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Biomedical subjects

R Hammond

Publications and source records attributed to R Hammond.

At least 55 records · Page 3Linked to original sources
PubMed1991

HTLV-I-associated myelopathy/tropical spastic paraparesis in the United States.

HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is endemic in the Caribbean basin and Japan. Because of the close proximity of the United States to the Caribbean and the presence of HTLV-I-seropositive persons in the United States, we sought reports of patients who were HTLV-I seropositive and had a slowly progressive myelopathy. Over a 2-year period, there were 25 patients reported, 19 of whom were black and 12 of whom had been born in the United States. All patients except two had become symptomatic while living in the United States. Six patients had no apparent risk factor for acquiring HTLV-I. These data demonstrate that HAM/TSP is occurring in the United States and that the diagnosis of HAM/TSP should be considered in patients with a slowly progressive myelopathy regardless of risk factors for acquiring HTLV-I.

Adult↗
PubMed1991

The histologic reliability of laser cone biopsy of the cervix.

Laser conization of the cervix has been advocated as the technique of choice for the treatment of cervical intraepithelial neoplasia (CIN) in preference to ablative techniques, because it provides a specimen for histologic diagnosis while retaining the advantages of an outpatient procedure with minimal short- and long-term morbidity. To determine whether specimens so obtained are adequate for reliable histologic diagnosis, we reviewed 77 laser conizations performed for lesions confirmed to contain CIN in a colposcopically directed biopsy and satisfying the criteria for local ablation and scored the cones for the presence of epithelial denudation and laser coagulation artifact that interfered with the diagnosis of CIN or the assessment of the margins of excision. Thirty specimens (39%) were negative for CIN. Twenty-eight (36%) showed extensive epithelial denudation, ten (13%) contained coagulation artifact that made recognition of CIN extremely difficult or impossible, and in 11 (14%), assessment of margins was extremely difficult or impossible because of laser coagulation artifact. We conclude that these difficulties with the histologic interpretation of laser cone specimens make it an unsuitable excisional technique when reliable histologic diagnosis of cervical lesions is required.

Adult↗
PubMed1989

Nucleotide sequence and proposed secondary structure of Columnea latent viroid: a natural mosaic of viroid sequences.

The Columnea latent viroid (CLV) occurs latently in certain Columnea erythrophae plants grown commercially. In potato and tomato, CLV causes potato spindle tuber viroid (PSTV)-like symptoms. Its nucleotide sequence and proposed secondary structure reveal that CLV consists of a single-stranded circular RNA of 370 nucleotides which can assume a rod-like structure with extensive base-pairing characteristic of all known viroids. The electrophoretic mobility of circular CLV under nondenaturing conditions suggests a potential tertiary structure. CLV contains extensive sequence homologies to the PSTV group of viroids but contains a central conserved region identical to that of hop stunt viroid (HSV). CLV also shares some biological properties with each of the two types of viroids. Most probably, CLV is the result of intracellular RNA recombination between an HSV-type and one or more PSTV-type viroids replicating in the same plant.

Base Composition↗
PubMed1989

Effects of collateral blood vessel ligation and electrical conditioning on blood flow in dog latissimus dorsi muscle.

Utilization of skeletal muscle as a myocardial substitute requires it to undergo two major modifications: mobilization to the site of action and adaptation to continuous activity. We have examined the effects of collateral blood vessel ligation, which would accompany mobilization, on blood flow in control and electrically conditioned canine latissimus dorsi (LD) muscle. Blood flows were measured at rest and during a vigorous isometric fatigue test. In 22 control muscles, electrical stimulation during the fatigue test resulted in a sevenfold increase in muscle blood flow (0.26 +/- 0.18 ml/g/min at rest, 1.69 +/- 0.84 ml/g/min during stimulation). No difference was detected in flow to distal and proximal portions of the muscle. In three muscles where collateral vessels were ligated immediately before measurement of blood flow, flow in the proximal portion of the muscle was not significantly different from control, but in the distal portion, stimulation failed to elicit an increase in flow (0.12 +/- 0.13 ml/g/min at rest, 0.16 +/- 0.07 ml/g/min during stimulation). In animals allowed a 3-week recovery period following collateral vessel ligation, stimulation-induced increases in blood flow were detected but remained lower than control. Muscles which had been conditioned by continuous electrical stimulation for 6-7 weeks at 2 or 10 Hz generated less peak isometric tension than controls (peak tension = 4.5 +/- 1.7 kg control, 2.4 +/- 0.7 kg following 2 Hz conditioning, 1.6 +/- 0.4 kg following 10 Hz conditioning). However, these muscles demonstrated an increased resistance to fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1988

