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Biomedical subjects

P Foëx

Publications and source records attributed to P Foëx.

At least 19 recordsLinked to original sources
PubMed1992

Left ventricular regional function and relaxation: effects of inotropic stimulation.

The effects of increasing doses of two inotropes, isoproterenol and calcium chloride (CaCl2), on left ventricular regional myocardial function and isovolumic relaxation were studied in six anesthetized sheep. After baseline data, CaCl2 was given as intravenous boluses to yield doses of 10 mg/kg, 20 mg/kg, 40 mg/kg, 80 mg/kg, and 160 mg/kg. After a second series of baseline data were obtained, constant infusions of isoproterenol were begun with doses of 0.025 micrograms/kg/min, 0.05 micrograms/kg/min, 0.1 micrograms/kg/min, 0.2 micrograms/kg/min, and 0.4 micrograms/kg/min. During each stage of the protocol with both inotropes, data were recorded during acute constriction of the descending thoracic aorta. Left ventricular relaxation was assessed by analysis of peak negative left ventricular (LV) dP/dt and the time constant of isovolumic left ventricular relaxation (Trelax). Regional myocardial function showed little change in either apical or basal segments until high doses of the inotropes. Peak negative LV dP/dt significantly changed from baseline (775 +/- 60 mmHg/s) with 0.2 micrograms/kg/min (1780 +/- 400 mmHg/s, P < 0.05 v baseline) and 0.4 micrograms/kg/min (2,220 +/- 380 mmHg/s, P < 0.05 v baseline) of isoproterenol, and was unchanged by CaCl2. Trelax was significantly decreased by all doses of isoproterenol, whereas only one dose of CaCl2 decreased Trelax. Trelax was increased with afterloading and this effect was altered by isoproterenol. It is concluded that isoproterenol hastens, whereas CaCl2 does not alter, left ventricular relaxation. This may reflect beta-adrenergic modulation of calcium fluxes during isovolumic relaxation.

Animals↗
PubMed1992

Canine end-systolic pressure-length relationships: depressed by diltiazem, invalidated by ischemia.

This study was designed to determine whether the end-systolic pressure-length relationship (ESPLR) reflects changes in regional contractility during the imposition of graded ischemia, and whether it is modified by diltiazem during propofol anesthesia. Seven beagles were anesthetized and instrumented to measure left ventricular pressure and subendocardial segment lengths (sonomicrometry) in the region of the left anterior descending (LAD) and circumflex (LC) arteries. Afterload was increased by the tightening of a snare around the descending thoracic aorta. Pressure-length loops were constructed and the slope of the ESPLR and the x-axis intercept, Lo, were calculated. Graded ischemia of the apical myocardium only was accomplished by the tightening of a micrometer-controlled snare around the LAD to produce Critical Constriction (CC), Ischemia 1 and 2 (I1, I2), and Total Occlusion (TO). In the basal LC region, LAD ischemia had no effect on either the ESPLR slope or Lo. In contrast, the ESPLR slope in the LAD area was decreased by ischemia at I1 (-40%), increased at TO (+69%), and unchanged at CC and I2, and was reduced by diltiazem at CC and I2 (-31% and -36%, respectively). The LAD ESPLR Lo was increased by ischemia by 64% and 61% at I2, and 91% and 122% at TO, before and after diltiazem, respectively. In the LC region, diltiazem decreased systolic shortening and the ESPLR slope. These results indicate that diltiazem has negative inotropic properties in both ischemic and nonischemic areas. Also, Lo is not a constant and must always be redetermined for every intervention. In the absence of ischemia, the ESPLR may be a reliable measure of myocardial contractility.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Postoperative hypoxaemia after major abdominal vascular surgery.

We have studied the severity and duration of nocturnal hypoxaemia before operation and for the first five nights after operation after elective major abdominal vascular surgery. Oxygen supplementation was almost 100% effective in keeping oxygen saturation greater than 90% during the early postoperative period; however, 50% of patients spent prolonged periods with an SpO2 less than 85% during at least one night after operation. The risk of severe hypoxaemia persists well beyond the current prescription of supplementary oxygen in these high risk patients. A significant association exists between the mean preoperative overnight saturation value and the nocturnal saturation observed subsequently in the later postoperative period.

Adult↗
PubMed1992

Effect of graded infusion rates of propofol on regional and global left ventricular function in the dog.

