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Biomedical subjects

C A Perez

Publications and source records attributed to C A Perez.

At least 37 records · Page 2Linked to original sources
PubMed2000

Two-point vibrotactile discrimination related to parameters of pulse burst stimulus.

Tactile spatial resolution is an important factor in the design of vibrotactile arrays. The two-point discrimination distance is used as a measure of tactile spatial resolution. An experimental study is presented showing the effect of pulse burst stimulus parameters, pulse repetition period and duty cycle on two-point vibrotactile spatial discrimination. An array of piezoceramic vibrators is used to measure two-point spatial discrimination on the index finger. In a group of 14 subjects, the average two-point discrimination distance for a pulse repetition period of 1/25s is 2.1 mm (SD = 1.0), whereas for 1/500 s it is 5.1 mm (SD = 0.9). Differences in discrimination distances are statistically significant according to the ANOVA analysis (p < 0.001). Results show that the two-point discrimination distance is better for longer pulse repetition periods. Therefore the pulse repetition period in an excitatory waveform composed of bursts of pulses is important for tactile resolution. No statistically significant differences in discrimination distances are found between bursts of pulses of 50% duty cycle and those of lower duty cycle. The latter result indicates that, by choosing low-duty cycle waveforms for vibrotactile stimulation, the power can be reduced with no loss in two-point discrimination capacity.

Adult↗
PubMed2000

Effects of dietary fat on benz-a-pyrene-induced forestomach tumorigenesis in mice chronically exposed to arsenic.

The modulating effect of As (As2O3) in drinking water plus dietary fatty acids on benzo-a-pyrene (BP) induced forestomach tumorigenesis was assayed in mice fed with corn oil (CO), Olein (O), palmstearin (PS) and cod liver oil (CLO) enriched formulae, and a mixed-fat (S-stock) diet during 28 weeks. Neither pre-or neoplastic lesions were recorded in esophagus or forestomach of mice treated with As alone. CLO diet showed a protective effect. Indeed, multiple epidermal hyperplasia were significantly reduced compared to S group and a reduction in papillomas multiplicity with respect to S, CO and O groups was also observed. Mice fed on PS formula showed minor papillomas per mouse with respect to CO and O. These results indicate that As plus BP did not exhibit any synergistic effect on the development of epidermoid tumor lesions, whereas CLO diet exerted antipromoting activity . In spite of their common essential fatty acid deficiency (EFAD) condition, PS and O lots showed contradictory results. Hence, the dietary enrichment in 18:1 n-9 (O diet) per se, and not the EFAD state, may play a deleterious role. Corn diet showed no promoting activity on the epidermoid tumor development in this model.

Animals↗
PubMed2000

Pyloroplasty improves long-term gastric emptying in rats undergoing fundoplication.

BACKGROUND: Conflicting reports exist regarding the permanence of improved gastric emptying (GE) after fundoplication for gastroesophageal reflux in children. METHODS: Changes in gastric volume (GV) and GE of a radiolabeled mixed meal induced by a Nissen fundoplication (NF) were compared with those with a NF plus pyloroplasty (NF + P). GE was measured preoperatively, 15 and 30 days postoperation, in 24 Sprague-Dawley rats; 12 had NF alone, and 12 had NF + P Results were expressed as percent gastric retention at 90 minutes (GR90). GV was measured at the same time periods in 20 additional rats. RESULTS: NF rats had enhanced GE with reduction of preoperative GR90 from 37.6% to 23.7% at 15 days (P < .05); however, at 30 days the GR90 increased to 34.3%. NF + P rats had enhanced GE with reduction in GR90 from 37.2% to 20.8% at 15 days (P< .05), which persisted at 30 days (20.4%). Mean GV decreased from (1.36 mL/100 g body weight) preoperation to 0.86 at 15 days (P< .05) at 15 days in the NF group, and returned to 1.29 at 30 days. Mean GV decreased from 1.36 to 0.91 at 15 days in the NF + P rats and persisted at 0.90 at 30 days. CONCLUSION: In the rat model, NF enhances GE transiently, whereas NF + P produces long-term enhancement of GE.

