Search PubMed⌕ Search

Biomedical subjects

B J Martin

Publications and source records attributed to B J Martin.

At least 55 records · Page 3Linked to original sources
PubMed1995

CO2 dependence of retinal arterial and capillary blood velocity.

OBJECTIVE: Blood flow to the brain is extremely sensitive to changes in PCO2. While animal studies show a similar potent PCO2 dependence in retinal and choroidal vessels, the PCO2-retinal blood flow relationship has never been adequately studied in humans. METHODS: Video scanning laser ophthalmoscopy after fluorescein angiography was used to analyze retinal arterial and capillary blood velocity under conditions of mild hypercapnia and hypocapnia. Control conditions (end-tidal PCO2 = 38.3 +/- 0.4 mmHg) were contrasted with hyperventilation-induced hypocapnia (PCO2 = 34.0 +/- 0.4 mmHg) and hypercapnia (PCO2 = 42.3 +/- 0.5 mmHg) created by PCO2 addition to inspired gas. RESULTS: Both larger vessel and macular capillary blood velocity was dependent upon PCO2: arteriovenous passage time fell as PCO2 rose, and both mean arterial dye velocity and capillary blood velocity rose as PCO2 rose (all p < 0.05). These changes in flow velocity occurred despite unchanged heart rate, arterial systolic and diastolic blood pressure, intraocular pressure, and calculated ocular perfusion pressure. Contrast sensitivity was also unchanged by PCO2 variation. CONCLUSIONS: The human retinal circulation, like the whole cerebral circulation, may be strongly dependent upon PCO2 in a manner that is unrelated to perfusion pressure and apparently outside strict autoregulatory controls.

Adult↗
PubMed1994

Color Doppler analysis of ocular vessel blood velocity in normal-tension glaucoma.

The pathogenesis of normal-tension glaucoma remains unknown. Because ocular vasospasm has been proposed as a possible mechanism, we investigated ocular vessel flow velocity in normal-tension glaucoma patients at rest and under treatment with a cerebral vasodilator. Ten normal-tension glaucoma patients and nine age- and gender-matched controls had flow velocity measured in three vessels (ophthalmic artery, central retinal artery, and temporal short posterior ciliary artery) by using color Doppler imaging, under baseline conditions and during carbon dioxide supplementation sufficient to increase end-tidal PCO2 by 15%. Peak systolic and end-diastolic velocities were measured, and the resistance index (peak systolic velocity minus end-diastolic velocity, divided by peak systolic velocity) was calculated. Compared with controls, these normal-tension glaucoma patients had significantly lower end-diastolic velocities (P = .002) and higher resistance indices (P = .007) in the ophthalmic artery at baseline. When PCO2 was increased, control subjects remained unchanged, whereas it increased end-diastolic velocity in patients (P = .003) and abolished the difference in resistance index between the two groups. Patients and control subjects differed little in their baseline or carbon dioxide response velocities or in resistance in the other two vessels. These results indicate that at baseline these normal-tension glaucoma patients may have increased vascular resistance distal to the ophthalmic artery, although this increased resistance cannot be specifically ascribed to the central retinal arterial or to temporal short posterior ciliary arterial vascular beds. The responsiveness of these patients to a cerebral vasodilator (increased PCO2) indicates further that the increased resistance distal to the ophthalmic artery may be the reversible result of vasospasm.

Adult↗
PubMed1994

The association of swallowing dysfunction and aspiration pneumonia.

The medical literature has emphasized that aspiration of gastric contents or oral bacteria is a common cause of aspiration pneumonia. Swallowing disorders have been implicated in this disease but not studied at the time that aspiration pneumonia was diagnosed. A significant difference was found in the incidence of videofluoroscopically confirmed oropharyngeal swallowing problems in a group of patients diagnosed with aspiration pneumonia (AP) when compared with patients with nonaspiration pneumonia (NAP). Six of the 9 patients in the AP group aspirated during the videofluoroscopic evaluation and 2 others were considered to be at risk for aspiration. None of the 7 NAP patients demonstrated swallowing problems or aspiration. A significant difference in oral transit time also occurred between the two groups. Liquid was found to have a significantly faster oral transit time than paste or a cookie. Pharyngeal transit times were not found to be significantly different. Although there were only a small number of patients who met the criteria for this pilot study, a strong association was found between swallowing dysfunction and aspiration pneumonia.

Adult↗
PubMed1994

Indications and techniques of endoscopy in evaluation of cervical dysphagia: comparison with radiographic techniques.

