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Biomedical subjects

R J Martin

Publications and source records attributed to R J Martin.

At least 343 records · Page 19Linked to original sources
PubMed1988

The distribution of numbers of open channels in multi-channel patches.

Assumptions inherent in use of the binomial distribution are relaxed in order to identify alternative distributions with different variances, for fitting to the frequency distributions of numbers of open channels in multi-channel patches. The variance is less than that for the binomial distribution with the same expectation when either there is a negative interaction between channels or channels have different probabilities of being open. When the variance is greater, this may be because of positive interaction between channels or non-stationary behaviour. Use of the distributions and lack-of-fit statistics is illustrated.

Ion Channels↗
PubMed1988

The effects of adrenergic agonists and age on lipogenesis in avian hepatocytes.

1. Adrenergic inhibition of lipogenesis was examined in vitro using hepatocytes isolated from chickens 2-9 weeks old. 2. Lipogenesis was inhibited by beta 1, beta 2 and alpha 1 agonists. Greatest inhibition occurred when more than one type of receptor was stimulated. 3. Clonidine (alpha 2-agonist) may have stimulated lipogenesis. 4. Responsiveness to the agonists decreased as the chickens got older.

Aging↗
PubMed1988

Effect of head position on distribution of nasal airflow in preterm infants.

Supine preterm infants characteristically adopt a lateral head position; however, it is not known whether this influences the distribution of nasal airflow. Ventilation was measured in 12 healthy preterm infants (postconceptional age 34 +/- 2 weeks) by employing a nasal mask pneumotachygraph that separated airflow between the left and right nasal passages. In the midline supine position, the percent of total tidal volume (%VT) through the right nasal passage ranged from 31% to 64% and varied by less than 5% between active and quiet sleep in any infant. Lateral positioning of the head caused %VT to increase on the dependent side and decrease through the upper nasal passage. When the right side was dependent, mean %VT on that side increased from 52 +/- 9% to 67 +/- 14% (P less than 0.01) and decreased to 43 +/- 10% (P less than 0.05) when the right side was up. In the midline position, the presence of a nasogastric tube caused %VT through the nasal passage with the tube to fall from 54 +/- 8% to 39 +/- 8% (P less than 0.01). The %VT fell farther, to 25 +/- 10% (P less than 0.01), when the nasal passage with the nasogastric tube was up. Despite these changes in VT distribution, total VT remained constant during these maneuvers. We speculate that when supine preterm infants adopt a lateral head position, the decrease in airflow through the upper nasal passage results from partial obstruction of the oropharyngeal or nasopharyngeal airway on that side.

Head↗
PubMed1988

Developmental changes in response to overfeeding: effect on composition of gain, liver metabolism and adipocyte cellularity in rats.

It has been proposed that voluntary food intake limits growth rate. The experiment described here investigated the effects of increased food intake on growth rate. Four age groups of female rats were given either 150 or 100 of ad libitum intake by oral gavage. Animals were tube-fed at these levels of intake for 1 wk. Overfeeding significantly increased carcass weight and fat for all ages examined. Carcass protein was significantly elevated in the overfed animals for the two youngest age groups. Differences between age groups in apparent energetic efficiency were small. Hepatic palmitate oxidation was depressed and esterification increased in all overfed rats. Fat cell size was increased by overfeeding in all age groups. In conclusion, the effects of overfeeding on the four age groups of rats studied were independent of age.

Adipose Tissue↗
PubMed1988

Effect of sera from control and overfed rats on preadipocyte growth in culture.

Increased body lipid was induced in 4-wk-old rats through oral gavage. Rats were either fed ad libitum, tube-fed 100% or tube-fed 150% of the ad libitum intake. After 1 wk of tube-feeding animals were killed and sera collected. Sera were used to support the growth of rat stromal-vascular cells in culture. Sera were also analyzed for growth hormone and insulin concentrations. In rats that were tube-fed, levels of adiposity were greater but sera from these rats decreased stromal-vascular and preadipocyte proliferation in culture when compared with sera from ad libitum-fed rats. Sera from tube-fed animals promoted an increase in preadipocyte differentiation as revealed by esterase staining. Results indicate that overfeeding in juvenile rats causes sera changes that support fat cell differentiation but not fat cell hyperplasia.

Adipose Tissue↗
PubMed1988

Airway obstruction during periodic breathing in premature infants.

