Biomedical subjects

J Dankelman

Publications and source records attributed to J Dankelman.

At least 37 records · Page 2Linked to original sources

PubMed2001

Problems with laparoscopic instruments: opinions of experts.

INTRODUCTION: Laparoscopic surgery is particularly known for its complex technique, which calls for operative analysis of laparoscopic instruments. This study investigates the opinion of experts about clinical problems with instruments occurring during laparoscopic surgery. METHODS: A questionnaire was used to obtain the opinions of expert laparoscopic surgeons about difficulties experienced operatively using laparoscopic instruments. RESULTS: The laparoscopic surgeons indicated that coagulators were especially prone to cause complications of the gastro-intestinal tract, vascular injuries, and bile duct injuries. Dissectors were considered to play a role in the occurrence of solid organ and bile duct injuries, and retractors to cause solid organ injuries. Insufficient functionality of the instruments and insufficient quality of the image were indicated to contribute to the instrument's risks. CONCLUSION: The questionnaire identified technological deficiencies prone to cause operative complications. The results provide a basis for the interaction between surgeons and engineers, and serve as pilot information on which to base an in-depth object evaluation of instrument problems.

Dissection↗

PubMed2001

Evidence for stretch-induced resistance increase of proximal coronary microcirculation.

We investigated the influence of stretch on regional hemodynamic parameters of the septal circulation. We used a similar experimental setup and mathematical model, as described previously (14). Five ventricular septa were isolated from anesthetized dogs, sutured to a biaxial stretching apparatus, and perfused with an oxygenated perfluorochemical emulsion at maximal vasodilation. Under unloaded and biaxially stretched conditions, flow and septal thickness (to index vascular volume) were measured continuously. Pressure was varied sinusoidally at 30, 50, and 70 mmHg with amplitude of 7.5 mmHg over frequencies ranging between 0.015 and 7 Hz. Admittance (flow/pressure) and capacitance (thickness/pressure) transfer functions were calculated and interpreted in terms of a two-compartmental model with volume-dependent resistances. Parameter estimation showed that the proximal resistance and compliance were unaffected, whereas the resistance of the proximal part of the microcirculation, including the small arterioles, increased with stretch. The effect of stretch on the distal resistance and capacitance, however, could not be determined unequivocally.

Animals↗

PubMed2000

Dynamics of flow, resistance, and intramural vascular volume in canine coronary circulation.

Varying coronary volume will vary vascular resistance and thereby have an effect on coronary hemodynamics. Six ventricular septa were isolated from anesthetized dogs, dispersed in a biaxial stretch apparatus at diastolic stress, and perfused artificially with an oxygenated perfluorochemical emulsion at maximal vasodilation. Flow and thickness were measured continuously by an electromagnetic flow probe and sonomicrometer. Pressure was varied sinusoidally around 30, 50, and 70 mmHg with an amplitude of 7.5 mmHg; frequencies ranged between 0.015 and 7 Hz. Bode plots of admittance (flow/pressure) and capacitance (scaled thickness/pressure) were constructed. A two-compartment model was used in which the resistances vary with volume. Realistic values of microvascular compliance ( approximately 0.3 ml x mmHg(-1) x 100 g(-1)) were found. Values 10 times higher were then found when resistances were forced to be constant. We concluded that volume dependence of resistances have to be taken into account when dynamic or static pressure-flow relations are studied and conceal the effect of a large intramyocardial compliance on arterial hemodynamics.

Animals↗

PubMed2000

Myogenic reactivity and resistance distribution in the coronary arterial tree: a model study.