Animals↗
PubMed2000

Comparison of intratracheal pulmonary ventilation and hybrid intratracheal pulmonary ventilation with conventional mechanical ventilation in a rabbit model of acute respiratory distress syndrome by saline lavage.

OBJECTIVES: To study changes in PaCO2 and PaO2 during intratracheal pulmonary ventilation (ITPV) and hybrid intratracheal pulmonary ventilation (h-ITPV) compared with conventional mechanical ventilation (CMV) in a rabbit model of respiratory failure, and to define the technique of h-ITPV that combines conventional mechanical ventilation and ITPV. DESIGN: Prospective, interventional study. SUBJECTS: Twelve adult New Zealand White rabbits. INTERVENTIONS: Surfactant deficiency was induced by saline lavage, and rabbits were randomized to either ITPV or h-ITPV. The study consisted of four phases: phase 0, CMV after saline lavage, ventilator rate 30 breaths/min; phase I, ITPV or h-ITPV initiated at the same pressure and rate as in phase 0; phase II, ITPV or 1.0 L/min h-ITPV bias flow, with peak inspiratory pressure (PIP) decreased and ventilator rate increased to achieve the lowest tidal volume while maintaining adequate gas exchange; and phase III, animals returned to CMV. MEASUREMENTS AND MAIN RESULTS: In phase I, no difference in PaCO2 was observed between ITPV, h-ITPV, or CMV. There was a decrease in PaO2 when switching from CMV to ITPV but not to h-ITPV. In phase II, it was possible to decrease PIP (average of 37% for ITPV and 36% for h-ITPV) and tidal volume (average of 64% for ITPV and 53% for h-ITPV) without compromising gas exchange (p < .05). Oxygenation tended to improve from phase 0 to the end of phase II. In phase III, PaCO2 increased (average of 71% for ITPV and 79% for h-ITPV) and pH decreased (p < .05). Normocapnia was achieved using significantly higher PIP and tidal volume, compared with phase 0 (p < .05). CONCLUSIONS: ITPV and h-ITPV can effectively ventilate and oxygenate rabbits with surfactant-deficient lungs at tidal volumes and therefore pressures lower than required with CMV. Maximum benefit appears to occur at high ventilator rates. These findings suggest that both modes of ventilation may represent powerful new tools in the management of patients with acute respiratory failure. (Crit Care Med 2000; 28:774-781)

Acute Disease↗
PubMed2000

Biologic variables in the outcome of stages I and II neuroblastoma treated with surgery as primary therapy: a children's cancer group study.

PURPOSE: To determine prospectively whether surgery alone is sufficient therapy for Evans stages I and II neuroblastoma and to define biologic and clinical features having prognostic potential for this group. PATIENTS AND METHODS: Between June 1989 and August 1995, 374 eligible children (age range, 0 to 18 years) with newly diagnosed stage I (n = 141) and stage II (n = 233) neuroblastoma were registered onto Children's Cancer Group trial 3881. Surgical resection was the only primary therapy except in cases with spinal cord compression, where radiation therapy was allowed. Event-free survival (EFS) and overall survival (OS) were analyzed by life-table methods according to clinical and biologic features. RESULTS: EFS and OS (mean +/- SE) for all stage I patients were 93% +/- 3.0% and 99% +/- 1.0%, respectively, compared with 81% +/- 4.0% and 98% +/- 2. 0%, respectively, for stage II patients. The significantly higher recurrence rate among stage II patients was managed successfully in 38 of 43 children with either surgery or multimodality treatment. There was one death among stage I patients and six among stage II. For stage II patients tumor MYCN gene amplication, unfavorable histopathology, an age greater than 2 years, and positive lymph nodes predicted a lower OS (P <.05). CONCLUSION: Children with stages I and II neuroblastoma have 98% survival with surgery alone as primary therapy. Supplemental treatment was necessary in only 10% of stage I patients and 20% of stage II patients. In children with localized neuroblastoma, a subset of patients that are at higher risk for death can be defined as those with stage II disease who have tumor MYCN amplification or who are >/= 2 years of age with either unfavorable histopathology or positive lymph nodes.

