Medical & Biological Engineering & Computing, Mar 1, 1990
In this study the response of driving pressure/flow ration on an abrupt change in heart rate was ... more In this study the response of driving pressure/flow ration on an abrupt change in heart rate was analysed. The difference between the response obtained with constant pressure and constant flow perfusion was also studied. The responses show a fast initial reversed phase followed by a slow phase caused by regulation. To test whether the initial phase could be the result of mechanical changes in the coronary circulation, a model for regulation was extended by the addition of four different mechanical models originating from the literature. These extended models were able to explain the fast initial phase. However, the mechanical model consisting of an intramyocardial compliance (C = 0.08 ml mm Hg-1 100 g-1) with a variable venous resistance, and the model consisting of a waterfall and a small compliance (C = 0.007 ml mm Hg-1 100g-1) both explained these responses best. The analysis showed that there is no direct relationship between rate of change of vascular tone and rate of change of pressure/flow ratio. However, on the basis of the two extended models, it can be predicted that the half-time for the response of regulation to be complete is about 9s with constant pressure perfusion and 15 s with constant flow perfusion.
To explain the characteristics of steady state control of the coronary circulation, many metaboli... more To explain the characteristics of steady state control of the coronary circulation, many metabolic hypotheses have been formulated in the past. In this chapter, an oxygen-based model and an adenosine-based model are compared to the experimental findings in the literature. In these models the specific assumptions on cause and effect are made explicit by mathematical expressions. The comparison yielded a good fit for the oxygen-based model. For the adenosine model the requirement of the absence of a washout term was essential. Since experiments have shown washout of adenosine, making this latter requirement unrealistic, only the oxygen-based model was extended to the dynamic situation.
Medical & Biological Engineering & Computing, Sep 1, 1995
A functional distribution of coronary volume can be estimated from the response of arterio-venous... more 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.
In this chapter some effects of pressure dependent changes in vascular volume on resistance and c... more In this chapter some effects of pressure dependent changes in vascular volume on resistance and capacitance in the microcirculation will be analysed. First some additional evidence for a significant intramyocardial compliance will be given. This evidence has been obtained from experiments where both arterial and venous coronary signals were measured. Further it is shown that the intramyocardial compliance is not situated at the very end of the coronary circulation, epicardial veins, but that a significant distal resistance must be present. A compartmental model based on pressure dependency of coronary vessels can describe relations between pressure and flow signals quite well. This model shows that time constants characterizing the changes of microvascular volume and relating quantities are in order of a second. The arterial signals show transients with characteristic time constants that are smaller than the duration of diastole and systole. However, the effect of compliance and changing resistance on coronary arterial flow are counteracting and hence concealing each other. We conclude that arterial signals do not provide sufficient information about the events in the microcirculation and models solely based on these signals can provide misleading results.
The use of linear models is very common in studying the mechanical events of the coronary circula... more The use of linear models is very common in studying the mechanical events of the coronary circulation. In this chapter some of the these linear models are discussed. However, special attention is devoted to a nonlinear model. This nonlinear model consists of an arteriolar, capillary, and a venular compartment, each composed of transmural pressure-dependent resistances and compliances. With this model, the influence of pressure-dependent resistances and compliances on the arterial signals is analyzed. This analysis shows that the phasic arterial signals mainly depend on the pressure dependency of the arteriolar compartment. Changes in the parameters of capillary and venular compartments hardly affected the arterial phasic signals. Furthermore, it can be concluded that the interpretation of results obtained by application of linear system theory is highly questionable and could easily lead to misleading conclusions on the magnitude of coronary compliance.
Background Laparoscopy is a minimally-invasive surgical procedure that uses long slender instrume... more Background Laparoscopy is a minimally-invasive surgical procedure that uses long slender instruments that require much smaller incisions than conventional surgery. This leads to faster recovery times, fewer infections and shorter hospital stays. For these reasons, laparoscopy could be particularly advantageous to patients in low to middle income countries (LMICs). Unfortunately, sterile processing departments in LMIC hospitals are faced with limited access to equipment and trained staff and poses an obstacle to safe surgical care. The reprocessing of laparoscopic devices requires specialised equipment and training. Therefore, when LMIC hospitals invest in laparoscopy, an update of the standard operating procedure in sterile processing is required. Currently, it is unclear whether LMIC hospitals, that already perform laparoscopy, have managed to introduce updated reprocessing methods that minimally invasive equipment requires. The aim of this study was to identify the laparoscopic st...
