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J W Hicks

Publications and source records attributed to J W Hicks.

At least 37 records · Page 2Linked to original sources
PubMed1999

Respiratory consequences of feeding in the snake Python molorus.

Snakes can ingest large meals and exhibit marked increases in metabolic rate during digestion. Because postprandial oxygen consumption in some snakes may surpass that attained during exercise, studies of digestion offers an alternative avenue to understand the cardio-respiratory responses to elevated metabolic rate in reptiles. The effects of feeding on metabolic rate, arterial oxygen levels, and arterial acid-base status in the snake Python molorus are described. Four snakes (180-250 g) were cannulated in the dorsal aorta and blood samples were obtained during 72 h following ingestion of a meal (rat pups) exceeding 20% of body weight. Oxygen consumption increased from a fasting value of 1.71 +/- 0.08 to 5.54 +/- 0.42 ml kg-1 min-1 at 48 h following feeding, and the respiratory gas exchange ratio increased from 0.67 +/- 0.02 to a maximum of 0.92 +/- 0.03 at 32 h. Plasma lactate was always less than 0.5 mM, so the postprandial increase in metabolic rate was met by aerobic respiration. In fasting animals, arterial PO2 was 66 +/- 4 mmHg and haemoglobin-O2 saturation was 92 +/- 3%; similar values were recorded during digestion, but haematocrit decreased from 15.8 +/- 1.0 to 9.8 +/- 0.8 due to repeated blood sampling. Plasma [HCO3-] increased from a fasting level of 19.3 +/- 0.8 to 25.8 +/- 1.0 mmol l-1 at 24 h after feeding. However, because arterial PCO2 increased from 21.1 +/- 0.5 to 27.9 +/- 1.4 mmHg, there was no significant change in arterial pH from the fasting value of 7.52 +/- 0.01. Acid-base status returned to pre-feeding levels at 72 h following feeding. The increased arterial PCO2 is most likely explained by a reduction in ventilation relative to metabolism, but we predict that lung PO2 does not decrease below 115 mmHg. Although ingestion of large meals is associated with large metabolic changes in pythons, the attendant changes in blood gases are relatively small. In particular, the small changes in plasma [HCO3-] and stable pH show that pythons respond very differently to digestion than alligators where very large alkaline tides have been observed. It is unclear why pythons and alligators differ in the magnitude of their responses, but given these interspecific differences it seems worthwhile to describe arterial blood gases during digestion in other species of ectothermic vertebrates.

Acid-Base Imbalance↗
PubMed1999

Goblet cell-specific expression mediated by the MUC2 mucin gene promoter in the intestine of transgenic mice.

The regulation of MUC2, a major goblet cell mucin gene, was examined by constructing transgenic mice containing bases -2864 to +17 of the human MUC2 5'-flanking region fused into the 5'-untranslated region of a human growth hormone (hGH) reporter gene. Four of eight transgenic lines expressed reporter. hGH message expression was highest in the distal small intestine, with only one line expressing comparable levels in the colon. This contrasts with endogenous MUC2 expression, which is expressed at its highest levels in the colon. Immunohistochemical analysis indicated that goblet cell-specific expression of reporter begins deep in the crypts, as does endogenous MUC2 gene expression. These results indicate that the MUC2 5'-flanking sequence contains elements sufficient for the appropriate expression of MUC2 in small intestinal goblet cells. Conversely, elements located outside this region appear necessary for efficient colonic expression, implying that the two tissues utilize different regulatory elements. Thus many, but not all, of the elements necessary for MUC2 gene regulation reside between bases -2864 and +17 of the 5'-flanking region.

Animals↗
PubMed1999

Hypoxic hypometabolism in the anesthetized turtle, Trachemys scripta.