To characterize changes in pulmonary resistance, timing, and respiratory drive during periodic breathing, we studied 10 healthy preterm infants (body wt 1,340 +/- 240 g, postconceptional age 35 +/- 2 wk). Periodic breathing in these infants was defined by characteristic cycles of ventilation with intervening respiratory pauses greater than or equal to 2 s. Nasal airflow was recorded with a pneumotachometer, and esophageal or pharyngeal pressure was recorded with a fluid-filled catheter. Pulmonary resistance at half-maximal tidal volume, inspiratory time (TI), expiratory time (TE), and mean inspiratory flow (VT/TI) were derived from computer analysis of five cycles of periodic breathing per infant. In 80% of infants periodic breathing was accompanied by completely obstructed breaths at the onset of ventilatory cycles; the site of airway obstruction occurred within the pharynx. The first one-third of the ventilatory phase of each cycle was accompanied by the highest airway resistance of the entire cycle (168 +/- 98 cmH2O.l-1.s). In all infants TI was greatest at the onset of the ventilatory cycle, VT/TI was maximal at the midpoint of the cycle, and TE was longest in the latter two-thirds of each cycle. A characteristic increase and subsequent decrease of 4.5 +/- 1.9 ml in end-expiratory volume also occurred within each cycle. These results demonstrate that partial or complete airway obstruction occurs during periodic breathing. Both apnea and periodic breathing share the element of upper airway instability common to premature infants.

Airway Obstruction↗
PubMed1988

Differences in CO2 threshold of respiratory muscles in preterm infants.

Because neonatal apnea is frequently associated with airway obstruction, we compared relative changes in activity between various upper airway muscles and the diaphragm during hypercapnic stimulation. The technique of hyperoxic CO2 rebreathing was employed in 17 healthy, sleeping preterm infants studied at a postnatal age of 32 +/- 12 days. Surface diaphragm (DIA) electromyograms (EMGs) were recorded in all infants, and noninvasive measurements of posterior cricoarytenoid (PCA), genioglossus (GG), and alae nasi (AN) EMGs were analyzed in 11, 9, and 8 infants, respectively. During the control period, consistent phasic EMGs were recorded from the DIA in all infants and from the PCA in 8 infants, but from the GG and AN each in only one infant. During CO2 rebreathing, minute ventilation and end-tidal CO2 increased linearly as CO2 rose from 31 +/- 5 to 51 +/- 5 Torr. DIA and PCA EMGs also had proportional and comparable increases throughout rebreathing. In contrast, both GG and AN responses differed from the DIA and PCA (P less than 0.001) and exhibited minimal or absent responses at low levels of hypercapnia. Consistent GG and AN EMGs appeared at comparable levels of end-tidal CO2 (47 +/- 5 and 45 +/- 5 Torr, respectively) and subsequently increased linearly in most infants. We conclude that during CO2 rebreathing the initially delayed and subsequently linear responses of the GG and AN EMGs indicate a high CO2 threshold for these muscles.

Carbon Dioxide↗
PubMed1988

Metabolic development of porcine fetal adipose tissue. A role for central regulation.

The influence of neural and endocrine status upon the metabolic activity and insulin responses of developing adipose tissue of fetal swine was examined. Central neural and endocrine regulation were removed by decapitation of fetuses at 45 days of gestation. Decapitated (decap) fetuses and intact littermates were removed at 65, 85 or 110 days of gestation. Fatty acid synthesis from glucose increased fivefold in slices of subcutaneous adipose tissue from intact fetuses and tenfold in tissue from decaps, between days 65 and 110 gestation. Insulin had minimal effects in intact tissue but stimulated glucose metabolism as early as 65 days of gestation in decap adipose tissue. Lactate was utilized for oxidation and fatty acid synthesis at rates as high or higher than glucose throughout gestation. These results indicate possible roles for lactate and insulin in producing the increased adiposity of decapitated fetal pigs reported previously. Secondly, the more active metabolism of decap tissue indicates that fatty acid synthesis in normal fetal adipose tissue is suppressed by development of inhibitory factors regulated by central mechanisms during late gestation.

Adipose Tissue↗
PubMed1988

Estimates of ventilation from inductance plethysmography in sleeping asthmatic patients.

To assess the accuracy of the respiratory inductance plethysmograph (RIP) for monitoring ventilation during sleep-associated bronchoconstriction, five adult patients with nocturnal worsening of their asthma were monitored overnight in the sleep laboratory. Three of the five patients demonstrated episodic paradoxic respiratory motion of the lower rib cage undetected by the RIP. Such paradoxic motion was consistently associated with overestimation of volumetric data by RIP compared to pneumotachygraphic measurements. With onset of lower rib cage paradox, the mean error of RIP-derived VT measurements increased from 9.1 +/- 1.7 to 27.9 +/- 3.8 percent (p less than .001). Flow measurements derived from RIP were also inaccurate in the presence of lower rib cage paradox, with the mean error of the measurement increasing from 9.0 +/- 2.5 to 33.5 +/- 5.3 percent (p less than .001). We conclude that RIP is an unreliable technique for quantitatively monitoring ventilation in sleeping asthmatic patients.

