without CBF increasing. Clinically these findings indicate a potential rapid detrimental effect of breathing with non-humidified air via bypassed upper airways and the short-term effects of nebulized osmotic agents that increase MTV.

Brachial arterial temperature as an indicator of core temperature: proof of concept and potential applications.

There is potential for heat loss and hypothermia during anesthesia and also for hyperthermia if heat conservation and active warming measures are not accurately titrated. Accurate temperature monitoring is particularly important in procedures in which the patient is actively cooled and then rewarmed such as during cardiopulmonary bypass surgery (CPB). We simultaneously measured core, nasopharyngeal, and brachial artery temperatures to investigate the last named as a potential peripheral temperature monitoring site. Ten patients undergoing hypothermic CPB were instrumented for simultaneous monitoring of temperatures in the pulmonary artery (PA), aortic arterial inflow (AI), nasopharynx (NP), and brachial artery (BA). Core temperature was defined as PA temperature before and after CPB and the AI temperature during CPB. Mean deviations of BA and NP temperatures from core temperature were calculated for three steady-state periods (before, during, and after CPB). Mean deviation of BA and NP temperatures from AI temperature was also calculated during active rewarming. A total of 1862 measurements were obtained and logged from eight patients. Mean BA and NP deviations from core temperature across the steady-state periods (before, during, and after CBP) were, respectively: .23 +/- .25, -.26 +/- .3, and -.09 +/- .05 degrees C (BA), and .11 +/- .19, -.1 +/- .47, and -.04 +/- .3 degrees C (NP). During steady-state periods, there was no evidence of a difference between the mean BA and NP deviation. During active rewarming, the mean difference between the BA and AI temperatures was .14 +/- .36 degrees C. During this period, NP temperature lagged behind AI and BA temperatures by up to 41 minutes and was up to 5.3 degres C lower than BA (mean difference between BA and NP temperatures was 1.22 +/- .58 degrees C). The BA temperature is an adequate surrogate for core temperature. It also accurately tracks the changing AI temperature during rewarming and is therefore potentially useful in detecting a hyperthermic perfusate, which might cause cerebral hyperthermia.

Thermal stability of intralipid optical phantoms.

We investigated the stability of light transmission through Intralipid-based optical phantoms in the wavelength range of 400-950 nm at temperatures between 35 and 70 °C. Optical phantoms are materials commonly used to simulate the light scattering and absorption properties of biological materials. These simulations require the phantom to be optically stable. We demonstrate that the scattering properties of Intralipid remain stable at higher temperatures, varying less than 0.5%. We also present results that show this is not the case for absorption below 700 nm at 35 and 70 °C, with greater instability at 70 °C. For example, at 500 nm, the light intensity transmitted through 15 mm of Intralipid dropped 39% over 12 h. We demonstrate that oxidation of fatty acids in Intralipid could account for this effect and show, by flushing the system continuously with nitrogen gas, the instability is reduced.

Temporal sensitivity of the wavelength calibration of a photodiode array spectrometer.

Subtle differences in the relationship between wavelength and pixel on photodiode array spectrometers contribute to difficulties in transferring calibrations from one instrument to another and may even introduce errors on a single instrument over time. To quantify the level of drift that might be expected in photodiode instruments, we calibrated the wavelength scale of two Zeiss MMS-1 photodiode spectrometers weekly over a 12-month period. We found no evidence of drift in the wavelength calibration. The wavelength calibration was consistent within 0.03 nm over at least 150 days and better than 0.1 nm over the year. To provide context for the wavelength accuracy, we applied small perturbations to wavelength in two partial least squares (PLS) models. We found that wavelength perturbations introduced a linear increase in bias of about 7%/nm (for example, a 1-nm perturbation shifted fruit dry matter prediction from 14% to 21%) in a kiwifruit dry-matter model and about 3.6 °C/nm in an Intralipid temperature model. By including small wavelength perturbations in the training sets, we were able to reduce this error to less than 1.7%/nm and 0.2 °C/nm in the dry-matter and temperature models, respectively. These results suggest that the wavelength scale of photodiode instruments can be very stable. However, in light of the high sensitivity of the PLS models we examined, we recommend testing and, where possible, mitigating the sensitivity of PLS models to small wavelength shifts.

