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Biomedical subjects

M Gevers

Publications and source records attributed to M Gevers.

12 recordsLinked to original sources
PubMed1997

Nuclear translocation of constitutive heat shock protein 70 during S phase in synchronous macroplasmodia of Physarum polycephalum.

The level of constitutive heat shock protein 70 (HSC70) in Physarum polycephalum was analyzed by means of Western blots during the synchronous cell cycle of macroplasmodia. Total amounts as well as nuclear and cytoplasmic contents were determined separately and evaluated densitometrically. A drastic increase of nuclear HSC70 was observed 10-40 min after the initiation of S phase (600% of the M phase value) and thereafter a slow decline toward the next M phase. Total HSC levels showed a slight (30%) increase during S phase whereas cytoplasmic HSC70 was about 30% lower during S phase compared to mitosis.

Animals↗
PubMed1996

Accuracy of oscillometric blood pressure measurement in critically ill neonates with reference to the arterial pressure wave shape.

OBJECTIVE: To perform further evaluation of the oscillometric device for neonatal arterial blood pressure (ABP) measurement, using a catheter-manometer system (CMS) for accurate intraarterial measurement. We aimed to describe the influence of the radial artery wave shape on oscillometric ABP determination, as pressure wave-shape influences the relationships between systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) in the wave. These relationships are part of the algorithms contributing to the final ABP determination in the oscillometric device. DESIGN: Intra-patient comparison of two blood pressure measurement systems. SETTING: Neonatal intensive care unit. PATIENTS: In 51 critically ill newborn infants, ABP was determined oscillometrically in the brachial artery and, simultaneously, invasively in the radial artery using a high-fidelity CMS. Clinical data of the infants were: gestational age: 29 (25-41) weeks; birthweight: 1200 (500-3675) g, postnatal age: 6 (2-46) h. METHODS: Statistical analysis was performed with the paired Student's t-test. Multiple regression analysis was used to determine the influence of birthweight and height of the blood pressure on the results. MEASUREMENTS AND MAIN RESULTS: In 51 infants, 255 paired values of SAP, DAP and MAP were recorded. In all recordings, we determined the relationship between SAP, DAP and MAP, using the equation: MAP = alpha%(SAP - DAP) + DAP. For SAP, DAP, MAP and alpha, we computed mean differences (bias) and the limits of agreement (precision). Biases for SAP, DAP, MAP and alpha were significantly different from zero (P < 0.001) and the limits of agreement for SAP, DAP and MAP were wide: 18.8 mmHg, 17.2 mmHg and 15.2 mmHg respectively. The relationship between invasive and noninvasive values is only partly (7-19%) influenced by the height of the blood pressure; low values of SAP, DAP and MAP tend to give overestimated oscillometric values. In the relationship between SAP, DAP and MAP, alpha was found to be 47% invasively (as generally found in the radial artery in newborns) and 34% noninvasively (as generally found in the brachial/radial artery in adults). CONCLUSIONS: Inaccuracy of the oscillometric device may be partly explained by the incorporation of an inappropriately fixed algorithm for final ABP determination in newborns. Care should be taken when interpreting the oscillometrically derived values in critically ill newborn infants.

Adult↗
PubMed1996

Bisferiens peaks in the radial artery pressure wave during patent ductus arteriosus in newborn infants: relationship with ascending aortic flow.

Previously, we found evidence that bisferiens peaks in the radial artery pressure wave in the newborn infant may suggest the presence of a left-to-right shunt through a patent ductus arteriosus (PDA). The purpose of the present study was to analyze the origin of this pulsus bisferiens. Starting from the assumption that the radial artery pressure wave form is similar to the aortic pressure wave form, as described previously, we attempted to explain the bisferiens peaks on the basis of echocardiographically obtained ascending aortic flow. We studied 11 preterm mechanically ventilated infants with a left-to-right shunt through a PDA and 7 without. Aortic volume flow was established echocardiographically, and radial artery blood pressure measurement was performed with a high fidelity cathetermanometer system. Ascending aortic peak flow during PDA was significantly higher in the case of PDA, compared with the case without PDA. An augmented peak flow with an abrupt decline after the high peak in PDA, resulting in a sharp pressure peak with a steep decline after the peak, was thought to explain the first sharp peak of pulsus bisferiens. An abrupt decline of flow after peak flow is thought to be due to the fast runoff of blood through the ductus. According to the pulsatile pressure dynamics theories, which state that pressure wave forms consist of forward and backward wave forms, the second peak of the pulsus bisferiens can be explained by the return of the reflected (backward) wave form when the forward wave form has already considerably decreased. We conclude that the bisferiens peaks found in PDA result from a combination of large stroke volume (augmented first peak) and large runoff (quick decline of the forward wave) before the return of the reflected wave.