Adolescent↗
PubMed1999

Lack of effect of tumor size on the prognosis of carcinoma of the uterine cervix Stage IB and IIA treated with preoperative irradiation and surgery.

PURPOSE: The purpose of this analysis was to evaluate the prognostic significance of cervical tumor size in patients with Stages Ib and IIa carcinoma of the cervix treated with preoperative irradiation and radical or conservative hysterectomy. METHODS AND MATERIALS: This study is a retrospective analysis of 177 patients. One hundred forty-one patients had Stage Ib and 36 patients had Stage IIa carcinoma of the cervix. All patients were treated with preoperative irradiation and surgery. Radiation therapy consisted of external pelvic irradiation and intracavitary brachytherapy; total doses ranged from 30 to 60 Gy to the pelvic sidewall and 60 to 70 Gy to point A. Surgery consisting of radical hysterectomy and lymph node dissection or a conservative hysterectomy and lymph node dissection was performed 4 to 6 weeks after completion of irradiation. RESULTS: The 5-year progression-free survivals were 80% for Stage Ib and 63% for Stage IIa (p = 0.03). The 5-year cumulative pelvic failure rates for Stage Ib were 16% for tumors <3 cm and 9% for tumors >3 cm (p = 0.90). The 5-year cumulative pelvic failure rates for Stage IIa were 22% for tumors <3 cm and 22% for tumors >3 cm (p = 0.75). The corresponding cumulative distant metastasis failure rates at 5 years for Stage Ib were 21% for tumors <3 cm and 21% for tumors >3 cm (p = 0.60). For patients with Stage IIa disease, the 5-year cumulative distant metastasis rates were 33% for tumors <3 cm and 36% for tumors >3 cm (p = 0.70). A multivariate analysis was performed to evaluate prognostic factors for the endpoint of progression-free survival. The variables that were analyzed were patient age, tumor histology, tumor size, clinical stage, point A and pelvic lymph node irradiation dose, and cervical tumor status and pelvic lymph node status at the time of hysterectomy. The variables that were found to be of independent significance for progression-free survival by multivariate analysis were pelvic lymph node irradiation dose (p <0.001), pelvic lymph node status at the time of hysterectomy (p = 0.01), and clinical stage (p = 0.02). Cervical tumor size at the time of diagnosis and the presence of tumor cells in the cervix in the hysterectomy specimen was not an independent prognostic factor by multivariate analysis. The overall severe complication rate was 11% for all patients. CONCLUSIONS: For this population of patients treated with preoperative irradiation and surgery, pelvic lymph node status at the time of hysterectomy and the preoperative irradiation dose to the pelvic lymph nodes are independent predictors of progression-free survival and the development of distant metastasis. The pretreatment cervical tumor size is of less importance for predicting progression-free survival and the development of distant metastasis but clinical stage is an important prognostic variable. These results are in contrast with those of surgery or irradiation alone, in which primary tumor size is a critical prognostic factor for all outcome parameters.

Adolescent↗
PubMed1999

Clinical dose-volume histogram analysis for pneumonitis after 3D treatment for non-small cell lung cancer (NSCLC)

PURPOSE: To identify a clinically relevant and available parameter upon which to identify non-small cell lung cancer (NSCLC) patients at risk for pneumonitis when treated with three-dimensional (3D) radiation therapy. METHODS AND MATERIALS: Between January 1991 and October 1995, 99 patients were treated definitively for inoperable NSCLC. Patients were selected for good performance status (96%) and absence of weight loss (82%). All patients had full 3D treatment planning (including total lung dose-volume histograms [DVHs]) prior to treatment delivery. The total lung DVH parameters were compared with the incidence and grade of pneumonitis after treatment. RESULTS: Univariate analysis revealed the percent of the total lung volume exceeding 20 Gy (V20), the effective volume (Veff) and the total lung volume mean dose, and location of the tumor primary (upper versus lower lobes) to be statistically significant relative to the development of > or = Grade 2 pneumonitis. Multivariate analysis revealed the V20 to be the single independent predictor of pneumonitis. CONCLUSIONS: The V20 from the total lung DVH is a useful parameter easily obtained from most 3D treatment planning systems. The V20 may be useful in comparing competing treatment plans to evaluate the risk of pneumonitis for our individual patient treatment and may also be a useful parameter upon which to stratify patients or prospective dose escalation trials.