The objectives of this study were to evaluate the myogenic behavior of blood vessels and their interaction within the coronary arterial tree and to evaluate the possible role of the myogenic response in autoregulation. The model consists of 10 compartments in series, each representing a class of vessel sizes. Diameter and resistance in each class are determined by their value at full dilation (d(p,) R(p)) and by the myogenic response. Three distributions of R(p) and three distributions of myogenic strength, M(i) (slope of pressure-diameter curve, range -0.05 to -0.4%/mmHg) were evaluated (9 cases). It was found that larger vessels attenuate the myogenic activity of smaller vessels and that myogenic responsiveness is sufficient to achieve autoregulation. When M(i) has a maximum in vessels of 84 microm, the maximum effect of perfusion pressure on active diameter occurs in vessels between 123 and 181 microm, depending on the distribution of R(p). Distribution of resistance and control mechanisms in the coronary arterial tree are important for interpretation of individual vessel responses as observed in vivo.

Algorithms↗

PubMed1999

Prolonged diastolic time fraction protects myocardial perfusion when coronary blood flow is reduced.

BACKGROUND: Because coronary blood flow is impeded during systole, the duration of diastole is an important determinant of myocardial perfusion. The aim of this study was to show that coronary flow modulates the duration of diastole at constant heart rate. METHODS AND RESULTS: In anesthetized, open-chest dogs, diastolic time fraction (DTF) increased significantly when coronary flow was reduced by lowering perfusion pressure from 100 to 70, 55, and 40 mm Hg. On average, DTF increased from 0.47+/-0.04 to 0.55+/-0.03 after a pressure step from 100 to 40 mm Hg in control, from 0.42+/-0.04 to 0.47+/-0.04 after administration of adenosine, and from 0.46+/-0.07 to 0.55+/-0.06 after L-NMMA (mean+/-SD, 6 dogs for control and adenosine, 4 dogs for L-NMMA, all P<0.05). Flow normalized to its value at full dilation and pressure of 90 mm Hg (375+/-25 mL/min) increased during the period of reduced pressure at 40 mm Hg; control, from 0.005+/-63 (2 seconds after pressure step) to 0.09+/-0.06 (15 seconds after pressure step); with adenosine, from 0.19+/-0.06 to 0. 22+/-0.06; and with L-NMMA, from 0.013+/-0.007 to 0.12+/-0.02 (all P<0.05). The increase in DTF at low pressure may be explained by a decrease in interstitial volume at low pressure, which either decreases the preload of the myocytes or reduces the buffer capacity for ions determining repolarization, thereby causing an earlier onset of relaxation. CONCLUSIONS: Because the largest increase in DTF occurs at pressures below the autoregulatory range when blood flow to the subendocardium is closely related to DTF, modulation of DTF by coronary blood flow can provide an important regulatory mechanism to match supply and demand of the myocardium when vasodilatory reserve is exhausted.

Adenosine↗

PubMed1999

Interaction between Gregg's phenomenon and coronary flow control: a model study.

Coronary perfusion pressure, Pp, affects coronary arterial resistance, Ra, (autoregulation) as well as myocardial oxygen consumption, MVO2 (Gregg's phenomenon). The interaction between the effects of Pp and MVO2 on coronary flow control was investigated using a coronary flow control model. Model analysis predicts that response of the pressure-flow ratio, p/q(t), following a change in Pp depends on the sensitivity of Ra to a change in tissue oxygen concentration (tone sensitivity) and on the sensitivity of MVO2 to a change in capillary pressure (Gregg's sensitivity). At high tone sensitivity Gregg's effect is small, whereas at high Gregg's sensitivity autoregulation is attenuated. In experiments glibenclamide decelerated the p/q(t) in response to a pressure step by a factor of four. However, the proposed model demonstrates that this is compatible with a reduction in rate of change of Ra by a factor of ten. This is due to the interaction of negative and positive feedback gains in the model. Model analysis demonstrates that autoregulation and Gregg's phenomenon compete with each other in controlling coronary flow.

Animals↗

PubMed1999

Chronic cardiac denervation affects the speed of coronary vascular regulation.