Abdomen↗
PubMed1988

Sera from pigs infected with Sarcocystis suicanis and cachectin decrease preadipocyte differentiation in primary cell culture.

The macrophage-secreted hormone cachectin depressed lipoprotein lipase activity and lipogenic enzymes in adipose cells. Cachectin reduced differentiation of preadipocytes in cultures of stromal-vascular cells from rat adipose tissue. Differentiation was measured by two methods of estimating lipid accumulation. Adipocytes were separated from the stromal-vascular cells by centrifugation and staining (oil red 0) for intracellular lipid. Lipolytic activity was measured by using esterase histochemistry. Sera from pigs that were infected with Sarcocystis suicanis showed cachectin-like activity compared with sera collected from the same animals before infection. Cachectin and sera collected from infected animals specifically decreased fat cell number without decreasing the stromal-vascular cell number.

Adipose Tissue↗
PubMed1988

Increasing arterial carbon dioxide tension: influence on transcutaneous carbon dioxide tension measurements.

Despite widespread use of transcutaneous PCO2 (TcPCO2) monitoring, the precise relationship between TcPCO2 and PaCO2 remains unclear. It has been widely assumed that theoretical correction of TcPCO2 (combining temperature correction with a constant metabolic factor of 4 mm Hg) accounts for the elevation of TcPCO2 over PaCO2. To test this assumption, TcPCO2 was measured with a 44 degrees C electrode and compared to PaCO2 in 60 normotensive infants with cardiorespiratory disease during the first four +/- six days of life (mean +/- SD) (range one to 36 days). During hypocapnea, from PaCO2. In contrast, during normocapnea, theoretically corrected TcPCO2 exceeded PaCO2 by 5 +/- 4 mm Hg (P less than .001), and similarly during hypercapnea, theoretically corrected TcPCO2 exceeded PaCO2 by 9 +/- 6 mm Hg (P less than .001). These data suggest that, as PaCO2 increases, there may be an imbalance between tissue CO2 production and removal, resulting in a progressively increasing gradient between TcPCO2 and PaCO2. Clarification of the relationship between TcPCO2 and PaCO2 should enhance the interpretation of TcPCO2 measurements in infants.

Blood Gas Monitoring, Transcutaneous↗
PubMed1988

Bronchoscopic findings in infants treated with high-frequency jet ventilation versus conventional ventilation.

To identify tracheobronchial abnormalities associated with assisted ventilation, 40 infants with respiratory distress syndrome randomized to receive either short-term (48 hours) conventional or high-frequency jet ventilation were studied. Flexible fiberoptic bronchoscopy (n = 13) was performed and/or clinical and radiographic assessments were used to evaluate for laryngeal, tracheal, and bronchial lesions. There was no bronchoscopic evidence of necrotizing tracheobronchitis after either high-frequency jet ventilation (n = 8) or conventional ventilation (n = 5). Laryngotracheomalacia and nodular vocal cords were the most common abnormalities noted, and they occurred with equal frequency in both groups. Study infants who were not bronchoscoped had no clinical or radiographic evidence of tracheal or mainstem bronchial obstruction. One patient did have microscopic evidence of necrotizing tracheobronchitis at autopsy, however. It is concluded that short-term treatment of respiratory distress syndrome with high-frequency jet ventilation may be performed without undue risk of tracheobronchial injury.

Bronchi↗
PubMed1988

Influence of genetic obesity on maternal and fetal serum and lipoprotein lipids in swine.

Serum and lipoprotein lipids were measured in sows and fetuses of a genetically obese strain and a lean strain of pigs. Total triglyceride, VLDL-triglyceride and free fatty acid concentrations tended to be greater, and VLDL- and HDL-cholesterol concentrations tended to be lower, in obese sows when compared with lean sows. In contrast to lean fetuses, obese fetuses had significantly greater concentrations of total cholesterol, total triglyceride and VLDL-triglyceride, and tended to have greater concentrations of VLDL- and HDL-cholesterol and free fatty acids. Distribution of cholesterol between the lipoprotein fractions was similar between strains and between sows and fetuses, but distribution of triglyceride was significantly influenced by both of these factors. Serum lipid patterns of obese pigs were similar to those seen in obese humans, suggesting that the pattern is characteristic of obesity in general. Fetal triglyceride transport was altered by genetic background, but fundamental differences still existed between fetal and maternal lipid profiles. This genetically obese strain of swine appears to be a useful model to study the development of abnormal lipoprotein metabolism, as well as to study the effect of obesity on the relationships between maternal and fetal lipid metabolism.