Adult↗
PubMed1999

Radiation therapy morbidity in carcinoma of the uterine cervix: dosimetric and clinical correlation.

PURPOSE: To quantitate the impact of total doses of irradiation, dose rate, and ratio of doses to bladder or rectum and point A on sequelae in patients treated with irradiation alone for cervical cancer. METHODS AND MATERIALS: Records were reviewed of 1456 patients (Stages IB-IVA) treated with external-beam irradiation plus two low-dose rate intracavitary insertions to deliver 70 to 90 Gy to point A. Follow-up was obtained in 98% of patients (median, 11 years; minimum, 3 years; maximum, 30 years). The relationships among various dosimetry parameters and Grade 2 or 3 sequelae were analyzed. RESULTS: In Stage IB, the frequency of patients developing Grade 2 morbidity was 9%, and Grade 3 morbidity, 5%; in Stages IIA, IIB, III, and IVA, Grade 2 morbidity was 10% to 12% and Grade 3 was 10%. The most frequent Grade 2 sequelae were cystitis and proctitis (0.7% to 3%). The most common Grade 3 sequelae were vesicovaginal fistula (0.6% to 2% in patients with Stage I-III tumors), rectovaginal fistula (0.8% to 3%), and intestinal obstruction (0.8% to 4%). In the bladder, doses below 80 Gy correlated with less than 3% incidence of morbidity and 5% with higher doses (p = 0.31). In the rectosigmoid, the incidence of significant morbidity was less than 4% with doses below 75 Gy and increased to 9% with higher doses. For the small intestine, the incidence of morbidity was less than 1% with 50 Gy or less, 2% with 50 to 60 Gy, and 5% with higher doses to the lateral pelvic wall (p = 0.04). When the ratio of dose to the bladder or rectum in relation to point A was 0.8 or less, the incidence of rectal morbidity was 2.5% (8 of 320) vs. 7.3% (80 of 1095) with higher ratios (p < or = 0.01); bladder morbidity was 2.3% (7 of 305) and 5.8% (64 of 1110), respectively (p = 0.02). The incidence of Grade 2 and 3 bladder morbidity was 2.9% (10 of 336) when the dose rate was less than 0.80 Gy/h, in contrast to 6.1% (62 of 1010) with higher dose rates (p = 0.07). Rectal morbidity was 2% to 5% in Stage IB, regardless of dose rate to the rectum; in Stages IIA-B and III, morbidity was 5.2% (28 of 539) with a dose rate of 0.80 Gy or less and 10.7% (37 of 347) with higher dose rates (p < 0.01). Multivariate analysis showed that dose to the rectal point was the only factor influencing rectosigmoid sequelae, and dose to the bladder point affected bladder morbidity. CONCLUSIONS: Various dosimetric parameters correlate closely with the incidence of significant morbidity in patients treated with definitive irradiation for carcinoma of the uterine cervix. Careful dosimetry and special attention to related factors will reduce morbidity to the lowest possible level without compromising pelvic tumor control.

Brachytherapy↗
PubMed1999

Radiation therapy for clinically localized prostate cancer: a multi-institutional pooled analysis.