We have studied the effects of graded infusion rates of propofol (0.2-0.5 mg kg-1 min-1) on left ventricular global and regional function, in eight acutely instrumented dogs. Global function was assessed by measurement of aortic and left ventricular pressure, LV dP/dtmax, aortic blood acceleration and stroke volume. Regional function was assessed by measurement of systolic shortening and the end-systolic pressure-length relationship. The response of the coronary circulation to short periods of occlusion was also assessed. Administration of propofol significantly reduced left ventricular preload, as indicated by reductions in end-diastolic pressure and length; contractility was depressed, the depression being greater in the apex than in the base of the left ventricle. High infusion rates impaired relaxation. Regulation of coronary blood flow was not disrupted. Reductions in preload and contractility contributed to the propofol-induced hypotension. After 60 min, recovery from the greatest infusion rate was incomplete.

Animals↗
PubMed1992

Effects of progressive myocardial ischaemia on systolic function, diastolic dysfunction, and load dependent relaxation.

OBJECTIVE: The aims were to determine (1) the relationship between changes in contractile function (systolic shortening) and the appearance of diastolic dysfunction (postsystolic shortening) during progressive regional left ventricular ischaemia; (2) the effects of increased afterload (acute constriction of the descending thoracic aorta) on ischaemic contractile dysfunction; and (3) the effects of loading during ischaemia on load dependent relaxation. METHODS: Regional myocardial function, using sonomicrometry, was measured in the short and long axes of the apex of the left ventricle of eight open chest anaesthetised dogs (16-20 kg). Progressive apical ischaemia was induced by graded reductions in left anterior descending coronary artery flow (critical constriction, ischaemia 1, ischaemia 2, total coronary occlusion, and postocclusive maximum reactive hyperaemia). Acute afterloading was induced by a snare placed around the descending aorta. RESULTS: Consistent decreases in systolic shortening and increases in postsystolic shortening relative to the total segmental shortening in the short axis of the apical region were seen with worsening ischaemia. Aortic constriction increased the magnitude of apical postsystolic shortening and decreased apical systolic shortening in the short axis during critical constriction, ischaemia 1, and ischaemia 2. Long axis function changed in a qualitatively similar but quantitatively different manner. There was a significant decrease in the load dependency of relaxation with total coronary occlusion. CONCLUSIONS: (1) Changes in systolic and diastolic function occurred concomitantly as mild regional myocardial ischaemia developed and intensified; (2) afterloading significantly worsened regional systolic and diastolic dysfunction during mild ischaemia; and (3) progression of regional ischaemia resulted in loss of load dependent relaxation.

Animals↗
PubMed1992

Regional interaction and its effect on patterns of myocardial segmental shortening and lengthening during different models of asynchronous contraction in the dog.

OBJECTIVE: The aim was to examine the effect of asynchrony and regional myocardial interaction on the pattern of segmental contraction and relaxation. METHODS: Three models of asynchrony were produced. Firstly the left anterior descending artery was abruptly occluded for 60 s. Secondly, the same artery was gradually occluded to produce four degrees of ischaemia based on the severity of the mechanical dysfunction. Finally, asynchrony was created by infusing isoprenaline (0.04 microgram.ml-1) into the left circumflex artery. Twelve anaesthetised beagles, weighing 16-21 kg, were used for the study. RESULTS: The patterns of contraction and relaxation were characterised by analysing the phases of shortening and lengthening, the peak lengthening rate (dL/dt), and the timing from the onset of systole to minimum systolic length. A consistent pattern of shortening and lengthening was evident during all three models of asynchrony. There were reciprocal relations between the extent of isovolumetric shortening in the normal segment and in the abnormal segment, and on occasion between the extent of isovolumetric shortening in the normal segment and the extent of isovolumetric lengthening in the same segment. Normal segments that showed minimal shortening or even some lengthening during isovolumetric systole tended to shorten beyond ejection, while segments that shortened significantly during isovolumetric contraction, lengthened earlier. Despite no change in isovolumetric shortening, segments also shortened after ejection when the opposite segment lengthened in late systole and early diastole. CONCLUSIONS: The pattern of shortening and lengthening depends on the path of contraction or on its entire loading pattern throughout systole. It is also possible that during early isovolumetric systole a segment can either be unloaded or preloaded by an opposing segment.

