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Biomedical subjects

G J Scheffer

Publications and source records attributed to G J Scheffer.

At least 55 records · Page 3Linked to original sources
PubMed1996

Atracurium induced vasodilatation is not mediated by histamine in the isolated femoral artery of the rabbit.

Atracurium causes a decrease in systemic vascular resistance (SVR) and mean arterial blood pressure (MAP) which has been ascribed to histamine release. However, histamine receptor blockade does not prevent these decreases completely. The hypotensive side effects of atracurium may not only be caused by histamine. In this study we examined the vasoactive effects of atracurium with and without histamine receptor blockade in an isolated femoral artery preparation of the rabbit. We also investigated whether vasodilatation caused by atracurium depends on the presence of endothelial cells. Tyrode perfused, rabbit femoral arteries were constricted with noradrenaline (NA) to +/- 70% of their passive diameter. Endothelial function was checked with acetylcholine (ACh). The vessels were divided into two groups. In both groups the responses to histamine (1.0-10(-6)M) and atracurium (3.2-10(-5)M) were determined. In group one (n = 5), the histamine and atracurium responses were repeated during histamine receptor blockade. In group two (n = 5), the diameter responses to histamine and atracurium before and after endothelium removal were compared. Also, some vessel segments (n = 5) were histologically prepared and examined for mast cells. The vasodilatory responses to atracurium both with and without histamine receptor blockade were the same. Removal of endothelium caused an increase in the histamine response, while the dilating response to atracurium remained constant. We conclude that in the isolated femoral artery of the rabbit, atracurium induces, vasodilatation that is not mediated by histamine release and cannot be prevented with histamine receptor blockade. The mechanism of atracurium induced dilation is independent of the endothelium and is located in the smooth muscle cell.

Acetylcholine↗
PubMed1996

Standardization of non-invasive impedance cardiography for assessment of stroke volume: comparison with thermodilution.

Since its introduction by Kubicek and colleagues, impedance cardiography has been suggested as a non-invasive, simple, safe and cost-effective method of measuring stroke volume. Several controversial reports on its validity have been published. Pitfalls of this method included the nature of the electrode system and the validity of the equations. Therefore, the purpose of this study was to compare two different spot electrode arrays and the two most frequently used stroke volume equations with each other and with thermodilution. In 37 patients, 24-36 h after cardiac surgery, we performed simultaneous measurements of stroke volume with impedance cardiography (SVIC) and with thermodilution (SVTD). SVIC was obtained using the lateral spot (LS) electrode array, according to Bernstein, and a newly proposed modified semi-circular (MSC) spot electrode array. The equations of Kubicek and Sramek-Bernstein were used to calculate SVIC. The Sramek-Bernstein equation was valid only when the LS array was used; the Kubicek equation determined SVTD correctly only when the MSC array was used. However, a considerably better correlation and agreement (mean difference (2 SD)) was found between SVIC and SVTD for the latter (r = 0.90, 0.5 (17.1) ml vs r = 0.64, -4.9 (31.8) ml for the Sramek-Bernstein equation). We conclude that the most valid measurement of stroke volume using impedance cardiography was obtained when the MSC array was used together with Kubicek's equation.

Adult↗
PubMed1995

Effects of ketanserin on heart rate and blood pressure variability: implications for the effect on the baroreflex mechanisms.

Ketanserin is an antihypertensive drug with affinity to both serotonin S2- and alpha 1-adrenoceptors. The specific effects of ketanserin on the baroreflex are not fully understood. We, therefore, studied baroreflex regulation based on blood pressure (BP) and heart rate (HR) responses to several maneuvers before and after the administration of 2 x 5 mg of ketanserin i.v. both in supine and in standing posture. Seven young healthy volunteers were investigated. We measured spontaneous variability in HR and BP (Finapres), and performed deep inspiration, Valsalva, and lying-to-standing tests. We also used a modified Valsalva maneuver that consist of Deep Inspiration Breath-holding with closed glottis and EXpiration: DIBEX maneuver. From the BP recordings, peripheral resistance (TPR) and stroke volume (SV) were estimated by the Modelflow method. Thirty minutes after the administration of ketanserin, there was no significant change in mean HR, BP, spectral power of HR and BP variability, baroreflex sensitivity, or Valsalva ratio. Thus ketanserin did not affect the cardiac baroreflex mechanism. However, in standing position, SV increased and TPR decreased under the influence of ketanserin, and BP overshoot after the Valsalva and DIBEX maneuver was significantly decreased as well. There was also no reflex recovery of BP during the DIBEX maneuver in three volunteers, who felt faint. These observations indicate that there is a lack of vasoconstriction. We conclude that ketanserin is not a vasodilator but seems to inhibit vasoconstriction.