OBJECTIVE: We tested the hypothesis that the rate of adaptation of coronary metabolic vasodilatation and autoregulation is modulated by the cardiac nerves. METHODS: Anaesthetised dogs (seven innervated (control) and seven with denervated hearts) were subjected to controlled pressure perfusion of the left main coronary artery. Heart rate was controlled by pacing. RESULTS: The steady state autoregulation curves and metabolic regulation curves were similar in the two groups. A sudden increase or decrease in heart rate was associated with a faster response (22% shorter half-times) in the innervated than the denervated dogs (P < 0.001). A sudden increase or decrease in coronary arterial perfusion pressure was associated with a slower response (24% longer half-times) in the innervated than the denervated hearts (P < 0.005). CONCLUSIONS: We conclude that the speed of response to metabolic and perfusion pressure changes is partly mediated by cardio-cardiac reflexes. Reflex coronary vasodilatation appears to reinforce the metabolic vasodilatation of a heart rate increase and oppose the vasoconstriction in response to increased perfusion pressure.

Analysis of Variance↗

PubMed1999

Peroperative time-motion analysis of diagnostic laparoscopy with laparoscopic ultrasonography.

BACKGROUND: Advanced technology is being introduced rapidly into laparoscopic procedures, frequently without an accurate evaluation of its functioning. In this study, standardized time-motion analysis was applied to evaluate the peroperative surgical process and the technical equipment used in 18 cases of diagnostic laparoscopy with laparoscopic ultrasonography (DLLU). METHODS: The image through the laparoscope, the ultrasonograph and an overview of the operating theatre were recorded simultaneously. The time for each phase, efficient actions (e.g. identifying lesions by inspection, making an ultrasonogram or taking a biopsy) and limiting factors (e.g. technical problems, time spent waiting) were determined, and a current standard was defined. RESULTS: Of the actions performed, 52 per cent were qualified as efficient, 17 per cent were classified as time spent waiting for personnel, instruments were positioned in 13 per cent, and unnecessary instrument exchanges were involved in 10 per cent. The evaluation led to a significant reduction in delay times and resulted in design criteria for improved biopsy instruments. The current standard was calculated from the mean time and number of actions determined for each phase. CONCLUSION: This time-motion study provided detailed insight into the peroperative process of DLLU, leading to improvements in the surgical process and instruments used. The defined current standard will enable evaluation of the learning curve and new technologies.

Humans↗

PubMed1999

Quantitative analysis of the functionality and efficiency of three surgical dissection techniques: a time-motion analysis.

The increasing technological complexity of surgery demands objective evaluation of surgical techniques. In particular, alternatives for laparoscopic ligation, such as monopolar coagulation and the relatively new bipolar scissors combining dissection with coagulation, should be analyzed and compared. This study tests the efficacy of quantitative time-motion analysis in evaluating and comparing the functionality and efficiency of dissection and ligation techniques in a clinical setting. Standard dissection with ligation of vessels, bipolar scissors, and monopolar coagulation were consecutively applied to dissect 4 of the small bowel mesentery of pigs, in random order. All actions performed were recorded and analyzed, using a standard action list. The efficiency of each technique was expressed in mean dissection time and number of actions, and the safety in occurrence of complications and severity of microscopic damage. Time-motion analysis evaluated the efficiency objectively and reproducibly (ICC 0.98). Bipolar scissors were significantly more efficient (time 7 +/- 2 min, actions 129 +/- 33) than the standard technique (28 +/- 6, 771 +/- 185) and monopolar coagulation (14 +/- 5, 368 +/- 32) (p < 0.01). Furthermore, bipolar coagulation needed significantly less recoagulation of an oozing vessel (0.5% of the total dissected vessels) than did monopolar coagulation (10.4%), and the damaged zone was significantly smaller (p < 0.05). Significantly less time was spent waiting or exchanging instruments with bipolar scissors than with the standard technique (p < 0.05). This time-motion analysis objectively compared the efficiency and functionality of three surgical dissection techniques during clinical use. Bipolar scissors were more efficient than were both other techniques, and they coagulated vessels more safely than did monopolar coagulation.

Animals↗

PubMed1996

Rate of coronary flow adaptation in response to changes in heart rate before and during anesthesia for coronary artery surgery.