Animals↗
PubMed1992

Thoracic electrical bioimpedance measurement of cardiac output and cardiovascular responses to the induction of anaesthesia and to laryngoscopy and intubation.

Noninvasive methods of determining cardiac output (by thoracic electrical bioimpedance) and arterial pressure (by intermittent oscillometry) were used to record minute-by-minute changes in heart rate, mean arterial pressure, stroke volume, cardiac output and systemic vascular resistance following induction of general anaesthesia and laryngoscopy and intubation in 60 healthy female patients who were either unpremedicated, or premedicated with temazepam or papaveretum-hyoscine. Anaesthesia was induced with a sleep dose (3-5 mg.kg-1) of thiopentone and maintained with 70% nitrous oxide in oxygen with 0.5-1% enflurane. Tracheal intubation was facilitated by administration of vecuronium 0.1 mg.kg-1. Mean arterial pressure and cardiac output decreased maximally 5 min after induction in all premedication groups by mean estimates of 21-25% and 14-22% respectively. Heart rate increased initially one minute after induction, but decreased to less than the baseline value 5 min after induction. Systemic vascular resistance was unchanged. The stimulus of laryngoscopy and tracheal intubation was accompanied by a significant pressor response and tachycardia one minute after intubation (with mean increases in mean arterial pressure and heart rate of 29-34% and 22-33% respectively). The increase in mean arterial pressure was secondary to an increase in systemic vascular resistance (36-57%), and was accompanied by a decrease in stroke volume (-25 to -31%). These changes were significant in all three groups. Cardiac output decreased only in unpremedicated patients. There were wide variations in the different haemodynamic indices.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

[The evaluation of the end-ejection pressure-length relation as an index of regional contractility].

Although end-systolic pressure-length relationship (ESPLR) is now widely used as a regional substitute for the end-systolic pressure-volume relationship, there are some reservations about its use as an index of systolic performance. This study aimed at assessing whether by using end-ejection (zero aortic flow) as a definition of end-systole, ESPLR can be used to characterize myocardial performance independent of load, and if the choice of the region where to implant the sonomicrometers is critical. Ten anaesthetized dogs (16 +/- 2 kg) were instrumented with a left ventricular (LV) pressure micromanometer and an aortic flow probe. Sonomicrometers were implanted in the apical (L1) and the mid-ventricular (L2) regions of the anterior LV wall, and in the basal region of the lateral wall (L3). End-systolic pressure-length relationships were obtained during acute preload reduction induced by the inflation of a vena caval balloon. This evaluation was repeated after increasing end-diastolic pressure to 14-18 mmHg (delta PL), after increasing systolic pressure by 15 (delta P-I) and 25 mmHg (delta P-II) with graded descending aorta occlusion, and during dobutamine infusions at 2.5 (Db 2.5) and 5 micrograms/kg/min (Db5). End-systolic pressure-length relationships (r > 0.97; pressure range: 70-100 mmHg) were characterized by their slopes (Ees), the extrapolated intercept at zero pressure (L0) and the values of segment length at a pressure of 75 (L75) and 100 mmHg (L100). In all the myocardial regions studied by sonomicrometry, the increments in preload and afterload did not significantly shift ESPLR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Pressure-length loop area: its components analyzed during graded myocardial ischemia.

The changes in total pressure-length loop area were compared with changes in effective shortening area, systolic lengthening area and postsystolic shortening area (defined with respect to end-diastolic and end-systolic lengths) of the pressure-length loop during myocardial ischemia in seven anesthetized dogs instrumented for measurement of left ventricular pressure and regional segmental wall motion (sonomicrometry) in the minor axis of the apical region of the left ventricle. Ischemia was induced by gradual tightening of a micrometer-controlled snare around the left anterior descending coronary artery, which supplied the apical myocardium. Data were obtained at normal flow, after critical constriction (loss of pulsatile coronary flow), mild ischemia (ischemia 1: onset of regional dysfunction, i.e., postsystolic shortening and mild hypokinesia) and moderate ischemia (ischemia 2: marked hypokinesia). At each stage, acute afterloading was performed by partially occluding the descending thoracic aorta. The pressure-length loops were analyzed in terms of four areas: total loop area, effective shortening area, postsystolic shortening area and systolic lengthening area. Total loop area decreased only when marked hypokinesia was present (176 +/- 18.3 mm Hg x mm at ischemia 2 versus 245.1 +/- 26.9 mm Hg x mm at ischemia 1, p less than 0.05). However, effective shortening area (98.2 +/- 0.8% of total loop area at baseline; 93.8 +/- 2.4% at critical constriction; 76.3 +/- 7.2% at ischemia 1; 51.9 +/- 12.2% at ischemia 2) and postsystolic shortening area (1.8 +/- 0.8% of total loop area at baseline; 5.2 +/- 1.9% at critical constriction; 14.3 +/- 3/4% at ischemia 1; 23.8 +/- 5.1% at ischemia 2) changed significantly with each progressive stage of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Calcium-channel blockers and anaesthesia.

