Search PubMed⌕ Search

Biomedical subjects

T P Graham

Publications and source records attributed to T P Graham.

160 records · Page 9Linked to original sources
PubMed1968

Control of myocardial oxygen consumption: relative influence of contractile state and tension development.

Myocardial oxygen consumption was measured in 11 anesthetized, open-chest dogs in order to compare in the same heart the relative influence on oxygen usage of tension development and the contractile or inotropic state, as reflected in V(max.) the maximum velocity of shortening of the unloaded contractile elements. The isovolumetrically contracting left ventricle was studied with left ventricular volume, heart rate, and systemic perfusion rate controlled. Wall tension, contractile element velocity, and V(max) were calculated. Peak developed tension was increased at a constant V(max) by increasing ventricular volume, and the effect on oxygen consumption was determined. Oxygen utilization was then redetermined at an increased V(max) but at a constant peak developed tension by infusing norepinephrine (0.76 to 7.6 mug/min) and decreasing ventricular volume to match the tension existing before norepinephrine infusion. Oxygen consumption consistently increased with increases in both developed tension and V(max) with the following multiple regression equation relating these variables: myocardial oxygen consumption (mul/beat per 100 g in LV) = K + 0.25 peak developed tension (g/cm(2)) + 1.43 V(max) (cm/sec). These data indicate that the oxygen cost of augmentation of contractility is substantial, can be independent of any change in fiber shortening, and is similar in order of magnitude to the effect of alterations in tension development

Animals↗
PubMedDate not supplied

Effects of postnatal maturation on myocardial contractile responses to calcium antagonists and changes in contraction frequency.

The inotropic responses to verapamil and nitrendipine (5.0 X 10(-8)-1.0 X 10(-5) M) were compared in right ventricular papillary muscles isolated from immature (14-21 days of age) and adult rabbits. In addition, the effects of changing the contraction frequency (force-frequency response) were studied in both age groups in the presence and absence of the calcium antagonists. Immature myocardium exhibited a greater sensitivity to the negative inotropic effect of both calcium antagonists. The concentrations of verapamil which reduced basal developed tension by 50% were 0.70 X 10(-6) M in the immature rabbit and 4.51 X 10(-6) M in the adult (p less than 0.05). For nitrendipine, these values were 0.48 X 10(-6) M in the immature rabbit and 1.21 X 10(-6) M in the adult (p less than 0.05). Raising the contraction frequency increased the contractile force (positive staircase) in both age groups, and verapamil abolished the positive staircase in both groups. Nitrendipine preserved but attenuated the positive staircase in the adult, but, in contrast, augmented the positive-staircase response in the immature myocardium. These age-related differences suggest that the mechanisms regulating calcium influx across the sarcolemma undergo postnatal maturation.

Aging↗
PubMedDate not supplied

Noninvasive delineation of normal right ventricular contractile motion with magnetic resonance imaging myocardial tagging.

As the importance of the right ventricle in many diseases and conditions has been realized, the need for quantitative assessment of the motion and contraction of the right ventricular free wall (RVFW) has become apparent. This study applied the myocardial tagging magnetic resonance imaging (MRI) technique to the normal RVFW to elucidate normal heterogeneity in RV motion and contractile patterns. The RVFW was divided into three segments (inferior, mid and superior) in each of three slices (apical, mid and basal) to allow for a detailed analysis of the motion and contraction. Percent segmental shortening (PSS) was used to measure the amount of contraction, and a vector analysis was used to quantitate the trajectory of the RVFW through systole. PSS increased monotonically through time to an average across all segments of 12% in the basal slice, 14% in the mid-ventricular slice, and 16% in the apical slice of the heart. The trajectory of the RVFW was characterized by a wave of motion toward the septum and outflow tract. The data provided in this study provide a better understanding of normal RV kinematics and can serve as a comparison for disease states.

Adult↗