Search PubMed⌕ Search

Biomedical subjects

J L Martin

Publications and source records attributed to J L Martin.

At least 361 records · Page 20Linked to original sources
PubMed1983

Migrating action-potential complexes in vitro in cholera-exposed rabbit ileum.

The objective of this study was to determine whether cholera-exposed rabbit ileum exhibits altered myoelectric activity in vitro, without central nervous system connections. Whole-cell lysate of Vibrio cholerae, 100 mg in 1 ml saline, was injected into the jejunum of New Zealand White rabbits. Segments of ileum were removed at 12 and 24 h after inoculation and studied in vitro using myoelectric recording techniques. Propagating ring contractions were visualized and corresponded to intense action-potential activity that propagated over consecutive electrode sites. This altered myoelectric activity was similar to the previously described migrating action-potential complex (MAPC) in vivo after infection of rabbit ileum with live V. cholerae, its wholecell lysate, or the purified enterotoxin choleragen, with one exception. All MAPC activity propagated aborally in the in vivo-infected loops; in contrast 26% of the MAPCs propagated retrograde in the in vitro loops. Control segments were injected with saline, and no in vitro MAPCs were observed. Thus, the MAPC stimulated by cholera toxin may be maintained by the enteric nervous system of the gut wall. Although a role for extrinsic nerves is not excluded, our observations suggest that the small intestine may work autonomously, independent of the central nervous system.

Action Potentials↗
PubMed1983

Effect of hydralazine on perfusion and metabolism in the leg during upright bicycle exercise in patients with heart failure.

The aerobic exercise capacity of patients with chronic heart failure is frequently impaired because of inadequate O2 transport to working skeletal muscle. To determine whether hydralazine improves O2 transport to working muscle, we examined the effect of intravenous hydralazine on blood flow (measured by thermodilution) and metabolism in the leg during maximal upright bicycle exercise in 10 patients with chronic heart failure. Hydralazine increased maximal exercise cardiac output (5.6 +/- 0.7 to 6.7 +/- 0.6 l/min; p less than .01) and decreased systemic O2 extraction (79 +/- 3% to 65 +/- 2%; p less than .01) but did not alter maximal O2 uptake (787 +/- 105 vs 779 +/- 82 ml/min). Leg blood flow at maximal exercise increased from 1.6 +/- 0.2 to 2.1 +/- 0.4 l/min (p less than .03); the proportion of cardiac output delivered to the leg remained unchanged (59 +/- 3% vs 57 +/- 9%). This increase in flow was associated with a decrease in O2 extraction in the leg (84 +/- 2% to 79 +/- 2%; p less than .01) and no change in peak femoral venous lactate (59.1 +/- 7.4 vs 54.1 +/- 5.3 mg/dl), suggesting that there is functional or anatomic shunting of the augmented limb flow rather than delivery to metabolizing muscle. These data suggest that hydralazine augments flow to the exercising limb in patients with heart failure but that this augmented flow does not increase oxygen availability within working muscle.

Aged↗
PubMed1983

Altered myoelectric activity in the experimental blind loop syndrome.

Nutrient malabsorption and diarrhea are characteristic of the blind loop syndrome. Alterations in motility have been implicated as a cause of bacterial overgrowth, but the possibility that altered motility may result from alterations in the flora has not been explored. The purpose of this study was to characterize the myoelectric activity of the small intestine in the blind loop rat model. Eight groups of rats were studied: rats with self-filling blind loops, which develop bacterial overgrowth; rats with self-emptying blind loops, which are surgical controls that do not develop overgrowth; unoperated litter mates; rats with self-filling blind loops and unoperated controls treated with chloramphenicol, 200 mg/d i.p.; rats with surgically removed self-filling blind loops; operated control rats; and gnotobiotic rats with self-filling blind loops. In the untreated rats with self-filling blind loops, there was altered myoelectric activity characterized by an increased percentage of slow waves occupied by action potentials and by organized activity similar to the migrating action potential complex. Migrating action potential complex activity and percentage of slow waves occupied by action potentials were significantly decreased with chloramphenicol therapy; that decrease correlated with a decrease in aerobes and anaerobes. Migrating action potential complex activity was abolished in rats with surgically removed self-filling blind loops; they also showed a significant decrease in percentage of slow waves occupied by action potentials. Gnotobiotic rats with self-filling blind loops showed no alteration in myoelectric activity. These data indicate: (a) bacterial overgrowth is associated with a significant increase in percentage of slow waves occupied by action potentials and migrating action potential complex activity; (b) chloramphenicol significantly reduced both percentage of slow waves occupied by action potentials and migrating action potential complex activity; and (c) surgical removal of the loop reduced the alterations in motor function. This study suggests that the altered myoelectric activity in this model of bacterial overgrowth was due, in part, to the abnormal bacterial flora and supports the concept that alterations in motility may contribute to the diarrhea that is characteristic of the blind loop syndrome.

