Biomedical subjects
Publications and source records attributed to M Nitzan.
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Constant blood temperature in the pulmonary artery is assumed when the thermal dilution method is used for cardiac output determination. In some cases, however, slow temperature fluctuations (2-6 cycles per min.) occur in arterial and venous blood and interfere in the measurement. Those thermal fluctuations were investigated in the pulmonary artery and venae cavae of dogs. The temperature variations were found to be correlated with blood pressure waves: an increase of blood pressure was accompanied by an increase in the blood temperature in the pulmonary artery and a decrease in the blood temperature in the venae cavae. Therefore, measurement of the temperature of the pulmonary artery relative to that of the venae cavae does not rule out those fluctuations, and will not improve the thermal dilution method.
The noninvasive transient clearance method provides absolute quantitative measurement of skin blood flow. It is based on thermally insulating the skin under investigation and measuring the time constant of the resultant exponential skin temperature increase. Conventional assessment of the time constant, by measuring the temperature increase until final equilibrium skin temperature is achieved, has the disadvantage of long time of measurement. A procedure shortening the measurement time is presented. The time constant of the exponential temperature increase is calculated without obtaining the final equilibrium temperature. The method can be used for calculating the time constant of an exponential change of any variable, even though the asymptotic value of that variable is not known.
We have succeeded in recording short and middle latency vestibular evoked responses in human subjects. The head was held rigidly in a special, patented head holder, constructed individually for each subject, which gripped the teeth of the upper jaw. The stimulus consisted of 2/sec steps of angular acceleration impulses produced by a special motor with intensities of about 10,000 degrees/sec 2 and with a rise time of 1-2 msec. The electrical activity was recorded as the potential difference between special forehead and mastoid electrodes having a large, secure contact area with the skin. The activity was digitally filtered and averaged in 2 separate channels by means of a Microshev 2000 evoked response system. The short latency responses, with peaks at about 3.5 msec (forehead positive), 6.0 msec (forehead negative) and 8.4 msec (forehead positive; bandpass: 200-2000 Hz; average of 1024 trials), had amplitudes of about 0.5 microV. The middle latency responses had peaks at about 8.8 msec (forehead positive), 18.8 msec (forehead negative) and 26.8 msec (forehead positive; 30-300 Hz; N = 128 trials), with larger amplitudes (about 15 microV). These responses were consistently recorded in the same subject at different times and were similar in different normal subjects. Strenuous control experiments were conducted in order to ensure that these responses are not artefacts due to the movement of conducting media (head, electrodes and leads) in the electromagnetic field of the motor and are elicited by activation of normal labyrinths.(ABSTRACT TRUNCATED AT 250 WORDS)
A 7-year-old boy with glycogen storage disease type III developed transient acute cortical blindness associated with hypoglycemia on two separate occasions; the patient also demonstrated transient high-voltage slowing on the electroencephalogram over both occipital areas. This patient is the second examined in our pediatric department during a 5 year period with acute cortical blindness associated with hypoglycemia.
In the present study the effect of chemical sympathectomy on the development of small intestinal enzymes in the rat was analyzed. Eight doses of guanethidine sulfate were administered subcutaneously every 48 h to 34 newborn rats, starting at birth. The last dose was given at 14 days of age. Twenty-two littermates served as controls. Intestinal lactase, maltase, sucrase, and alkaline phosphatase were determined at 15, 17, 20, 23, and 25 days of age. Sympathectomy was demonstrated by reduction of the number of perikarya in the superior cervical ganglia in treated rats as compared with control rats. A normal developmental pattern of activities of the disaccharidases in the small intestine was observed in both groups. The activity of alkaline phosphatase was significantly lower (p less than 0.01) in the 15- and 17-day-old treated animals.
Umbilical artery velocity waves were obtained by Doppler ultrasonography before, during, and after 20 episodes of fetal heart rate (FHR) variable decelerations (VD) during the active stage of labor in 8 women. During 50% of the VD periods, the umbilical artery resistance flow parameters increased significantly (p < 0.01). The increase in resistance preceded the decrease in FHR in six episodes (30%) of VD (AR-VD group; arterial resistance VD) and did not precede the change in FHR in another ten episodes (50%) of VD (VR-VD group; venous resistance VD). In the AR-VD group the FHR accelerations occurred before the decelerations in only 1 case (17%), while in the VR-VD group FHR accelerations preceded the decelerations in 8 out of the 10 episodes (80%). Using these Doppler studies, it may be possible to differentiate between two groups of VD: AR-VD - which are caused by umbilical artery occlusion and thus preceded by a measurable increase in umbilical artery resistance - and VR-VD - which are not preceded by a measurable increase in umbilical artery resistance and may be caused by fetal hypoxia.
Umbilical artery flow curves were obtained by Doppler ultrasonography before, during, and after episodes of fetal bradycardia in the active stage of labor in 6 women. Between 126 and 1,607 Doppler wave forms were analyzed for each patient. During the periods of bradycardia all the umbilical artery resistance flow parameters increased (p < 0.00001). The increase in resistance did not precede the change in heart rate. This study presents an accurate and reproducible method for continuous evaluation of the changes in the impedance of fetal blood flow during fetal heart rate changes, thereby enabling detailed assessment of circulatory disturbances occurring during labor and delivery.
Evaluation of the adequacy of fetal growth by measurements of fetal size required theoretical formulae for the assessment of present size from previous measurements. The various models presented in the literature assume the same mathematical formula for the whole pregnancy. In this study, a model of different polynomial approximations for the early and late stages of the pregnancy is compared to two models which assume a single formula for both stages of the pregnancy. The standard error of estimate is lower for the sectioned model.
Ultrasound examination at 9 weeks of gestation in a 34-year-old primigravida showed a twin pregnancy, with discrepancy in the sizes of the two gestational sacs, whereas the crown-rump lengths and fetal heart rates were virtually identical-the result being an abnormal sac size/crown-rump length ratio (early oligohydramnios). By 14 weeks discordant heart rates and umbilical artery flow velocities were detected, the discordance between the twins increasing as pregnancy progressed. Biparietal diameters, femoral lengths, and abdominal circumferences were also progressively discordant, and at 28 weeks the smaller twin had no heart beat. At 30 weeks the patient was delivered of a live 1,350-gram infant and a 400-gram dead fetus. This case suggests, in contradistinction to several previous reports, that fetal discordance in twin pregnancies (and perhaps intrauterine growth retardation in general) may be present as early as the first trimester.
Skin blood flow and microvascular resistance were measured in the feet of hypertensive and normotensive subjects by the non-invasive transient thermal clearance method. Skin blood flow decreased and microvascular resistance increased as a function of systolic brachial blood pressure for the non-diabetic subjects who were not treated by vasoactive medication. The relationship between blood flow and systolic blood pressure for diabetic patients and for patients who were treated by enalapril was poor. The average resistance for non-diabetic patients treated by enalapril was lower than that of untreated non-diabetic subjects. For diabetic patients no significant difference in resistance between enalapril treated and untreated patients was found. The results demonstrate that for non-diabetic patients the role of microvascular resistance in hypertension is significant while it is less important in diabetic patients.