Modeling the partially coherent behavior of few-mode far-infrared grating spectrometers.

Modeling ultra-low-noise far-infrared grating spectrometers has become crucial for the next generation of far-infrared space observatories. Conventional techniques are awkward to apply because of the partially coherent form of the incident spectral field, and the few-mode response of the optics and detectors. We present a modal technique for modeling the behavior of spectrometers that allows for the propagation and detection of partially coherent fields, and the inclusion of straylight radiated by warm internal surfaces. We illustrate the technique by modeling the behavior of the long wavelength band of the proposed SAFARI instrument on the well-studied SPICA mission.

Histatin 1 Enhances Cell Adhesion to Titanium in an Implant Integration Model.

Cellular adhesion is essential for successful integration of dental implants. Rapid soft tissue integration is important to create a seal around the implant and prevent infections, which commonly cause implant failure and can result in bone loss. In addition, soft tissue management is important to obtain good dental aesthetics. We previously demonstrated that the salivary peptide histatin 1 (Hst1) causes a more than 2-fold increase in the ability of human adherent cells to attach and spread on a glass surface. Cells treated with Hst1 attached more rapidly and firmly to the substrate and to each other. In the current study, we examine the potential application of Hst1 for promotion of dental implant integration. Our results show that Hst1 enhances the attachment and spreading of soft tissue cell types (oral epithelial cells and fibroblasts) to titanium (Ti) and hydroxyapatite (HAP), biomaterials that have found wide applications as implant material in dentistry and orthopedics. For improved visualization of cell adhesion to Ti, we developed a novel technique that uses sputtering to deposit a thin, transparent layer of Ti onto glass slides. This approach allows detailed, high-resolution analysis of cell adherence to Ti in real time. Furthermore, our results suggest that Hst1 has no negative effects on cell survival. Given its natural occurrence in the oral cavity, Hst1 could be an attractive agent for clinical application. Importantly, even though Hst1 is specific for saliva of humans and higher primates, it stimulated the attachment and spreading of canine cells, paving the way for preclinical studies in canine models.

Phase locking of a 2.7 THz quantum cascade laser to a microwave reference.

We demonstrate the phase locking of a 2.7 THz metal-metal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier chain (x12) from a microwave synthesizer at approximately 15 GHz. Both laser and reference radiations are coupled into a bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. The spectral analysis of the beat signal confirms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range.

Hemodynamic effects of intermittent manual lung hyperinflation in patients with septic shock.

OBJECTIVE: The purposes of this study were to investigate the hemodynamic changes induced by intermittent manual lung hyperinflation (MHI) and to assess if these changes are adverse enough to warrant prohibition of MHI as a routine procedure in the care of patients with septic shock. DESIGN: The study's design was experimental prospective. SETTING: The settings were university hospital intensive care units. PATIENTS: Subjects included 13 consecutive mechanically ventilated patients with septic shock who met the inclusion criteria. MEASUREMENTS AND RESULTS: Phasic MHI-related increments in mean inspiratory airway pressure were concordant to changes in mean pulmonary artery pressure (MPAP) (r(2) = 0.67) with a 0.6 mm Hg rise in MPAP per cm H(2)O airway pressure. The magnitude of MPAP changes was not reflected in magnitude of stroke volume index (SVI) (r(2) = 0.06). On average, MHI did not induce statistically significant hemodynamic changes and mean values returned to baseline level within 15 minutes. SVI during MHI increased slightly in 9 patients, from 37 +/- 15 (mean +/- SD) to 41 +/- 17 mL/m(2) (P <.05), and decreased in 4, from 60 +/- 10 to 50 +/- 14 mL/m(2) (not significant). Patients with an increase in SVI had lower baseline values for SVI, cardiac index, and left ventricular stroke work index (P <.05) and higher values for systemic vascular resistance index compared with patients with a decrease in SVI (P <.05). Left ventricular stroke work index was higher in patients with a decrease in SVI than in patients with an increase in SVI (52 +/- 9 vs 34 +/- 8; P <.05). Tidal volume increased from 499 +/- 176 mL before MHI to 587 +/- 82 mL, 5 minutes after MHI (P <.05) with a return to baseline values within 15 minutes after the procedure. CONCLUSION: The hemodynamic effects of intermittent MHI in patients with septic shock are relatively small and insignificant and seem to be related to the cardiovascular state before the procedure. The risk of inducing hemodynamic changes with MHI should not be considered as a contraindication in patients with septic shock who are mechanically ventilated.

Estimation of beat-to-beat changes in stroke volume from arterial pressure: a comparison of two pressure wave analysis techniques during head-up tilt testing in young, healthy men.