Animals↗
PubMed1987

Analysis of monoamines and their metabolites by high performance liquid chromatography with coulometric electrochemical detection.

High performance liquid chromatography with coulometric electrochemical detection has been used to achieve simultaneous determination of norepinephrine, epinephrine, 5-hydroxytryptophan, normetanephrine, dopamine, metanephrine, 3,4-dihydroxyphenylacetic acid, N-acetyldopamine, tyramine, tryptophan, 5-hydroxyindoleacetic acid, 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, homovanillic acid, tyrosine, p-octopamine, N-acetyl-p-octopamine, and p-synephrine. The procedure has been applied to study monoamine degradation in the insect brain and to demonstrate that N-acetylation rather than oxidative deamination is the primary route of monoamine catabolism in insects.

Animals↗
PubMed1987

Current correction factors inadequately predict the relationship between transcutaneous (tc) and arterial PCO2 in sick neonates.

Despite widespread tcPCO2 monitoring the relationship between tcPCO2 and PaCO2 remains unclear. It has been assumed that after standard temperature correction, a constant metabolic factor can explain the elevation of tcPCO2 over PaCO2. Our data demonstrate a progressive increase in the difference between temperature corrected tcPCO2 and PaCO2 as PaCO2 increases. Thus a constant metabolic factor cannot account for the elevation of temperature corrected tcPCO2 over PaCO2. We speculate that as PaCO2 rises, CO2 production exceeds removal resulting in a progressive gradient between temperature corrected tcPCO2 and PaCO2.

Blood Gas Monitoring, Transcutaneous↗
PubMed1987

Effects of fetal versus postnatal sera upon adipose tissue stromal-vascular cells in primary culture.

This experiment was conducted to determine if serum factors are responsible for differences in cellularity of prenatal and postnatal pig adipose tissue as determined by in vitro measurement of cellular proliferation and enzyme-histochemical metabolic development. Cellular proliferation of stromal-vascular cells derived from rat inguinal adipose tissue was measured by [3H]-thymidine incorporation. Coverslip cultures were used for analysis of histochemical differentiation. Cells were incubated in media containing 10% fetal bovine, fetal pig, mature pig, or various combinations of these sera. Fetal bovine serum promoted more [3H]-thymidine incorporation than fetal or postnatal pig sera. Fetal pig sera also stimulated more [3H]-thymidine incorporation than mature pig sera. Sera from adult pigs promoted differentiation and lipid filling of adipocytes. Fetal pig sera stimulated histochemical expression of enzymes, but did not induce lipid filling. Fetal bovine serum produced histochemically undifferentiated cells. Addition of fetal bovine serum to media containing mature pig sera reduced lipid accumulation and histochemical reactivity of cells. This effect of fetal serum was thus due to specific inhibition of lipid deposition and not substrate restriction. These experiments demonstrated that serum factors have a major influence on morphological development of fetal and postnatal adipose tissue.

Adipose Tissue↗
PubMed1987

Randomized trial of high-frequency jet ventilation versus conventional ventilation in respiratory distress syndrome.

To compare high-frequency jet ventilation (HFJV) with pressure-limited time-cycled conventional ventilation (CV), we randomized 41 infants with clinical and radiographic evidence of respiratory distress syndrome during the first day of life to receive either HFJV or CV. Standardized ventilatory protocols were used for 48 hours, after which CV was administered to both groups. Despite comparable oxygenation (arterial/alveolar oxygen tension ratio), mean airway pressure was lower in the HFJV group (9 +/- 2 vs 13 +/- 2 cm H2O, P less than 0.001), and thus the arterial/alveolar oxygen tension ratio corrected for mean airway pressure was improved in the HFJV group (P less than 0.05). PaCO2 was lower during HFJV (37 +/- 3 vs 42 +/- 3 mm Hg, P less than 0.05) despite a comparable peak inspiratory pressure. The incidence of air leaks, progression of intraventricular hemorrhage, and mortality during the 48-hour period did not differ between the two groups. Bronchoscopies in eight infants given HFJV and five given CV revealed no microscopic evidence of necrotizing tracheobronchitis, but one infant given HFJV had evidence of necrotizing tracheitis at autopsy. We conclude that for 48 hours during the acute stage of respiratory distress syndrome, HFJV can maintain adequate gas exchange at lower mean airway pressure than during CV, without an increase in the incidence of side effects.

Clinical Trials as Topic↗