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Biomedical subjects

Y Houdas

Publications and source records attributed to Y Houdas.

18 recordsLinked to original sources
PubMed1992

Cold exposure and ischemic heart disease.

Exposure to cold causes a vasoconstriction and a tachycardia, both resulting in a rise of blood pressure and cardiac work. This last effect may have a deleterious influence on people suffering from ischaemic heart disease (IHD). Moreover, coronary artery spasm could occur if vasoconstriction extends to the heart vessels. Epidemiologic studies have shown that mortality from IHD was correlated to the ambient temperature. There will be more deaths per day in the winter, and fewer in the summer. However, the daily number of deaths also increases during the heat waves. During a cold test, the coronary blood flow remains normal or slightly increased in normal subject. There is never a coronary artery spasm. Subjects who suffer from angina but have normal coronary arteries behave in the same way as normal subjects. Patients with IHD show a decrease in coronary blood flow. In a few cases, those patients may exhibit a coronary spasm with chest pain and even myocardial infarction. It is concluded that people with normal cardiovascular function are unaffected by cold stress whereas those with IHD may be crippled, although rarely, by exposure to cold, especially if they perform a physical work.

Blood Pressure↗
PubMed1992

[Left intraventricular gradients measured by Doppler echocardiography at rest, during exercise and during isoproterenol test in hypertrophic cardiomyopathy].

Doppler echocardiography has been shown to be an accurate method of assessing left ventricular outflow obstruction in hypertrophic cardiomyopathy (HCM). One of the characteristics of this pressure gradient is its variability and, therefore, we measured this parameter during dynamic exercise testing in 33 patients. The results were compared with those recorded during isoproterenol infusion, the reference stress test for patients with HCM. Submaximal exercise in the recumbent position is usually well tolerated and resulted in a 43% increase in heart rate and a 47% increase in pressure gradient. There was a significant correlation between resting and exercise outflow obstruction (r = 0.90; p = 0.001). Moreover, exercise echo revealed obstruction in 26% of patients without resting pressure gradients (latent obstruction). The interpretation of results obtained with isoproterenol infusion is more difficult: this test resulted in an important increase in the left ventricular pressure gradient (231%) and "revealed" obstruction in 84% of cases. Therefore, we believe that exercise is more physiological and better tolerated than isoproterenol stress infusion and should be adopted as the investigation of choice in HCM even without obstruction at rest. If it is not possible to perform the exercise or no outflow tract obstruction can be demonstrated, an isoproterenol infusion may be used but this is not always well tolerated and the results should be interpreted with caution.

Cardiomyopathy, Hypertrophic↗
PubMed1991

Influence of ventilation of the face on thermoregulation in man during hyper- and hypothermia.

It has been suggested that a thermal countercurrent exchange may occur in the cerebral vascular bed of humans, thereby creating for the brain a state of relative thermal independence with regard to the rest of the body. However, worrying questions have arisen concerning this suggestion. Experiments were carried out on seven young male volunteers. Hyper- and hypothermic conditions were produced by immersion in water at 38.5 degrees C and 25 degrees C, respectively. During the last few minutes of immersion, the face was cooled or warmed by ventilation with a 200 l.min-1 air flow at 5 degrees C or 40 degrees C, respectively. Internal and peripheral temperatures were recorded. Blood flow in the anastomotic vessels between face and brain was measured by Doppler techniques associated with computerized frequency analysis. The general responses were as classically described, i.e. an increase in peripheral and central temperatures during immersion in the warm bath and a decrease in these variables in the cold bath. The reactions produced by cooling or warming the face were small and easily explained by the direct changes of the heat load they induced. Whatever the thermal conditions, the blood flow in the anastomotic vessels between the vascular bed of the face and that of the brain was never reversed. It was concluded that there was no experimental evidence for an efficient thermal counter-current exchange in the vascular bed of the human head.

Adult↗