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Biomedical subjects

R Meloche

Publications and source records attributed to R Meloche.

At least 19 recordsLinked to original sources
PubMed1992

Maternal inspired oxygen concentration and fetal oxygenation during caesarean section.

This study was designed to determine whether fetal arterial and venous PO2 could be increased by increasing maternal FIO2 in the period between hysterotomy and birth. Two groups of ten patients were studied. All were anaesthetised with the same technique except for the FIO2 after hysterotomy. One group inspired 50% oxygen and the second group inspired 100% oxygen. Although the maternal arterial PO2 was higher at birth in the 100% O2 group (177.4 +/- 42.3 mmHg vs 281.0 +/- 94.2 mmHg), there were no differences between the arterial umbilical cord PO2 (19.3 +/- 5.7 mmHg vs 18.5 +/- 7.3 mmHg) and the venous umbilical cord PO2 (31.1 +/- 7.6 mmHg vs 33.0 +/- 10.8 mmHg). Awareness was present in one patient in the 50% O2 group and in four patients in the 100% O2 group but this difference was not statistically significant. It is concluded that a higher inspired maternal oxygen concentration between hysterotomy and birth does not result in any increase in fetal PO2.

Anesthesia, Inhalation↗
PubMed1989

[Is isoflurane a calcium antagonist?].

The vasodilating and myocardial depressant effects of isoflurane have been allocated to calcium channel blockade. The present study aimed to test this hypothesis by assessing the effect of isoflurane on the contractile response to potassium stimulation of vascular smooth muscle. Seventy two left anterior descending and circumflex coronary artery rings were removed in twelve dogs and mounted in organ chambers filled with Krebs-Ringer bicarbonate solution and aerated with 95% O2-5% CO2. Rings were pretreated with either 3.8% isoflurane (2.5 MAC in the dog) or 10(-8) mol.l-1 nifedipine, a calcium entry blocker. They were stimulated by addition of 10 to 150 mmol.l-1 potassium chloride. At 70 mmol.l-1 K+, the tension generated by the untreated rings was 119 +/- 4.25% of control, while in the isoflurane treated group the tension was 99 +/- 2.4% of control. In the opposite, the tension was 25 +/- 7.11% in the nifedipine treated rings. Likewise, when isoflurane was added to rings preconstricted with 40 mmol.l-1 potassium chloride, no relaxation occurred, while nifedipine produced relaxation. Isoflurane, unlike nifedipine, had a weak effect on ring tension. The calcium-entry blockade effect of isoflurane appeared weak, dose-dependent and virtually absent at clinical concentrations. Therefore, the vasodilation seen with clinical concentrations of isoflurane is mediated by mechanisms other than calcium-entry blockade.

Adult↗
PubMed1986

Respiratory phase locking during mechanical ventilation in anesthetized human subjects.

The coupling patterns between the rhythm of a mechanical ventilator and the rhythm of spontaneous breathing were studied in enflurane-anesthetized adult human subjects. The spontaneous breathing pattern was altered in response to different frequencies and amplitudes of forced lung inflations. A 1:1 phase locking (the frequency of the mechanical ventilator is matched by the frequency of spontaneous breathing with a fixed phase between the 2 rhythms) was observed in a range of up to +/- 40% of some of the subject's spontaneous breathing frequencies. During 1:1 phase locking, there were marked changes in the expiratory duration as measured from the electromyogram of the diaphragm. The phase relationship between onset of inflation and onset of inspiration depended on the frequency and amplitude of mechanical inflation. At ventilator settings that did not give 1:1 phase locking, other simple phase-locked patterns, such as 1:2 and 2:1, or irregular non-phase-locked patterns were observed. Reflexes arising from lung inflation, which may underlie the entrainment, are discussed in the context of these results.

Adolescent↗
PubMed1977

The use of aminophylline for correction of haemodynamic repercussions of clamping of the aorta.

Occlusion of the abdominal aorta induces an increased impedance to ejection, leading to a reduction in cardiac output. The magnitude of the haemodynamic disturbances seemed important enough to justify the use of a vasodilator drug. In that respect the use of aminophylline was evaluated in twelve patients. The potentially dangerous increase in systemic resistance is prevented by aminophylline, which effectively neutralizes the increase in afterload. Moreover, a positive inotropic action can be inferred from the increase in stroke volume and ventricular systolic work. It must be stressed that this drug must be withheld in patients with cardiac irritability, for it has a beta-mimetic action.

Aged↗
PubMed1977

Haemodynamic changes due to clamping of the abdominal aorta.

Haemodynamic changes due to aortic cross-clamping were examined in 18 patients. It has been shown that the distal occlusion of the abdominal aorta induces an increased impedance to ejection. Because the mechanisms controlling the auto-regulation of cardiac output and the circulatory reflexes are damped by anaesthesia, the augmentation of resistance is not followed by any increase in contractility or vasomotor tone and thus the cardiac output falls. Patients with chronic obstructive disease (Leriche) did not differ significantly from subjects with more acute obstruction (aneurysm), though the latter have a tendency to show more important changes in their haemodynamic response.

Adult↗
PubMed1975

Physiological changes associated with unilateral pulmonary ventilation during operations on the lung.

No important changes in the respiratory parameters were observed during one-lung anaesthesia. However, this kind of thoracic intervention can be accompanied by a dramatic fall in arterial oxygen tension. Methods to avoid tissue hypoxia have been described. In our series no complications whatever occurred in the operative and post-operative periods which could be related to the oxygenation of the patient.

Adult↗