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P Knaapen

Publications and source records attributed to P Knaapen.

5 recordsLinked to original sources
PubMed2004

Regional timing of myocardial shortening is related to prestretch from atrial contraction: assessment by high temporal resolution MRI tagging in humans.

Earlier studies have shown substantial nonuniformity in normal left ventricular (LV) myocardial function concerning both the degree of shortening and timing of shortening. We hypothesized that nonuniform LV function may be related to nonuniform prestretch induced by atrial contraction. Eleven healthy human subjects were studied using MRI myocardial tagging and strain analysis. The amount of circumferential prestretch was assessed in 30 LV segments. Prestretch was defined as the difference in strain between end diastole (at ECG R wave) and diastasis. Furthermore, both the degree of shortening (quantified as peak circumferential shortening, peak systolic shortening rate, and amount of postsystolic shortening) and timing of shortening (quantified as the onset time of shortening and time to peak shortening) were assessed. LV prestretch was found to be nonuniform, with the highest values in the lateral wall. The amount of segmental prestretch correlated significantly with peak shortening (r = 0.79), peak shortening rate (r = 0.50), amount of postsystolic shortening (r = 0.67), onset time of shortening (r = -0.57), and time to peak shortening (r = 0.71) (P < 0.001 for each of these relations). These relations may be explained by regional differences in wall stress or by a regional Frank-Starling effect. The correlation between timing of shortening and prestretch demonstrates that mechanical timing is not determined by electrical phenomena alone. In conclusion, regional variation in LV function correlates with the nonuniform prestretch from atrial contraction.

Adult↗
PubMed2001

Carbon-11 acetate as a tracer of myocardial oxygen consumption.

Estimation of myocardial oxygen consumption (MVO2) and myocardial blood flow (MBF) is important for the understanding of various (patho)physiological mechanisms and diseases. Clearance rates of carbon-11 labelled acetate, determined with positron emission tomography, allow estimation of MVO2 on a segmental level and non-invasively. In addition, MBF can be determined from uptake rates. In this review, the background to estimation of MVO2 and MBF is discussed, as well as the currently available literature that has used 11C-acetate to estimate MVO2 and MBF.

Acetates↗
PubMedDate not supplied

Feasibility of planar myocardial carbon 11-acetate imaging.

BACKGROUND: Myocardial oxygen consumption can be determined by using carbon 11-acetate (11C-acetate) and positron emission tomography (PET). The aim of this study was to validate planar 11C-acetate scintigraphy in healthy individuals by relating the myocardial clearance rate of dynamic 11C-acetate scintigraphy with the rate-pressure product, which is used as a measure of cardiac work. Also, the optimal curve-fitting procedure of the time-activity curve and the intraobserver and interobserver variation of determining the clearance rates were assessed. METHODS AND RESULTS: Six subjects were studied at rest, and seven subjects were studied during dobutamine stimulation. Imaging was performed with a planar camera equipped with high-energy collimators for 45 minutes after the injection of 185 MBq of 11C-acetate. Myocardial time-activity curves were corrected for decay. During the study, heart rates and blood pressures were measured to calculate the rate-pressure product. Myocardial time-activity curves showed a clear biphasic pattern. Clearance rates were expressed in k values. The best fitting procedure, as assessed by means of the lowest error of k and the best correlation with the rate-pressure product, proved to be a monoexponential fit on the first part of the time-activity curve (kmono). Subjects studied during dobutamine infusion had significantly higher rate-pressure product (15.0 +/- 2.1*10(3) vs 8.6 +/- 1.2*10(3), P < .001) and 11C-acetate clearance rates (kmono = 0.0657 +/- 0.0110 vs 0.0313 +/- 0.0056, P < .0001) than subjects studied at rest. There was low intraobserver and interobserver variation in determining kmono values. A significant correlation between the rate-pressure product and the monoexponential clearance rate was found (kmono = 5.11*10(-6)*RPP-0.012; r = 0.94, P < .001). CONCLUSIONS: The estimation of myocardial oxygen consumption is feasible with planar 11C-acetate scintigraphy. Clearance rates and the relation with the rate-pressure product are similar to those reported in PET studies. This technique may be used for the assessment and follow-up of global myocardial metabolic abnormalities, eg, in patients with hypertensive heart disease, cardiomyopathy, myocarditis, and valvular disease.

Acetates↗