Adult↗
PubMed1995

Endoluminal pulse oximetry in ischemic colon in a swine model.

BACKGROUND: Postoperative sigmoidal ischemia after aortic grafting is a severe complication. No simple methods are available to detect this entity at an early stage. This study was done to monitor for sigmoidal ischemia with a new endoluminal probe based on pulse oximetry (SmO2). STUDY DESIGN: A prospective controlled animal study was done. Five pigs with low flow in the caudal mesenteric artery (20 percent of the basal flow) and four pigs in a control group were included. General and local circulatory parameters were monitored in the carotid and pulmonary artery and in the caudal mesenteric vein (CMV). Mucosal biopsy specimens were taken for histologic examination. Statistical analysis was done with the Wilcoxon and Mann-Whitney rank sum test and with analysis of variance. RESULTS: During the first two hours of ischemia, no sigmoidal pulse was detected. During the third hour, in three pigs the pulse curve reappeared with a SmO2 of 48 to 88 percent. After two hours, the mean oxygen saturation in the CMV of the ischemic group was 64 percent (compared with the control group, 77 percent, p < 0.05). After one hour, the mean lactate concentrations were 2.0 and 1.3 mmol per L, respectively (p < 0.05). Significant histologic changes occurred with neutrophilic infiltration in the crypts, in the lamina propria, and in the submucosa. CONCLUSIONS: Low-flow sigmoidal ischemia can be detected and monitored with endoluminal pulse oximetry in this model of early sigmoidal ischemia.

Analysis of Variance↗
PubMed1994

Effects of epidural analgesia and atropine on heart rate and blood pressure variability: implications for the interpretation of beat-to-beat fluctuations.

Cardiovascular variables such as heart rate, arterial blood pressure, stroke volume and the shape of electrocardiographic complexes all vary beat-by-beat. This variability occurs because of the dynamic response of cardiovascular regulatory systems to perturbations in cardiovascular function. We applied spectral analysis to the effects of sympathetic vasomotor blockade by epidural analgesia and parasympathetic blockade of the heart by atropine on the beat-to-beat variability of heart rate and blood pressure in humans. High-frequency fluctuations in heart rate (+/- 0.2 Hz) are caused by respiratory induced fluctuations of blood pressure, mediated by the vagus nerve. Low-frequency fluctuations (0.06-0.12 Hz) are related to sympathetic baroreflex control of vasomotor activity and heart rate. In our study, even partial parasympathetic blockade of the heart by atropine decreased the power in the high and low frequency heart rate fluctuations. There were no significant changes in blood pressure fluctuations in either frequency range. Sympathetic blockade by epidural analgesia decreased only low-frequency fluctuations of both heart rate and blood pressure. From a cardiovascular model and our experimental results we support the view that high frequency fluctuations in heart rate are due to the vagal response to blood pressure fluctuations caused by respiration and that the fluctuations around 0.1 Hz in both heart rate and blood pressure have their origin in the sympathetic baroreflex control loop of vasomotor activity.

Adolescent↗
PubMed1993

Noninvasive continuous blood pressure measurement: a clinical evaluation of the Cortronic APM 770.

The Cortronic APM 770 (Cortronic, Ronkonkoma, NY) is a commercial device that claims to measure blood pressure noninvasively and continuously with the use of a standard blood pressure cuff. The aim of our study was to assess the performance of the continuous-mode blood pressure readings of the Cortronic during anesthesia and surgery. We recorded blood pressure in 5 patients bilaterally. An interaarterial pressure (IAP) curve was recorded from 1 arm and the Cortronic pressure curve (CPC) was recorded from the other. For statistical analysis the period between 2 Cortronic recalibrations was defined as the intercalibration interval. The duration of these intervals ranged from 20 to 0.5 minutes. Four paired samples were drawn from each interval. The first sample in an interval represented the recalibration blood pressure; the other samples represented the continuous blood pressure. A total of 1,232 samples were taken, of which 308 were recalibration. The median of the differences and the 2.5th and 97.5th percentile limits of agreement were determined. Their respective values for diastolic and systolic recalibration measurements were 5, -17, and 34 mm Hg, and 6, -12, and 38 mm Hg. Their values for continuous measurements were 4, -23.5, and 32 mm Hg, and 6, -30, and 70 mm Hg. Changes in CPC were evaluated against changes in the corresponding IAP by plotting them in 4-quadrant graphs. In these graphs the Spearman rank correlations were between r = -0.17 and r = 0.01. We observed opposite CPC and IAP trends on 24 occasions during this study. We performed a simple simulation study to better understand the measurement method of the Cortronic.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Oxygen consumption after cardiopulmonary bypass--implications of different measuring methods.

