PubMed Health⌕ Search

Biomedical subjects

S M Shapiro

Publications and source records attributed to S M Shapiro.

49 records · Page 3Linked to original sources
PubMed1989

Alveolar pressure and airway resistance during maximal and submaximal respiratory efforts.

A digital computing technique was used to extract continuous calculations of average alveolar pressure and airway resistance from body plethysmographic measurements during forced inspiratory and expiratory vital capacity maneuvers and tidal breathing in human subjects. Derived alveolar pressures were similar to those obtained using an interrupter technique (linear regression slope, 0.99 +/- 0.02; r = 0.98) and by comparison with esophageal pressure measurements. Studies in normal subjects revealed a characteristic pattern of increasing airway resistance throughout the expiratory phases of maximal and submaximal respiratory maneuvers, with maximal resistance of 33 to 110 cm H2O/L/s at low lung volumes during forced vital capacities. In contrast, inspiratory resistance remained low and constant throughout maximal and submaximal inspiratory maneuvers. Patients with COPD showed substantially higher inspiratory and expiratory resistances. In three patients with flow-volume loops suggestive of variable extrathoracic upper airway obstruction, measurements of alveolar pressure and airway resistance made it clear that two of the patients had upper airway obstruction, whereas the other was exerting an inadequate effort. We conclude that this noninvasive technique provides valid estimates of alveolar pressure and airway resistance continuously throughout both phases of the respiratory cycle over a wide range of volumes and flow rates. It may prove to be useful in the assessment of effort and airway obstruction in patients with a variety of pulmonary conditions.

Adult↗
PubMed1989

Brain stem auditory evoked potentials in jaundiced Gunn rats.

Bilirubin encephalopathy causes potentially preventable brain damage and hearing loss. The site of auditory dysfunction is controversial, despite pathologic studies showing damage to brain stem auditory nuclei in humans and experimental animals. We studied the effects of bilirubin toxicity on the auditory system of homozygous jaundiced Gunn rats by use of brain stem auditory evoked potentials. Small but statistically significant abnormalities were found for wave latencies, interwave intervals, and amplitudes.

Animals↗
PubMed1988

Development of brainstem auditory evoked potentials in heterozygous and homozygous jaundiced Gunn rats.

Bilirubin toxicity is a significant clinical problem causing neurologic and audiologic sequelae. To better understand the pathogenesis of bilirubin toxicity in the immature nervous system we studied the development of brainstem auditory evoked potentials (BAEPs) in jaundiced (jj) Gunn rats and their non-jaundiced (Jj) littermates. Littermate pairs of Jj and jj rats were studied serially from early infancy to adulthood. Replicated BAEPs to click stimuli at two different intensities (45 and 75 dB SPL) and rates (33 and 89/s) were obtained from animals anesthetized with ketamine and acepromazine and maintained at a constant rectal temperature. Jaundiced (jj) rats had increased latencies of waves II and III and the I-II and I-III intervals, and decreased amplitudes of waves II and III from 17 days of age through adulthood. For both groups, all latencies and interwave intervals decreased with age (P less than 0.0001 for each wave and interwave interval by repeated measures ANOVA), and the amplitude of II increased with age (P less than 0.0001). No group differences were found in wave I latency or amplitude, or in the latency change of waves I, II or III as a function of intensity (about 11 microseconds/dB at all ages), suggesting that peripheral auditory function is normal in jj rats. Finally, there were no different effects of stimulation rate on BAEP wave latencies between groups. The findings suggest dysfunction of the central (brainstem) auditory pathways at and rostral to the cochlear nuclei, and are consistent with studies showing destruction of the cochlear nuclei in this animal model and in humans with bilirubin toxicity. The central abnormalities previously found in adult, jaundiced rats are now demonstrated in animals as early as 17 days of age, when serum bilirubin concentration is maximum. The BAEP findings are similar to changes found in hyperbilirubinemic human neonates, and support the use of the Gunn rat animal model for the study of bilirubin encephalopathy.

Acoustic Stimulation↗
PubMed1988

Acute brainstem auditory evoked potential abnormalities in jaundiced Gunn rats given sulfonamide.