Cloned riboprobe for detection of a mycoplasmalike organism.

A [32P]-labeled single stranded-RNA probe (riboprobe) was constructed with plasmid vector pSP64 and used to detect and specifically identify an uncultured pathogenic mycoplasmalike organism in infected host. The riboprobe was more sensitive and reliable than complementary double stranded-DNA probe in detection of western X mycoplasmalike organism. When concentration of a double stranded-DNA probe was increased, nonspecific hybridization signal was observed with nucleic acid from healthy plants and from plants infected by other mycoplasmalike organisms. In contrast, sensitivity of detection with the complementary riboprobe was increased at elevated probe concentrations without nonspecific hybridization.

Cloning, Molecular↗
PubMed1987

Canine diaphragm muscle after 1 yr of continuous electrical stimulation: its potential as a myocardial substitute.

Skeletal muscle has been rendered fatigue resistant by chronic stimulation and therefore has potential as an active substitute for damaged myocardium. It is therefore important to know whether stimulation produces any deleterious effects in the long term. Hemidiaphragm muscles of four dogs were examined after chronic stimulation for 1 yr at either 2 or 4 Hz. The stimulated hemidiaphragms appeared normal on gross inspection and were still contracting vigorously. By histochemical and immunohistochemical criteria, they had acquired a uniformly type I character, in contrast to the mixed fiber type composition of the unstimulated hemidiaphragms. This transformation was also reflected in their complement of myosin isozymes. There was some enzymatic evidence of an associated shift towards aerobic pathways of energy generation. Histological examination revealed no evidence of degenerative changes. Trends, observed in the shorter term (6-8 wk), toward a decrease in fiber area and an increase in connective tissue showed no further progression at 1 yr. Thus hemidiaphragm muscle stimulated at frequencies at or above the normal heart rate does not appear to undergo adverse long-term changes that would constrain its use in a myocardial assist role.

Animals↗
PubMed1986

Hydraulic pouches of canine latissimus dorsi. Potential for left ventricular assistance.

We have studied the fatigue rates of hydraulic pouches constructed in the form of a multilayered conical spiral using the latissimus dorsi muscle of 17 beagles. The roles that electrical muscle conditioning and early interruption of collateral blood supply have in the prevention of pouch fatigue were evaluated. The length of time that a pouch could generate flow in a hydraulic test system was measured; afterload was set at 80 mm Hg and preload 24 mm Hg. Pouches (N = 3) fashioned from muscles subject to neither electrical conditioning nor a vascular delay generated an initial flow of 990 +/- 346 ml/min, but could sustain flow for only 2.3, 3.8 and 3.6 minutes. Pouches (N = 5) constructed with electrically unconditioned muscles after a vascular delay (median 3 weeks) demonstrated a variable improvement in fatigue rates (initial flow 826 +/- 265 ml/min; time to no forward flow, 2.5, 7.5, 7.5, 10, and 200 minutes). Four of six pouches that received the benefit of long-term electrical muscle conditioning and a vascular delay (N = 6) were able to generate flow for a 4 hour period, at which time the experiment was terminated (initial flow 478 +/- 204 ml/min; final flow 195 +/- 157 ml/min). After the 4 hour fatigue test was completed, one electrically conditioned pouch was placed in series with the heart and served as a counterpulsator. The initial volume of blood pumped by the muscle pouch was 262 ml/min or 13.8% of cardiac output. After the pouch had contracted at a rate of approximately 45 beats/min for 1 hour, the volume of blood pumped was 178 ml/min, or 11% of cardiac output. In three other animals a pouch was fashioned and then left in situ for a 1 to 3 week period before hydraulic testing. These pouches generated significant initial flows (390 +/- 60 ml/min), which demonstrates the feasibility of further study of permanent pouches. These results suggest that permanent electrical muscle conditioning and perhaps a vascular collateral delay might permit an auxiliary skeletal muscle-powered ventricle to assume a portion of left ventricular function.