Action Potentials↗
PubMed1982

A safe and rapid technique for retrograde catheterization of the left ventricle in aortic stenosis.

The present report describes our experience in 82 patients with a pigtail-straight guide wire system for crossing stenotic aortic valves. The technique was successful in 95% of all the attempts and the average fluoroscopic time was three minutes. There were no major complications of the procedure. The technique allowed for consistent, high quality ventriculograms in 73 patients enabling us to define the severity of concomitant mitral regurgitation in 27 of the patients, as well as a preoperative ejection fraction in all 73 patients. We conclude that the technique as described is a safe and efficient way to obtain both hemodynamic and angiographic information at minimum risk in patients with severe aortic stenosis.

Adult↗
PubMed1982

Electrocardiographic changes following endocardial resection for ventricular tachycardia.

The ECG changes resulting from endocardial resection, with or without aneurysmectomy and coronary artery bypass grafting (CABG), are reported in 82 patients. Angiographic and surgical features and peak creatine kinase (CK) levels are correlated with ECG findings. Twenty-three of 82 patients (28%) had the following ECG changes postoperatively: decreased ST segment elevation = 3 (4%), loss of R wave amplitude = 4 (5%), increased R wave amplitude = 5 (6%), new Q wave = 4 (4%), axis shift greater than or equal to 45 degrees = 6 (7%), and new bundle branch block = 6 (7%). Five of six new cases of bundle branch block were left bundle type and resulted from resection of the inferoposterobasal and contiguous septal endocardium. ECG anterior infarction, anterior aneurysm, and anteroseptal endocardial resection were associated with a significantly lower incidence of postoperative ECG changes. Aneurysmectomy and the performance of CABG were not significantly associated with postoperative ECG changes, but more bypass grafts per patient grafted appeared in the group with postoperative ECG changes, suggesting that coronary artery disease may be more severe in that group. Peak CK did not correlate with postoperative ECG findings. We conclude that ECG changes occur infrequently after endocardial resection and that the factors responsible are not clear, although severity of coronary artery disease may be contributory. Left bundle branch block is a significant complication of inferoposterobasal resection, but complete heart block appears not to be. The diagnosis of myocardial necrosis is difficult in these patients.

Adult↗
PubMed1982

Escherichia coli heat-stable toxin: its effect on motility of the small intestine.

Escherichia coli heat-stable enterotoxin is a low-molecular-weight substance that has been shown to induce the active secretion of fluid and electrolytes in the small intestine. In this study, we have characterized the effects of purified E. coli heat-stable toxin (ST, strain 18D, serotype 042:K86:H37) on the motility of rabbit small intestine by using myoelectric recording techniques. Substances, such as cholera toxin, that activate the adenylate cyclase-cAMP system induced predominantly migrating action-potential complex activity. E. coli ST, a toxin that activates the guanylate cyclase-cGMP system, was infused into isolated in vivo ileal loops of New Zealand White rabbits. Inactivated toxin was also studied by exposing the ST to 1 mM dithiothreitol for 90 min. Active E. coli ST induced only repetitive bursts of action potentials. When the toxin was inactivated with dithiothreitol, no alteration in myoelectric activity was observed. We speculate that repetitive bursts of action-potential activity may represent a virulent factor of the bacterium, altering motor activity to slow transit and allowing for bacterial proliferation and invasion.

Action Potentials↗
PubMed1982

Load dependence of mammalian heart relaxation during cardiac hypertrophy and heart failure.

