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Biomedical subjects

T M Smits

Publications and source records attributed to T M Smits.

11 recordsLinked to original sources
PubMed1998

[A swelling in the distal part of the thigh].

A swelling in the distal thigh may be caused by a tumour of bone or soft tissues, an aneurysm or an inflammation. Signs of inflammation may render interpretation more difficult. Four males aged 60, 48, 15 and 81 years had had a swelling in the popliteal space or above the knee, in some cases with pain. Supplementary examinations, especially MRI scanning and arteriography did not always result in a diagnosis. The diagnosis could be made, however, during operation: an empyemic thrombosed popliteal artery aneurysm, a liposarcoma, pyomyositis and suture dehiscence of a plastic prosthesis of the popliteal artery. After treatment, consisting of or started during the operation, uneventful recovery occurred.

Adolescent↗
PubMed1995

Variability of continuously measured arterial pH and blood gas values in the near term fetal lamb.

In fetal sheep, arterial blood gas values show considerable spontaneous fluctuations. The aim of the present study was to obtain quantitative data on fetal blood gas variability. Accurate assessment of the intraindividual variations can hardly be obtained from intermittent blood samples, but requires continuous measurement. For this purpose we developed a small extracorporeal flow-through cuvette, containing pH and blood gas electrodes and the fiber optic probe of an oximeter. The cuvette is connected through two catheters to the fetal circulation. Blood from the carotid artery flows through the cuvette at a constant rate of 2 mL/min and is drained into the jugular vein. Continuous recordings for 6 h were obtained from five chronically instrumented sheep fetuses at 134-137-d gestational age. Intraindividual variability of fetal arterial blood pH (pHa), partial pressure of arterial blood CO2 (Paco2) and O2 (Pao2), and saturation of arterial blood (Sao2) is quantitatively described. The individual variation coefficients ranged from 0.1 to 0.4% (pHa), from 1.4 to 7.6% (Paco2), from 2.5 to 5.5% (Pao2), and from 3.6 to 7.0% (Sao2). The 5th to 95 percentile intervals (delta) of the individual blood gas values ranged from 0.03 to 0.09 (pHa), from 0.3 to 1.6 kPa (Paco2), from 0.22 to 0.5 kPa (Pao2), and from 10.5 to 26.0% (Sao2). These findings indicate that considerable fluctuations in fetal arterial blood gases occur during a 6-h period. These fluctuations are associated with uterine contractures and changes in maternal and fetal activity.

Analysis of Variance↗
PubMed1992

The microvascular architecture of the scalp in the human fetus at term. Implications for measuring blood gases and flow rate.

A microscopic study is presented on the depth distribution of the microvessels in the scalp of two human fetuses at term. The basal membrane showed a smooth line without papillary structures resulting in a thin epidermal layer of 25 microns. The distance from the scalp surface to the periosteum appeared to be almost 1.8 mm. The capillary density showed a peak of approximately 1.2 capillary cross-sections per 10(4) microns 2 in the first 200 microns of the dermis. In the middle of the dermis the capillary density fell to 0.2 cross-sections per 10(4) microns 2 to rise again in the lower part of the dermis to 1.6 cross-sections per 10(4) microns 2, which remained the approximate count in the subcutaneous tissue. The arterioles and venules showed significant numbers in the lower part of the dermis and were virtually absent in the subcutis. Of all 4570 microvessel cross-sections that were studied in a tissue volume of 0.6 mm3, not a single one showed the features of an arteriovenous anastomosis. The possible implications for laser Doppler flowmetry and continuous blood gas measurement of the fetal scalp are discussed.

Blood Flow Velocity↗
PubMed1990

Scalp blood flow, measured by laser Doppler flowmetry, and transcutaneous PO2 and PCO2 in the lamb.

To describe the relation between scalp blood flow and transcutaneous PO2 and PCO2, these three signals were recorded simultaneously in eight experiments on four healthy lambs in the first weeks after birth. Scalp blood flow was recorded by a laser Doppler flow sensor that was incorporated in the transcutaneous PO2 electrode. Scalp blood flow was varied by applying a circular pressure on the scalp surrounding the sensors. A decrease in laser Doppler blood flow was associated with a decrease in transcutaneous PO2 and an increase in transcutaneous PCO2, according to a hyperbolic curve. The steep parts of the hyperbolic curves were observed at low scalp blood flow, whereas the flat parts were found at high flow values. Even during heat-induced hyperemia only a small part of these hyperbolic curves showed a reasonable independence of the transcutaneous blood gas values of changes in blood flow. In view of the previously observed decrease in intrapartum scalp blood flow, the present data render the transcutaneous measurement of blood gas values doubtful for fetal monitoring during labor.

