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Biomedical subjects

J L Semmlow

Publications and source records attributed to J L Semmlow.

At least 55 records · Page 3Linked to original sources
PubMed1987

Myoelectric assessment of bowel viability.

A device capable of quantitative measurement of intestinal ischemic damage has been designed. The device is called the electrical contractility meter and employs a clip-on strain gauge transducer that delivers a precisely controlled electrical stimulus to the bowel. Threshold stimulus level (TSL) is the stimulus current in milliamperes (mA) that is necessary to produce a clearly defined smooth-muscle contraction. In 30 dogs, TSL was used to establish viability boundaries in 40 cm ischemic bowel segments. Bowel viability was assessed with the use of TSL in comparison with gross features (color, peristalsis) and blood flow measured by means of Doppler ultrasound at 2 cm intervals in the ischemic small-bowel segments. The TSL scale ranges to 100 mA and varied from a low of 22 +/- 2 mA in normal bowel outside the ischemic segment to 97 +/- 4 mA in grossly gangrenous bowel. There was a consistent correlation between rising TSL and worsening bowel color, disappearance of visible peristalsis, and progressive disappearance of audible Doppler signals. Resection and anastomosis were performed in three groups of 10 dogs at TSL measurements of 30 mA, 40 mA, and 50 mA, respectively. Dogs were killed and anastomoses were inspected on the tenth postoperative day. There were no leaks at TSL = 30 mA, one leak at TSL = 40 mA, and four leaks at TSL = 50 mA. The number of leaks at TSL = 50 mA was significantly greater than at TSL = 30 mA (p less than 0.04, Fisher's exact test). These results show that the quantitative myoelectric parameters established by this device provide a reliable in vivo assessment of bowel viability. The electrical contractility meter is easy to use and may have clinical applicability.

Animals↗
PubMed1986

Static vergence and accommodation: population norms and orthoptics effects.

The steady-state characteristics of the accommodation and vergence systems can be described by a model with six major oculomotor parameters. These include the system biases (tonic vergence and accommodation) and forward-loop gains (vergence and accommodative gains), as well as the interactive system gains (AC/A and CA/C ratios). We investigated these parameters in two populations: (1) 22 visually-normal asymptomatic individuals, and (2) 21 visually-abnormal symptomatic individuals before and after conventional orthoptic therapy. Two parameters related to system gain differentiated between the symptomatic and asymptomatic individuals: the slope of the fixation disparity curve with accommodation open-looped and the slope of the accommodative response/stimulus curve. Following orthoptic therapy, 4 static model parameters and 1 dynamic clinical parameter showed changes toward the normal mean; this included tonic accommodation, slope of the fixation disparity curve with accommodation closed-loop (2.5D), slope of the accommodative response/stimulus curve, the CA/C ratio, and the +/- 2D monocular accommodative flipper rate.

Accommodation, Ocular↗
PubMed1986

Quantitative myoelectric determination of bowel viability.

A new device designed to quantitatively measure viability in ischemic bowel was studied in 20 dogs. This strain gauge device is clipped on the serosal surface and can rapidly deliver an electrical stimulus. The threshold stimulus level (TSL) was the stimulus necessary to produce a clearly defined smooth muscle contraction. TSL was compared with blood flow measured by Doppler ultrasound at 2-cm intervals in 30-cm ischemic segments as a determinant of bowel viability. Doppler readings were taken from the bowel wall (BW), peripheral arteriolar branches of the marginal artery (PA), and marginal artery (MA), itself, at each 2-cm interval. Bowel color and peristalsis were correlated with Doppler and TSL data. TSL scale ranged from 0 to 100 mA and varied from 21 +/- 2 mA in normal bowel to 98 +/- 2 mA in gangrenous bowel. At the locus of the last audible Doppler signal in the BW, PA, and MA, mean TSL readings were 27 +/- 5, 34 +/- 6, and 48 +/- 16 mA, respectively. These readings were each significantly greater than the TSL of normal bowel at P less than or equal to 0.0001 level. Portions of each ischemic segment were resected and reanastomosed. Absence of Doppler signals in the BW and PA did not preclude healing of ischemic bowel. These data suggest that TSL measurement is more sensitive than either Doppler ultrasound or gross visual evaluation in assessment of bowel viability.