BACKGROUND: The rate of adaptation of coronary blood flow in response to stepwise changes in heart rate (HR) has been extensively studied in dogs and goats to improve our understanding of the dynamics of coronary regulation processes and their pathophysiology and to obtain time constants for mathematical modeling of the coronary regulation. However, little is known about the dynamic characteristics of coronary flow adaptation in humans. In patients undergoing coronary artery surgery, we investigated the rate of coronary adaptation in response to stepwise changes in HR, in the awake and anesthetized states. METHODS: In 11 patients with stable coronary artery disease, arterial blood pressure, right atrial pressure, and coronary sinus blood flow, measured by continuous thermodilution, were calculated per beat. The ratio of beat-averaged arterial blood pressure minus right atrial pressure and coronary sinus blood flow was calculated to obtain an index of coronary resistance. The rate of change of coronary resistance index was quantified by t50, defined as the time required to establish 50% of the total change in coronary resistance index. Responses of coronary resistance index after HR changes, before and after induction of anesthesia, were compared. The anesthesia technique consisted of 100 micrograms.kg-1 fentanyl and 0.1 mg.kg-1 pancuronium bromide in combination with oxygen in air ventilation (FIO2 = 0.5). RESULTS: In the awake situation, t50 values of the dilating and constricting responses, induced by an increase and a decrease in HR were 5.0 +/- 2.1 (SD) s (range 2.6-9.0 s) and 5.7 +/- 1.2 s (range 4.1-7.8 s), respectively. During fentanyl/pancuronium anesthesia, the rate of coronary flow adaptation was significantly slower, with t50 values of 10.2 +/- 2.1 s (range 7.7-13.1 s) after an HR step-up and 9.8 +/- 2.1 s (range 6.6-13.2 s) after an HR step-down. Compared to the awake situation, arterial blood pressure was significantly reduced during anesthesia, but coronary vascular resistance remained unchanged. This implies that the steady-state static regulation of coronary blood flow had not changed. CONCLUSIONS: These preliminary data suggest that, in patients with coronary artery disease, the rate of change in coronary vascular resistance in response to pacing-induced changes in HR is mitigated by fentanyl/pancuronium anesthesia during positive pressure ventilation. A further qualification of our findings in a larger number of patients is warranted.

Adaptation, Physiological↗

PubMed1996

Transients in myocardial O2 consumption after abrupt changes in perfusion pressure in goats.

The dynamic oxygen content differences were analyzed in the present study. The left main coronary artery of the anesthetized, open-chest goat was perfused at constant pressure (Pp). Pp(t), arterial flow [Qa(t)], and the arteriovenous oxygen content difference [a-vO2(t)] were averaged per beat. The a-vO2 signal was corrected for mixing processes in the capillaries and transport time from capillaries to the venous measuring site [a-vO2(t)]. A change in Pp of 20 mmHg induced a temporary change in MVO2, referred to as the dynamic Gregg effect. With an increase in Pp, the maximal change of myocardial oxygen consumption [MVO2(t) = Qa(t).a-vO2(t)] was 15.0 +/- 3.6% (means +/- SE) during control and 31.3 +/- 2.3% with glibenclamide. With a decrease in Pp these changes were 16.3 +/- 2.9 and 21.0 +/- 1.1%. During control, the half-time for the rate of return of the MVO2 response was 4.2 +/- 0.8 s for an increase and 4.0 +/- 1.0 s for a decrease in Pp. With glibenclamide these values were 16.9 +/- 2.2 and 22.6 +/- 2.0 s. This study confirms that during steady state the Pp-induced MVO2 (steady-state Gregg effect) is diminished by autoregulation. However, it is concluded that during transients following abrupt changes in Pp, large changes in MVO2 occur depending on the rate of regulation (dynamic Gregg effect).

Animals↗

PubMed1995

Heart rate affects the dependency of myocardial oxygen consumption on flow in goats.