OBJECTIVE: To determine whether intra-pulmonary oxygen consumption or whole body oxygen consumption is the main determinant of the hypermetabolic response after cardiopulmonary bypass. Secondly, which method of measuring oxygen consumption best quantifies this hyperdynamic response. DESIGN: We measured oxygen consumption by analysing respiratory gas (VO2-gas), carbon dioxide excretion (VCO2), and respiratory exchange ratio (RER = VCO2/VO2), and calculated oxygen consumption using the Fick-method (VO2-Fick) and intra-pulmonary oxygen consumption (VO2-gas - VO2-Fick) in patients at fixed times before and after elective cardiac surgery. Next, comparisons were made between methods and also between measurements at different times before and after bypass. SETTING: University hospital. PATIENTS: 10 elective cardiac surgical patients. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: VO2-gas, VCO2 and RER were measured with an open circuit indirect calorimeter. VO2-Fick was calculated: VO2-Fick = cardiac index x (arterial - mixed venous oxygen content). Intrapulmonary oxygen consumption was calculated as the difference between VO2-gas and VO2-Fick. Both VO2-gas and VO2-Fick were about 20% higher after bypass than after induction of anaesthesia. Absolute values of VO2-gas were about 30% higher than VO2-Fick. Intra-pulmonary oxygen consumption accounted for 32% of whole body oxygen consumption after induction of anaesthesia and did not increase after bypass. CONCLUSION: Whole body oxygen consumption and not intra-pulmonary oxygen consumption is the main determinant of the hypermetabolic response after bypass. Increased intra-pulmonary oxygen consumption is not related to bypass. VO2-gas best quantifies this hypermetabolic response directly after bypass, and not VO2-Fick, VCO2 or intra-pulmonary oxygen consumption, since VO2-Fick excludes intra-pulmonary oxygen consumption and VCO2 does not reflect metabolism directly after bypass.

Aged↗
PubMed1993

The validity and reproducibility of the skin vasomotor test--studies in normal subjects, after spinal anaesthesia, and in diabetes mellitus.

Skin sympathetic vasomotor control can be examined in the extremities by the skin vasomotor test. In this test the change in skin blood flow and skin temperature in the hand and foot in response to a cold stimulus is utilized as an index of distal sympathetic nerve fibre integrity. This is of importance in conditions such as diabetes mellitus as peripheral autonomic neuropathy is associated with orthostatic hypotension and diabetic foot complications. The validity and reproducibility of the test as a marker of distal sympathetic nerve function has been studied. The test was performed in nine healthy control subjects and in nine subjects (undergoing minor surgery) after a sympathetic nerve conduction block (L2-L3) was achieved in the lower extremities by spinal analgesia. Changes in skin temperature (p < 0.001) and skin blood flow (p < 0.005) in responses to cooling were significantly larger in the control group than in the group with spinal analgesia. Repeated skin temperature measurements on 42 occasions (test-retest period of 4 weeks) in eight healthy and 34 diabetic subjects indicated a reliability coefficient of 80%. We conclude, therefore, that the skin vasomotor test provides a valid and reproducible quantitative assessment of skin sympathetic nerve function in upper and lower extremities.

Adult↗
PubMed1993

Effects of thiopentone, etomidate and propofol on beat-to-beat cardiovascular signals in man.