OBJECTIVE: The aim of this study was to compare beat-to-beat changes in stroke volume (SV) estimated by two different pressure wave analysis techniques during orthostatic stress testing: pulse contour analysis and Modelflow, i.e., simulation of a three-element model of aortic input impedance. METHODS: A reduction in SV was introduced in eight healthy young men (mean age, 25; range, 19-32 y) by a 30-minute head-up tilt maneuver. Intrabrachial and noninvasive finger pressure were monitored simultaneously. Beat-to-beat changes in SV were estimated from intrabrachial pressure by pulse contour analysis and Modelflow. In addition, the relative differences in Modelflow SV obtained from intrabrachial pressure and noninvasive finger pressure were assessed. RESULTS: Beat-to-beat changes in Modelflow SV from intrabrachial pressure were comparable with pulse contour measures. The relative difference between the two methods amounted to 0.1+/-1% (mean +/- SEM) and was not dependent on the duration of tilt. The difference between Modelflow applied to intrabrachial pressure and finger pressure amounted to -2.7+/-1.3% (p = 0.04). This difference was not dependent on the duration of tilt or level of arterial pressure. CONCLUSIONS: Based on different mathematical models of the human arterial system, pulse contour and Modelflow compute similar changes in SV from intrabrachial pressure during orthostatic stress testing in young healthy men. The magnitude of the difference in SV derived from intrabrachial and finger pressure may vary among subjects; Modelflow SV from noninvasive finger pressure tracks fast and brisk changes in SV derived from intrabrachial pressure.

Continuous cardiac output in septic shock by simulating a model of the aortic input impedance: a comparison with bolus injection thermodilution.

BACKGROUND: To compare continuous cardiac output obtained by simulation of an aortic input impedance model to bolus injection thermodilution (TDCO) in critically ill patients with septic shock. METHODS: In an open study, mechanically ventilated patients with septic shock were monitored for 1 (32 patients), 2 (15 patients), or 3 (5 patients) days. The hemodynamic state was altered by varying the dosages of dopamine, norepinephrine, or dobutamine. TDCO was estimated 189 times as the series average of four automated phase-controlled injections of iced 5% glucose, spread equally over the ventilatory cycle. Continuous model-simulated cardiac output (MCO) was computed from radial or femoral artery pressure. On each day, the first TDCO value was used to calibrate the model. RESULTS: TDCO ranged from 4.1 to 18.2 l/min. The bias (mean difference between MCO and TDCO) on the first day before calibration was -1.92 +/- 2.3 l/min (mean +/- SD; n = 32; 95% limits of agreement, -6.5 to 2.6 l/min). The bias increased at higher levels of cardiac output (P < 0.05). In 15 patients studied on two consecutive days, the precalibration ratio TDCO:MCO on day 1 was 1.39 +/- 0.28 (mean +/- SD) and did not change on day 2 (1.39 +/- 0.34). After calibration, the bias was -0.1 +/- 0.8 l/min with 82% of the comparisons (n = 112) < 1 l/min and 58% (n = 79) < 0.5 l/min, and independent of the level of cardiac output. CONCLUSIONS: In mechanically ventilated patients with septic shock, changes in bolus TDCO are reflected by calibrated MCO over a range of cardiac output values. A single calibration of the model appears sufficient to monitor continuous cardiac output over a 2-day period with a bias of -0.1 +/- 0.8 l/min.

Finger arterial versus intrabrachial pressure and continuous cardiac output during head-up tilt testing in healthy subjects.

1. The aims of this study were to determine the clinical feasibility of continuous, non-invasive Finapres recordings as a replacement for intrabrachial pressure during a 30 min head-up tilt, and the reliability of continuous cardiac output computation by pulse contour analysis from the finger arterial versus the brachial waveform. 2. In eight healthy subjects a 30 min 70 degrees passive head-up tilt was performed. Finger arterial (FINAP) and intrabrachial (IAP) pressures were measured simultaneously. Beat-to-beat changes in stroke volume were computed using a pulse contour algorithm. 3. Accuracy (the group-averaged FINAP-IAP difference) and precision (the SD of the difference) of Finapres measurements were 4 and 9 mmHg for systolic blood pressure, -5 and 9 mmHg for mean blood pressure and -5 and 9mmHg for diastolic blood pressure. 4. The time course of the FINAP-IAP differences during head-up tilt showed a linear trend (P < 0.001 for all pressure levels). Averaged for the group, the difference increased 7 mmHg for mean blood pressure. The difference in stroke volume computed from FINAP and IAP was 0.3 +/- 5% (mean +/- SD), and independent of the duration of the tilt (P > 0.05). This difference did not change at low blood pressure levels (0.5 +/- 6%). 5. The qualitative performance of the Finapres allows it to be used in the clinical setting as a monitor of sudden changes in blood pressure induced by a 30 min head-up tilt. Relative changes in stroke volume, as obtained by pulse contour analysis of the finger arterial waveform, closely follow intrabrachial values during long-duration head-up tilt and associated arterial hypotension.