The problem created by myocardial structure in assessing function.
The clinical understanding of the dynamics of myocardial contraction is hampered by an over-simplified interpretation of the intramural pattern of force generation. This limits the anaesthetist's knowledge of the direct effects of commonly used anaesthetics. A discrimination between a negative inotropic effect and changes in pre- and afterload is usually impossible in clinical conditions. By using needle force probes, it is now possible to measure intramyocardial mesh tension in volumes as small as 3 mm3. Force mapping in 20 to 30 layers of the hearts of five normal dogs has shown that there are different patterns in the basal, middle and apical portions of the free wall of the left ventricle. An inhomogeneity is also observed when myocardial hypertrophy is produced by a 6-week period of aortic banding. However, this decreased the gradient in wall tension between the basal and the other portions of the ventricle. Inhomogeneities in wall tension increase the difficulty of assessing the contractile state of heart muscle. It may, however, be useful to compare local wall dynamics in the more isometrically-contracting basal segment with those in the middle portion which brings about most of the emptying of the ventricle. In the future, transoesophageal echocardiography may be used to measure variations in wall thickness which change the global loading conditions in the basal midwall compartments of the left ventricle.
Lunkenheimer
P P
PP
Clinic for Anaesthesia and Operative Intensive Care, University Hospital of Munster, Nurnberg, W. Germany.
Redmann
K
K
Whimster
W F
WF
Theissen
J
J
Frieling
G
G
Lunkenheimer
A
A
D000818:Animals; D001696:Biomechanical Phenomena; D004285:Dogs; D006321:Heart / Q000502:physiology*; D009200:Myocardial Contraction; D016276:Ventricular Function