The technique of fiberoptic endoscopic evaluation of swallowing disorders (FEES), and a comparison of its utility with that of videofluoroscopic examination in patients with dysphagia, was presented in a workshop session. Viewpoints were expressed by two speech pathologists and an otolaryngologist experienced in assessment and treatment of patients with dysphagia, and representative cases, illustrated with videotaped FEES and videofluoroscopic studies, were discussed. Some of the major advantages and disadvantages of each of these modalities are discussed in the following three articles.

Deglutition Disorders↗
PubMed1994

Increased abdominal pain during final examinations.

Anecdotes and animal experiments alike suggest that physiological and psychological stress can profoundly alter gastrointestinal function. However, few studies have examined, in humans, real-world stress to see if free-living persons exhibit gut alterations similar to those produced in the laboratory. To investigate this possibility, we studied 16 medical and premedical students during final written examinations. As compared to a control day, the examination created a classic stress response: elevated serum cortisol (16 +/- 1 to 21 +/- 3 micrograms/dl; P < 0.05), ACTH (31 +/- 1 to 33 +/- 1 pg/ml; P < 0.05), heart rate (72 +/- 3 to 79 +/- 3 beats/min; P < 0.05), arterial blood pressure (systolic pressure 106 +/- 2 to 120 +/- 2 torr; P < 0.05; diastolic pressure 72 +/- 2 to 77 +/- 1 torr; P < 0.05), and subjective anxiety (raw score 28 +/- 2 to 47 +/- 3; P < 0.0001). In contrast, subjects displayed identical orocecal liquid transit time (of 0.36 g/kg lactulose in a 240-ml, 250-kcal liquid meal) under control (103 +/- 8 min) and examination conditions (106 +/- 8 min; P = NS). Mean subjective reports of gas, diarrhea, and borborygmi were unchanged on the day of the experiment, although the examination did increase reported abdominal pain (from 0.5 +/- 0.4 to 2.1 +/- 0.5 on a 0-5 analog scale; P < 0.05). We conclude that examination stress in humans can increase gastrointestinal symptoms without altering orocecal transit.

Abdominal Pain↗
PubMed1994

Investigation of applied forces in alphanumeric keyboard work.

This paper considers one way that occupational health professionals can assess the force exerted by keyboard users and the possible relationship between that force and the key force-displacement relationship. First, three personal-computer keyboards with the standard QWERTY layouts were tested as described by the American National Standard for Human Factors Engineering of Visual Display workstations (ANSI/HFS 100-1988) to determine the peak forces, 0.47-0.89N; displacements prior to the "breakaway" force that acknowledges key registration, 2.0-2.5 mm; and total key travel, 3.3-4.3 mm. Second, keyboard reaction forces were recorded while 10 subjects typed 4 alphanumeric sentences on the keyboards. It was found that the peak forces corresponding to each keystroke were 2.5 to 3.9 times the required activation forces, indicating that the subjects consistently displaced the keys to their limits. The average of the peak forces for all keystrokes was lowest for the keyboard with the lowest required activation force. It was concluded that keyboard reaction forces can be used as an index of finger forces for keying tasks. Further studies are necessary to evaluate the relationship between keyboard reaction forces, fatigue, and chronic muscle, tendon, and nerve disorders.

Biomechanical Phenomena↗
PubMed1994

Retinal blood velocities during carbogen breathing using scanning laser ophthalmoscopy.

Hyperoxic-hypercapnic gas mixture ('carbogen': 6% CO2-94% O2) is widely used clinically. Its influence on retinal perfusion remains unclear, since past work suggests that high O2 may reduce and high CO2 may increase retinal blood flow. To examine the changes in retinal blood velocity during 'hyperoxic-hypercapnic' gax mixture breathing, we quantified retinal blood velocity indices. Twenty-eight healthy subjects were studied using scanning laser video fluorescein angiograms at baseline and after gas inhalation. Retinal arteriovenous passage time and mean arterial dye velocity were measured by means of a digital image processing system. Arterial diameter measurements showed no change (4%) during carbogen breathing. Increased arterial Pco2 and Po2 resulted in small but statistically significant increases in systolic and diastolic blood pressure and heart rate (each c. 8%, p < 0.05), and a dramatic increase in mean dye velocity (27%, p < 0.01), with parallel reduction in arteriovenous passage time (40%, p < 0.01). The substantial acceleration of retinal dye velocity and transit under combined hyperoxia and hypercapnia strongly suggests that this clinically standard gas mixture may indeed improve oxygenation without reducing retinal perfusion.

Adult↗
PubMed1994

Coordination between respiration and swallowing: respiratory phase relationships and temporal integration.

