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- Bak, Zoltan, 1950-
(author)
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Cardiovascular response to hyperoxemia, hemodilution and burns : a clinical and experimental study
- 2007
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Doctoral thesis (other academic/artistic)abstract
- The last decades less invasive monitoring and analytical tools have been developed for the evaluation of myocardial mechanics in clinical praxis. In critical care, these are longed-for complements to pulmonary artery catheter monitoring, additionally offering previously inaccessible information. This work is aimed, during fluid-replacement and oxygen therapy, to determine the physiological interface of ventricular and vascular mechanical properties, which result in the transfer of blood from the heart to appropriate circulatory beds. In prospective clinical studies we investigated previously cardiovascular healthy adults during hyperoxemia, and during preoperative acute normovolemic hemodilution or early fluid resuscitation of severe burn victims. Echocardiography was used in all studies, transthoracic for healthy volunteers and transesophageal for patients. For vascular parameters and for control purposes pulmonary artery Swan-Ganz catheter, calibrated external pulse recordings, whole body impedance cardiography, and transpulmonel thermodilution method were applied.We detected no significant change in blood pressure or heart rate, the two most often used parameters for patient monitoring. During preoperative acute normovolemic hemodilution a reduction of hemoglobin to 80 g/l did not compromise systolic or diastolic myocardial function. Cardiac volumes and flow increased with a concomitant fall in systemic vascular resistance while oxygen delivery seemed maintained. Supplemental oxygen therapy resulted in a linear dose-response between arterial oxygen and cardiovascular parameters, suggesting a direct vascular effect. Cardiac flow decreased and vascular resistance increased from hyperoxemia, and a decrease of venous return implied extracardial blood-pooling. Severe burns result in hypovolemic shock if not properly treated. The commonly used Parkland fluid replacement strategy, with urinary output and mean arterial pressure as endpoints, has recently been questioned. Applying this strategy, only transient early central hypovolemia was recorded, while dimensional preload, global left ventricular systolic function and oxygen delivery or consumption remained within normal ranges during the first 36 hours after accident. Signs of restrictive left ventricular diastolic function were detected in all patients and regional unstable systolic dysfunction was recognized in every other patient, and was consistent with myocardial marker leakage. Severe burns thereby cause myocardial stiffness and systolic regional dysfunction, which may not be prevented only by central normovolemia and adequate oxygenation.
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| 2. |
- Nilsson, Lena, 1956-
(author)
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Respiratory monitoring using reflection mode photoplethysmography : clinical and physiological aspects
- 2005
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Doctoral thesis (other academic/artistic)abstract
- Photoplethysmography (PPG) is a non-invasive optical technique for monitoring variations in blood volume and blood flow in skin and other tissues. Light from a light-emitting diode is absorbed, scattered and reflected from the skin, and detected by a photodetector as a plethysmogram. The plethysmogram contains variations of different frequencies. The most clinically utilised is the pulse synchronous variation in the PPG application pulse oximetry, but there is also a respiratory rate synchronous variation (PPGt).The aims of this work were to evaluate PPG as a clinical method for detection of breaths during anaesthesia, postoperative and intensive care, and to investigate possible circulatory factors in the physiological background of the respiratory synchronous part of the reflection mode PPG signal.It was concluded that respiratory variations in reflection mode PPG derived from the forearm could be detected with high sensitivity and specificity. PPG, was not significantly affected by awake or anaesthetised state, though indirect signs of reduced sympathetic tone in the anaesthetic state were present, or by spontaneous or positive pressure ventilation. There were no significant differences between men and women or between young and old subjects. Circulatory pressure variations in phase with respiration were present on both the arterial and venous side and they showed the same degree of variation, as did PPG when provoking respiration. Squared coherence, cross-correlation and visual techniques for evaluating time differences were equally good.Respiratory monitoring in the clinical setting is challenging and no golden standard exists. Methods based on airflow are mostly considered advantageous in detecting apnoea, but are less well tolerated by patients. The results indicate that PPG has a potential as a tool for monitoring respiratory rate. It is non-invasive, well tolerated and can be used for continuous monitoring.
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