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Biomedical subjects

P C Njemanze

Publications and source records attributed to P C Njemanze.

At least 19 recordsLinked to original sources
PubMed1999

Application of risk analysis and geographic information system technologies to the prevention of diarrheal diseases in Nigeria.

Among the poor in developing countries, up to 20% of an infant's life experience may include diarrhea. This problem is spatially related to the lack of potable water at different sites. This project used risk analysis (RA) methods and geographic information system (GIS) technologies to evaluate the health impact of water source. Maps of Imo State, Nigeria were converted into digital form using ARC/INFO GIS software, and the resulting coverages included geology, hydrology, towns, and villages. A total of 11,537 diarrheal cases were reported. Thirty-nine water sources were evaluated. A computer modeling approach called probabilistic layer analysis (PLA) spatially displayed the water source at layers of geology, hydrology, population, environmental pollution, and electricity according to a color-coded five-point ranking. The water sources were categorized into A, B, and C based on the cumulative scores < 10 for A, 10-19 for B, and > 19 for C. T-test showed revealed significant differences in diarrheal disease incidence between categories A, B, and C with mean +/- SEM values of 1.612 +/- 0.325, 6.257 +/- 0.408, and 15.608 +/- 2.151, respectively. The differences were significant between categories A and B (P = 0.0000022), A and C (P = 0.0000188), and B and C (P = 0.0011348). The PLA enabled estimation of the probability of the risk of diarrheal diseases occurring at each layer and solutions to eliminate these risks.

Adolescent↗
PubMed1996

Cerebral lateralization in random letter task in the visual modality: a transcranial Doppler study.

Seven right handed volunteers were studied to determine cerebral lateralization patterns for a visually presented random letter task. The subjects participated in three conditions, which included resting baseline, passive fixation (nonlinguistic), and random letter (linguistic) tasks. Mean blood flow velocity (MBFV) was recorded using bilateral simultaneous transcranial Doppler measurements in the posterior cerebral arteries in these conditions. The experimental conditions produced an increase in MBFV during both tasks but the linguistic task showed a greater change. There was a tendency toward right lateralization with the linguistic compared to the nonlinguistic tasks. There is a physiological correlate of right hemisphere participation in the processing of the random letter task.

Adolescent↗
PubMed1994

Cerebrovascular dysautoregulation syndrome complex--brain hypoperfusion precedes hypotension and cardiac asystole.

A 43-year-old male with history of recurrent episodes of syncope, non-sustained wide complex tachycardia and structurally normal heart was studied. Syncope was induced with upright tilt provocation, while monitoring cerebral blood flow velocity with Doppler ultrasound, concurrently with invasive blood pressure, heart rate and rhythm determination. Postural induced cerebral hypoperfusion preceded hypotension and cardiac asystole. Treatment with ephedrine and transdermal scopolamine was effective in preventing symptoms.

Adult↗
PubMed1993

Isoproterenol induced cerebral hypoperfusion in a heart transplant recipient.

To determine the effect of tilt isoproterenol provocation on cerebral perfusion in a patient with denervated heart, transcranial Doppler sonography was used to assess changes in cerebral blood flow velocity during upright tilt test. A 51-year-old man with history of syncopal spells after heart transplantation was evaluated by using upright tilt test with and without isoproterenol for 30 minutes, respectively, at 80 degrees inclined. Mean cerebral blood flow was measured in the main stem of the right middle cerebral artery. Blood pressure and heart rate were noninvasively monitored. Tilt isoproterenol provocation but not tilt alone induced a significant reduction in cerebral blood flow velocity, without remarkable hypotension. There was no change in respiratory activity. This may indicate that vagal reflexes are not implicated in the mechanism of isoproterenol to induce cerebral hypoperfusion and hence neurally mediated syncope.

Blood Flow Velocity↗
PubMed1993

Perfusion of the visual cortex during pressure breathing at different high-G stress profiles.

