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Biomedical subjects

J M Riddle

Publications and source records attributed to J M Riddle.

At least 19 recordsLinked to original sources
PubMed1993

Echocardiograms during six hours of bedrest at head-down and head-up tilt and during space flight.

Left ventricular end-diastolic volume increased after 4 1/2 to 6 hours of space flight, but was significantly decreased after 5 to 6 days of space flight. To determine the role of acute gravitational effects in this phenomenon, responses to a 6-hour bedrest model of 0 gravity (G; 5 degrees head-down tilt) were compared with those of fractional gravity loads of 1/6 G, 1/3 G, and 2/3 G by using head-up tilts of 10 degrees, 20 degrees, and 42 degrees, respectively. On 4 different days, six healthy male subjects were tilted at one of the four angles for 6 hours. Cardiac dimensions and volumes were determined from two-dimensional and M-mode echocardiograms in the left lateral decubitus position at control (0), 2, 4, and 6 hours. Stroke volume decreased with time (P < .05) for all tilt angles when compared with control. Ejection fraction (EF) at -5 degrees was greater than at +20 degrees and +42 degrees (not significant); EF at +10 degrees was greater than at +42 degrees (not significant). For the tilt angles of -5 degrees, +10 degrees, and +20 degrees, mean heart rate decreased during the first 2 hours, and returned to control or was slightly elevated above control (+20 degrees) by 6 hours (not significant). At the +42 degrees angle of tilt, heart rate was increased above control at hours 2, 4, and 6. There were no significant differences in cardiac output at any time point for any tilt angle.(ABSTRACT TRUNCATED AT 250 WORDS)

Bed Rest↗
PubMed1993

The ultrastructure of photochemically induced thrombi with embolization in a rat model.

BACKGROUND AND PURPOSE: Photochemical techniques, currently used in stroke and cancer research, produce endothelial damage and thrombosis. To further characterize these thrombi and to determine whether they embolize, we studied the ultrastructure of photochemically damaged carotid arteries and small vessels distal to the irradiated carotid. METHODS: The right carotid artery of 9 Wistar rats was irradiated with a laser (632 nm, 200 mW/cm2, 15 minutes) after the injection of the photosensitizing dye Photofrin II, 12.5 mg/kg. There were 6 additional control rats: laser only, 2 rats; dye only, 2; carrier only (5% dextrose), 1; and normal, 1. The carotid artery and cerebral arterioles were studied using scanning and transmission electron microscopy. RESULTS: Endothelial damage was present in all irradiated carotid arteries, and consisted of exposure of the subendothelium and the formation of a nonocclusive thrombus. Although most cerebral arterioles were normal, 32 of these vessels contained peripheral blood elements, with platelet or red blood cell aggregates present in 15. The endothelium adjacent to the aggregates was intact. A few scattered endothelial cells had been lost in the carotid artery of control animals (compatible with normal cell turnover), with a few platelets adhering to the exposed subendothelium. CONCLUSIONS: Aggregates of blood cells and platelets in cerebral vessels in the absence of endothelial denudation verifies embolism as the mechanism for cerebral vascular occlusion in this experimental model. The possibility of embolization distal to the site of photochemical irradiation has implications for potential applications of photochemistry for cancer treatment and the ablation of vascular malformations and/or aneurysms.

Animals↗
PubMed1992

Mitochondrial abnormalities in myocardium of dogs with chronic heart failure.

The number, size and structural integrity of mitochondria (MIT) were evaluated in the myocardium of 12 dogs with chronic heart failure (CHF) produced by sequential intracoronary microembolizations (EMB). Tissue specimens for transmission electron microscopy were obtained from the left ventricular (LV) free wall, septum and right ventricular free wall 3 to 4 months after the last EMB. Comparisons were made with samples obtained from identical sites in 9 control dogs. In dogs with CHF, LV ejection fraction decreased from 61 +/- 1% at baseline (prior to EMB) to 22 +/- 2% 3 to 4 months after the last EMB (P < 0.01) while plasma norepinephrine (PNE) concentration increased from 364 +/- 12 pg/ml to 837 +/- 150 pg/ml (P < 0.01). The number of MIT in an area of 100 square sarcomeres was greater in CHF dogs compared to controls (92 +/- 5 vs 64 +/- 2) (P < 0.001); whereas the average size of MIT was smaller (0.53 +/- 0.03 vs. 0.78 +/- 0.04 microm2) (P < 0.001). Injury ranging in severity from matrix depletion to myelinization and membrane disruption was present in 27 +/- 4% of MIT of CHF dogs compared to only 3 +/- 1% of MIT of controls (P < 0.001). MIT abnormalities were present to the same extent in all three regions of the heart. The severity of MIT injury, assessed on the basis of an injury index, was significantly higher in CHF dogs with PNE > or = 600 pg/ml (0.64 +/- 0.07) compared to CHF dogs with PNE < 600 pg/ml (0.32 +/- 0.08) (P < 0.01). Among CHF dogs, the MIT injury index was linearly related to PNE concentration (r = 0.57, P < 0.05), LV ejection fraction (r = 0.57, P < 0.05) and LV end-diastolic pressure (r = 0.57, P < 0.05). These data indicate that profound MIT abnormalities are present in the myocardium of dogs with CHF and are related to PNE concentration and to the severity of LV dysfunction.

Animals↗
PubMed1991

Orthostatic function during a stand test before and after head-up or head-down bedrest.