Analysis of beat-to-beat fluctuations of heart rate and blood pressure is a promising new approach to the clinical diagnosis and management of alterations in cardiovascular regulation. We investigated the effects of three induction agents on beat-to-beat heart rate and blood pressure fluctuations in man. Beat-to-beat fluctuations were analysed by spectral analysis. Two spectral areas are of main interest. One area is centred on the respiratory frequency and shifts with changes in respiratory rate (High Frequency area). These high frequency fluctuations in heart rate are caused by respiratory-induced blood pressure fluctuations, mediated by the vagus nerve through the baroreflex mechanism. Variability in the Low Frequency area, which occurs between 0.06 and 0.12 Hz is considered to be related to haemodynamic fluctuations due to the sympathetic baroreflex control loop of vasomotor activity and heart rate. Results from our study indicate that thiopentone, etomidate and propofol show considerable differences in their effects on beat-to-beat variability of heart rate and blood pressure. These differences can be explained by their specific effects on the cardiovascular system.

Adult↗
PubMed1993

Regional entrainment of atrial fibrillation studied by high-resolution mapping in open-chest dogs.

BACKGROUND: It recently has been demonstrated that during atrial fibrillation, a short and variable excitable gap exists, allowing regional control of atrial fibrillation by local stimulation. In the present study, we visualized the process of excitation during regional entrainment of atrial fibrillation by rapid pacing. METHODS AND RESULTS: In six open-chest dogs, the excitation of the left atrial free wall was mapped using a spoon-shaped mapping electrode (248 points). Episodes of atrial fibrillation were induced by burst pacing (50 Hz, 2 seconds). During atrial fibrillation, the electrograms showed rapid irregular activity with a median cycle length of 98 +/- 16 ms (mean +/- SD, n = 6). Rapid pacing in the center of the mapping electrode at intervals slightly shorter or longer than the median atrial fibrillation interval resulted in regional capture of atrial fibrillation. The window of entrainment was 16 +/- 5 ms. Mapping of atrial fibrillation showed that the left atrium was activated by fibrillatory wavelets coming from different directions. During entrainment, a relatively large area with a diameter of about 4 cm was activated by uniform wave fronts propagating away from the site of stimulation. The area of entrainment was limited by intra-atrial conduction block and by collision with fibrillation waves. Regional control of atrial fibrillation was lost by pacing either too slowly or too rapidly. In the first case, retrograde invasion of the area of entrainment by fibrillatory waves resulted in depolarization of the pacing site prior to the stimulus. Pacing too rapidly caused acceleration of atrial fibrillation by induction of local intra-atrial reentry circuits with a revolution time shorter than the pacing interval. CONCLUSIONS: During atrial fibrillation, an area with a diameter of about 4 cm can be entrained by local pacing. The resulting reduction in fibrillating tissue mass was not sufficient to terminate atrial fibrillation. Extension of the area of entrainment was limited by intra-atrial conduction block, whereas entrainment at a too high rate resulted in acceleration of atrial fibrillation by induction of local microreentry.

Animals↗
PubMed1991

Regional control of atrial fibrillation by rapid pacing in conscious dogs.

BACKGROUND: In five chronically instrumented conscious dogs, we studied the effects of rapid pacing on sustained electrically induced atrial fibrillation. METHODS AND RESULTS: Twenty-three unipolar atrial electrograms were recorded simultaneously from the bundle of Bachmann and the lateral wall of the right and left atria. During sustained atrial fibrillation, the surface electrocardiogram showed continuous irregularities of the baseline without P or F waves as well as an irregular ventricular rhythm with narrow QRS complexes. The atrial electrograms showed rapid irregular activity with a median cycle length of 85 +/- 8 msec and a range (P5-95) of 33 +/- 18 msec. Overdrive pacing of atrial fibrillation was performed using symmetric biphasic rectangular stimuli (2-msec duration, sixfold that of threshold) applied to a pair of stimulating electrodes at the left atrial appendage. Stimulation was started at pacing intervals of about 10 msec longer than the local median fibrillation interval and subsequently shortened in steps of 1 msec. At a critical pacing interval slightly shorter than the median fibrillation interval, the atrium around the pacing site was suddenly captured by the electrical stimuli. The area of local capture had a diameter of 6.1 +/- 1.6 cm. The time window of capture was 12 +/- 4 msec. CONCLUSIONS: These observations show that during electrically induced atrial fibrillation in chronically instrumented conscious dogs, a short excitable gap is present, permitting regional control of the fibrillatory process by rapid pacing.

Animals↗
PubMed1991

Atrial and His-Purkinje conduction times during isoflurane anaesthesia in humans.

