Novel directional coupled waveguide photodiode-concept and preliminary results.

A novel photodiode is presented using a directional coupler incorporated with a UTC style photodiode with 0.88 A/W responsivity and 35 dBm OIP3 at 25 mA. The device responsivity is characterized at various photocurrents up to 10 mA and the OIP3 is measured up to 25 mA and 10 GHz. Additionally, the device capacitance is measured and used to model the capacitance limited OIP3 of the device. The failure of the device was compared to a traditional waveguide photodiode showing burnout no longer occurs at the front of the device and demonstrated the potential of the new design to control the photocurrent density profile for a waveguide style photodiode.

Behaviors of the third order intercept point for p-i-n waveguide photodiodes.

Waveguide PIN photodiodes with different absorber thicknesses and lengths were fabricated and characterized for linearity. Device A has a thicker absorber and shorter length, resulting in a bandwidth of 20 GHz while device B reduces the absorber by half while maintaining the intrinsic layer thickness and almost doubles the length, resulting in a smaller optical overlap factor and a bandwidth of 10 GHz. Device B shows a significant enhancement in OIP3 with a record high maximum value for a PIN waveguide photodiode of 42.4 dBm at 28 mA and -4V bias compared to device A which has a maximum OIP3 of 32.7 dBm at 10 mA and -4V bias. The increased linearity in device B is attributed to the reduction in optical overlap factor and increase in device length resulting in an easing of the front facet photocurrent density and overall device heating. The DC saturation points are about 75 mA and >160 mA for device A and B at -2V bias.

Hyperkalemic cardioplegia-induced myocyte swelling and contractile dysfunction: prevention by diazoxide.

BACKGROUND: Hyperkalemic cardioplegia (9 degrees C) results in significant myocyte swelling and reduced contractility, representing a possible mechanism of myocardial stunning. Adenosine triphosphate-sensitive potassium channel (KATP) openers have been shown to ameliorate stunning. This study evaluated the hypothesis that a KATP opener would prevent hyperkalemic cardioplegia-induced myocyte swelling and reduced contractility. METHODS: Isolated rabbit myocytes were perfused with 37 degrees C Tyrode's solution for 20 minutes, followed by test solution (9 degrees C or 37 degrees C) including control Tyrode's, Tyrode's + 100 micromol/L diazoxide (KATP opener), St. Thomas's solution; or 9 degrees C St. Thomas's + 100 micromol/L diazoxide or St. Thomas's + 100 micromol/L diazoxide + 20 micromol/L HMR1098 or 50 micromol/L 5-hydroxydeconoate (KATP blockers) for 20 minutes (n = 8 per group). Myocytes were then reexposed to 37 degrees C Tyrode's solution for 20 minutes. Volume and contractility were measured by videomicroscopy and video-based edge detection, respectively. RESULTS: St. Thomas's solution (9 degrees C) caused significant myocyte swelling and associated reduced contractility (p < 0.05). The addition of diazoxide abolished myocyte swelling (p < 0.0001), and eliminated the associated reduced contractility (p < 0.05). Findings were unchanged by the addition of HMR 1098 and 5-hydroxydeconoate. CONCLUSIONS: Diazoxide prevented myocyte swelling and reduced contractility secondary to hyperkalemic cardioplegia, and this was unchanged by the addition of either KATP channel blocker. Prevention of myocyte swelling was associated with improved contractility, consistent with the hypothesis that myocyte swelling may be a mechanism of myocardial stunning. Diazoxide may play a role in myocyte volume homeostasis by means of a mechanism separate from opening the KATP channel.

Right atrial and ventricular adaptation to chronic right ventricular pressure overload.

BACKGROUND: Increased mortality in patients with chronic pulmonary hypertension has been associated with elevated right atrial (RA) pressure. However, little is known about the effects of chronic right ventricular (RV) pressure overload on RA and RV dynamics or the adaptive response of the right atrium to maintain RV filling. METHODS AND RESULTS: In 7 dogs, RA and RV pressure and volume (conductance catheter) were recorded at baseline and after 3 months of progressive pulmonary artery banding. RA and RV elastance (contractility) and diastolic stiffness were calculated, and RA reservoir and conduit function were quantified as RA inflow with the tricuspid valve closed versus open, respectively. With chronic pulmonary artery banding, systolic RV pressure increased from 34+/-7 to 70+/-17 mm Hg (P<0.001), but cardiac output did not change (P>0.78). RV elastance and stiffness both increased (P<0.05), suggesting preserved systolic function but impaired diastolic function. In response, RA contractility improved (elastance increased from 0.28+/-0.12 to 0.44+/-0.13 mm Hg/mL; P<0.04), and the atrium became more distensible, as evidenced by increased reservoir function (49+/-14% versus 72+/-8%) and decreased conduit function (51+/-14% versus 28+/-8%; P<0.002). CONCLUSIONS: With chronic RV pressure overload, RV systolic function was preserved, but diastolic function was impaired. To compensate, RA contractility increased, and the atrium became more distensible to maintain filling of the stiffened ventricle. This compensatory response of the right atrium likely plays an important role in preventing clinical failure in chronic pulmonary hypertension.