Verapamil was the first calcium-channel blocker (CCB). It has been used since 1962 in Europe then in Japan for its antiarrhythmic and coronary vasodilator effects. The CCB have become prominent cardiovascular drugs during the last 15 years. Many experimental and clinical studies have defined their mechanism of action, the effects of new drugs in this therapeutic class, and their indications and interactions with other drugs. Due to the large number of patients treated with CCB it is important for the anaesthetist to know the general and specific problems involved during the perioperative period, the interactions with anaesthetics and the practical use of these drugs.

Anesthetics↗
PubMed1991

Dose-related effects of isoflurane associated with low plasma concentrations of verapamil on global and regional function in normal and compromised canine myocardium.

Global and regional myocardial functions were studied in seven open-chest dogs with constant low plasma concentrations of verapamil as increasing concentrations of isoflurane (0.75, 1, 1.5 MAC) were administered in the presence of normal myocardial perfusion and after application of critical constriction of the left anterior descending coronary artery. In the presence of verapamil, increases in isoflurane concentrations caused dose-dependent myocardial depression both before and after critical coronary constriction. The systemic and coronary vasodilatation associated with high concentrations of isoflurane did not occur in the presence of verapamil. The association of verapamil with isoflurane caused regional myocardial dysfunction that worsened at high isoflurane concentrations. This regional dysfunction could not be antagonized in two dogs. The effects of isoflurane on regional function were not modified by application of a critical coronary constriction.

Animals↗
PubMed1991

Preoperative silent myocardial ischaemia: incidence and predictors in a general surgical population.

We have studied before operation 156 patients aged more than 40 yr presenting for elective vascular or non-vascular surgery, using ambulatory ECG monitoring to detect silent myocardial ischaemia (SMI). The prevalence of SMI was 18.2% in the vascular group (n = 102) and 7.6% in the non-vascular group (n = 54). A history of ischaemic heart disease, or an abnormal ECG suggestive of a previous myocardial infarction, predicted a high risk of SMI (28% compared with 9% in the absence of these variables). However, a significant amount of SMI (36% of the total) occurred in patients without one of the defined risk factors. In addition, 24 of the patients with abdominal aortic disease underwent cardiac gated blood pool (MUGA) scans. Abnormal ventricular wall function was observed in 62.5% of the patients. Twenty-nine percent of the patients studied with MUGA scans had SMI and 21% had ejection fractions less than 40%. A significant association (P less than 0.05) existed between the presence of SMI and a ventricular ejection fraction of less than 40%.

Adult↗
PubMed1991

Postoperative myocardial ischaemia: temporal association with nocturnal hypoxaemia.

Three patients presenting for elective aortic surgery were studied before operation and for up to 3 days after operation with ambulatory electrocardiographic monitoring and nocturnal pulse oximetry. Supplementary oxygen was administered for the first 2 days after operation and withdrawn on the 3rd morning after operation. Heart rate remained increased for the first 3 days after operation. Two patients developed episodes of myocardial ischaemia during the first 48 h after operation while their arterial oxygen saturation remained greater than 90%. On the third day, and during the third night after operation, both the severity and duration of myocardial ischaemia increased markedly, associated with arterial hypoxaemia. A temporal relationship between decreases in oxygen saturation and fluctuations in ST segment level were observed in the three patients.

Aged↗
PubMed1991

Non-invasive measurement of cardiac output by thoracic electrical bioimpedance: a study of reproducibility and comparison with thermodilution.

