Ilse Coomans

Limitations of Doppler echocardiography for the post-operative evaluation of aortic coarctation

Doppler blood flow measurements and derived pressure differences, through the Bernoulli equation, are used in the diagnosis of aortic coarctation, a congenital stenosis distal to the left subclavian artery. Doppler velocities remain elevated at the coarctation site after successful repair of coarctation, leading to high Doppler derived pressure differences without significant arm-leg pressure differences. We studied this apparent contradiction of two diagnostic methods, in vivo using patient and control data, and in vitro using a hydraulic model. Clinical and echocardiographic data from 31 patients, aged 13.0 +/- 4.0, 10.5 +/- 4.7 yr after coarctectomy by end-to-end anastomosis, and 18 age-matched healthy subjects were reviewed. Doppler peak velocities at the aortic isthmus were elevated in patients (2.2 +/- 0.4 vs. 1.2 +/- 0.2m/s, P < 0.001), corresponding to significant Doppler differences (20 +/- 7 mmHg), however, without significant arm-leg pressure differences. In all patients, a mild anatomic stenosis could still be observed. Local stiffness was increased. The hypothesis that the less distensible surgical scar in post-coarctectomy patients leads to a significant dynamic obstruction in systole was validated in a latex model of the aorta. Rigid rings (0.5-1.5 cm), matching the unloaded aortic diameter, were mounted around the aorta. Under loading conditions, Doppler peak velocities increased by 40 +/-7%, yielding Doppler differences of 21 +/- 3 mmHg, without a significant pressure drop. An alternative expression to calculate pressure differences, using both velocity and geometric information, was validated in the model. In conclusion, post-operatively, Doppler velocities remain elevated due to a mild anatomical and significant dynamic narrowing, but the specific geometry, resembling a tubular hypoplasia rather than an abrupt stenosis, permits an almost complete pressure recovery explaining the occurrence of Doppler differences in disagreement with the negligible arm-leg pressure difference.

Non-invasive assessment of hemodynamics in adolescents with arterial tonometry and Doppler ultrasound during a conventional stress test

Aiming to improve early diagnosis of people at cardiovascular risk, we are developing a custom set-up to allow an adequate hemodynamic analysis of heart function and arterial circulation properties, based on non-invasive acquisition of pressure (arterial tonometry) and flow (Doppler ultrasound techniques) waveforms. In an experimental setting 15 healthy volunteers were examined on a custom made supine bicycle. Able to record usable data throughout the bicycle test and automatically analyse derived hemodynamic parameters such as compliance, peripheral resistance, etc., we also applied the set-up in a real clinical environment. This research contributes to a more complete cardiovascular examination without significant additional discomfort for the patient or prolongation of the test protocol.

Evaluation of cardiopulmonary exercise testing, heart function, and quality of life in children after allogenic hematopoietic stem cell transplantation

Physical fitness is an important determinant of quality of life (QOL) after hematopoietic stem cell transplantation. Cardiac function can influence exercise performance. The aim of this study was to assess these factors and their interrelationship.

156 Exercise performance in children with mild cystic fibrosis (CF): Are there arguments to enhance physical activity?

Objectives Physical activity is strongly recommended in children with CF to improve exercise capacity and quality of life. The aim of this study is to investigate exercise performance and oxygen consumption in children with CF and mild respiratory involvement. Methods Children with mild CF (FEV1>60%) who where referred for cardiopulmonary exercise testing (CPET) were enrolled. Maximal heart rate (HR), oxygen consumption (VO2max), respiratory exchange ratio (RER), VO2 at anaerobic threshold (AT) and HR at AT were analysed. Data were compared with a healthy control group. Results 20 CF patients (9 boys, 12.5±2.7 yrs, weight 47.1±11.2 kg, length 156.1±14.7cm) performed a CPET. FEV1 was 91.8±15.9%, not different from a normal population. They were compared with 60 healthy controls (30 boys, age 11.5±2.3 yrs, weight 43.6±12.4 kg, length 151.2±13.6cm). MaxHR was 180.7±13.7 bpm in CF and 185.2±12.7 in controls (P>0.05). RER at maximal exercise was 1.1±0.1 in CF versus 1±0.1(P Conclusion Children with mild CF have lower VO2max despite equal maximal load, test duration and HR. They reach AT at a lower HR and VO2, which highlights the impaired condition. We can conclude that it is important to stimulate physical activity in children with mild CF to improve VO2 during exercise.

