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Biomedical subjects

D Laurent

Publications and source records attributed to D Laurent.

At least 91 records · Page 5Linked to original sources
PubMed1984

Sympathetic nervous system activation in postextrasystolic potentiation: role of catecholamine release in enhancement of ventricular function.

The role of catecholamines in postextrasystolic potentiation was assessed in 30 patients during continuous coupled right ventricular pacing. Hemodynamic data were recorded in 15 patients (group 1); in the other 15 patients (group 2), coronary blood flow and metabolic variables, including catecholamines, were measured. Data were recorded in the control state and after 10 minutes of coupled pacing. Both groups had similar control pulse rates and mean aortic pressures: these variables decreased abruptly by 32 beats/min and 12 mm Hg, respectively, (p less than 0.001 for each) after the initiation of coupled pacing. In group 1, all indexes of left ventricular function and contractility increased during coupled pacing (p less than 0.001 for each), thus confirming postextrasystolic potentiation. In group 2, coupled pacing increased coronary blood flow, myocardial oxygen consumption and free fatty acid uptake (p less than 0.001 for each) but not lactate extraction. Plasma epinephrine was unchanged, but norepinephrine levels increased in arterial (421 +/- 27 to 576 +/- 41 ng/liter) and coronary sinus plasma (611 +/- 46 to 836 +/- 46 ng/liter) (p less than 0.001 for both). Indirectly calculated norepinephrine release within the myocardium increased from 25.6 +/- 2.8 to 39.7 +/- 5.2 ng/min (SEM) (p less than 0.05), suggesting a sympathetic nervous system activation. It is argued that coupled pacing acutely lowered mean aortic pressure, leading to baroreflex sympathetic activation which may contribute to augmented cardiac contractility in postextrasystolic potentiation.

Adolescent↗
PubMed1984

Overall myocardial energetics in physiological conditions and in acute volume overloading.

Left ventricular heat production (PH,lv) was compared with myocardial O2 consumption (P met O2) and mechanical parameters in intact anaesthetized dogs before and after acute volume overload induced by a perfusion of LMW dextran. From myocardial blood flow and coronary arterio-venous temperature differences, the coronary heat loss was determined. Thermodilution techniques were used to estimate the ratio between heat carried away by the coronary system and total heat production as the left ventricular volumes. Compared with P met O2, PH,lv bore a linear correlation. Heat production per beat was highly correlated to mean systolic wall force, midwall circumferential length, midwall fibre shortening and mean circumferential shortening rate (MCSR). Mechanical efficiency computed from heat production (EH) appeared to be very close to the efficiency computed from oxygen consumption (EO). Acute overload was characterized by a very large increase in both stroke volume and MCSR. The dramatic increase observed in heart external power was accompanied by a moderate increase in PH,lv and mechanical efficiency. Nevertheless, the changes in efficiency appeared to be strongly dependent upon the changes observed in heart rate (HR). When HR was increased, the heat production per beat was moderately decreased and efficiency was drastically improved. Conversely, dogs in which HR remained stable exhibited a marked increase in the energetic cost of each beat, with efficiency being practically unmodified. Thus, since myocardial energetics is involved in acute volume overload, two possible means of adaptation may be considered: (a) tachycardia may alleviate the energetic cost of each beat, thus improving heart mechanical efficiency and (b) conversely, if HR remains stable, it may do so at the expense of the energetic cost of the myocardium for each beat, with efficiency not actually being enhanced.

Animals↗
PubMed1984

Conditions for effective Nd-YAG laser angioplasty.

To establish the optimal conditions for recanalisation of obstructed arteries without damage to vessel walls, a Nd-YAG laser coupled to a 0.2 mm diameter optic fibre was used on obstructed human cadaver coronary and peripheral arteries and on popliteal arteries in amputated limbs. Vaporization of atheromatous plaques was consistently obtained with an energy of 360-600 J and a diluted blood perfusate (3 g/100 ml haemoglobin) at a rate of 20 ml/min. The arterial wall was protected from thermal injury by inserting the optic fibre into an inflated balloon catheter and by cooling the system with the perfusate. Since recanalisation of occluded arteries was consistently obtained without damage to the arterial wall or debris and thin and flexible optic fibres were easy to guide in the arteries, percutaneous transluminal Nd-YAG laser angioplasty was used in obstructed femoral and popliteal arteries in three patients. The first European trials in man showed the method to be feasible, effective, and harmless, although further studies are required to improve penetration of the obstruction and increase the diameter of tunnel.

Angioplasty, Balloon↗
PubMed1984

[Energy cost of postextrasystolic potentiation in man].