Astronauts may exhibit orthostatic dysfunction upon returning to 1 g after space flight. Understanding cardiovascular changes at 0 G will provide insights into the mechanisms of the loss of orthostatic tolerance, whether due to space flight or bedrest. Bedrest is one model used to produce cardiovascular changes that are associated with space flight. In the current study, young male adults were placed at -5 degrees, +10, +20, or +42 degrees bedrest (0, 1/6, 1/3, and 2/3g, respectively) for 6 hours on 4 different days. This was preceded and followed by a stand test: 5 minutes in the supine position, and then 5 minutes in the standing position, with the feet 9 inches apart and 6 inches from the wall. Cardiovascular values were measured at 1-minute intervals. Systolic and diastolic pressures were measured using an automated blood pressure device; mean arterial pressure (MAP; mm Hg) was calculated. Heart rate (bpm) and cardiac parameters were measured with a thoracic impedance device. Minute 3, 4, and 5 values were used to determine whether there were time or angle effects. Of six subjects, one reported nausea upon 3 minutes of standing after 6 hours of bedrest at -5 degrees. The same subject was lightheaded in the first minute of standing after 6 hours of bedrest at +10 degrees. Mean heart rate pre-bedrest in the supine position was 63 and increased by 24 bpm on standing. Heart rate post-bedrest in the supine position was 65 and increased by 35 bpm on standing; standing heart rate increased 11 bpm after -5 degrees bedrest. The increases after +10 degrees, +20 degrees, and +42 degrees tilts were 4, 3, and 4 bpm, respectively. Changes in the mean arterial blood pressure were minimal. Results from the stand test pre- and post- 6 hours of bedrest at -5 degrees but not at +10 degrees, +20 degrees, or +42 degrees are similar to those after space flight.

Adult↗
PubMed1990

Acute and intermediate cardiovascular responses to zero gravity and to fractional gravity levels induced by head-down or head-up tilt.

Determination of early cardiovascular responses to simulated gravity levels between 0 and 1 G will add knowledge of cardiovascular responses to space flight. Cardiovascular responses to 6 hours in a -5 degrees head-down bedrest model of weightlessness (0 G) were compared to those in head-up tilts of +10 degrees, +20 degrees, and +42 degrees (1/6, 1/3, and 2/3 G, respectively). Six healthy young adult males experienced the four angles on separate days. Impedance cardiography was used to measure thoracic fluid index, cardiac output, stroke volume, and peak flow. Although much intersubject variation occurred, the mean thoracic fluid content at -5 degrees decreased during the first hour and remained decreased; 6-hour values were similar to +10 degrees and +20 degrees. Heart rate decreased the first 2 hours for all angles, then increased, converging at 3-4 hours, and reached control by hour 6. Stroke volume decreased for the first 3 hours at -5 degrees, +10 degrees, +20 degrees; values at all four angles converged at hour 3 and increased in unison thereafter. Cardiac output and peak aortic flow reflected the angle at start of tilt; values at all angles converged by the second hour, decreased through the third hour, and increased thereafter. Pulse pressure decreased for the first 3 hours for angles -5 degrees, +10 degrees, and +20 degrees, converged at the fourth hour, and returned to control. Peak flow at +42 degrees was constant for the first 3 hours and increased thereafter. Blood pressure decreased for the first 2 hours, although the greatest decrease occurred at -5 degrees and +42 degrees; thereafter, values at all angles increased in unison and converged at the fourth hour. Total peripheral resistance increased during the first hour at -5 degrees and +20 degrees and decreased from hour 3 to hours 5-6 at the +42 degrees angle. Cardiovascular values were related to tilt angle for the first 2 hours of tilt, but after hour 3 values at all four angles began to converge, suggesting that cardiovascular homeostatic mechanisms seek a common adapted state regardless of effective gravity level (tilt angle) up to 2/3 G.

Bed Rest↗
PubMed1990

Deposits of crystalline material containing silicon in surgically excised human valves.

Ninety-seven surgically excised natural cardiac valves were examined by scanning electron microscopy and x-ray energy spectroscopy to assess the occurrence of crystalline deposits that contain the element silicon. Valves examined included 33 mitral valves, 63 aortic valves, and 1 tricuspid valve. To reduce the possibility of surface contamination, the deep layers of some valves were examined after exposure by fracture of the valve. Crystalline material containing silicon was observed in the deep tissue. Such crystalline material was sometimes entwined within subendothelial fibers. Crystalline deposits that contained silicon were associated with 34 of 97 of these valves (35%). Among the 34 valves that showed silicon, 24 (71%) also showed microdeposits of calcific material. In view of evidence that silicon may participate in the calcification of bone, and is found in the intima of arteries, a role for this element in ectopic calcification of valves may exist.

Adult↗
PubMed1989

Evidence for the presence of red and white cells within "platelet" aggregates formed in whole-blood.

Collagen-induced platelet aggregation and secretion (ATP-release) in whole-blood and platelet-rich plasma was compared. Although the amount of ATP released was comparable in whole-blood and platelet-rich plasma, the maximum extent of aggregation was greater when platelets were studied in their natural milieu, i.e. whole-blood. A scanning electron microscopic survey of the "platelet" aggregate formed in whole-blood showed that it contained erythrocytes and leucocytes as well as aggregated platelets.

Adenosine Triphosphate↗