The effect of flow steps in coronary arterial flow (Qa) on myocardial oxygen consumption (MVo2) was investigated at different heart rates (HR) to further elucidate the dependency of myocardial oxygen consumption on perfusion. In six anesthetized goats the left main coronary artery and the great cardiac vein were cannulated. The hearts were paced alternately at 60 and 130 beats per min. Flow steps were applied at both HR during control and maximal vasodilation by adenosine. MVo2, in steady state before and after the flow step, was calculated by multiplication of Qa and arterio-venous oxygen content difference (Fick's law). Heart rate affected the MVo2 dependency on flow during control as well as during maximal vasodilation. With vascular tone present, the MVo2 dependency on flow (DeltaMVo2/DeltaQa), in mu l O2/ml, was 16.0 +/- 3.6 at HR 60 and 21.7 +/- 3.9 at HR 130. During maximal vasodilation, these values were 9.5 +/- 2.9 and 17.0 +/- 5.3 at HR 60 and 130, respectively. The higher MVo2 dependency on flow at high HR may be explained via a dependency of MVo2 on microvascular pressure. The pressure change in the microvessels induced by a flow step is probably larger at high HR than at low HR because of increased venous resistance at high HR, due to increased compression by the heart contraction.

Animals↗

PubMed1995

Comparison of different oxygen exchange models.

A functional distribution of coronary volume can be estimated from the response of arterio-venous O2 content difference (AVO2) to a flow step. However, the results depend on the assumed O2 exchange model. The previously used model consisted of a single mixed compartment with O2 exchange (reference model). The purpose of this study is to provide an estimate of the errors made in the volume estimations by not taking into account factors as flow heterogeneity, different mixing sites or Krogh-like O2 exchange. The approach is indirect: the response of the AVO2 to a flow step has been calculated with alternative O2 exchange models in which factors mentioned are incorporated. These transients are fitted with the reference model. The resulting estimated volumes are different from the volumes assumed in the alternative models. Large differences are obtained with some of the alternative models, e.g. the model with Krogh characteristics. However, these models seem unrealistic because capillary pO2 is higher than venous pO2. Only small differences in volume are obtained with the more realistic models. Therefore, these results indicate that the coronary volumes are approximated well by the estimations obtained with the reference model. These volume estimations were 9.9 and 3.8 ml 100 g-1 for the O2 exchange vessels and the distal venous volume, respectively.

Blood Volume↗

PubMed1994

Classical Krogh model does not apply well to coronary oxygen exchange.

By fitting of simulations with an oxygen exchange model to measured responses of the arteriovenous oxygen content difference after a flow step, coronary volumes can be estimated. In this study the dependence of the volume estimates on the choice of the oxygen exchange model for the coronary circulation was investigated. A model consisting of a single well-mixed compartment results in smaller volume estimates than a series array of mixed compartments in which PO2 declines gradually (Krogh-like model). Use of the former model for data analysis resulted in realistic volume estimates. Thus, these results indicate that the oxygen exchange vessels are better represented by a single mixed compartment than by a cylinder having Krogh characteristics. This conclusion agrees with capillary PO2 being equal to or smaller than venous PO2 which cannot be explained by a Krogh model. From these arguments we conclude that though both models are rough representations of the coronary circulation, the coronary O2 exchange vessels of the beating heart can be represented better by a single mixed compartment than by a series array of mixed compartments which has Krogh characteristics.

Animals↗

PubMed1994

Glibenclamide decelerates the responses of coronary regulation in the goat.

