Search PubMed⌕ Search

Biomedical subjects

M J Davis

Publications and source records attributed to M J Davis.

At least 163 records · Page 9Linked to original sources
PubMed1985

Capillary pressures in rat intestinal muscle and mucosal villi during venous pressure elevation.

Whole-organ experiments designed to estimate the capillary filtration coefficient require information about the numerical relationship between capillary pressure and venous pressure. Indirect estimates using isogravimetric and isovolumetric methods indicate that 62-85% of a step change in venous pressure reaches the intestinal capillaries, taken as a whole. We have made direct measurements of capillary pressure with a servo-null micropressure system in the microcirculation of both the intestinal muscle and the mucosal villi of rats during local elevation of venous pressure. Consistent regional differences in the relationship between capillary pressure and venous pressure were observed. During increased venous pressure, submucosal arterioles constricted, while muscularis arterioles dilated. The diameter changes of the small arterioles were consistent with blood flow redistribution from mucosa to muscle during venous pressure elevation, but inconsistent with a pure myogenic response. These data raise questions about the exact role for the expression of the myogenic response during venous pressure elevation in the intestine and about previous interpretations of whole-organ experiments concerned with intestinal blood flow and fluid exchange.

Animals↗
PubMed1984

Cigarette smoking and ventricular arrhythmia in coronary heart disease.

With use of 24-hour ambulatory electrocardiographic monitoring, the effect of 1 hour of cigarette smoking on cardiac rhythm in 73 patients with coronary heart disease was studied. Fifteen subjects had no arrhythmia; 37 subjects had fewer than 2 atrial or ventricular premature complexes (APCs or VPCs)/hour, with APCs possibly related to smoking in 2 and VPCs related to smoking in 1. Nineteen subjects had more than 2 VPCs/hour (range 4 to 368) and had 16 +/- 29 VPCs/hour (+/- standard deviation) less during than before smoking (p less than 0.05), associated with an increase in heart rate of 4.6 +/- 6.8 beats/min (p less than 0.01). In none of the 9 subjects with unifocal VPCs did multiform beats develop during or after smoking, whereas 3 of 10 subjects with multiform VPCs had only unifocal beats during and immediately after smoking. In 1 of these 19 subjects, frequent APCs developed during smoking. One other subject had frequent APCs unaffected by smoking and another had sinoatrial block, which disappeared during smoking on 1 of 3 monitorings. In conclusion, no sustained or high-grade ventricular arrhythmia was provoked by smoking; although APCs may have been related to smoking in a few persons, the frequency and complexity of VPCs tended to be reduced in these subjects with coronary artery disease.

Arrhythmias, Cardiac↗
PubMed1984

Mechanics of smooth muscle in isolated single microvessels.

In vivo studies on frog mesenteric arterioles (4) indicate that segmental differences in the response of microvessels to physical and chemical stimuli can be explained simply in terms of the length-tension characteristics of vascular smooth muscle at different points along the vascular tree. Studies on single, isolated arterioles in vitro were initiated to examine more closely the validity of this explanation for regional response differences. This paper reports some of the results. First-, second-, and third-order arterioles (18-60 micron i.d.) were dissected from hamster cheek pouches. The vessels were cannulated with a modified Burg microperfusion system, and their mechanical properties studied using the methods described by Duling and Gore. Vessels were activated in four stages with K+ and norepinephrine. During activation, transmural pressures were adjusted to minimize vascular smooth-muscle shortening. Active pressure-diameter curves were recorded while adjusting transmural pressure through the range 5 to 400 cm H20 in 5-25 cm steps. Vessel dimensions were measured with a videomicrometer. Passive curves were obtained after equilibration overnight in Ca2+-free medium. The vessels were then fixed and prepared for histologic sectioning, and measurements of vessel-wall composition were made. The Laplace relationship was used to construct length-tension diagrams, and the histologic data were used to normalize the dimensional data to smooth-muscle lengths. Maximum active tension of second-order arterioles (1,170 dynes/cm) was two times previous values reported by Gore et al. This was due presumably to refinements in techniques and dissection procedures. Maximum active stress averaged 3.9 X 10(+6) dynes/cm2 for second-order arterioles. This number is identical to data obtained from hog carotid strips by Dillon et al.

Animals↗
PubMed1984

A comparison of intravenous and intracoronary streptokinase in acute myocardial infarction.

A randomised study of intravenous and intracoronary streptokinase therapy was carried out in 20 subjects with acute myocardial infarction and angiographically confirmed complete obstruction of the associated coronary artery. Two dose levels of therapy were used. Although more recanalisations occurred with intracoronary than intravenous therapy at the low dose levels, overall there was not a significant difference between the two groups; one million IU intravenously over 20 minutes recanalised four of five arteries. While seven of nine recanalisations with intracoronary therapy occurred within an hour, only two of five with intravenous therapy did so. Hence prolonged angiographic observation is necessary to document recanalisation with intravenous therapy adequately. Nevertheless, the time disadvantage of large dose intravenous therapy is not great and it may yet prove as effective as, and more practical than, intracoronary therapy.

Female↗
PubMed1984

Transvenous ablation of atrioventricular conduction for refractory or malignant supraventricular arrhythmias.

In nine patients with recurrent disabling supraventricular arrhythmia refractory to, or intolerant of, multiple drug combinations, and two patients with Wolff-Parkinson-White (WPW) syndrome and documented malignant atrial fibrillation, transvenous ablation of atrioventricular (AV) conduction, utilising synchronised unipolar DC shocks delivered by catheter to the AV node-His bundle or to the accessory AV pathway, was attempted. One to two 200-300 J discharges produced complete heart block in all of the nine patients, with markedly improved symptomatic status at one to ten month follow-up including the one patient with recovery of modified AV conduction. Single 100-150 J shocks ablated pre-excitation for five to fifteen minutes in the two WPW patients without subsequent modification of accessory pathway conduction. There were no complications. This simple technique has great potential and may supplant some open-heart procedures. With refinement it may be possible to slow rather than to ablate AV-His conduction, to ablate conduction via accessory AV pathways permanently and to interrupt ventricular re-entrant circuits.