A hypometabolic response during acute exposure to hypoxia has been measured in both endothermic and ectothermic vertebrates. In the turtle, we determined the metabolic response to normocapnic hypoxia and hypercapnic hypoxia. In addition, we tested the hypothesis that hypoxic hypometabolism was a regulated response that did not depend on O(2) availability. Metabolic, cardiovascular, and blood gas measurements were collected in anesthetized turtles under two conditions: during normocapnic hypoxia [fractional inspired O(2) FI(O(2)) = 0.1 and 0.05] and during hypercapnic hypoxia [FI(O(2)) = 0.1 and 0.05 plus fractional inspired CO(2) (FI(CO(2))) = 0.05]. During normoxia, rate of O(2) consumption (VO(2)) was 0.82 ml. min(-1). kg(-1) and was reduced by nearly 30% at the lowest FI(O(2)). Normocapnic hypoxia of FI(O(2)) = 0.1 had no significant effect on VO(2). The addition of 5% CO(2) to the inspired air did not enhance the effects of hypoxia. Injections of 2,4-dinitrophenol increased VO(2) during hypercapnic hypoxia in some animals to levels greater than those measured during normoxia. We conclude that hypoxia produces a hypometabolic state in anesthetized turtles, and the pharmacological stimulation of VO(2) counteracts the effects of hypoxia on metabolism. The hypoxic hypometabolism in turtles most likely represents a regulated response and does not reflect limited O(2) availability at the cellular level. Finally, we hypothesize that hypoxemia induced by the right-to-left cardiac shunt often associated with diving may trigger the development of a hypometabolic state and therefore contribute to the prolongation of aerobic dive times.

2,4-Dinitrophenol↗
PubMed1997

MUC3 human intestinal mucin. Analysis of gene structure, the carboxyl terminus, and a novel upstream repetitive region.

MUC3 is a large mucin glycoprotein expressed by the human intestine and gall bladder. In this manuscript, we present details of the deduced protein structure of MUC3. The MUC3 carboxyl-terminal domain is 617 residues in length, including 511 residues of a non-repetitive mucin-like domain (27% Thr, 22% Ser, and 11% Pro) and a 106-residue Cys-rich domain with homology to the epidermal growth factor (EGF) -like structural motifs found in many proteins. The region of MUC3 located upstream of the previously described 51-base pair (bp) tandem repeats, which encode a major Ser and Thr-rich domain, consists of a second type of repetitive structure with an imperfect periodicity of approximately 1125 bp. This domain is also mucin-like and appears to be considerably larger than 2000 residues (6000 bp). The MUC3 gene itself is large and complex. Using pulse field gel electrophoresis and blot analysis, the smallest fragment found that contained all human genomic DNA hybridizing to the 51-bp tandem repeat probe was 200 kilobases with restriction enzyme SwaI. Both PvuII and PstI produced two sets of hybridizing fragments that were hypervariable within the human population with a pattern suggestive of both a variation in the number of tandem repeats (VNTR) and sequence polymorphism. These fragments varied independently of each other, but no genetic recombination was detected in a study of 40 human families. Thus, the MUC3 gene encodes a very large glycoprotein with a structure very different from that of any mucin currently described.

Amino Acid Sequence↗
PubMed1997

Identification and characterization of the MUC2 (human intestinal mucin) gene 5'-flanking region: promoter activity in cultured cells.

The initiation point for MUC2 gene transcription is located within a 7000-base GC-rich region of the mucin gene cluster found on chromosome 11p15.5. The promoter activity of the 5'-flanking region of the MUC2 gene was examined following its cloning into the luciferase-producing pGL2-Basic reporter vector. A short segment comprising bases -91 to -73 relative to the start of transcription was found to be important for basal promoter activity in all cell lines tested. Electrophoretic mobility shift assays demonstrated nuclear protein binding to this region, which contains the consensus CACCC motif (5'-GCCACACCC). This element has been shown to be functionally important in several promoters that are active in diverse cell types. Competition experiments using an Sp1 oligonucleotide and antibody supershift experiments indicated that both Sp1 and other Sp1 family members bind to this element. Inclusion of the region between bases -228 and -171 in pGL2-Basic constructs increased normalized luciferase reporter activity by almost 3-fold in C1a cells, which produce relatively high levels of MUC2 mRNA. Significantly lower levels of normalized luciferase activity resulted when the same construct was transfected into cultured cell lines that express low or undetectable levels of MUC2, suggesting a possible role for this region in conferring cell-type specificity of expression. We also demonstrate, using actinomycin D, that the MUC2 mRNA is long-lived, at least in cultured cells. Moreover, no evidence was found that the MUC2 mRNA turned over more rapidly in LS174T cells, which produce relatively low levels of MUC2 mRNA, as compared with C1a cells, which produce high levels of mRNA. Thus a long mRNA half-life appears to be an important mechanism involved in achieving elevated levels of MUC2 mRNA.