Animals↗
PubMed1986

Quantitative assessment of disparity vergence components.

Earlier evidence suggests qualitatively that at least two control modes may mediate a single vergence response. Thus, in a vergence response to step disparity, the transient component drives the initial fast dynamic portion of the response, while the sustained component maintains the latter slower portion of the response. The authors extended this hypothesis by quantitatively defining the stimulus pattern and dynamics that elicit this dichotomous behavior. The disparity target consisted of vertical lines 2 deg in height presented to each eye. Ramp disparity velocities ranged from 0.7 deg/sec to 36 deg/sec with amplitude of up to 4 deg. Photoelectric recordings of eye movements from both eyes were subtracted to give the vergence response. Fast and slow ramp stimulus velocities were found to elicit transient and sustained component responses respectively. In addition, the finding of staircase-like responses to fast ramp stimuli has strong implications on control mechanisms, indicating a sampling process in the transient component of the disparity vergence system.

Eye Movements↗
PubMed1984

Accommodative stimulus/response function in human amblyopia.

Three parameters are essential to describe static accommodative behavior in a comprehensive, quantitative manner: the slope of the stimulus/response curve, the depth of focus, and the tonic response. These parameters were obtained in amblyopes, former amblyopes, strabismus without amblyopia, and normals. Results showed that the accommodative response in the amblyopic eye was characterized by a reduction in the slope of the stimulus/response curve and increased depth of focus. Similar abnormalities but of lesser magnitude were found in the non-dominant eye of some former amblyopes and some strabismus without amblyopia. Orthoptic therapy always increased the slope of the stimulus/response curve in the amblyopic eye. We believe that the reduced accommodative responses found in amblyopic eyes reflect a primary sensory loss over the central retinal region that occurs as a result of prolonged, early, abnormal visual experience associated with the presence of strabismus and/or anisometropia.

Accommodation, Ocular↗
PubMed1983

Static aspects of accommodation in human amblyopia.

Static aspects of accommodation in human amblyopia were investigated. Abnormalities uncovered included decrease in accommodative controller gain, decrease in slope of the accommodative stimulus/response curve, decrease in accommodative amplitude, and increase in depth of focus. Orthoptic therapy improved accommodative function in the amblyopic eye. Similar defects, but of lesser magnitude, were frequently found in the nondominant eyes of subjects in related test groups. This included former amblyopes who had received successful orthoptic therapy in their youth, which suggested lack of complete and/or maintained recovery of accommodative function, and strabismics without amblyopia, which suggested that the effects of strabismic suppression contributed to the accommodative deficits found in some strabismic amblyopes. The accommodative abnormalities found in our amblyopes were attributed to the effects of early, prolonged, abnormal visual experience on the sensory visual system.

Accommodation, Ocular↗
PubMed1983

Identification of accommodative vergence contribution to the near response using response variance.

An experimental method was developed to isolate accommodative and disparity vergence contributions to coordinated near vergence motor responses. The variability normally associated with the neural control signal was used as an identifying marker or tag. Using this approach, the results showed an increased variability associated with the blur-driven, accommodative vergence component that is particularly noticeable during the latter half of the movement. This indicated that accommodative vergence provides a moderate contribution to the near vergence response primarily in the late and post-transient period when the movement is essentially complete. Presence of this accommodative contribution lends further support to the "dual interactive model" of near triad control.

Accommodation, Ocular↗
PubMed1981

The relation between uterine cervix temperature differentials and epithelial abnormalities.

Temperature measurements of the human cervix uteri were made at various locations by a direct-contact thermistor probe. These measurements were compared to both colposcopic findings and histologic examination of tissue biopsies. A correlation between loci of temperature elevation and tissue abnormality was found; however, the measurements were not able to predict the severity of this abnormality.

Body Temperature↗
PubMed1980

Binocular interactions of vergence components.

Classical theories describing the interaction between blur-driven and disparity-driven components of the visual motor near triad are examined and the underlying assumptions explicitly stated. Experimental evidence is presented that refutes one necessary assumption behind the traditional structuring of vergence components proposed by Maddox. An alternative theory of binocular interaction is outlined, and experimental support for the new theory is provided.

Accommodation, Ocular↗