The effects of pressure breathing for G protection (PBG) on perfusion of the visual cortex were studied in a subject during various high-G stress profiles. Blood flow velocity was measured in the posterior cerebral artery using a transcranial Doppler (TCD) ultrasound instrument. The G profiles examined included gradual and rapid onset rates. Mean cerebral blood flow velocity (MCBFV) declined with increasing +Gz with G-suit protection alone. The MCBFV increased in direct proportion with increase in +Gz acceleration with PBG. The mediating mechanisms for the effects of PBG may include improved gaseous exchange, the diminished sympathicoadrenal discharges, and cardiopulmonary reflexes. A role for TCD in further research is indicated.

Adult↗
PubMed1993

Cerebral circulation dysfunction and hemodynamic abnormalities in syncope during upright tilt test.

OBJECTIVE: To assess the hemodynamic features, including monitoring of cerebral circulation, blood pressure and heart rate, in syncope patients during upright tilt test. DESIGN: Nonrandomized sequential patients with history of syncope of uncertain etiology compared with healthy subjects. SETTING: Noninvasive hemodynamic laboratory of a tertiary referral centre. PATIENTS: Twenty patients with history of syncope and 10 controls without syncope. PROCEDURES: Transcranial Doppler measurement or middle cerebral artery flow velocity, noninvasive and invasive blood pressure monitoring, electrocardiography and pulse oximetry monitoring during upright tilt testing. Measurements were taken in patients at the height of symptoms in supine and upright posture. MAIN RESULTS: Ten patients, while still normotensive, had a drop of 53 +/- 10% (mean +/- SD) in cerebral bloodflow velocity (P = 0.0001) and an increase in heart rate by 58 +/- 35%. The remaining 10 patients had a 58 +/- 15% reduction in cerebral bloodflow velocity (P = 0.0001), a drop in blood pressure of 33 +/- 8% (P = 0.0001) and no change in heart rate. The controls showed no significant changes in cerebral bloodflow velocity and a 25 +/- 12% increase in heart rate (P = 0.0002). CONCLUSIONS: Transcranial Doppler monitoring of cerebral bloodflow velocity during upright tilt testing may improve insight into the complex physiology of syncope.

Adult↗
PubMed1992

Cerebral lateralization and color perception: a transcranial Doppler study.

Eight normal subjects were examined in dark, light and color conditions. Mean cerebral blood flow velocity (MBFV) were recorded almost simultaneously from their posterior cerebral arteries (PCA) using transcranial Doppler (TCD) ultrasound. The side-to-side difference was significant during the dark (p = 0.0159) and color stimulation (p = 0.0001) but not in light condition. This side-to-side difference in MBFV was used to characterize lateralization of color perception. This showed that the right PCA was always greater than the left during the presentation of color stimuli. Primary psychological colors (blue, yellow, red and green) induced greater lateralization as compared with color resulting from a mixed blue-green wavelength. This suggests that the right visual cortex is selectively sensitive to wavelengths.

Adolescent↗
PubMed1992

Critical limits of pressure-flow relation in the human brain.

BACKGROUND: This study was designed to determine the minimal mean flow velocity and pressure-flow relation necessary to preserve human consciousness. METHODS: Passive upright tilt provocation was used in conjunction with transcranial Doppler in 80 patients with a history of syncope of unknown etiology. Cerebral blood flow velocity, blood pressure, and heart rate were monitored noninvasively. RESULTS: Forty patients remained asymptomatic, and the rest had clinically induced true syncope or premonitory symptoms. In the asymptomatic group, there was a 23 +/- 16% (p = 0.000) drop in mean flow velocity, but no significant changes in systolic and diastolic blood pressures. In the symptomatic patients, there was a 58 +/- 14% (p = 0.000) drop in mean flow velocity, 37 +/- 23% (p = 0.000) fall in systolic pressure, and 31 +/- 20% (p = 0.000) fall in diastolic pressure. In 80% of symptomatic patients, the critical lower limit of mean flow velocity was at -50% of resting baseline while patients were lying supine. The symptomatic group had lower mean flow velocity and blood pressure responses as compared with the asymptomatic group. The slope and intercept values of the pressure (y axis) to flow velocity (x axis) regression curves indicate a greater degree of impaired autoregulation in the symptomatic group (y = 0.529 x-6.11, r2 = 0.108, p = 0.038) as compared with the asymptomatic (y = 0.317 x + 0.966, r2 = 0.14, p = 0.017). CONCLUSIONS: The critical lower limit of cerebral perfusion lies at 50% below baseline supine mean flow velocity.