Amino Acid Sequence↗
PubMed1997

The effects of artificial lung inflation on pulmonary blood flow and heart rate in the turtle Trachemys scripta.

As for most ectothermic vertebrates, the breathing pattern of turtles is episodic, and pulmonary blood flow (Qpul) and heart rate (fH) normally increase several-fold during spontaneous ventilation. While some previous studies suggest that these cardiovascular changes are caused by stimulation of pulmonary stretch receptors (PSRs) during ventilation, it has been noted in other studies that blood flows often change prior to the initiation of breathing. Given the uncertainty regarding the role of PSRs in the regulation of central vascular blood flows, we examined the effect of manipulating lung volume (and therefore PSR stimulation) on blood flows and heart rate in the freshwater turtle Trachemys scripta. Turtles were instrumented with blood flow probes on the left aortic arch and the left pulmonary artery for measurements of blood flow, and catheters were inserted into both lungs for manipulation of lung volume. In both anaesthetized and fully recovered animals, reductions or increases in lung volume by withdrawal of lung gas or injection of air, N2, O2 or 10% CO2 (in room air) had no effect on blood flows. Furthermore, simulations of normal breathing bouts by withdrawal and injection of lung gas did not alter Qpul or fH. We conclude that stimulation of PSRs is not sufficient to elicit cardiovascular changes and that the large increase in Qpul and fH normally observed during spontaneous ventilation are probably caused by a simultaneous feedforward control of central origin.

Animals↗
PubMed1997

Ventilation and gas exchange in lizards during treadmill exercise.

The extent to which lizards ventilate their lungs during locomotion is controversial. Direct measurements of airflow across the nostrils suggest a progressive reduction in tidal volume and minute ventilation with increased running speed, while other studies have demonstrated that arterial PO2 remains constant during exercise. To resolve these conflicting findings, we measured minute ventilation and gas exchange rate in five specimens of Varanus exanthematicus and five specimens of Iguana iguana during treadmill locomotion at speeds between 0.14 and 1.11ms-1 at 35 degrees C. These speeds are much lower than maximal running speeds, but are greater than the maximal aerobic speed. In both species, the ventilatory pattern during locomotion was highly irregular, indicating an interference between locomotion and lung ventilation. In Varanus exanthematicus, treadmill locomotion elicited a six- to eightfold increase in minute ventilation from a pre-exercise level of 102mlkg-1min-1, whereas the rate of oxygen uptake increased approximately threefold (from 3.9 to 12.6mlkg-1min-1). After exercise, both minute ventilation and gas exchange rate decreased immediately. Because minute ventilation increased more than did oxygen consumption, an increase in lung PO2 during exercise is predicted and, thus, Varanus exanthematicus appears effectively to ventilate its lungs to match the increased metabolic rate during locomotion at moderate speed. In Iguana iguana, both minute ventilation and gas exchange rate increased above resting values during locomotion at 0.28ms-1, but both decreased with further increases in locomotor speed. Furthermore, following exercise, both minute ventilation and oxygen uptake rate increased significantly. Iguana iguana, therefore, appears to be unable to match the increased oxygen demand with adequate ventilation at moderate and higher speeds.

Animals↗
PubMed1996

Adrenergic and cholinergic response of ventricular muscle from the turtle, Trachemys (Pseudemys) scripta.

