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Biomedical subjects

J P Shaffer

Publications and source records attributed to J P Shaffer.

7 recordsLinked to original sources
PubMed2005

Femtosecond multidimensional imaging of a molecular dissociation.

The coupled electronic and vibrational motions governing chemical processes are best viewed from the molecule's point of view-the molecular frame. Measurements made in the laboratory frame often conceal information because of the random orientations the molecule can take. We used a combination of time-resolved photoelectron spectroscopy, multidimensional coincidence imaging spectroscopy, and ab initio computation to trace a complete reactant-to-product pathway-the photodissociation of the nitric oxide dimer-from the molecule's point of view, on the femtosecond time scale. This method revealed an elusive photochemical process involving intermediate electronic configurations.

Journal Article↗
PubMed2004

Non-adiabatic intramolecular and photodissociation dynamics studied by femtosecond time-resolved photoelectron and coincidence imaging spectroscopy.

Time-resolved photoelectron spectroscopy (TRPES) is emerging as a useful tool for the study of non-adiabatic dynamics in isolated polyatomic molecules and clusters due to its sensitivity to both electronic and vibrational dynamics. A powerful extension of TRPES, coincidence imaging spectroscopy (CIS), based upon femtosecond time-resolved 3D momentum vector imaging of both photoions and photoelectrons in coincidence, is a new technique for the study of complex dissociative processes. Here we show how these spectroscopies can be used to study both non-adiabatic intramolecular and photodissociation dynamics in polyatomic molecules. Intramolecular dynamics in the alpha, beta-enones acrolein, crotonaldehyde and methyl vinyl ketone are studied using both TRPES and laser-induced fluorescence of HCO(X) product yields. The location of the methyl group is seen to have very dramatic effects on the relative electronic relaxation rates and the HCO(X) yield. Applying both TRPES and CIS to the 200 nm and 209 nm photodissociation of the nitric oxide dimer, (NO)2, we observe the fs time-scale evolution of the excited parent neutral via its photoelectron spectrum and the emergence of the NO(A) photofragment including its energy and angular distributions.

Journal Article↗
PubMed1998

The use of expandable metal stents to facilitate extubation in patients with large airway obstruction.

OBJECTIVE: To determine the clinical utility of placing airway stents to facilitate weaning in ventilator-dependent patients with large airway obstruction. METHODS: A chart review of mechanically ventilated patients who received expandable metal airway stents to attempt a facilitation of weaning. RESULTS: Eight patients, 3 women and 5 men, ranging in age from 37 to 82 years, had respiratory failure associated with large airway obstruction and underwent flexible bronchofluoroscopic placement of 12 expandable metal stents (7 Wallstents [Schneider; Minneapolis, MN], 2 Palmaz [Johnson & Johnson; Warren, NJ], and 3 Ultraflex [Microinvasive; Natick, MA]). Six had respiratory failure that was secondary to malignant airway disease, and two had benign airway disease. Seven patients with tracheal or mainstem bronchial obstruction were weaned from the ventilator within 0 to 11 days of stent placement after having previously required mechanical ventilation from 2 to 52 days. There were no associated complications. Following prolonged attempts at weaning, one patient with lobar bronchus obstruction died after mechanical ventilation was withdrawn. CONCLUSIONS: Expandable metal airway stents may be safely deployed in mechanically ventilated patients and can facilitate weaning from the mechanical ventilator. Mechanically ventilated patients with tracheal and mainstem bronchus obstruction are the best candidates for deployment of expandable airway stents to facilitate weaning.

Adult↗
PubMed1997

Massive hemoptysis as the presenting manifestation in a child with histoplasmosis.

A previously healthy and asymptomatic 7-year-old white boy presented with a history of two episodes of hemoptysis productive of bright red blood in the 5 days preceding admission. After admission he developed massive hemoptysis that, on bronchoscopy, was noted to be emanating from the right lower lobe. An emergency right lower lobe resection was done. Pathological examination revealed hilar adenopathy and peripheral lesions with caseating granulomas containing yeast, morphologically consistent with Histoplasma capsulatum.

Amphotericin B↗