Animals↗
PubMed1989

Fetal scalp blood flow as recorded by laser Doppler flowmetry and transcutaneous PO2 during labour.

Laser Doppler flowmetry was used to evaluate the relationship between the changes in scalp blood flow and transcutaneous PO2 (PtcO2) during labour. Laser Doppler flow (LDF) and PtcO2 were measured simultaneously in fourteen women using a combined sensor. Scatter diagrams of LDF and PtcO2 show a hyperbolic curve, i.e. at high flow levels PtcO2 is independent of the flow rate and will reflect the arterial PO2 value, whereas at lower flow levels PtcO2 becomes highly dependent on the blood flow rate. The latter situation occurred in most of the fetuses when labour progressed. An inverse relationship between LDF and PtcO2 was observed in two fetuses in those parts of the recordings which coincided with repetitive severe variable decelerations++ in the FHR tracing (r = -0.59 and -0.65), suggesting a compensatory increase in scalp blood flow during hypoxemia. It is concluded that the PtcO2 signal is considerably influenced by local scalp blood flow in the majority of the patients and thus is a questionable parameter for monitoring fetal carotid arterial PO2.

Blood Gas Monitoring, Transcutaneous↗
PubMed1987

Hyperventilation-induced changes in periodic oscillations in forehead skin blood flow measured by laser Doppler flowmetry.

Rhythmic oscillations in forehead skin blood flow were studied with the laser Doppler technique in thirteen healthy subjects. During voluntary hyperventilation, a three-fold increase in relative amplitude of the spontaneous rhythmic oscillations in forehead skin blood flow was observed, whereas mean blood flow decreased by 15%. During hyperventilation, the relative amplitude of the oscillations was on average 36% of the mean blood flow value. The mean incidence of the oscillations increased significantly, from 68% of the measuring time before, to 96% of the measuring time during hyperventilation. The oscillation frequency was not affected by hyperventilation. Before, during and after hyperventilation the average oscillation frequency was 0.140 Hz (8.4 min-1), 0.145 Hz (8.7 min-1) respectively. The application of heat or a local anaesthetic to the skin attenuated the relative amplitude of the oscillations in forehead skin blood flow during hyperventilation as well as before and after.

Adult↗
PubMed1986

Red blood cell flow in the fetal scalp during hypoxemia in the chronic sheep experiment: a laser Doppler flow study.

Reliable monitoring of arterial blood gas values in the fetal scalp microcirculation requires an unimpaired local skin blood flow. Previous studies have shown that in the fetus blood flow to "nonvital" organs and tissues is reduced during hypoxemia. However, data on fetal scalp blood flow during hypoxemia have not been reported. Therefore, the influence of hypoxemia on scalp blood flow was studied in four chronically catheterized fetal lambs of 125-135 days of gestation. Red blood cell flow in the fetal scalp was continuously measured by the laser Doppler method during nine experiments. Reducing the oxygen saturation of fetal carotid arterial blood from an average control value of 52 to 21% for 20 min resulted in an average decrease of the laser Doppler flow index of 7%. In vitro studies revealed that more than half of the observed decrease in laser Doppler flow index could be attributed to enhanced absorption of light from the HeNe-laser caused by the deoxygenation of oxyhemoglobin itself. In the first 20 min after hypoxia, fetal scalp blood flow remained below the prehypoxic value. It is concluded that moderate hypoxemia causes only a small decrease in fetal scalp blood flow, certainly when compared to the dramatic fall in scalp blood flow that has been observed when local or circular pressure is exerted onto the fetal scalp.

Animals↗
PubMed1984

Variability of fetal scalp blood flow during labour: continuous transcutaneous measurement by the laser Doppler technique.

Variability of fetal scalp blood flow was measured in 15 patients in labour. Using the continuous transcutaneous laser Doppler technique adapted for fetal intrapartum measurements, it was possible to obtain recordings from a cervical dilatation of 3 cm until delivery. The general trend of fetal scalp blood flow showed a decrease in the majority of the patients during the first and the second stages of labour, with a fall of more than 50% of the initial value at the end of the first stage in seven. During the second stage the decrease in flow was generally less pronounced, although in one fetus scalp blood flow fell to 18% of the initial level by the end of the second stage. Of all the uterine contractions recorded, 57% were accompanied by a transient decrease in blood flow, often by 40-50%, but a temporary increase in scalp blood flow was found in 25% of contractions. Caput succedaneum formation was associated with a more pronounced transient decrease in local scalp blood flow during contractions. It is concluded that during labour a considerable reduction in fetal scalp blood flow occurs. It follows that the reliability of fetal transcutaneous blood gas monitoring techniques, which need a substantial increase in local capillary blood flow, seems highly questionable.

Doppler Effect↗