Muscle strips were dissected from the ventricle of the turtle, Trachemys (Pseudemys) scripta. Individual strips were placed in a muscle bath, set at a resting tension of three grams and electrically paced at 24 min(-1) for a control period of 1 hr. Cumulative dose-response curves were constructed using the adrenergic agonist, epinephrine (Epi) and the cholinergic agonist, metacholine (MCh). The administration of Epi to the muscle bath resulted in a dose-dependent increase in active tension development. The maximum tension developed was 40% above the control values and the concentration producing a half-maximal response (EC50) was 7.5 x 10(-7) M. The positive inotropic effect of Epi was diminished following the administration 1 x 10(-7) M propranolol. This reduced the maximum active tension by over 80% at the highest dose of Epi. In addition, the EC50 was increased to 8.9 x 10(-6) M. The administration of MCh resulted in a dose-dependent decrease in active tension development. The maximum decrease in active tension was 35% below the control values and the EC50 was 2.5 x 10(-6) M. The negative inotropic effect of MCh was diminished by the application of 1 x 10(-6) M atropine, with the EC50 increasing to 2.5 x 10(-4) M. These findings show that the isolated, in vitro turtle ventricle responds to adrenergic and cholinergic agonist. The results of this study support the hypothesis that the ventricular function, in reptiles, is controlled by both subdivisions of the autonomic nervous system.

Acetylcholinesterase↗
PubMed1996

The interaction of pulmonary ventilation and the right-left shunt on arterial oxygen levels.

In adult mammals, arterial blood gases closely reflect lung gas composition, and arterial blood gases can, therefore, be effectively regulated through changes in ventilation. This is not the case among most ectothermic vertebrates, where the systemic and pulmonary circulations are not completely separated, resulting in central vascular shunts. In the presence of a right-to-left shunt (R-L shunt), the O2 levels (PO2 and haemoglobin O2-saturation) of systemic arterial blood are depressed relative to those of the blood returning from the lungs. Arterial blood gas composition is, accordingly, not determined only by ventilation, but also by the magnitude of admixture as well as the blood gas composition of systemic venous blood. Changes in the central shunt patterns, therefore, represent an alternative mechanism by which to control arterial blood gas levels. The primary aim of this report is to evaluate the relative importance of the R-L shunt and ventilation in determining arterial blood gas levels. Using standard equations for gas exchange and the two-compartment model, we predicted arterial O2 levels at physiologically relevant levels of ventilation, R-L shunt and blood flows. The analyses show that the effects of changing ventilation and the size of the R-L shunt on arterial O2 levels vary with parameters such as the rate of O2 uptake, the blood O2-carrying capacity and the level of hypoxia. The relative importance of ventilation and the R-L shunt in determining arterial PO2 values is largely explained by the sigmoidal shape of the O2 dissociation curve. Thus, if lung PO2 is high relative to blood O2 affinity, a large change in ventilation may have little effect on pulmonary venous O2 content, although PO2 may have changed considerably. If an R-L shunt is taking place, this, in turn, implies that arterial O2 content is affected only marginally, with a correspondingly small effect on PO2. These predictions are discussed in the light of the limited existing experimental data on cardiac shunts in lower vertebrates; we propose that, in future experiments, the measurement of both ventilatory and cardiovascular parameters must be combined if we aim to understand the regulation of arterial blood gas levels in lower vertebrates.

Animals↗
PubMed1996

The effect of altering pulmonary blood flow on pulmonary gas exchange in the turtle Trachemys (Pseudemys) scripta.

