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Biomedical subjects

T Irvine

Publications and source records attributed to T Irvine.

25 records · Page 2Linked to original sources
PubMed1999

Dobutamine stress echocardiography: improved endocardial border definition and wall motion analysis with tissue harmonic imaging.

BACKGROUND: We performed a study to determine whether tissue harmonic imaging (THI) facilitates wall motion analysis at rest and whether these benefits extend through the stages of a dobutamine stress echocardiography (DSE) study. We also assessed the impact of THI on the feasibility of DSE in technically difficult patients. Finally we tested the hypothesis that THI by improving endocardial border definition (EBD) could enhance the interobserver agreement between trainees and experienced operators for interpreting DSE studies. METHODS: Twenty unselected patients underwent DSE by standard protocol. Parasternal and apical views were obtained with the use of fundamental mode (FND) and THI at baseline, low dose, and peak stress. Segmental EBD was characterized as 1 to 4 (1 = excellent) and segmental wall motion was characterized as 1 to 4/x (1 = normal, x = unable to interpret) by a consensus of 2 experienced observers. A trainee in stress echocardiography independently scored all segments, and these results were compared with the consensus of the experienced readers. RESULTS: EBD improved with THI in 26 +/- 6.7 of 48 segments per patient (54%, 95% confidence interval [CI] 0.40 to 0.68) and deteriorated with THI in only 2 +/- 2.7 (4%, 95% CI 0 to 0.09). Of the total of 48 segments per patient, a mean of 10 +/- 5.7 (21%, 95% CI 0.10 to 0.31) were of inadequate quality to be interpreted for wall motion on FND, and this changed to 4 +/- 3.4 (6%, 95% CI 0.06 to 0.12) on THI (P <.001). EBD improved in a similar degree in all DSE stages 53%, 54%, and 53% for rest, low dose, and peak stress, respectively. Six of the 20 study patients were deemed unsuitable for DSE on FND, and all were changed to suitable subjects on THI. Of the 205 segments deemed unsuitable for interpretation on FND, 140 (68%) were of the anterior and lateral walls of the LV. Improvement with THI was also more prominent on these walls. The mean coefficient of agreement (kappa) for wall motion analysis was 0.82 +/- 0.14 on FND and improved to 0. 92 +/- 0.09 on THI (P <.001). CONCLUSIONS: THI dramatically improves EBD and the ability to confidently score segmental wall motion. Interobserver agreement is also significantly enhanced. These benefits extend to the peak stage of a DSE study. Routine use of THI may enhance the diagnostic accuracy of DSE and extend its application to technically difficult patients previously deemed unsuitable.

Adult↗
PubMed1999

Acoustically stimulated transient power scattering explains enhanced detection of the very low velocities in myocardial capillaries by power Doppler imaging: an in vitro study.

BACKGROUND: Although enhanced detection of myocardial perfusion signals by power Doppler imaging during contrast echocardiography has been noted, flow velocities in the coronary microvasculature should generally be below the threshold for Doppler motion detection. It has been suggested that in this situation nonlinear scattering related to acoustically stimulated microsphere oscillation or destruction may be responsible for the detected Doppler shift. METHODS AND RESULTS: This study examined the behavior of MRX 115 (ImaRx Pharmaceuticals) microbubbles during harmonic and nonharmonic power Doppler imaging at varying power outputs (mechanical indexes 0. 3, 0.5, 0.7, and 0.9) in a perfusion tube model under zero-flow conditions. Boluses of MRX 115 0.5-mL suspension were introduced into the model, and flow was halted during each imaging period. Once power Doppler imaging was implemented, a signal was detected as unique sparkling color pixels corresponding to individual bubble destruction events, even in the absence of contrast movement. This phenomenon continued until all contrast bubbles disappeared from the region subjected to power Doppler imaging, usually within 35 to 40 seconds. Off-line videointensity measurements showed that initial power Doppler signal intensity and maximum signal decay rates increased parallel to increasing power output and were substantially greater for nonharmonic than for harmonic imaging modes. CONCLUSION: This relationship between signal intensity and decay rate and acoustic power output suggests that transient scattering related to bubble destruction is responsible for generation of the power Doppler signal in the absence of flow. This would explain the enhanced detection of the very low velocity flows in the myocardial capillaries by power Doppler contrast imaging.

Blood Flow Velocity↗
PubMed1998

Transoesophageal echocardiography in the management of whole lung lavage.

The effects of two lung ventilation, one lung ventilation and alveolar lavage on right ventricular mechanics in a patient have been observed using transoesophageal echocardiography (TOE). Alveolar lavage resulted in additional stresses to those of one lung ventilation (OLV) and the point when these were noted to be resulting in right ventricular changes was used as the signal to terminate the filling phase of a cycle of alveolar lavage. A significant increase in right ventricle afterload occurred on starting OLV. The response to lung lavage was biphasic, initially a further increase in afterload followed by a reduction in preload. Because there was rapid adaptation to these changes, it was felt appropriate to perform sequential lung lavage during the same anaesthetic. In similar circumstances where pulmonary vascular resistance is changed, information obtained from TOE may be used to guide therapy.

Adult↗
PubMed1994

Misuse of metered-dose inhalers in hospitalized patients.

Metered-dose inhalers (MDIs) have been associated with a high rate of misuse. Medical personnel also have a poor understanding of MDI technique. Hospitalized patients had their MDI technique observed before and after a series of inservices were provided to hospital personnel on correct MDI use. The rate of misuse did not change with 55 of 72 (76 percent) patients making errors in the first group before, and 45 of 55 (82 percent) patients making errors in the second group after staff education (p = 0.46). The average number of errors per patient was 2.39 in group 1 and 2.45 in group 2 (p = 0.93). Alternatives to deal with this high rate of MDI misuse are discussed.

Administration, Inhalation↗
PubMedDate not supplied

Effects of transmyocardial laser revascularization by using a prototype pulsed CO2 laser on contractility and perfusion of chronically ischemic myocardium in a porcine model.

The purpose of this study was to test a new prototype pulsed CO2 laser to be used for transmyocardial laser revascularization (TMR). We wanted to determine whether it can reduce thermal damage and mitigate induced ischemia with improvement in contractile reserve of the heart as evidenced by contrast echocardiography at rest and under dobutamine stress. TMR is an emerging surgical strategy for treatment of myocardial ischemia not amenable to conventional percutaneous or surgical revascularization. Eleven pigs underwent ameroid occluder placement at the origin of the circumflex coronary artery. Six weeks later, occlusion of the circumflex coronary artery was documented. TMR was then carried out on 10 pigs by using a prototype pulsed CO2 laser that delivered 8-12 joules in 1.5 ms with a spot size of 1 mm. Six weeks after TMR, the pigs were restudied. The animals developed significant ischemia after 6 weeks of ameroid occlusion, at rest (p = 0.01) and at peak stress (p = 0.004). Wall motion for the ischemic segments improved significantly 6 weeks after TMR at peak stress (p = 0.02). TMR results in an improvement in wall motion in our model of chronic ischemia and improves wall motion score index more during induced stress than at rest.

Animals↗