Aorta↗
PubMed1995

Intra-arterial pressure measurement in neonates: dynamic response requirements.

A computer simulation of a catheter manometer system was used to quantify measurement errors in neonatal blood pressure parameters. Accurate intra-arterial pressure recordings of 21 critically ill newborns were fed into this simulated system. The dynamic characteristics, natural frequency and damping coefficient, were varied from 2.5 to 60 Hz and from 0.1 to 1.4, respectively. As a result, errors in systolic, diastolic and pulse arterial pressure were obtained as a function of natural frequency and damping coefficient. Iso-error curves for 2%, 5% and 10% were constructed. Using these curves, the maximum inaccuracy of any neonatal catheter manometer system can be determined and used in the clinical setting.

Blood Pressure Determination↗
PubMed1995

Bisferiens peaks in the radial artery pressure wave in newborn infants: a sign of patent ductus arteriosus.

Previously, we found evidence that radial artery pressure wave forms in newborns represent central aortic wave forms, provided that pressure is measured with adequate accuracy. Therefore, we postulated that the neonatal radial artery wave form, like the adult aortic wave form, may contribute to cardiovascular diagnosis. We investigated whether radial artery wave forms in infants suffering from patent ductus arteriosus (PDA) are different from the wave forms as seen without the presence of PDA. We studied 34 newborn infants with a radial artery line and with the possible clinical diagnosis of PDA with left-to-right shunt. On the basis of echocardiographic examination to assess PDA, these infants were divided in two groups: infants with PDA (n = 24) and without PDA (n = 10). In 15 out of 24 infants with PDA, recordings were repeated after ductal closure. Blood pressure measurement was performed with a high fidelity cathetermanometer system using a tip-transducer (natural frequency 95 Hz, damping coefficient 0.15). Contour analysis was performed by describing morphology of the waves during PDA and without PDA. In 23 out of 24 infants with PDA, a pulsus bisferiens was present: two peaks separated by a deep cleft. The average pressure difference between the first pressure peak and the cleft [delta Ppeak1] was 0.35 +/- 0.19 kPa, and the average difference between the cleft and the second pressure peak [delta Ppeak2] was 0.44 +/- 0.23 kPa. the ratio of mean magnitude of delta Ppeak1 and delta Ppeak2 was 0.81 +/- 0.26. None of the 10 infants without PDA showed pulsus bisferiens.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed1995

Radial artery blood pressure measurement in neonates: an accurate and convenient technique in clinical practice.

To achieve accurate blood pressure measurement through radial artery catheters in infants, we previously developed an experimental high-fidelity catheter-manometer system (CMS). As this system lacks facilities for flushing and for blood sampling, we aimed to further develop this technique in order to make the system suitable for clinical practice. In addition, we aimed to develop methods to automate processing of the pressure wave forms. The high-fidelity system to be improved consisted of a 24 Gauge catheter, a threeway stopcock and a tip-manometer. We inserted this system in the catheter-manometer system as routinely used i.e. the remaining end of the stopcock was connected to the fluid-filled CMS as used routinely. This combined system became clinically applicable, since blood samples could be obtained and flushing could be performed. The measurement chain was completed by application of a modified physiological monitor and a computerized method to analyze pressure wave forms. In this manner accurate beat-to-beat pressure parameters were obtained. This technique was applied to 25 neonates admitted for intensive care and requiring arterial access. Gestational age of these infants ranged from 25-40 (median 29) weeks and birth weight ranges from 500-3375 (median 1060) grams. In all infants the technique was found to be convenient and the high-fidelity blood pressure measurements were performed without any problems. The advantage of the present system is the potential for both correct intermittent recordings of arterial wave forms in close relation to clinical condition and for the establishment of accurate radial artery beat-to-beat pressure values in clinical practice.

Blood Pressure↗
PubMed1994

Prevention of air introduction in catheter-manometer systems for accurate neonatal blood pressure measurement: an in vitro study.