In resting reptiles, the PO2 of pulmonary venous return (PLAO2; left atrial blood) may be 20 mmHg (1 mmHg = 0.1333 kPa) lower than the PO2 of gas in the lung. This level of PO2 is considerably higher than that observed in resting mammals and birds and results from ventilation-perfusion (V/Q) heterogeneity, pulmonary diffusion limitation and intrapulmonary shunting. However, the relative contribution of each of these factors is unknown. Many reptiles, particularly chelonians, exhibit an intermittent ventilation pattern where pulmonary blood flow (QL) increases during the ventilatory periods and, therefore, we hypothesized that V/Q matching would improve with increasing QL. We applied the multiple inert gas elimination technique in anaesthetized turtles at 22 degrees C. Turtles were continuously ventilated at a rate of 140 ml kg-1 min-1, equivalent to the rate of ventilation within a ventilatory period. Trace amounts of six inert gases were infused through the jugular vein. Blood samples from the pulmonary artery and the left atrium and mixed expired gases were collected for analysis. QL was reduced by a factor of six (low flow) using a vascular occluder placed around the common pulmonary artery or increased by a factor of two (high flow) through bolus injection of adrenaline. V/Q heterogeneity was significantly reduced with increasing pulmonary blood flow (P < 0.05). Consistent with these changes, the effective lung-pulmonary artery PO2 difference (PLO2-PLAO2) was reduced (P < 0.05) from 58 +/- 16 mmHg to 29 +/- 5 mmHg (means +/- S.E.M.) and PLAO2 increased significantly (P < 0.05) from 88 +/- 17 mmHg (low flow) to 120 +/- 14 mmHg (high flow). There was evidence of pulmonary diffusion limitation under all conditions, which was unchanged with increasing blood flow. These findings suggest that increased pulmonary blood flow during a ventilatory period results in both temporal and spatial matching of ventilation and perfusion, without altering pulmonary diffusion limitation.

Animals↗
PubMed1996

Analysis of cardiac shunting in the turtle Trachemys (Pseudemys) scripta: application of the three outflow vessel model.

Blood distribution within the ventricle was analysed in acutely prepared turtles Trachemys scripta by measuring the oxygen concentration and flow rates of blood in the central vessels. Pulmonary (Qp) and systemic (Qs) blood flow rates were similar when total cardiac output (Qtot) was below 40 ml min-1 kg-1. Above this value, increments of Qtot were directed to the pulmonary circuit, with Qs levelling off at approximately 20 ml min-1 kg-1. When Qtot was larger than 40 ml min-1 kg-1, the systemic circuit was almost exclusively perfused by left atrial blood and systemic venous return was almost all directed towards the lungs. Blood oxygen levels and flow rates were consistently higher in the right aorta than in the left aorta. Blood movement within the ventricle, coupled with differences in ejection timing, is probably the decisive factor determining this pattern of blood distribution in the turtle heart.

Animals↗
PubMed1996

The mechanism of cardiac shunting in reptiles: a new synthesis.

The mechanism of cardiac shunting in reptiles is controversial. Recent evidence suggests that a right-to-left shunt in turtles results primarily from a washout mechanism. The mechanism that accounts for left-to-right (L-R) shunting is unresolved. This study used haemodynamic analysis and digital subtraction angiography to determine the mechanism of L-R cardiac shunting in the turtle Trachemys (Pseudemys) scripta. Animals were instrumented with ultrasonic blood flow probes (Transonic Systems, Inc.) for the measurement of total pulmonary blood flow and total systemic blood flow. In addition, catheters were inserted into the common pulmonary artery (PA), the systemic arteries, the left atrium and right atrium. These catheters were used for the measurement of blood pressure or for the infusion of radio-opaque material. Haemodynamic conditions were altered by electrical stimulation of the afferent (VAF) or efferent vagal nerves or by infusion of vasoactive drugs. Under control conditions, the peak systolic pressure in the systemic arteries was slightly higher than that in the PA (30.6 versus 28.3 mmHg; 4.08 versus 3.77 kPa), whereas diastolic pressure in the PA was significantly less than that in the systemic arteries (9.8 versus 24.4 mmHg; 1.31 versus 3.25 kPa). During VAF stimulation, the peak systolic pressures in the PA and aortae almost doubled. Diastolic pressure in the systemic arteries also doubled, but it increased by only 45% in the PA. Ejection of blood into the PA preceded that into the left aorta by 53 ms under control conditions. This difference increased (by as much as 200 ms) as the difference in the diastolic pressures between the two circulations increased during VAF stimulation. This resulted in the development of a large net L-R shunt. Under these conditions, digital subtraction angiography showed that the L-R shunt resulted from a combination of both washout and pressure mechanisms.