The coordination of breathing and swallowing was studied in 13 young healthy adult subjects during the administration of graduated volumes of water (3, 10, and 20 ml). Simultaneous submental electromyography, respiratory plethysmography, and fiber-optic endoscopy revealed a well-timed pattern between physiological respiratory events and related swallowing events. Expiration was the phase of respiration that was most closely associated with deglutition. Respiration was usually maintained at the onset of deglutition and halted before the onset of laryngeal elevation. The apneic interval was approximately 1 s for the 3-, 10-, and 20-ml boluses. A large-volume (100-ml) straw swallow resulted in variable respiration-swallowing patterns and in statistically significant differences (P < 0.01) in the duration of apneic pause and laryngeal excursion. The expiratory phase of respiration resumed nearly 0.50 s before the completion of swallowing. Clinical implications of the findings are addressed and related to aspiration and pulmonary complications in dysphagic patients.

Adolescent↗
PubMed1994

Ultrastructural changes in arteries proximal to short-term experimental carotid-jugular arteriovenous fistulae in rabbits.

The afferent arteries of 10 carotid-jugular arteriovenous fistulae in rabbits were examined by transmission electron microscopy to determine the early ultrastructural changes in the vicinity of haemodynamically induced tears of the internal elastic lamina. No significant changes appeared to precede the development of the tears but radially orientated partial fractures were observed adjacent to some major tears. The elastic tissue tears became more numerous, extended proximally along the artery and with time involved the innermost medial elastic laminae. Endothelial discontinuities were present over only a few early tears and the small size suggested repair was rapid. Endothelial cells overlying the elastic tissue tears increased in density and thickness. They were adherent to the underlying matrix and eventually to the thickened and multilaminated basal lamina. In the floor of the tears between the edges of the torn internal elastic lamina there were some smooth muscle cells of the synthetic type, degenerative and necrotic muscle cells and areas devoid of matrix with scarce proteoglycan material suggestive of oedema. Sixteen days post-operatively the smooth muscle cells in the floor of the tears were all of the contractile variety with thickened basal laminae overlaid by a relatively normal endothelial layer. There was no suggestion that inflammatory cells were responsible for the elastic tissue tears. The abrupt edges and the adjacent microfractures are consistent with the concept of mechanical failure of the elastic tissue.

Animals↗
PubMed1993

Loperamide abolishes exercise-induced orocecal liquid transit acceleration.

Previous work in our laboratory has found that mild physical activity accelerates mouth-to-large intestinal transit of lactulose in a mixed liquid meal. Because loperamide is commonly used as an antidiarrheal agent, we wondered if it would blunt the orocecal transit acceleration provoked by mild exercise. We investigated this equation in 12 healthy persons by comparing orocolonic liquid transit at rest and in mild exercise. Each subject ingested 8 mg loperamide 1 hr prior to study under both resting and exercise conditions. With loperamide treatment, exercise (walking at 5.6 km/hr) failed to hasten increased H2 excretion (mean transit time 72 +/- 12 min at rest, 90 +/- 15 min in exercise; P = NS). This result contrasts sharply with previously reported controls: loperamide completely abolished exercise-induced orocecal transit acceleration (-23 +/- 5 min in controls; +18 +/- 13 min with loperamide; P < 0.05). Compared with these same controls, resting transit was not significantly slowed by the drug, while transit in exercise was retarded (64 +/- 5 min in controls, 90 +/- 15 min with loperamide; P = 0.06). Loperamide left unchanged the heart rate and oxygen uptake rises associated with exercise. In summary, by showing that loperamide blocks an exercise effect on the upper gut, these results suggest that the drug might prove effective in treating some gut symptoms induced by physical activity.

Adult↗
PubMed1993

Normal laryngeal valving patterns during three breath-hold maneuvers: a pilot investigation.

Synchronized videonasendoscopy and respiratory recordings were conducted in six healthy male subjects to evaluate activity of the arytenoid cartilages, true vocal folds, false vocal folds, and epiglottis during repeated trials of three breath-hold maneuvers: EASY hold, INHALE HARD hold, and INHALE/EXHALE HARD hold. Five of the six subjects demonstrated maximal laryngeal valving on the HARD breath-hold conditions. One subject showed maximal laryngeal valving on the EASY hold condition, and rarely demonstrated any medial displacement or contact of the laryngeal valves on either effortful breath-hold maneuver. Arytenoid approximation and true vocal fold closure were produced consistently by the majority of subjects on all breath-hold maneuvers, but false vocal fold approximation and anterior arytenoid tilting were accomplished by the majority of subjects only during the effortful breath-hold conditions. Intratrial and intersubject variation indicated that presence or degree of laryngeal valving cannot be assumed during a breath-hold maneuver. We conclude that videonasendoscopy has merit in assessing a patient's laryngeal valving ability and progress in effectively using a breath-hold maneuver for safe swallowing function.