Adolescent↗
PubMed1992

Effect of cardiac dysfunction upon diastolic cerebral blood flow.

The transcranial Doppler (TCD) studies performed in 54 patients with various forms of cardiac dysfunction were reviewed and the results compared with those of normal individuals. There were 4 patients with aortic insufficiency, 5 being treated by intra-aortic balloon pumps, 12 patients with atrial fibrillation, 11 with syncope, and 22 undergoing cardiopulmonary resuscitation. In all instances, significantly low or even absent diastolic cerebral perfusion was found. The importance of this parameter, in the future evaluation and management of similar patients, is discussed.

Cardiovascular Diseases↗
PubMed1991

Cerebral lateralization in linguistic and nonlinguistic perception: analysis of cognitive styles in the auditory modality.

Twenty-two normal subjects (9 left-handers, 13 right-handers) and five dyslexic patients (3 right-handers, and 2 left-handers) were characterized by physiologic hemisphere dominance. The latter was determined by the response of the middle cerebral artery (MCA) blood flow velocity, measured using the transcranial Doppler (TCD) technique, to hypoventilation (hypercapnia). Using bilateral almost simultaneous TCD measurements of mean blood flow velocity in the MCA, lateralization was determined in response to linguistic and nonlinguistic paradigms. In relation to the linguistic paradigm, left-handers, showed lateralization to the physiologic nondominant hemisphere, while right-handers showed lateralization to the physiologic dominant hemisphere; dyslexic patients show trends opposite to those in normals.

Adolescent↗
PubMed1991

Fourier analysis of the cerebrovascular system.

We performed Fourier analysis of the middle cerebral artery blood flow velocity waveform envelope in 14 normal subjects (group A) and 15 patients, of whom five had arteriovenous malformations (group B), five had cerebral vasospasm (group C), and five had arterial hypertension (group D). Measurements were obtained under conditions of normocapnia, hypercapnia, and hypocapnia. The Fourier coefficients measured in the first five harmonics of the Doppler waveforms of group A were used as the reference baseline and were compared with the coefficients found in the other three groups. Group B showed significantly lower Fourier coefficients, while groups C and D showed higher coefficients (p less than 0.05). The elevation of the Fourier coefficients occurred in an alternating pattern in group C and a decremental pattern in group D. This distinction was attributed to possible differences in the underlying pathophysiological processes. The degree of vascular distensibility of the cerebral arterioles, inferred from the shape of the Fourier analysis curves, was compared in all four groups. Vascular distensibility was characterized as abnormal in arteriovenous malformations, vasospasm, and arterial hypertension. Fourier coefficients may be better indicators of cerebrovascular abnormalities than mean blood flow velocity in hypertension and pulsatility index in arteriovenous malformations, vasospasm, and hypertension.

Adult↗
PubMed1991

Transcranial Doppler evaluation of syncope: an application in aerospace physiology.

A non-invasive method which combines the simultaneous measurement of mean arterial blood pressure (MBP), heart rate (HR) and mean cerebral blood flow velocity (MFV) was used to monitor patients with history of syncope, in horizontal and vertical posture tilt at 80 degrees. MFV in the right middle cerebral artery was measured using a transcranial Doppler instrument (TCD). MFV decreased concurrently with the onset of symptoms, and at the time of syncope reached an average of 68% below pre-tilt values. At the same time MBP showed an average decline of 25%, and HR increased by 38%. There was no correlation between MBP and MFV, at the onset of tilt, presyncope and syncope. MFV, but not HR or MBP, showed significant transition from one condition to the other. These data suggest that there may be a useful application of TCD measurements of MFV in aeromedical evaluation of syncope or syncopal tendency. These measurements would necessarily be used in conjunction with a tilt-table procedure. The possibility exists that MFV might be useful to preclude the actual occurrence of syncope in test subjects, or to show an abnormal tendency toward syncope, but will require more extensive testing than that carried out in the present study.

Adult↗