Optical detection of rapidly moving objects in space.

We compare the sensitivity of photon-counting and charged-coupled-device (CCD) imagers for rapidly moving objects. Our test case involves the detection of small objects in space, seen against a diffuse zodiacal light background, as observed from a space platform. We contrast photon-counting detectors, with excellent time resolution and negligible readout noise, against CCDs with a significantly larger quantum efficiency. For fast moving objects and small fields of view, the photon-counting detectors are able to detect significantly smaller targets, with the added benefit of providing angle-angle-time metric information in addition to high-time-resolution light curves. For larger fields of view and slower moving objects, the CCDs are more sensitive. These results may motivate the further development of microchannel-plate photon-counting systems and amplified CCDs for detecting and tracking space objects.

A prospective, single-center clinical trial of a modified Cox maze procedure with bipolar radiofrequency ablation.

OBJECTIVE: The Cox maze III procedure has excellent long-term efficacy in curing atrial fibrillation. It has not been widely practiced because it is technically challenging and requires prolonged cardiopulmonary bypass. The aim of this study was to examine a simplified Cox maze III procedure that uses bipolar radiofrequency energy as an ablative source. METHODS: Beginning January 2002, a total of 40 consecutive patients underwent a modified Cox maze III procedure with bipolar radiofrequency energy. Nineteen had a lone maze procedure and 21 had a maze procedure plus a concomitant operation. One month after the operation, the first 8 patients were investigated with high-resolution magnetic resonance imaging. Patients were followed up monthly with clinical examination and electrocardiography. RESULTS: There was no operative deaths. The crossclamp times were 47 +/- 26 minutes for the modified lone Cox maze III procedure and 92 +/- 37 minutes for the Cox maze III procedure plus concomitant procedures. These were significantly shorter than our previous times for the traditional Cox maze III procedure (93 +/- 34 minutes and 122 +/- 37 minutes, respectively, P <.05). Follow-up magnetic resonance imaging showed no evidence of pulmonary vein stenosis, and atrial contractility was preserved in all patients. There were no late strokes. At 6-month follow-up, 91% of patients (21/23) were in sinus rhythm. CONCLUSIONS: Bipolar radiofrequency ablation can be used to replace the surgical incisions of the Cox maze procedure. This energy source did not result in pulmonary vein stenosis. The modification of the Cox maze III procedure to use bipolar radiofrequency ablation simplified and shortened this procedure without sacrificing short-term efficacy.

Lung transplantation in children.

OBJECTIVE: To report the authors' experience with pediatric lung transplantation (LTX) to provide an overview of patients selected for this procedure and their outcomes. SUMMARY BACKGROUND DATA: Pediatric LTX differs from adults in many ways, including recipient size, indications, posttransplant care, and rehabilitation. METHODS: Two hundred seven isolated lung transplants on 190 children under the age of 18 years were performed from 1990 to the present. This represents the single largest series of lung transplants in children in the world. Thirty-two patients were less than 1 year of age, 22 were 1 to 5 years of age, 32 were 5 to 10 years of age, and 121 were 10 to 18 years old. The groups by major diagnostic category were cystic fibrosis (n = 89), pulmonary vascular disease (n = 44), bronchiolitis obliterans (n = 21), pulmonary alveolar proteinosis (n = 12), pulmonary fibrosis (n = 15), and other (n = 26). The average age at the time of transplant was 9.5 +/- 5.9 years (range 36 days to 18 years). RESULTS: Survival by Kaplan-Meier analysis was 77% at 1 year, 62% at 3 years, and 55% at 5 years. There was no significant difference in survival according to primary diagnosis leading to LTX or age at LTX. There were 25 early (<60 days) and 61 late deaths. The most common cause of early deaths was graft failure (13/25, 52%). The most common causes of late death were bronchiolitis obliterans (35/61, 57%), infection (13/61, 21%), and posttransplant malignancies (11/61, 18%). No patient died of acute rejection. In those surviving greater than 3 months (mean follow-up 3.5 years, range 3 months to 11 years), the overall rate of occurrence of bronchiolitis obliterans was 46% (80/175) and the overall incidence of posttransplant malignancies was 24/175 (14%). Major risk factors for the development of bronchiolitis obliterans were age older than 3 years, more than two episodes of acute rejection, and organ ischemic time longer than 180 minutes. CONCLUSIONS: In children, LTX is a high-risk but viable treatment for end-stage pulmonary parenchymal and vascular disease. The major hurdle to overcome in long-term survival is bronchiolitis obliterans.