The role of blocking ATP-sensitive potassium (KATP) channels by glibenclamide on the dynamic responses of coronary resistance to abrupt changes in perfusion pressure and heart rate was investigated. The left main coronary artery of the open-chest anesthetized goat was perfused with constant pressure (Pp). Pp and arterial flow were averaged per beat, and their ratio was calculated as index of coronary resistance. Responses of resistance index after heart rate (HR) and Pp changes before and after administration of glibenclamide were compared. Their rate of change was quantified by t50, the required time to obtain half of the complete response. During control, t50 for the dilating response induced by a decrease in Pp or increase in HR was 3.8 +/- 0.2 and 6.2 +/- 0.5 (SE) s, respectively. With glibenclamide these values were 24.4 +/- 1.6 and 14.9 +/- 2.1 s. For the constricting response, the numbers for control were 5.8 +/- 0.3 (increase Pp) and 7.2 +/- 0.8 (decrease HR) s. With glibenclamide these values were 22.1 +/- 1.5 and 16.0 +/- 2.9 s. The steady-state adjustment of coronary flow was not altered by glibenclamide. It was concluded that glibenclamide has a minor effect on coronary flow control but reduces the rate of change of coronary resistance index up to a factor of four. Because glibenclamide is supposed to act on KATP channels, it may be concluded that these channels play a major role in the dynamics of coronary blood flow regulation.

Animals↗

PubMed1993

Theoretical analysis of coronary blood flow and tissue oxygen pressure-control.

Coronary blood flow is tightly coupled to the myocardial oxygen consumption. We have presented a control model based on the assumption that the tissue oxygen pressure is the controlled variable. The coronary blood flow in itself is not a controlled variable but merely the result of a different control system: the tissue oxygen pressure. From our control equation there is no relation between the slope of the autoregulation curve and the gain of the tissue PO2 control system. The slope is independent of the level of oxygen consumption.

Animals↗

PubMed1993

Left ventricular pressure transmission to myocardial lymph vessels is different during systole and diastole.

In six open-thorax-anaesthetized dogs with paced hearts and a retrogradely cannulated epicardial lymph vessel, the sensitivity of myocardial lymph pressure to left ventricular pressure during systole and during diastole was determined. The lymph vessels were cannulated using PE-90 tubing, and lymph pressure was measured by connecting the cannula to a microtip pressure transducer. To obtain the systolic sensitivity, left ventricular pressure was changed by clamping the descending aorta, which caused left ventricular pressure to increase. The diastolic sensitivity was obtained from natural variation to left ventricular pressure caused by atrial contractions during induced long diastoles. The mean ratio of the pulse in lymph pressure to the pulse in left ventricular pressure was determined: systole: 0.069 +/- 0.013, n = 213, diastole: 0.76 +/- 0.16, n = 249 and, if possible, linear regression analysis between lymph and left ventricular pressure was performed. The systolic regression coefficients could be determined in six dogs and the diastolic coefficients in three dogs. During long diastoles lymph pressure variations are on average 76 per cent of those in the left ventricle. However, during systole, the sensitivity of lymph pressure to left ventricular pressure is more than ten times lower. It is not unlikely that the structural embedment of lymph vessels within the myocardium is such that volume variations by cardiac contraction are limited.

Animals↗

PubMed1993

Functional distribution of coronary vascular volume in beating goat hearts.

With use of hemoglobin-bound O2 as an endogenous tracer, intramyocardial blood volume distribution between vessels involved in O2 exchange and more distal vessels was estimated. In nine anesthetized open-chest goats, the left main coronary artery was cannulated and perfused at a constant flow. Coronary arteriovenous O2 content difference (AVOX) was measured. AVOX transients induced by a flow step could be characterized by two phases: delay time and slow change to a new steady state. AVOX responses were fitted by a two-compartment model consisting of a well-mixed compartment from which O2 is consumed with volume Vm, and a distal unmixed compartment without O2 exchange, with volume Vunm. The rate of change of the AVOX transient depends on Vm, whereas the delay time depends on Vunm. Measurements in nine goats resulted in a Vm value of 9.9 +/- 1.1 (SE) ml/100 g (n = 9) and a Vunm value of 3.8 +/- 0.3 ml/100 g. Maximal vasodilation caused a significant increase in Vm (13.1 +/- 1.3 ml/100 g; n = 5), whereas Vunm did not change (5.0 +/- 0.5 ml/100 g). Hence, the increase of intramyocardial blood volume induced by vasodilation must be expected in the capillary bed and not in the coronary veins.

Adenosine↗