WS21.8 Validity of the Oxygen Uptake Efficiency Slope (OUES) as a parameter of maximal and submaximal exercise testing in children with mild CF

Objective Maximal oxygen consumption (VO2max) is considered as gold standard of maximal exercise testing. The Oxygen Uptake Efficiency Slope is stated as a valuable parameter of submaximal exercise. We sought to investigate the validity of OUES at different levels of exercise duration in children with mild CF. Methods 20 CF-patients with mild respiratory limitation (9 boys, age 12.45 yrs, FEV1 91.8% and BSA 1.44 m 2 ) were analysed. OUES was calculated at three levels of exercise intensity: at 50%, 75% and 100% (OUES50, OUES75 and OUES100). OUES/BSA was correlated with VO2max, VO2max/kg, maximal minute ventilation at exercise (VE), VE/VCO2, respiratory exchange ratio (RER). Results OUES50/BSA (1254±205), OUES75/BSA (1332±234) and OUES100/BSA (1348±233) all correlated strongly with VO2max (1704±518 ml/min) (correlation coefficient 0.69, 0.69, 0.66 respectively, P=0.001) and VO2max/kg (36.2±7 ml/kg/min) (P Conclusion The strong correlation between OUES values at 50%, 75% or 100% of activity and VO2max proves that OUES values are valid submaximal parameters in children with mild CF. Due to the fact that only OUES75 is equal to OUES100, it is important that the patients can perform at least 75% of the predicted maximal exercise to be reliable. OUES values have no correlation with maximal minute ventilation during maximal exercise.

In vitro evaluation of an extended pulse pressure method for the estimation of total arterial compliance

The Pulse Pressure Method (PPM) is a reliable iterative technique to estimate total (and segmental) arterial compliance. However, due to the necessity of simultaneous aorta pressure and flow wave measurements, the application of the method is restricted to animal studies or specific clinical conditions that allow aorta flow measurements. The authors therefore propose an extended Pulse Pressure Method (EPPM) where the flow wave is restricted by a triangular wave reconstructed from cardiac output. Both the PPM and EPPM are validated on an in vitro model of the arterial tree. The model is a 1:1 scale representation of the aorta including the major branches to the head, upper and lower limbs, and abdominal organs. It contains 37 elastic tapering tubes, made of natural latex rubber (1 MPa). The model is connected to a pulse duplicator system of the human left heart to provide the model of normal (or pathological) pulsatile inflow. Downstream 28 vascular beds are the interface to the venous side, with individually adjustable resistances and compliances. This allows the simulation of physiological and pathological conditions. The EPPM and PPM are tested on a normal configuration (total compliance C=1.40 ml/mmHg, total resistance R=0.73 mmHg/ml/s, mean arterial pressure MAP=65 mmHg, cardiac output CO=5.1 l/min) and a pathological configuration (C=0.29 ml/mmHg, R=2.34 ml/mmHg, MAP=75 mmHg. CO=1.9 l/min). Heart rate is 60 beats per minute in all cases. For both conditions the PPM is found to be accurate and reproducible (0.29/spl plusmn/0.02 ml/mmHg for the stiff and 1.42/spl plusmn/0.04 ml/mmHg for the compliant model). The EPPM slightly underestimates total arterial compliance (0.27/spl plusmn/0.03 ml/mmHg and 1.37/spl plusmn/0.06 ml/mmHg for the pathological resp. normal case). The EPPM thus weakens the tight restrictions of the PPM and renders the method less invasive. It is also illustrated that the in vitro model is a useful tool for haemodynamic studies, and suitable to validate invasive and non-invasive clinical research protocols.