Angiography, Digital Subtraction↗
PubMed1996

Cardiorespiratory synchrony in turtles.

Many reptiles, particularly diving species, display characteristic cardiovascular changes associated with lung ventilation (cardiorespiratory synchrony). Previous studies on freshwater turtles show that heart rate and pulmonary blood flow rate (Qpul) increase two- to fourfold during ventilation compared with breath-holding, and some studies report concomitant decreases in systemic blood flow rate (Qsys). The primary aim of this study was to provide a detailed description of cardiorespiratory synchrony in free-diving and fully recovered turtles (Trachemys scripta). During breath-holds lasting longer than 5 min, Qpul averaged 15 ml min-1 kg-1 and increased more than threefold to a maximum value of 50 ml min-1 kg-1 during ventilation. Qsys also increased during ventilation compared with during breath-holds lasting longer than 5 min (from 44 to 73 ml min-1 kg-1 during ventilation). Neither Qpul nor Qsys was affected by the number of breaths in the ventilatory periods. Changes in Qpul and Qsys were accomplished entirely through a significant increase in heart rate during ventilation, while total stroke volume (systemic+pulmonary) remained constant. Irrespective of the ventilatory state, Qsys exceeded Qpul by 20-30 ml min-1 kg-1. Nevertheless, because Qpul increased relatively more than Qsys during ventilation, Qpul/Qsys increased from 0.29 during apnoea to 0.80 during lung ventilation. This study confirms cardiorespiratory synchrony in the turtle Trachemys scripta but, in contrast to earlier studies, a net right-to-left cardiac shunt prevailed regardless of ventilatory state.

Animals↗
PubMed1995

Human dipeptidyl peptidase IV gene promoter: tissue-specific regulation from a TATA-less GC-rich sequence characteristic of a housekeeping gene promoter.

The dipeptidyl peptidase IV gene encodes a plasma-membrane exopeptidase that is highly expressed in small intestine, lung and kidney. In order to better understand the mechanisms responsible for this tissue-specific expression we cloned, sequenced and functionally characterized the 5'-flanking region of the human dipeptidyl peptidase IV gene. The first 500 bases of the 5'-flanking sequence constituted an unmethylated CpG island, contained several Sp1-binding sites and lacked a consensus TATA box, all characteristics of gene promoters lacking tissue-specific expression. RNase-protection analysis using both small intestinal and Caco2 cell RNA indicated that the dipeptidyl peptidase IV transcript was initiated from no fewer than six major and 12 minor start sites. The 5'-flanking sequence also exhibited functional promoter activity in transient transfection experiments. Here, various lengths of the sequence were cloned upstream of a luciferase gene and introduced into cultured cells using lipofectin. A region located between bases -150 and -109 relative to the start of translation was found to be important for high-level promoter activity in both Caco2 and HepG2 cells. Moreover, Caco2 cells and HepG2 cells, which express high levels of dipeptidyl peptidase IV activity, exhibited much higher normalized luciferase activity after transfection than did 3T3, Jurkat or COS-7 cells, which have low enzyme levels. Sodium butyrate was found to increase both enzyme activity and normalized luciferase in HepG2 cells. Thus the dipeptidyl peptidase IV promoter possesses the ability to initiate transcription in a tissue-specific fashion in spite of having the sequence characteristics of a housekeeping gene promoter.

3T3 Cells↗
PubMed1995

Cardiovascular actions of frog urotensin II in the frog, Rana catesbeiana.