The effect of isoflurane 2.0 MAC on human atrioventricular conduction time was studied. A non-invasive recording system for the detection of His-Purkinje potentials based on signal averaging techniques was used. Recordings were made in 15 patients before and after induction with isoflurane. We were able to measure atrial (P-H) and His-Purkinje (HPS) conduction times in 11 patients. Mean (+/- SEM) P-H conduction time decreased from 101.8 +/- 5.3 to 89.3 +/- 3.3 ms (P less than 0.01). HPS conduction times did not change significantly. Heart rate increased significantly from 86.7 +/- 4.2 to 94.9 +/- 4.7 beats min-1 (P less than 0.05). Systolic blood pressure decreased from 117.3 +/- 4.6 to 94.1 +/- 4.7 mmHg (P less than 0.05). It is concluded that the effects of isoflurane on supraventricular conduction time in humans depend on interactions of several different mechanisms.

Adolescent↗
PubMed1989

Ten-year follow-up study of islet-cell antibodies and childhood diabetes mellitus.

To find out whether subclinical autoimmunity precedes onset of nonfamilial insulin-dependent diabetes mellitus (IDDM), 4806 schoolchildren aged 5-19 years from a township in Holland were followed-up for at least ten years after blood was sampled for measurement of islet-cell antibodies (ICA). ICA positivity conferred a relative risk of IDDM of 533 (95% CI 145-1955). In the 10 years of follow-up 4 of the 8 ICA-positive subjects became insulin dependent, whereas the probability of being free of IDDM was 99.9% for those who were ICA-negative at the start of the study. The findings suggest that, although chronic autoimmunity involving the pancreatic beta-cells may precede non-familial IDDM by many years, a positive ICA test on a single occasion predicts the development of IDDM in only 4 out of 8 subjects over a period of 10 years.

Adolescent↗
PubMed1989

Effects of halothane on the conduction system of the heart in humans.

The effects of 2.0 MAC halothane on atrioventricular conduction times in humans were studied. A real-time recording system for the detection of surface His-Purkinje potentials based on signal averaging techniques was used. Recordings were made in 23 patients before and after the administration of halothane. In 18 patients we were able to measure atrial (P-H) and His-Purkinje (H-V) conduction times (78%). A small but statistically significant decrease in P-H conduction times from 115.3 +/- 3.9 (SEM) to 110.8 +/- 4.2 ms was found (P less than or equal to 0.01). H-V conduction times did not change significantly. Heart rates decreased significantly from 87.6 +/- 2.6 to 74.8 +/- 2.5 beats/min (P less than or equal to 0.01). Systolic blood pressures decreased from 118.9 +/- 3.7 to 103.6 +/- 4.2 mm Hg. It is concluded that the decrease in heart rate and the decrease in atrial conduction time caused by halothane can be explained by interactions of several different mechanisms. The specific combination of slowing heart rate and a decrease of atrial conduction time provides a possible explanation for atrial arrhythmias during the administration of halothane.

Adolescent↗
PubMedDate not supplied

Central venous catheter placement using the ECG-guided Cavafix-Certodyn SD catheter.

STUDY OBJECTIVE: To evaluate the clinical use of a new ECG-guided central venous catheter with regard to positioning in the superior vena cava (SVC). DESIGN: Prospective study. SETTING: Operating rooms of a university hospital and a general hospital. PATIENTS: 89 elective and emergency adult surgical patients requiring central venous catheterization perioperatively. INTERVENTIONS: We performed ECG-guided placement of the central venous catheter from several insertion sites. After we observed an intra-atrial p-wave (p-atriale), the catheter was withdrawn 3 cm back into the SVC. Postoperative anterior-posterior chest radiographs were performed for verification of tip localization. MEASUREMENTS AND MAIN RESULTS: In all 81 patients who exhibited a p-atriale that reverted to a normal-size p-wave (p-SVC) after withdrawal of the catheter 3 cm, the tip was located in the SVC or the SVC-right atrial junction on the chest radiograph. In 7 of the 8 cases without a p-atriale, the catheter tip was shown to be located at an incorrect position on the chest radiograph. The size of the p-atriale was always at least twice that of the p-SVC. CONCLUSIONS: Use of this wire-conducted intravascular ECG signal is a reliable tool for positioning the central venous catheter via various insertion sites. The technique proved to be an inexpensive, easy, and clear method. When a p-atriale is seen, uncomplicated insertions do not require radiologic guidance to control catheter tip position.

Adult↗