The energetic costs of post-extrasystolic potentiation (PEP) were assessed by evaluating left ventricular function and coronary blood flow in 16 patients with different forms of cardiac disease during cardiac catheterisation under basal conditions and sustained coupled right ventricular pacing. The coronary blood flow was measured by thermodilution techniques with sampling in the aorta and coronary sinus to measure O2 concentration, glucose, and plasma lactate and catecholamine levels. Parameters of LV function were calculated from data obtained from biplane left cineventriculography. During PEP, the ejection fraction increased from 0.48 +/- 0.8 to 0.62 +/- 0.22, the mean velocity of circumferential fibre shortening from 0.79 +/- 0.37 to 1.12 +/- 0.45 circ/s (p less than 0.001) and systolic work from 97 +/- 46 to 139 +/- 67 g/m2 (p less than 0.05). Coronary blood flow increased from 176 +/- 60 to 305 +/- 155 ml/min; myocardial oxygen consumption per potentialized beat rose from 0.15 +/- 0.07 to 0.50 +/- 0.33 ml/beat (p less than 0.001) whilst cardiac efficiency fell from 19.1 +/- 8 to 9.2 +/- 4% (p less than 0.001). PEP was associated with increased myocardial noradrenaline secretion (-3.1 +/- 31.5 ng/min under basal conditions to 30.2 +/- 42.8 ng/min, p less than 0.05). Therefore, the inotropic effect of PEP imposes a high metabolic demand and is associated with increased myocardial noradrenaline secretion.

Adult↗
PubMed1982

Role of surface tension and tissue in rat lung stress relaxation.

When the volume of the lung is maintained constant after an initial change of volume, stress relaxation (SR) occurs as a slow decay of transpulmonary pressure (PTP). In order to define which structure in the lung is responsible for SR a multiple exponential fitting of the PTP variation has been made. Excised rat lungs were placed in a fluid-filled box with trachea connected to atmosphere and submitted to stepwise changes of volume. Single volume steps (0.2 ml) were performed for lungs filled with either air or saline and the variations of PTP were monitored until steady state was reached. An exponential model (time constant = 6.5 +/- 0.4 (SD) and 92 +/- 6 s) described adequately the SR for air-filled lungs (n = 6) whereas only one exponential (time constant = 6.7 +/- 1.3 s) was required for saline-filled lungs. Multiple volume step experiments were also performed in air-filled lungs to obtain pressure volume loops. These hysteresis loops have been adequately simulated by use of the exponential model. It can be concluded that (1) lung tissue and air-liquid interface are both responsible for the SR with, respectively, short and long time constants and (2) the same relaxation function is able to describe both stress relaxation and static hysteresis in such experimental conditions.

Animals↗
PubMed1982

A hybrid device for measurement of left ventricular heat production.

The presented hybrid system allows precise temperature measurements in various sites of the circulation, from the acquisition and preprocessing of dilution curves. From haemodynamic data and left ventricular heat production, an in situ estimate of left heart efficiency is made available. A simplifying hypothesis allows the determination of total left ventricular heat production from three data inputs: (1) the coronary sinus blood flowrate, (2) the thermal coronary veno-arterial difference, (3) the ratio of thermodilution curves areas recorded in the aortic root and the coronary sinus, following a rapid injection in the left ventricular cavity of cold isotonic glucose. Experiments were performed on anaesthetized, artificially ventilated, closed-chest dogs, into which five catheters and probes had been inserted.

Animals↗
PubMed1982

Improved method in the computer determination of plethysmographic thoracic gas volume.

To improve the computer determination of thoracic gas volume (TGV), two new approaches were worked out. 1) A new program was designed, which overcomes the difficulties encountered in the time recognition of the panting maneuver and rules out the artifacts. Such a procedure is based on the data analysis in the pressure-volume time derivatives plane. 2) A hyperbolic fitting of the signals recorded during the panting maneuver was introduced. This last procedure, lying on Boyle's law, has proved to be useful in case of large mouth pressure changes. In fact the error induced by the conventional linear fitting may reach 500 ml (9% of the TGV value).

Computers↗
PubMed1981

Correction for nonlinearity of body flow plethysmograph.