Mechanical properties of relaxation were studied in left ventricular rat papillary muscle during cardiac hypertrophy induced by chronic pressure and/or volume overload. Maximum velocity of isotonic lengthening was linearly related to total extent of isotonic shortening and to maximum velocity of isotonic contraction and depended on the type of chronic overloading without correlation with the degree of cardiac hypertrophy. Time to peak shortening was significantly increased in each group of hypertrophied heart muscles as compared to controls. The sensitivity of cardiac relaxation to the loading conditions was determined by the time course of relaxation. To quantify the degree of load sensitivity, we measured the ratio of isotonic area to isometric area, which was the area limited by the afterloaded force vs. time at 50% of the isometric peak tension divided by the area of the force vs. time trace in the isometric twitch below the same level of load. The value of this ratio was about 0.81 in normal rat and did not show any significant differences in hypertrophied heart muscles even at the terminal stage of congestive heart failure. During acute hypoxia the load sensitivity of relaxation disappeared both in normal and in hypertrophied hearts. Thus inadequacy in oxygen supply has more drastic effects, as compared with those induced by chronic overload, probably by affecting the sarcoplasmic reticulum uptake of activating calcium.

Animals↗
PubMed1982

Regional coronary anatomy in rest angina. Comparison of patients with rest and exertional angina using quantitative coronary angiography.

To determine if patients with rest angina have more severe regional ischemia than patients with exertional angina, we compared the severity of left coronary artery (LCA) stenosis in 29 patients with transient anterior ischemic ST-T changes at rest, and 30 patients with anterior ST changes only during exertion. The percentage diameter stenosis was measured with Vernier calipers as (2 x lesion diameter x 100 percent)/(prestenotic + poststenotic diameter). There was no difference between the two groups in the mean diameter stenosis of unoccluded LCA vessels either when all vessels were compared (rest: 69 +/- 12 percent; exertional: 70 +/- 13 percent [p = NS]) or when only the maximal stenosis in each patient was compared (rest: 74 +/- 10 percent; exertional: 75 +/- 12 percent [p = NS]). Total occlusion of at least one major vessel of the LCA also occurred with similar frequency in patients with rest (6/29) and exertional (12/30) angina (p = NS). However, collateral development distal to 76-100 percent LCA lesions was significantly less frequent in rest angina (4/21 vessels [19 percent]) than in exertional angina (21/30 vessels [70 percent]), (p less than .03). We conclude that patients with rest angina do not have more severe coronary stenosis than patients with exertional angina, but frequently may have more severe regional ischemia due to reduced collaterization of jeopardized myocardium.

Aged↗
PubMed1982

Myoelectric effects of Clostridium difficile: motility-altering factors distinct from its cytotoxin and enterotoxin in rabbits.

Clostridium difficile is a bacterium that causes antibiotic-associated pseudomembraneous enterocolitis. This bacterium produces a cytotoxin that induces tissue culture assay positivity and an enterotoxin that causes in vivo mucosal injury. In previous studies we have described two altered myoelectric patterns in response to certain diarrheagenic organisms in an in vivo rabbit model. The first pattern was called the migrating action potential complex and is associated with noninvasive agents; the second pattern was called repetitive bursts of action potentials and is characteristic of invasive or cytolytic agents. In this study, we evaluated the effects of purified cytotoxin (2.5-3.75 micrograms) and enterotoxin (140 micrograms) from C. difficile on the myoelectric activity in isolated ileal loops in New Zealand White rabbits. These observations in myoelectric activity were correlated with the results of similar studies by using the crude culture filtrates from C. difficile, or the products of Amicon XM50 filtration of its culture supernatant resulting in a high molecular weight product (0.3 mg protein/ml) and a low molecular weight product (0.57 mg protein/ml). Monopolar silver-silver chloride electrodes were used to record all myoelectric activity for an 8-h period. The animals were then killed, and tissue obtained from the ileal loops was histologically evaluated. Crude culture filtrates of C. difficile induced 7.0 migrating action potential complexes/hour and 6.8 repetitive bursts of action potentials/hour. Saline controls induced no migrating action potential complexes and 0.1 repetitive bursts of action potentials/hour. The high molecular weight filtration product obtained from the culture supernatant of C. difficile induced significantly more repetitive bursts of action potentials (41.1/h) than all agents studied. The purified cytotoxin or enterotoxin induced no migrating action potential complex activity and minimal repetitive bursts of action potential activity (0.9/h and 0.6/h, respectively). These values were not different from the saline controls; however, only the enterotoxin and the high molecular weight filtration product caused mucosal damage. These studies suggest that C. difficile produces a heat-labile substance or substances that alter the motility of the small intestine independent of the proteins responsible for in vivo tissue damage and cytotoxin assay positivity.

Action Potentials↗