The performance and reproducibility of the BoMED NCCOM3 thoracic electrical bioimpedance cardiograph (TEB) has been evaluated in volunteers and patients. In resting supine volunteers, we determined the coefficient of variability over short time periods (30 min) and over several days, and examined the effects of differences in electrode type and electrode placement. The mean (range) intra-subject coefficients of variation (CV) for thoracic fluid index (TFI) and stroke volume (SV) were 1.0% (0.4-1.8%) and 4.7% (2.1-8.5%), respectively over a 30-min period. The corresponding CV were 5.6% (2.3-10.9%) and 10.9% (6.1-14.8%) for measurements made at rest on four separate occasions. Use of different electrode types (RedDot and Medicotest) resulted in differences in TFI (P less than 0.01), but not in mean values for SV or cardiac output (Q); their use in individual subjects revealed differences of up to 20% in SV and Q. Alterations in electrode placement by 5 cm in the horizontal and diagonal planes produced no significant changes in TFI, SV or Q; changes in the longitudinal plane produced a graded change. Increases of 5 cm and 10 cm in thoracic length produced mean increases in TFI of 9.8% and 39.8%, respectively, and mean decreases in Q of 8.4% and 16.7% and SV of 7.5% and 15.8%. TEB measurements of Q and SV were compared with thermodilution (TD) in 16 intensive care patients. Mean (SEM) Q by TEB was 5.63 (1.10) litre min-1 compared with TD 4.38 (0.72) litre min-1 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

End systolic pressure-length relations in halothane anaesthetised dogs: effects of regional ischaemia and inotropic agents.

STUDY OBJECTIVE: The aim was to investigate the effects of regional myocardial ischaemia, calcium, and verapamil on (a) the hysteresis and (b) slope and length axis intercept of the left ventricular end systolic pressure-length relationship. DESIGN: Segment length in myocardium supplied by the left anterior descending coronary artery was measured in anaesthetised dogs using sonomicrometry. Three levels of regional myocardial ischaemia were produced by stenosis and occlusion of the left anterior descending artery (ischaemia 1, ischaemia 2, and occlusion). A snare placed around the descending thoracic aorta was used to obtain temporary aortic occlusions. SUBJECTS: Seven open chested mongrel dogs were used, weight 17 kg (range 16-20). MEASUREMENTS AND MAIN RESULTS: After abrupt release of temporary aortic occlusions, end systolic lengths were greater than before the occlusion in the normal myocardium. This hysteresis was abolished by regional myocardial ischaemia. However, hysteresis was insensitive to calcium and verapamil. The length axis intercept of the end systolic pressure-length relationship was increased during ischaemia 2, during coronary occlusion, and after administration of verapamil; its slope was increased after coronary occlusion. CONCLUSIONS: (1) Viscoelastic properties of the myocardium make a major contribution to hysteresis of the end systolic pressure-length relationship; and (2) the length axis intercept of this relationship is not constant and its slope does not appear to be a sensitive indicator of regional myocardial contractility during regional ischaemia.

Anesthesia↗
PubMed1991

Effects of altered PaO2 and PaCO2 on left ventricular function and coronary hemodynamics in sheep.

The effects of acute changes in arterial carbon dioxide and oxygen tension, produced by altering the inspired gas mixtures while maintaining constant-volume intermittent positive pressure ventilation, on global function, regional left ventricular function, and coronary hemodynamics were studied in eight sheep during halothane anesthesia. Hypercapnia (Paco2, 73.5 +/- 2.3 mm Hg, mean +/- SD) increased heart rate, stroke volume, and cardiac output but decreased systolic shortening in the base of the left ventricle. Hypocapnia (PaO2, 24 +/- 1.5 mm Hg) decreased cardiac output and coronary flow below levels seen with hypercapnia but not below levels seen with normocapnia. Systolic shortening decreased in both apical and basal regions, and left ventricular relaxation was impaired as evidenced by a reduction of the nadir of LV dP/dt. Hypoxemia (PaO2, 39 +/- 1.5 mm Hg) elicited a hyperdynamic response of the circulation, increased coronary blood flow, and exhausted the coronary flow reserve. Neither changes in PaCO2 nor changes in PaO2 caused postsystolic shortening, although hypercapnia caused nonuniformity of contraction in the left ventricle. Thus, marked alterations in oxygen and carbon dioxide tensions do not cause left ventricular dysfunction, even though moderate hypoxia reduces the coronary flow reserve.

Anesthesia, Inhalation↗