A modification of conventional signal processing for the pressure-compensated flow plethysmograph is proposed to correct the nonlinearity of the flow element that appears for high flows as encountered during forced expiration. Woven screens behave as porous media with a viscous and an inertial component in the resistance; this explains the nonlinearity (23% at 15.1.s-1 with a 400-mesh wire screen area = 50 cm2). It was shown that the pressure drop-flow relationship can be described by a second-degree equation, which can be included in the computation of the thoracic signal from the box pressure. The need for such a correction is evidenced by testing the plethysmograph with a flow step input (0-15 l.s-1) equivalent both in amplitude and in frequency to the thoracic flow during a forced expiration. Such correction for nonlinearity avoids an overestimation of the thoracic forced vital capacity of up to 0.5 liter in normal subjects.

Humans↗
PubMed1981

[A vascular complication of supra condylar fracture of the elbow. Report on a misleading arteriography. (author's transl)].

The authors have surgically explored the brachial artery in the course of operation for reduction and fixation of a supra-condylar fracture in a child. the artery appeared to be in spasm in an arteriography performed during operation, the artery being narrow but not obliterated. Arteriotomy, however, showed a lesion of the intima with blood clots. The value of arteriography is discussed.

Brachial Artery↗
PubMed1981

Determination of left ventricular heat production in working dog heart.

1 degree Total left ventricular heat production was reliably estimated from the coronary blood flow, the coronary arteriovenous thermal difference and the thermodilution curve areas recorded in aortic root and in coronary sinus after injection of cold glucose solution into the left ventricular cavity. The assumption was made that the distribution of a cold solution, purposely introduced into the coronary arteries, obeys the same law as the heat generated by the myocardium. 2 degrees Temperature measurements were achieved with thermistors and a linear ohmmeter. Experiments were performed on thoracotomized dogs, allowing the utilization of an ultrasonic method for determination of the entire coronary sinus blood flow diverted through a cannula positioned in the coronary sinus. The spontaneous changes in acid-base balance and hemodynamic state, which were not systematically avoided, provided a fairly large interval of variation for coronary flow and myocardial oxygen consumption. 3 degrees Within the power interval of 0.5-2.2 watts per 100 g of left ventricular weight, there was a good linear correlation between left ventricular oxygen consumption and the sum of left ventricular heat production and external pressure power. 4 degrees These results suggest that the proposed method is a valuable approach for determination of the cardiac energetics in the in situ working heart. This method permitted repeated determinations of left myocardial heat production and may lead to a practical approach for measuring the left ventricular efficiency in intact animals.

Animals↗
PubMed1981

[Relationship between symptoms and hemodynamics in aortic insufficiency (author's transl)].

To determine the relationship between functional classes (NYHA) and hemodynamics in patients (pts) with chronic aortic insufficiency, indices of left ventricular (LV) function derived from hemodynamic and biplane left cineventriculographic data were compared with the clinical status in 51 AI pts, including 15 pts in class I, 26 pts in class II and 10 pts in class III. Regurgitant fraction (0.55 +/- 0.15 mean +/- SD), cardiac index (3.1 +/- 0.7 l/mn/m2) and LV end-diastolic pressure (14 +/- 7 mmHg) were of the same order of magnitude in 3 classes patients. A significant correlation was evidenced between functional classes and 1/LV ejection fraction (0.53 +/- 0.13, 0.50 +/- 0.39, 0.42 +/- 0.17 in class I, II, III pts, respectively, p less than 0.04), 2/LV end-systolic volume (88 +/- 48, 90 +/- 31, 138 +/- 68 ml/m2 in class I, II and III pts, respectively p less than 0.02), 3/ and LV mass (168 +/- 57, 204 +/- 94, 291 +/- 128 g/m2 in class I, II and III pts respectively, p less than 0.003). Only the latter parameter could discriminate symptomatic from asymptomatic AI pts.

Adult↗
PubMed1980

Hydrostatic mechanism in the roll-over test.

The roll-over test has been reported to predict pregnancy-induced hypertension. The arm used to record blood pressure has never been specified. Since the level of the arm with reference to the heart is of great importance in the interpretation of blood pressure, we recorded the roll-over response (blood pressure change from left lateral to supine position) first in the right and then in the left arm of 9 men and 8 nonpregnant women. In addition, blood pressure was measured simultaneously in both arms in 10 pregnant primigravidas. In the men and nonpregnant women the mean diastolic blood pressure after rolling over rose when the right arm was used and fell when the left arm was used. The difference in the roll-over response (right versus left arm) was accounted for by the hydrostatic effect produced by the vertical distance between the corresponding brachial arteries with the subject in the left lateral recumbent position. In the pregnant subjects as well, there was a difference between the roll-over response in the right versus left arm, accounted for by hydrostatic factors. However, the increase in blood pressure was greater for both arms, suggesting a real change in central blood pressure.

Adult↗