Temperature-dependent optical properties of Intralipid measured with frequency-domain photon-migration spectroscopy.

We present the temperature dependence of absorption and reduced scattering coefficients of 1.8% Intralipid measured by frequency-domain photon-migration spectroscopy between 710 and 850 nm. These measurements were made in the physiologically relevant 30 to 40 degrees C temperature range. The temperature coefficients for absorption were consistent during heating and cooling and follow closely other reported results. The change in absorption coefficient at 740 nm suggests that a minimum temperature change of 4 degrees C is observable within the error limits. We found that the reduced scattering coefficient shows a hysteresis with temperature at 740 nm. The temperature coefficient for reduced scattering determined from heating cycle measurements agrees with theory and other measurements within the error limits.

Characterizing liquid turbid media by frequency-domain photon-migration spectroscopy.

We present a wavelength-tunable frequency-domain instrument for the characterization of liquid turbid media. The instrument employs a tunable titanium-sapphire laser modulated by an acousto-optic modulator. The absorption and reduced scattering coefficient of Intralipid(R) 20%, diluted to concentrations of 0.94 to 4.00%, are measured over the wavelength range 710 to 850 nm at 10-nm intervals. The standard measurement errors for the absorption and reduced scattering coefficients are 1 and 2.5%, respectively. Extrapolation to 0% Intralipid(R) concentration gives an absorption coefficient that closely follows that of water, overestimating the absorption of pure water by less than 10%. The reduced scattering coefficient is compared at 750 nm with published results and is found consistent within the experimental error. We compare the reduced scattering coefficient to an estimate based on Mie theory and find the reduced scattering coefficient underestimated the Mie theory result by about 9%.

Accurate and precise wavelength calibration for wide bandwidth array spectrometers.

Calibrating the wavelength scale of an array spectrometer typically involves measurements of lines at well-known wavelengths from a calibration lamp such as a mercury-argon source. This process is relatively straightforward when the lines are well separated, relative to the bandwidth of the spectrometer. When the spectrometer's bandwidth is large, compared with the distance between calibration wavelengths, it becomes increasingly difficult to accurately locate lines in the calibration spectrum. Even calibrations for instruments with a modest bandwidth of 12 nm can be difficult. Here we present results from a simple approach to improve the accuracy of wavelength calibration for an instrument with a large bandwidth (12 nm, center-to-center pixel spacing 3.3 nm). A monochromator has been used to filter the source so that each calibration line can be measured separately. For ten spectrometers, we were able to achieve accuracy better than 0.12 nm, or 0.09 nm on average; this is less than 3% of the pixel spacing. We anticipate this approach will be useful for improving the accuracy of measurements on array spectrometers and particularly in transferring multivariate calibrations between instruments.

Temperature dependence of near-infrared spectra of whole blood.

The temperature dependence (30 to 40 degrees C) of near-infrared spectra (500 to 1100 nm) of whole human blood, including red blood cells with intact physiological function, is investigated. Previous studies have focused on hemoglobin solutions, but the operation of red blood cells is critically dependent on intact cell membranes to perform normal oxygen transport and other physiological functions. Thus measurements of whole blood are more directly related to changes that occur in vivo. In addition to the response of hemoglobin to temperature in the spectra, a temperature response from water in the plasma is also detected. The temperature response of the water absorption at 960 nm is approximately ten times smaller than the temperature response of the oxyhemoglobin component in the blood at 610 nm. However, it is the most significant temperature effect between 800 and 1000 nm. This work will aid the precision and understanding of full spectrum near-infrared measurements on blood.

Measuring optical temperature coefficients of Intralipid.

The temperature sensitivities of absorption and reduced scattering coefficients in the range 700-1000 nm are determined for the liquid phantom Intralipid using spatially resolved continuous wave measurements. The measurements were conducted on a 10 L heated volume of 1% Intralipid subjected to a 40-30 degrees C cooling regime. The temperature sensitivities of the absorbance coefficients are similar to that expected for pure water. However, the reduced scattering coefficients are more sensitive than can be explained by temperature related density changes, and show an unexpected relationship with wavelength. We have also found that temperature perturbations provide a useful means to evaluate instrument model performance.