Bilirubin toxicity produces significant neurologic and audiologic sequelae. Successful therapeutic intervention requires an understanding of the timing of neural dysfunction after exposure to bilirubin. BAEP were used in an animal model of bilirubin encephalopathy to study the onset of neural dysfunction after acute injection of a sulfonamide used to displace bilirubin out of the bloodstream and into tissue. Fourteen pairs of jaundiced Gunn rats from eight litters were studied at postnatal day 18. Baseline BAEP recordings were performed in anesthetized animals; then either sulfadimethoxine or an equal volume of saline was injected into the peritoneum. Another BAEP was done immediately, and then 2, 4, and 8 h after injection. Human serum albumin was injected into an additional 10 animals after the 2-h BAEP recording to see if induced BAEP abnormalities could be corrected. The sulfonamide-treated jj rats developed increased latencies for waves II and III, and I-II and I-III interwave intervals (p less than 0.0001). The latencies were prolonged by 2 h after injection and became progressively longer at 4 and 8 h. The amplitudes of waves II and III progressively decreased at 2, 4, and 8 h (p less than 0.0001). Latency and amplitude of waves I and IV did not change. The rats injected with albumin at 2 h showed improvement of BAEP abnormalities at 8 h. These studies show that neurophysiologic abnormalities occur as early as 2 h after intraperitoneal injection of sulfadimethoxine, and are reversible with appropriate therapy. These abnormalities are hypothesized to be due to the sulfonamide driven net transfer of free, toxic bilirubin into the central nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Effect of metoprolol on the submaximal stress test performed early after acute myocardial infarction.

To determine the effect of beta-adrenergic blockade on the submaximal stress test after acute myocardial infarction (AMI), 36 post-AMI patients performed their treadmill test on 2 separate days, with and without metoprolol, in a double-blind, placebo-controlled, crossover design study. Rest and peak submaximal exercise heart rate was diminished by 100 mg of metoprolol administered twice daily (from 84 +/- 3 to 68 +/- 2 beats/min, p less than 0.001, and from 126 +/- 3 to 97 +/- 2 beats/min, p less than 0.001, respectively) compared with placebo. Rest and peak submaximal systolic blood pressure was also decreased (from 121 +/- 3 to 108 +/- 2 mm Hg, p less than 0.001, and from 151 +/- 4 to 124 +/- 3 mm Hg, p less than 0.001). Exercise-induced ST-segment depression of 1 mm or more from baseline occurred in 12 patients taking placebo. However, only 4 of these patients had ST depression when they exercised while taking metoprolol (p less than 0.05). Angina pectoris occurred in 4 patients taking placebo but in only 1 of these taking a beta-blocking drug. It is concluded that beta-blocking therapy renders the post-AMI submaximal stress test less sensitive for markers of exercise-induced ischemia than if the test is performed without the drug. Therefore, when using the prognostic information of published studies, it is important to define the conditions surrounding the exercise test.

Adult↗
PubMed1985

Cause of hearing loss in the high-risk premature infant.

Bilateral hearing loss occurred in 9.7% of infants who survived despite very low birth weight (less than or equal to 1500 gm), 16.7% of infants who survived neonatal seizures, and 28.6% of infants who survived both low birth weight and neonatal seizures. All neonates received treatment in a single neonatal intensive care unit between 1976 and 1980. Twenty-two of 36 hearing-impaired children were normal physically and mentally, with IQ scores of greater than or equal to 85. Significant neonatal predictors of hearing loss in high-risk premature infants (less than or equal to 36 weeks gestation), as determined by multivariable testing, were prolonged respirator care, high serum bilirubin concentration, and hyponatremia. Exchange transfusions were associated with a decreased risk of hearing loss.

Audiometry, Evoked Response↗
PubMed1984

Brain-stem auditory evoked potentials in rats with high-dose pentobarbital.

Brain-stem auditory evoked potentials (BAEPs) are relatively resistant to alteration by barbiturate drugs, but the effects of the high doses that are used clinically to produce deep barbiturate coma for the treatment of intracranial hypertension and postischemic anoxic encephalopathy on BAEPs are unknown. We gave high-dose pentobarbital infusions to mechanically ventilated rats while recording serial BAEPs from the scalp. Pentobarbital progressively suppressed and then abolished all peaks. First the later waves, then all but the first wave, and finally all waves were abolished at intravenous doses of 120, 220, and 260 mg/kg, respectively, in addition to the initial anesthetic dose of 60 mg/kg i.p. The changes were at least partially reversible; peaks returned in reverse order of their disappearance. Peak latencies increased with dose. The results show a significant effect of pentobarbital on BAEPs in the rat, suggesting that BAEPs may be useful in assessing the depth of and recovery from barbiturate coma.