Animals↗
PubMed1985

Pneumothorax during positive-pressure mechanical ventilation.

The hemodynamic and respiratory effects of unilateral pneumothorax were studied during positive-pressure mechanical ventilation in five sheep. The sheep were anesthetized, intubated, and placed on mechanical ventilation with positive end-expiratory pressure (5 cm H2O). After baseline studies, including chest roentgenograms, were taken, increments of air were injected into the right pleural cavity. Measurements were repeated at pneumothoraces of 500, 1,000, and 1,500 ml. There was a steady fall in cardiac output (p less than 0.02) at pneumothoraces of 1,000 and 1,500 ml. The decrease in cardiac stroke volume paralleled that of cardiac output. Heart rate rose (p less than 0.05) at a pneumothorax of 1,500 ml. There appeared to be a linear relationship between the percent increase in pneumothorax as estimated by roentgenogram and the percent fall in cardiac output (r = 0.991). There was a steady rise in mean pulmonary arterial, pulmonary arterial capillary wedge, superior vena caval, and inferior vena caval pressures, although the changes in inferior vena caval pressure were not statistically different from baseline. Peak airway pressure increased from baseline at pneumothoraces of 1,000 and 1,500 ml. Both right and left end-expiratory intrapleural pressures increased and were statistically different (p less than 0.01) from baseline. However, there was a substantially greater rise in right intrapleural pressure than left. Arterial oxygen tension remained physiological throughout the study. This study indicates that cardiac output decreases as the amount of pneumothorax increases in sheep during mechanical ventilation. This study also demonstrates that, during positive-pressure mechanical ventilation, a relatively benign-appearing pneumothorax by chest roentgenogram may be associated with a significantly depressed cardiac output. In addition, arterial oxygen tension may not be useful in predicting the onset of pneumothorax during mechanical ventilation.

Animals↗
PubMed1983

Palatal receptor contribution to and effects of palatal alteration on taste acuity thresholds.

To determine the contribution of the soft palate to the overall taste mechanism and the effects of palatal compromise (surgery, cleft palate, and trauma), four taste solutions representing sweet, salty, sour, and bitter were applied to the apex and base of the tongue and to the soft palate of 12 subjects in each of the control and palatally compromised groups. Each group was tested on two different occasions with the sessions 2 weeks apart and one in the morning and the other in the afternoon. Results indicate that the soft palate contributes to bitter and salty sensations to a greater degree than the other two sensations. Of these two, bitter is the more acutely experienced. Patients with compromised palates revealed higher taste acuity thresholds than the normal control group, particularly with bitter solutions. Taste acuity thresholds increased with age.

Adolescent↗
PubMed1978

Visual evoked cortical potentials in men during compression and saturation in He-O2 equivalent to 400, 800, 1200 and 1600 feet of sea water.

Visual evoked cortical potentials and related EEG activity were recorded from subjects during rapid compression and exposure to pressures of 400, 800, 1200 and 1600 fsw. In one phase, subjects made repeated excursions to 1200 fsw from a base at 800 fsw; in the second phase, the saturated base was 1200 fsw with excursions to 1600 fsw. The results included: (1) For the visual evoked potentials, sizeable and significant decreases in amplitude and increases in latency of the response with depth; (2) Changes in the visual evoked potentials which varied systematically with depth but not with related changes in compression rate or decompression. The changes were small but consistent alterations of normal responses to visual stimulation; and (3) Theta activity in discrete EEG recordings increased progressively with depth. With all subjects showed increases in theta activity the pattern of increase varied individually.

Alpha Rhythm↗