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Biomedical subjects

C R Lambert

Publications and source records attributed to C R Lambert.

At least 91 records · Page 5Linked to original sources
PubMed1983

Indices of ventricular contractile state: comparative sensitivity and specificity.

Twenty-four indices of ventricular contractile state were compared as to inotropic sensitivity using dobutamine infusion, as well as to preload and afterload independence using dextran and phenylephrine infusion. Experiments were done in 10 open-chest instrumented dogs and signal processing was done off-line by digital techniques. The indices studied, listed in order of decreasing sensitivity, are (1) power-averaged rate of generation of power density, (2) peak isovolumic rate of change of power, (3) ejection rate of change of power at peak tension, (4) peak second time derivative of ventricular pressure, (5) peak ejection rate of change of power, (6) peak isovolumic power, (7) energy-averaged power density, (8) mean aortic blood acceleration, (9) peak aortic blood acceleration, (10) peak first time derivative of ventricular pressure, (11) peak normalized fiber velocity, (12) peak fiber velocity, (13) peak aortic blood flow, (14) peak power, (15) extrapolated Vmax (total pressure), (16) mean normalized fiber velocity, (17) mean fiber velocity, (18) extrapolated Vmax (developed pressure), (19) mean aortic blood flow, (20) mean power, (21) stroke volume, (22) peak wall tension, (23) mean wall tension, (24) time-tension index. The most sensitive index which was statistically independent of preload and afterload manipulation was the ejection rate of change of power at peak tension.

Animals↗
PubMed1982

Study of prostaglandins E1 and F2 alpha on isolated mammalian cardiac tissue.

Prostaglandins (PG) E1 and F2 alpha over a dose range of 2.0 pg/ml to 15 micrograms/ml were tested to determine if they had an effect on the resting potential, action potential amplitude, or action potential duration of isolated superfused canine cardiac Purkinje fibers or feline papillary muscles. The effect of the PGs on spontaneous rate in Purkinje fibers was also tested. PGE1 and PGF2 alpha over a range of 1.0 pg/ml to 20 micrograms/ml were tested to determine if these compounds had an inotropic effect on feline papillary muscle. The data show that in the range of concentrations tested, PGE1 and PGF2 alpha do not significantly change the electrophysiologic or mechanical response tested.

Action Potentials↗
PubMed1979

Length-dependent activation of in situ canine skeletal muscle.

This study was designed to assess the contribution of length-dependent activation to the peak isometric twitch tension developed and the maximal rate of tension development (dP/dt) of in situ canine skeletal muscle. Length-developed tension and length-dP/dt relationships were generated for the dog gastrocnemius-plantaris muscle group at three different levels of inotropic state as determined by stimulation frequency. These relationships were then normalized with respect to maximal developed tension and maximal dP/dt and the normalized curves were superimposed for comparison. At progressively shorter muscle lengths the augmentation of tension production by a given increment in inotropic state was greater as measured by either developed tension or dP/dt. Thus, a given change in muscle length produced a greater change in performance in less potentiated muscles. These findings are similar to those from studies of isolated cardiac muscle and illustrate the lack of independence between activational state and muscle length for in situ skeletal muscle.

Animals↗
PubMed1979

Indices of myocardial oxygen consumption for isotonic contraction.

To investigate the model-independent mechanical determinants of energy expenditure, a respirometer was constructed to study isolated feline papillary muscles. Mechanical parameters recorded were the distance of shortening (deltaL), peak velocity of shortening (Vp), mean velocity of shortening (V), tension-time index (TTI), afterload (P), and the integral of the contraction portion of the phase plane trajectory of velocity and length (integral of VdL). Oxygen consumption (Vo2) during 15-min isotonic contraction periods was monitored with a polarographic electrode. Vp, V, and delta L were inversely related to Vo2 in a curvilinear manner. P and TTI were directly related to Vo2 in a curvilinear fashion. Integral of VdL was inversely related to Vo2 in a linear manner. In several experiments the contractile state of the muscles was augmented by addition of norepinephrine (7 X 10(-8) M). The relationship between integral of VdL and Vo2 was shifted above and parallel to that for the control muscles. These experiments indicate that the index integral of VdL is linearly related to the oxygen consumed in isotonic contraction of isolated mammalian ventricular myocardium at a given level of contractile state.

Animals↗
PubMed1976

Inhibitory effects of catecholamines in canine cardiac Purkinje fibers.

The effect of catecholamines over a wide range of concentrations was studied on 42K uptake and efflux, as well as on spontaneous rate in canine cardiac Purkinje fibers. Low levels of catecholamines (less than 10(-10) M epinephrine; less than 10(-9) M norepinephrine) decreased automaticity. This negative chronotropic effect was blocked by phentolamine and mimicked by phenylephrine. These low levels of epinephrine and norepinephrine also inhibited 42K uptake by Purkinje fibers but had no effect on 42K efflux. The inhibition of 42K uptake was blocked by phentolamine and verapamil and mimicked by phenylephrine. The data indicate an alpha-receptor-mediated negative response of rate and 42K uptake to low levels of catecholamine. The end result is discussed in terms of a competitive increase in the influx of Ca2+ rather than Na+ and an indirect inhibition of the Na+-K+ pump.

Animals↗
PubMed1975

The effect of verapamil on potassium fluxes in canine cardiac Purkinje fibres.

Electrophysiological studies of verapamil on isolated cardiac tissue show its effects to occur during Phase 2 and Phase 4 of the cardiac action potential and to be a result of blocking the slow inward Ca2+ current. It is important to know if verapamil effects the transmembrane movement of ions other than Ca2+. By studying uptake and efflux of 42K by canine cardiac Purkinje fibres in the presence and absence of verapamil (1.1 x 10-6 M-4.4 X 10-6 M), it was found that the drug inhibits both 42K uptake (15%) and efflux (30%).

Animals↗