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T C Gillebert

Publications and source records attributed to T C Gillebert.

46 records · Page 3Linked to original sources
PubMed1992

Intracavitary ultrasound impairs left ventricular performance: presumed role of endocardial endothelium.

Irradiation of isolated cardiac muscle by high-power, high-frequency, continuous wave ultrasound selectively damages endocardial endothelium (EE). We evaluated this ultrasound effect in vivo on the performance of the intact ejecting canine left ventricle (LV). A cylindrical ultrasound probe (0.9 MHz, 25 W), mounted on a catheter, was inserted in the LV cavity through an apical stab wound and was activated for 60, 120, and 240 s, followed each time by a recovery period of 10-15 min. Ultrasound transiently and repeatedly abbreviated the time interval from end diastole to peak (-)dP/dt (from 241 +/- 30 to 229 +/- 32 ms after 240 s; P < 0.001), accelerated LV pressure fall, did not alter peak (+)-dP/dt or peak systolic pressure, increased diastolic and systolic segment lengths, and decreased fractional shortening. Microscopic analysis revealed dispersed granulocytes attached to the EE. EE cells were visibly damaged only in a limited area surrounding the probe. Accordingly, high-power, high-frequency, continuous wave ultrasound reversibly modulated LV performance, presumably by transient alteration of EE function.

Animals↗
PubMed1991

Influence of systolic pressure profile on rate of left ventricular pressure fall.

We examined the influence of the systolic left ventricular pressure (LVP) waveform on the rate of isovolumetric LVP fall, as assessed by the time constant tau. Seven open-chest dogs were instrumented with a micromanometer in the left ventricle, with segment length gauges in the anterior and posterior midwall of the left ventricle, and with a balloon-tipped catheter in the proximal aorta. The intra-aortic balloon was inflated before the onset of ejection (early) or during midejection (late) to produce timed and graded increases in peak LVP of 2-20 mmHg. The rate of LVP fall slowed significantly more with late than with early increases in LVP (tau increased 1.5 +/- 0.5 vs. 0.5 +/- 0.3%/mmHg increase in peak LVP, respectively, P less than 0.001). For a similar increase in peak LVP, there was a progressively greater increase in tau when the timing of balloon inflation was progressively delayed from early to late ejection (in 10-ms increments). The differential effect of early vs. late pressure increases on tau was not related to regional differences in segment length behavior nor to an increase in regional nonuniformity between anterior and posterior sites. We conclude that under the experimental conditions of an intact, ejecting left ventricle, the systolic pressure profile is an important determinant of the rate of pressure fall. The rate of LVP fall slows in direct proportion to the magnitude of increase in systolic pressure. The sensitivity to systolic load increases progressively throughout the ejection period, so that the rate of LVP fall slows significantly more with late than with early pressure increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1990

Regulation of left ventricular pressure fall.

Left ventricular pressure (LVP) fall is a manifestation of relaxation and is therefore regulated by non-uniformity and load, besides regulation by muscle inactivation. Non-uniformity and load are important and independent regulators of LVP fall. Non-uniformity induces a premature onset and decreased rate of LVP fall. With regard to load, the effects of preload, systolic LVP levels and systolic LVP waveform are distinct. In order to assess underlying muscle inactivation with indexes of LVP fall, it is critical to control non-uniformity and various aspects of load. This control should be inherent in experiments designed to evaluate interventions. If careful control of non-uniformity and load cannot be achieved, at least the effects of non-uniformity and load on timing and rate of LVP falls should be appreciated. Isovolumetric left ventricular pressure fall is a complex event including a rapid early and slower late phase. As a consequence, LVP fall cannot be described by a single index. Peak--dP/dt is measured at the transition between early and late LVP fall. Its value can be affected by changes of both phases. Interpretation of peak-dP/dt should therefore be cautious. LVP fall at and after mitral valve opening might be regulated differently from late LVP fall, as evaluated by the time constant tau. Loading effects of LVP fall after mitral valve opening can therefore not always be predicted from changes in tau. Load dependence is a concept based on experimental observations in isolated cardiac muscle, which describes the separation in time between shorter isotonic and longer isometric twitches. Temporal separation is illustrated by the response of cardiac muscle to late systolic load.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Influence of loading patterns on peak length-tension relation and on relaxation in cardiac muscle.

To analyze the influence of loading patterns on cardiac pump performance and cardiac relaxation [corrected], the effects of preload on peak length-tension relation [corrected] and of systolic load clamps on peak length-tension relation and on relaxation were analyzed in isolated cat papillary muscles. Preload reduction and early loading clamps induced a shift to the left of the peak length-tension relation, that is, a smaller muscle length for the same tension at peak shortening. Unloading clamps induced a shift to the right of the peak length-tension relation, that is, a larger muscle length for the same tension at peak shortening. The effects of load clamps on relaxation depended on when they were applied during isotonic shortening. Changes induced by load clamps could not be summarized in terms of enhanced or delayed relaxation, illustrating that shortening duration, isometric tension decline and isotonic lengthening have different determinants. In conclusion, not only peak or mean systolic pressure but also the entire loading pattern has to be taken into account whenever pressure-volume data or relaxation variables are interpreted.

Animals↗
PubMed1989

Nonuniformity and volume loading independently influence isovolumic relaxation rates.

We examined the influence of loading conditions and nonuniformity of left ventricular (LV) function on the rate of LV pressure fall in seven anesthetized dogs. Loading conditions were altered with vena cavae occlusions and/or intravenous infusions of dextran. Nonuniformity was produced by injecting 8-20 ng of isoproterenol into the mild left anterior descending coronary artery to produce an asynchronous and early onset of segment lengthening in the anterior wall. Temporal and regional nonuniformity were quantified with indexes derived by comparing segment lengths in the anterior and posterior walls, measured with midwall sonomicrometers. The rate of LV pressure fall was assessed with peak -dP/dt, the time constant, tau, and the duration of isovolumic relaxation. Volume loading decreased the rate of LV pressure fall without altering the nonuniformity indexes. Intracoronary isoproterenol produced nonuniformity and decreased the rate of LV pressure fall without altering global loading conditions. The effects of isoproterenol (in a constant dose) were similar irrespective of the LV volume. We conclude that in the intact, ejecting left ventricle, loading conditions and nonuniformity are important determinants of the rate of LV pressure fall, but these two factors exert their influence by mechanisms that are largely independent.

Animals↗
PubMed1984

Coronary artery surgery in patients with myxoedema.

Thyroid replacement therapy in patients with myxoedema associated with coronary atherosclerosis often exacerbates angina or occasionally precipitates myocardial infarction. Coronary revascularization has been proposed for these patients. In an attempt to evaluate the risks of anesthesia and surgery in hypothyroidism against the possible occurrence of a coronary event during preoperative thyroid replacement therapy, we reviewed the literature and report an additional five hypothyroid patients undergoing coronary bypass grafting without operative complications. It seems recommendable not delay thyroid replacement therapy in hypothyroid patients, who need coronary artery surgery, until a few days after the intervention.

Acute Disease↗