Animals↗
PubMedDate not supplied

Cochlear microphonics in the jaundiced Gunn rat.

INTRODUCTION: Bilirubin toxicity causes brain damage and deafness. Brainstem auditory areas are damaged, but the effects of bilirubin toxicity on the peripheral auditory system are less well defined. As a first step in the study of cochlear physiology, we performed studies of scalp-derived cochlear microphonic (CM) responses in the jaundiced (jj) Gunn rat model of acute bilirubin toxicity. MATERIALS AND METHODS: CMs were obtained from scalp needle electrodes in response to acoustically delayed 500-, 1,000-, 2,000-, 4,000-, 6,000-, and 8,000-Hz tonebursts delivered by overhead speakers, and brainstem auditory-evoked potentials (BAEPs) were obtained to clicks. At 18 days of age, one nonjaundiced (Nj) and two jj Gunn rats in each of four litters were anesthetized. CMs and BAEPs were performed before and 4 hours after either (1) sulfonamide was injected into jj rats to produce acute bilirubin toxicity, (2) jj controls were injected with saline, or (3) Nj controls were given sulfonamide. In a second experiment, 16-day-old jj-sulfa and Nj-saline littermates were studied with insert speakers at 60 and 75 dB hearing level (HL) at baseline and 6 hours later, and CM amplitude was analyzed with a fast fourier transformation. RESULTS: No statistically significant differences were found by repeated measures analysis of variance in the CMs in either experiment between groups or after sulfonamide, despite BAEP changes of decreased amplitude of waves II and III and increased latency of I-II and I-III interwave intervals in jjs given sulfa. CONCLUSION: Alterations of CM after acute bilirubin toxicity did not occur at a time when there was electrophysiologic evidence of brainstem dysfunction. Although more subtle effects might be detected with a larger sample studied at longer intervals after the insult, CM seems insensitive or less sensitive to acute bilirubin toxicity than brainstem auditory function. These results suggest that retrocochlear tests of central auditory function may be more sensitive to the effects of hyperbilirubinemia than tests of peripheral auditory function in humans.

Acoustic Stimulation↗
PubMedDate not supplied

Pulmonic valve endocarditis as an underdiagnosed disease: role of transesophageal echocardiography.

Pulmonic valve endocarditis is a rare clinical entity. In spite of an increase in the frequency of right-sided endocarditis, primarily it is the tricuspid valve that is involved. Two-dimensional transthoracic echocardiography has improved our ability to diagnose infective endocarditis but has not identified many cases of pulmonic valve endocarditis. With the use of transesophageal echocardiography, three recent cases of pulmonic valve endocarditis were diagnosed by our laboratory. Each of these patients had clinical evidence of right-sided endocarditis, yet routine transthoracic echocardiograms failed to identify any pulmonic valve abnormalities. The true incidence of pulmonic valve endocarditis may be higher than previously reported, and the transesophageal echocardiogram is the preferred method for identifying and evaluating pulmonic valve endocarditis in adults.

Adult↗
PubMedDate not supplied

Use of transesophageal echocardiography during thrombolysis with tissue plasminogen activator of a thrombosed prosthetic mitral valve.

Inadequate anticoagulation in patients with mechanical prosthetic heart valves can result in a significant incidence of thromboembolic complications. An even more life-threatening complication is massive thrombosis of the valve itself. Thrombolytic therapy was given to a moribund 22-year-old woman with intractable heart failure caused by a thrombosed St. Jude prosthetic mitral valve (St. Jude Medical, Inc., St. Paul, Minn.). Although this form of therapy has been used before, this is the first report of a case in which transesophageal echocardiography was performed during thrombolytic therapy to continually record successful thrombolysis of the clotted prosthetic valve. Serial imaging during thrombolysis displayed progressive dissolution of the thrombus and progressive improvement in valve function. Transesophageal echocardiography is helpful in the diagnosis of prosthetic valve thrombosis and has the ability to monitor continually the effect of treatment with thrombolysis. Although thrombolytic therapy with recombinant tissue plasminogen activator is effective in treating prosthetic valve thrombosis, it carries a high risk for serious thromboembolic complications and thus should be reserved for critically ill patients who are too sick to undergo immediate surgery.

Adult↗