Background Strategies are needed to increase the availability of surgical equipment in low- and m... more Background Strategies are needed to increase the availability of surgical equipment in low- and middle-income countries (LMICs). This study was undertaken to explore the current availability, procurement, training, usage, maintenance and complications encountered during use of electrosurgical units (ESUs) and laparoscopic equipment. Methods A survey was conducted among surgeons attending the annual meeting of the College of Surgeons of East, Central and Southern Africa (COSECSA) in December 2017 and the annual meeting of the Surgical Society of Kenya (SSK) in March 2018. Biomedical equipment technicians (BMETs) were surveyed and maintenance records collected in Kenya between February and March 2018. Results Among 80 participants, there were 59 surgeons from 12 African countries and 21 BMETs from Kenya. Thirty-six maintenance records were collected. ESUs were available for all COSECSA and SSK surgeons, but only 49 per cent (29 of 59) had access to working laparoscopic equipment. Reus...
To comply with the large global need for surgery, surgical equipment that fits the challenging en... more To comply with the large global need for surgery, surgical equipment that fits the challenging environment in low- and middle-income countries (LMICs) should be designed. The aim of this study is to present a context-specific design of an electrosurgical unit (ESU) and a monopolar handheld to improve global access to surgery. This paper presents both a detailed description of electrosurgery in clinical practice in LMICs and the design of an ESU generator and monopolar handheld for this specific setting. Extensive fieldwork (by means of surveys, interviews, observations, and collection of maintenance records) was done by authors RO, KO, and LH. Feedback from users working in Kenya on the first demonstrator designs was obtained, after which the designs were adapted into conceptual prototypes. These were further evaluated by surveying respondents who attended the annual meeting of the College of Surgeons of East, Central, and Southern Africa (COSECSA) in Kigali, Rwanda in December 2018...
Human performance is not without error, and as a consequence errors occur. Studies have shown tha... more Human performance is not without error, and as a consequence errors occur. Studies have shown that 30–50 % of errors can be prevented. Adopting a system approach could reduce the occurrence of preventable patient safety incidents and could also be used to identify which technology needs to be developed or adapted to further improve patient safety. The system approach described here includes the interrelated components: Task, Individual, Team, Physical Work Environment, Organization & Management, and Political & Regulatory. Improving safety in the operating theatre requires changes on all these system levels and includes factors related to task performance, individual capability and (non)technical skills training, teamwork, the physical ergonomic work environment, learning capabilities of the organization and management, and political and regulatory demands on (inter)national level. Future interventions should take into account all these system levels, however, focusing first on teams and team skills, smart technology to support the operating theatre team and ‘training before the job’.
Medical & Biological Engineering & Computing, Mar 1, 1990
In this study the response of driving pressure/flow ration on an abrupt change in heart rate was ... more In this study the response of driving pressure/flow ration on an abrupt change in heart rate was analysed. The difference between the response obtained with constant pressure and constant flow perfusion was also studied. The responses show a fast initial reversed phase followed by a slow phase caused by regulation. To test whether the initial phase could be the result of mechanical changes in the coronary circulation, a model for regulation was extended by the addition of four different mechanical models originating from the literature. These extended models were able to explain the fast initial phase. However, the mechanical model consisting of an intramyocardial compliance (C = 0.08 ml mm Hg-1 100 g-1) with a variable venous resistance, and the model consisting of a waterfall and a small compliance (C = 0.007 ml mm Hg-1 100g-1) both explained these responses best. The analysis showed that there is no direct relationship between rate of change of vascular tone and rate of change of pressure/flow ratio. However, on the basis of the two extended models, it can be predicted that the half-time for the response of regulation to be complete is about 9s with constant pressure perfusion and 15 s with constant flow perfusion.
To explain the characteristics of steady state control of the coronary circulation, many metaboli... more To explain the characteristics of steady state control of the coronary circulation, many metabolic hypotheses have been formulated in the past. In this chapter, an oxygen-based model and an adenosine-based model are compared to the experimental findings in the literature. In these models the specific assumptions on cause and effect are made explicit by mathematical expressions. The comparison yielded a good fit for the oxygen-based model. For the adenosine model the requirement of the absence of a washout term was essential. Since experiments have shown washout of adenosine, making this latter requirement unrealistic, only the oxygen-based model was extended to the dynamic situation.
Medical & Biological Engineering & Computing, Sep 1, 1995
A functional distribution of coronary volume can be estimated from the response of arterio-venous... more 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.
In this chapter some effects of pressure dependent changes in vascular volume on resistance and c... more In this chapter some effects of pressure dependent changes in vascular volume on resistance and capacitance in the microcirculation will be analysed. First some additional evidence for a significant intramyocardial compliance will be given. This evidence has been obtained from experiments where both arterial and venous coronary signals were measured. Further it is shown that the intramyocardial compliance is not situated at the very end of the coronary circulation, epicardial veins, but that a significant distal resistance must be present. A compartmental model based on pressure dependency of coronary vessels can describe relations between pressure and flow signals quite well. This model shows that time constants characterizing the changes of microvascular volume and relating quantities are in order of a second. The arterial signals show transients with characteristic time constants that are smaller than the duration of diastole and systole. However, the effect of compliance and changing resistance on coronary arterial flow are counteracting and hence concealing each other. We conclude that arterial signals do not provide sufficient information about the events in the microcirculation and models solely based on these signals can provide misleading results.