Adolescent↗
PubMed1993

Effect of opiate and beta-adrenergic blockers on the gut transit response to mild exercise.

Acute mild exercise accelerates transit of material through the gastrointestinal tract via mechanisms that remain entirely unknown. Because exercise increases peripheral sympathetic drive, and can increase circulating opioids, in this study we examined the role that naloxone and propranolol-dependent pathways play in accelerating orocecal transit in exercise. Transit was determined in 11 subjects by H2 detection after ingestion of 0.36 g/kg lactulose in a 240 kcal, 250 ml liquid meal; the exercise was mild walking at 5.6 km/hr. Under naloxone treatment (0.4 mg intravenous bolus followed by infusion at 40 micrograms/kg/hr) transit acceleration in mild exercise was apparent: transit time (mean +/- SE) was 87 +/- 7 min at rest, 63 +/- 5 min in exercise (p < 0.05), a result identical to that seen in previous studies not involving drugs. In contrast, propranolol treatment (160 mg/day) accelerated the resting transit rate to equal the rate during exercise (65 +/- 6 vs. 60 +/- 4 min; p = NS). Under both conditions, exercise elevated oxygen consumption and heart rate, although propranolol predictably produced relative bradycardia at rest and exercise. These results suggest that mild exercise accelerates upper gut transit via an opiate-independent effect that, for gut propulsive motility, yields results similar to beta-adrenergic blockade.

Administration, Oral↗
PubMed1993

Myocardial force-frequency defect in mitral regurgitation heart failure is reversed by forskolin.

BACKGROUND: Postoperative ejection phase parameters and patient survival rates for mitral valve replacement surgery are considerably lower than for similar aortic valve surgery. While chordal transection probably is the major contributor to the lowered values, there is also evidence for decreased preoperative myocardial contractile reserve in mitral regurgitation patients. This study characterizes abnormalities in the force-frequency relation that may underlie impaired function of myocardium isolated from mitral regurgitation patients with New York Heart Association class II-III heart failure. METHODS AND RESULTS: Left ventricular epicardial myocardium was obtained by surgical biopsy during mitral valve replacement surgery in patients with mitral regurgitation heart failure (left ventricular ejection fraction, 0.64 +/- 0.05) and during coronary artery bypass surgery in patients with normal ventricular function. The steady-state twitch tension versus frequency relation was measured in myocardial strip preparations (37 degree C, 12 to 228 min-1) in the absence and presence of forskolin. Relative to normal function, peak isometric twitch tension in mitral regurgitation is depressed by 50% (P < .02) and 74% (P < .003) at contraction frequencies of 60 min-1 and 168 min-1, respectively. The slope of the tension-frequency curve is blunted and its peak is shifted to a lower frequency (mitral regurgitation: 134 min-1; normal function: 173 min-1; P < .02). The myosin heavy chain concentration did not differ between mitral regurgitation and normal function strips (53 +/- 4 versus 54 +/- 4 nmol/g blotted wt). Forskolin (0.5 mumol/L) completely reversed the tension depression, blunting, and the lowered peak frequency in the mitral regurgitation preparations. CONCLUSIONS: Preoperatively, myocardial tension generation in mitral regurgitation patients is severely depressed, and the force-frequency curve is blunted and has a negative slope in the exercise range of heart rates. The reversal of these defects by forskolin suggests that abnormal excitation-contraction coupling may underlie the decreased contractile reserve in mitral regurgitation patients.

Colforsin↗
PubMed1993

Mononuclear blood cell magnesium in older subjects: evaluation of its use in clinical practice.

Serum and mononuclear blood cell (MBC) magnesium were measured in 24 healthy community subjects, average age 76 years (67-93), and in 21 ill hospitalized subjects, average age 79 years (65-90). MBC magnesium, expressed as mumol/mg protein, was significantly lower in the in-patient group (P < 0.001), but tended to be higher in the same group when expressed as fmol/cell (not significant). Further samples from community subjects on the same day, and again at 7 days, revealed coefficients of variation for intrasubject analysis of 12% and 22%, respectively (fmol/cell). The equivalent intrasubject values for serum were 2.8% on the same day and 4% at 1 week. MBC magnesium values for inpatients were probably distorted by changes in cell size and cell protein content caused by illness. Biological variability and the effects of illness on the composition and size of cells seem to limit the usefulness of MBC magnesium measurement as a clinical tool for assessment of body magnesium status.

Aged↗