OBJECTIVE: Our objective was to find an optimum filling technique to prevent air entrapment in catheter-transducer systems. Ultimately, this may help achieve more accurate neonatal blood pressure measurement. METHODS: We first assembled a catheter-transducer system with a minimum of components fulfilling clinical requirements in neonatology. Then, we tested in vitro different filling techniques: flushing with CO2, flushing with alcohol, use of degassed filling liquid, and a combination of all three methods. After the filling procedure, dynamic response was determined by applying sinusoidal pressures. We calculated natural frequency (fn), damping coefficient (D), and the maximum frequency (fmax) up to which the amplitude response is uniform (+/- 10%). RESULTS: With the system filled in the usual clinical way, fmax was 27 Hz (fn = 94 Hz; D = 0.13). With application of the three methods separately, fmax increased to 34 to 39 Hz. With all methods combined, fmax increased to 51 Hz (fn = 182 Hz; D = 0.14). These techniques were not always successful. CONCLUSION: A clinical system can be assembled to fulfill the dynamic requirements for neonatal use. Dynamic response can be improved by special filling techniques. We fell that an in vivo quality test needs to be developed and evaluated in neonates to ensure accurate blood pressure measurements.

Air↗
PubMed1993

Arterial blood pressure wave forms in radial and posterior tibial arteries in critically ill newborn infants.

The aim of this study was to document arterial blood pressure wave forms at two sites along the arterial tree of the neonate: in the radial and posterior tibial arteries. Using a high-fidelity catheter tip-transducer system, peripheral arterial blood pressure wave forms in 26 critically newborn infants were studied. In 14 infants the radial artery and in 12 infants the posterior tibial artery was cannulated. Radial artery blood pressure waves resembled those of proximal aortic rather than those of the radial artery in adults. Quantitative analysis of the waves was performed to reassure this finding. Blood pressure waves obtained from posterior tibial artery resembled those of femoral artery rather than those of posterior tibial artery waves in adults. We conclude that radial and posterior tibial artery wave forms in neonates appear to have a central appearance. This phenomenon might be explained by the close proximity of the radial and posterior tibial artery to the central aorta and femoral artery respectively, due to the small and short limbs of the neonate. The finding allows an "easy central pressure look" at both ends of the neonatal aorta.

Birth Weight↗
PubMedDate not supplied

Calculated mean arterial blood pressure in critically ill neonates.

Mean arterial pressure (MAP) is the area under the pressure wave form averaged over the cardiac cycle. A widely used rule of thumb to estimate MAP of peripheral arterial pressure waves in adults is adding one-third of the pulse pressure (PP) to diastolic arterial pressure (DAP). However, radial artery pressure waves in newborns differ from those in adults and resemble proximal aortic pressure waves, so that the above-mentioned calculation of MAP may not be correct. The present study was set up to obtain an arithmetical approximation to derive MAP from blood pressure waves measured in the radial artery of the neonate. We accurately recorded about 300 invasively obtained blood pressure curves in the radial artery of 10 neonates admitted for intensive care. We found that MAP in the radial artery in these neonates can be well approximated by adding 46.6% PP to DAP (range 43.0-50.1%). We suggest that the rule of thumb to derive MAP from radial artery waves in the neonate to be approximately the average of systolic and diastolic pressure, as opposed to adding one-third of the pulse pressure to the diastolic value in the adult.

Blood Pressure↗
PubMedDate not supplied

Calculated mean arterial pressure in the posterior tibial and radial artery pressure wave in newborn infants.

Mean arterial pressure (MAP) is the area under the pressure wave averaged over the cardiac cycle, and therefore depends on pressure wave contour. A generally used rule of thumb to estimate MAP of peripheral arteries in adults is adding one-third of the arterial pulse pressure (PP) to diastolic arterial pressure (DAP). As peripheral pressure wave forms in neonates do not resemble adult peripheral wave forms, it may be expected that this rule of thumb does not hold for neonates. Previously, we found that MAP can be calculated by adding 50% PP to DAP in radial artery waves in neonates. In the present study, we investigated in neonates how MAP in the posterior tibial artery depends on systolic and diastolic pressure and we compared these findings to those found in the radial artery. Forty infants admitted for intensive care were studied. We analyzed 5000 invasively and accurately obtained blood pressure waves in the posterior tibial artery of 20 neonates and another 5000 waves similarly obtained from the radial artery in another group of 20 neonates. We found that MAP in posterior tibial artery waves is well approximated by adding 41.5 +/- 2.0% of PP to DAP, whereas MAP in radial artery waves can be calculated by adding 46.7 +/- 1.7% of PP to DAP. These values are significantly different (p < 0.0001). In conclusion, the rule of thumb as used in the adult to find MAP, where 33% PP is added to DAP, does not hold for the newborn. We recommend to calculate MAP in the tibial artery by adding 40% of PP to DAP and in the radial artery by adding 50% of PP to DAP.

Blood Pressure↗