The use of linear models is very common in studying the mechanical events of the coronary circula... more The use of linear models is very common in studying the mechanical events of the coronary circulation. In this chapter some of the these linear models are discussed. However, special attention is devoted to a nonlinear model. This nonlinear model consists of an arteriolar, capillary, and a venular compartment, each composed of transmural pressure-dependent resistances and compliances. With this model, the influence of pressure-dependent resistances and compliances on the arterial signals is analyzed. This analysis shows that the phasic arterial signals mainly depend on the pressure dependency of the arteriolar compartment. Changes in the parameters of capillary and venular compartments hardly affected the arterial phasic signals. Furthermore, it can be concluded that the interpretation of results obtained by application of linear system theory is highly questionable and could easily lead to misleading conclusions on the magnitude of coronary compliance.
Background Laparoscopy is a minimally-invasive surgical procedure that uses long slender instrume... more Background Laparoscopy is a minimally-invasive surgical procedure that uses long slender instruments that require much smaller incisions than conventional surgery. This leads to faster recovery times, fewer infections and shorter hospital stays. For these reasons, laparoscopy could be particularly advantageous to patients in low to middle income countries (LMICs). Unfortunately, sterile processing departments in LMIC hospitals are faced with limited access to equipment and trained staff and poses an obstacle to safe surgical care. The reprocessing of laparoscopic devices requires specialised equipment and training. Therefore, when LMIC hospitals invest in laparoscopy, an update of the standard operating procedure in sterile processing is required. Currently, it is unclear whether LMIC hospitals, that already perform laparoscopy, have managed to introduce updated reprocessing methods that minimally invasive equipment requires. The aim of this study was to identify the laparoscopic st...
Background Strategies are needed to increase the availability of surgical equipment in low- and m... more Background Strategies are needed to increase the availability of surgical equipment in low- and middle-income countries (LMICs). This study was undertaken to explore the current availability, procurement, training, usage, maintenance and complications encountered during use of electrosurgical units (ESUs) and laparoscopic equipment. Methods A survey was conducted among surgeons attending the annual meeting of the College of Surgeons of East, Central and Southern Africa (COSECSA) in December 2017 and the annual meeting of the Surgical Society of Kenya (SSK) in March 2018. Biomedical equipment technicians (BMETs) were surveyed and maintenance records collected in Kenya between February and March 2018. Results Among 80 participants, there were 59 surgeons from 12 African countries and 21 BMETs from Kenya. Thirty-six maintenance records were collected. ESUs were available for all COSECSA and SSK surgeons, but only 49 per cent (29 of 59) had access to working laparoscopic equipment. Reus...
To comply with the large global need for surgery, surgical equipment that fits the challenging en... more To comply with the large global need for surgery, surgical equipment that fits the challenging environment in low- and middle-income countries (LMICs) should be designed. The aim of this study is to present a context-specific design of an electrosurgical unit (ESU) and a monopolar handheld to improve global access to surgery. This paper presents both a detailed description of electrosurgery in clinical practice in LMICs and the design of an ESU generator and monopolar handheld for this specific setting. Extensive fieldwork (by means of surveys, interviews, observations, and collection of maintenance records) was done by authors RO, KO, and LH. Feedback from users working in Kenya on the first demonstrator designs was obtained, after which the designs were adapted into conceptual prototypes. These were further evaluated by surveying respondents who attended the annual meeting of the College of Surgeons of East, Central, and Southern Africa (COSECSA) in Kigali, Rwanda in December 2018...
Human performance is not without error, and as a consequence errors occur. Studies have shown tha... more Human performance is not without error, and as a consequence errors occur. Studies have shown that 30–50 % of errors can be prevented. Adopting a system approach could reduce the occurrence of preventable patient safety incidents and could also be used to identify which technology needs to be developed or adapted to further improve patient safety. The system approach described here includes the interrelated components: Task, Individual, Team, Physical Work Environment, Organization & Management, and Political & Regulatory. Improving safety in the operating theatre requires changes on all these system levels and includes factors related to task performance, individual capability and (non)technical skills training, teamwork, the physical ergonomic work environment, learning capabilities of the organization and management, and political and regulatory demands on (inter)national level. Future interventions should take into account all these system levels, however, focusing first on teams and team skills, smart technology to support the operating theatre team and ‘training before the job’.
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