Adult↗
PubMed1982

Histologic evaluation of gingival curettage facilitated by sodium hypochlorite solution.

Gingival curettage has long been used as a modality in periodontal therapy. Recent longitudinal studies have shown that diligent curettage of periodontal pockets may aid in maintaining the attachment levels around periodontally involved teeth. This study was designed to histologically evaluate the controlled use of concentrated sodium hypochlorite solution to facilitate gingival curettage therapy. The results indicate that the action of sodium hypochlorite solution may be adequately controlled to provide predictable chemolysis of the soft tissue wall of a periodontal pocket with minimal effect upon the adjacent tissues. The action of the solution appears to have no detrimental effect upon healing. Reduction of inflammation prior to the procedure and careful technique are important to assure predictability. The use of gingival curettage augmented by sodium hypochlorite solution may aid in the management of patients undergoing periodontal maintenance.

Gingiva↗
PubMed1982

Fluctuations in susceptibility to noise-induced temporary threshold shift as influenced by the menstrual cycle.

The relationship between the menstrual cycle and changes in HTL and in TTS (from exposure to "magenta" noise at 115 dBA for 10 min) was studied bidaily over 40 days in 9 normal-hearing (HTLs less than or equal to 15 db at .5-8 kc/s) aged from 20-30 years. All HTLs pre- and post-exposure were estimated from interrupted-tone, fixed-frequency Bekesy tracings. The analysis used was a technique developed to study such biological rhythms, a least-squares regression to a cosine function. An F ratio from the bivariate normal distribution was used to evaluate whether significant fluctuations across sessions occurred either in pre-exposure HTLs (2-8 kc/s) or in TTS (2,3,4, and 6 kc/s). No effects were frequency-dependent. For the pre-exposure HTLs 24 of 63 total measures showed a significant (p less than .05) fluctuation, ranging from 1.6 to 6.8 db. For the TTS data, 14 of 36 measures showed a significant fluctuation, ranging from 2.4 to 9.1 db. In general, pre-exposure HTLs were highest (poorer hearing) and TTS was least during menses.

Adult↗
PubMed1981

Microvascular pressure distribution and responses of pulmonary allografts and cheek pouch arterioles in the hamster to oxygen.

Despite extensive investigations of the pulmonary circulation using both in vitro and in vitro preparations, few direct microcirculatory studies have been made. Consequently, the mechanisms involved in the response of the pulmonary microvasculature to changes in oxygen tension remain unclear. The present study represents the first direct observation of the responses in pulmonary microvessels to alterations in oxygen tension. Neonatal lung tissue was transplanted into the hamster cheek pouch using a chamber technique. Both tissues were characterized with respect to their microvascular pressure profile and vascular response to hypoxia. The results showed the two tissues to be remarkably different. Small pulmonary and cheek pouch arterioles exhibited opposite responses to changes in oxygen environment; hypoxia elicited a constriction of pulmonary arterioles, but a dilation of cheek pouch arterioles. Pulmonary capillary pressure, although comparable to that measured in the intact lung (13 mm Hg), was substantially lower than cheek pouch capillary pressure, which was within the range of that described for several systemic vascular beds. The microcirculatory effects of oxygen on both tissues were confined to the arteriolar segments. The characteristics of this pulmonary microcirculation are such that it is a unique model for further physiological and pharmacological studies.

Animals↗
PubMed1981

Responses of pulmonary allograft and cheek pouch arterioles in the hamster to alterations in extravascular pressure in different oxygen environments.

The responses to changes in transmural pressure were investigated in pulmonary allograft and cheek pouch arterioles in two oxygen environments. Neonatal hamster lung tissue was transplanted into adult hamster cheek pouches. After vascularization (8-10 days), pulmonary and cheek pouch vessels were observed by intravital microscopy in hamsters anesthetized with pentobarbital. By gassing the suffusion solution (bicarbonate-buffered Ringer's) (pH 7.4 at 35-37 degrees C) with either low oxygen (95% N2/5% CO2) or high oxygen (75% N2/5% CO2/20% O2) and after sealing the top of the chamber, extravascular pressure was altered by varying the fluid volume of the closed chamber. Changes in arteriolar diameters in response to positive and negative square-wave pressure pulses were quantified using a video micrometer and close-circuit TV system. Pulmonary arterioles showed a passive dilation or constriction in response to increases or decreases in transmural pressure (+/-20 mm Hg). These responses were not altered either by changes in PO2 or nitroprusside. In contrast, cheek pouch arterioles showed myogenic responses by constricting when transmural pressure was increased and vice versa. These responses were potentiated at high PO2 and abolished with nitroprusside. It is concluded that a myogenic response is dominant in cheek pouch arterioles but not in pulmonary arterioles under these conditions. These latter observations are consistent with results obtained from isolated, intact lung.

Animals↗
PubMed1979

The syndrome of painful ophthalmoplegia. A case with intraorbital mass and hypervascularity.

A patient diagnosed as having Tolosa-Hunt syndrome on clinical grounds was found by arteriography to have an intraorbital mass with hypervascularity. To our knowledge, this radiologic finding has not previously been reported in either Tolosa-Hunt syndrome or in the syndrome of orbital pseudotumor, and supports the proposition that these two conditions are anatomical variants of the same pathological process.

Aged↗