The effects of synthetic frog urotensin II on cardiac output and arterial blood pressure and on the motility of isolated vascular smooth muscle were investigated in the bullfrog, Rana catesbeiana. Bolus injections of frog urotensin II (100 nmol/kg) into the left systemic arch produced a rapid and sustained fall in blood flow through the right branch of the truncus arteriosus (to 62 +/- 5% of preinjection values; n = 8). The response exhibited strong tachyphylaxis. There were no significant effects on heart rate and central arterial blood pressure but the fact that a fall in cardiac output was not accompanied by a fall in pressure suggests that the peptide produced an increase in peripheral vascular resistance. Rings of vascular smooth muscle from the proximal and distal regions of the left and right systemic arches responded to urotensin II with sustained and concentration-dependent contractions. The tissues from the different regions did not significantly differ in their maximum response and sensitivity to the peptide (EC50 values from 4.6 x 10(-9) to 6.5 x 10(-9) M; n = 6). Acetylcholine (3 x 10(-8) to 3 x 10(-6) M) significantly (P < 0.05) relaxed the rings in an endothelium-dependent manner but urotensin II did not produce relaxation at any concentration tested. The contractile effect of urotensin II (10(-7) M) was not affected by preincubation of the rings with atropine, tetrodotoxin, and somatostatin-14 but indomethacin produced a significant (P < 0.05) decrease in the amplitude of the contractions of the systemic arch (to 18 +/- 2% of control values; n = 6). Arachidonic acid (10(-5) M) also produced a sustained contraction of the rings. The data suggest an involvement of prostaglandin synthesis in the contractile action of urotensin II on isolated frog vascular smooth muscle but, unlike in mammals, urotensin II does not stimulate nitric oxide synthesis in this tissue.

Acetylcholine↗
PubMed1995

Absolute phasic blood flow measurement in the brain using digital subtraction angiography.

RATIONALE AND OBJECTIVES: In this study, an angiographic method using first-pass distribution analysis was used for quantification of phasic volumetric blood flow. Studies were conducted in an angiographic perfusion phantom and in an animal model (rabbit) after intraarterial injection of contrast material. METHODS: Digital subtraction angiography and first-pass distribution algorithm were used to assess the absolute volumetric flow rates. The method, based on the conservation of contrast material in successive angiographic images, uses the videodensitometric information in the arterial bed. Measurements were made by summing the pixel values in the region of interest, covering the whole perfusion bed. A contrast pass curve was generated for a sequence of images to obtain instantaneous volumetric flow rates. RESULTS: Instantaneous and mean absolute volumetric flow measurements made in the angiographic perfusion phantom and the common carotid artery of the animal models correlated well with validation measurements made using ultrasound flowprobes. The measured (M) and known (K) flow rates in the carotid artery were related by M = 0.87 K + 2.50 mL/minute (r = 0.96, standard error of the estimate = 3.79 mL/minute, n = 25) and M = 0.92 K - 1.00 mL/minute (r = 0.98, standard error of the estimate = 4.04 mL/minute, n = 38) using the videodensitometric and entrance vessel calibration techniques, respectively. Conclusion. Results demonstrate the potential use of the first-pass distribution method in conjunction with digital subtraction angiography for measuring phasic arterial blood flow in vivo.

Algorithms↗
PubMed1995

Central vascular flow patterns in the alligator Alligator mississipiensis.

Many different flow patterns have been described through the central circulation of crocodilian reptiles. We tested the hypothesis that the vagus nerve stimulation promotes right-to-left (R-L) shunting in the alligator. Flow patterns were investigated before and during stimulation of the intact left vagus nerve using three methods. 1) Atrial and aortic PO2 were measured simultaneously and continuously by gas probes. 2) Atrial outflows were tracked with a blood tracer (helium). 3) Flows were assessed with echocardiography. Four different flow patterns were observed before vagal stimulation: left ventricular (LV) blood flowed into both the right (RAo) and left (LAo) aortas, whereas right ventricular (RV) blood flowed only into the LAo; both aortas received a mixture of LV and RV blood; only LV blood perfused both aortas; and RV blood flowed into both aortas, but LV blood flowed only into the RAo. During vagal stimulation, both aortas received a mixture of LV and RV blood in half of the animals, and in the other half, both aortas received RV blood, but LV blood flowed only into the RAo. Doppler and contrast echocardiography demonstrated swirling flow in the foramen of Panizza and the base of the LAo during systole. These data indicate that vagal stimulation either maintains or produces R-L shunting, flow patterns are variable, and blood can swirl in the foramen of Panizza and LAo base.

Alligators and Crocodiles↗