CONTEXT: Prostate-specific antigen (PSA) evaluation leads to the early detection of both prostate cancer and recurrences following primary treatment. Prostate-specific antigen outcome information on patients 5 or more years following treatment is limited and available mainly as single-institution reports. OBJECTIVES: To assess the likelihood and durability of tumor control using PSA evaluation 5 or more years after radical external beam radiation therapy and to identify pretreatment prognostic factors in men with early prostate cancer treated since 1988, the PSA era. DESIGN AND SETTING: Retrospective, nonrandomized, multi-institutional pooled analysis of patients treated with external beam radiation therapy alone between 1988 and 1995 at 6 US medical centers. Follow-up lasted up to a maximum of 9 years. Outcome data were analyzed using Cox regression and recursive partitioning techniques. PATIENTS: A total of 1765 men with stage T1b, T1c, and T2 tumors treated between 1988 and 1995 with external beam radiation. The majority (58%) of patients were older than 70 years and 24.2% had initial PSA values of 20 ng/mL or higher. A minimum of 2 years of subsequent follow-up was required for participation. MAIN OUTCOME MEASURE: Actuarial estimates of freedom from biochemical failure. RESULTS: The 5-year estimates of overall survival, disease-specific survival, and the freedom from biochemical failure are 85.0% (95% confidence interval [CI], 82.5%-87.6%), 95.1% (95% CI, 94.0%-96.2%), and 65.8% (95% CI, 62.8%-68.0%), respectively. The PSA failure-free rates 5 and 7 years after treatment for patients presenting with a PSA of less than 10 ng/mL were 77.8% (95% CI, 74.5%-81.3%), and 72.9% (95% CI, 67.9%-78.2%). Recursive partitioning analysis of initial PSA level, palpation stage, and the Gleason score groupings yielded 4 separate prognostic groups: group 1, included patients with a PSA level of less than 9.2 ng/mL; group 2, PSA level of at least 9.2 but less than 19.7 ng/mL; group 3, PSA level at least 19.7 ng/mL and a Gleason score of 2 to 6; and group 4, PSA level of at least 19.7 ng/mL and a Gleason score of 7 to 10. The estimated rates of survival free of biochemical failure at 5 years are 81 % for group 1, 69% for group 2, 47% for group 3, and 29% for group 4. Of the 302 patients followed up beyond 5 years who were free of biochemical disease, 5.0% relapsed from the fifth to the eighth year. CONCLUSIONS: Estimated PSA control rates in this pooled analysis are similar to those of single institutions. These rates indicate the probability of success for subsets of patients with tumors of several prognostic category groupings. These results represent a multi-institutional benchmark for evidence-based counseling of prostate cancer patients about radiation treatment.

Aged↗
PubMed1999

Bone metastasis: review and critical analysis of random allocation trials of local field treatment.

PURPOSE: Compare and contrast reports of random allocation clinical trials of local field radiation therapy of metastases to bone to determine the techniques producing the best results (frequency, magnitude, and duration of benefit), and relate these to the goals of complete relief of pain and prevention of disability for the remaining life of the patient. METHODS AND MATERIALS: Review all published reports of random allocation clinical trials, and perform a systematic analysis of the processes and outcomes of the several trial reports. RESULTS: All trials were performed on selected populations of patients with symptomatic metastases and most studies included widely diverse groups with regard to: (a) site of primary tumor, (b) location, extent, size, and nature of metastases, (c) duration of survival after treatment All trial reports lack sufficient detail for full and complete analysis. Much collected information is not now available for reanalysis and many important data sets were apparently never collected. Several of the variations in patient and tumor characteristics were found to be much more important than treatment dose in the outcome results. Treatment planning and delivery techniques were unsophisticated and probably resulted in a systematic delivery of less than the assigned dose to some metastases. In general the use and benefit of retreatment was greater in those patients who initially received lower doses but the basis and dose of retreatment was not documented. Follow-up of patients was varied with a large proportion of surviving patients lost to follow-up in several studies. The greatest difference in the reports is the method of calculation of results. The applicability of Kaplan-Meier actuarial analysis, censoring the lost and dead patients, as used in studies with loss to follow-up of a large number of patients is questionable. The censoring involved is "informative" (the processes of loss relate to the outcome) and not acceptable since it results in artificial elevation of the frequency of response. Overall, higher dose fractionated treatment regimens produced a better frequency, magnitude, and duration of response than lower dose single-fraction regimens. Relapse after initial response was frequent. The "median duration of relief" was much shorter than the "median duration of survival" post-treatment. Thus the "net pain relief" is far less than the goal of pain relief for the total duration of life after treatment. CONCLUSIONS: The pain relief obtained in all studies is poor and our care practices need to be improved. Many patients never achieved complete relief and for most who did, the duration of relief was much less than their period of survival after treatment. Higher dose, fractionated treatments produced a greater frequency, magnitude, and duration of response with an improved "net pain relief." Additional trials with selection of comparable cases, good definition of extent of disease, exemplary treatment, and complete follow-up are required.

Analgesics↗