Biomedical subjects

Kathryn M Sibley

Publications and source records attributed to Kathryn M Sibley.

4 recordsLinked to original sources

PubMed2006

Effects of postural anxiety on the soleus H-reflex.

Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study investigated how soleus H-reflex amplitude was influenced by standing at heights that induced different levels of anxiety. H-reflexes were elicited in 15 participants standing at the center and edge of a platform raised from a low to a high height (with and without vision). Increased skin conductance confirmed the anxiety effect of elevated surface heights. When standing at the edge of the platform with vision, H-reflex amplitude was attenuated in the high compared to low height condition. Changes in background muscle activity could not explain observed H-reflex changes, suggesting the potential involvement of pre-synaptic inhibition or fusimotor drive on anxiety-related changes in reflex modulation. This study reveals that healthy participants reduce spinal reflex excitability in the presence of increased postural anxiety and a postural threat imposed by standing at the edge of a raised platform. These findings have implications for understanding control of standing balance in individuals with postural instability and/or fear of falling, such as the elderly or stroke.

Adult↗

PubMed2006

Do functional walk tests reflect cardiorespiratory fitness in sub-acute stroke?

BACKGROUND AND PURPOSE: The Six-Minute Walk Test (6MWT) has been employed as a measure of functional capacity, but its relationship to cardiorespiratory fitness in stroke is not well established. Gait speed measured over short distances is commonly used as an index of walking competency following stroke. We evaluated the relationship between the 6MWT, aerobic fitness (VO2peak) and walking competency in sub-acute stroke. METHODS: Thirty-six individuals (mean age +/- SD, 64.6 +/- 14.4 years; time post-stroke 16.2 +/- 13.3 days) were evaluated using the 6MWT (distance, speed, heart rate), a maximal exercise test (VO2peak, heart rate, exercise test duration), and walking competency using a five meter walk (speed, symmetry ratio). Correlation analyses were used to examine the relationships between these outcomes. RESULTS: There was a strong correlation between the 6MWT and five meter walk velocity for preferred (r = 0.79) and fast (r = 0.82) speed (p < 0.001). On average, the 6MWT speed was faster than the preferred gait speed (94.9 cm/s vs. 83.8 cm/s, p = 0.003), but slower than the fast-paced walk (115.1 cm/s, p < 0.001). There was significant though more moderate association between 6MWT distance and VO2peak (r = 0.56, p < 0.001) and exercise test duration (r = 0.60, p < 0.001). CONCLUSION: The speed selected during the 6MWT was strongly related to the velocities selected during the five meter walk distance (intermediate to the selected preferred and fast speeds). Although the 6MWT may be challenging to the cardiorespiratory system, it appears to be more strongly influenced by potential limits to walking speed rather than cardiorespiratory capacity. As a result, this test is not, by itself, an adequate measure of aerobic fitness early after stroke.

Journal Article↗

PubMed2006

Maximal exercise test results in subacute stroke.

OBJECTIVES: To establish the feasibility and reliability of graded maximal exercise testing, suitability of standard indexes of maximum oxygen consumption (Vo(2)max), and evidence of trial-to-trial practice effects in subacute stroke. DESIGN: Descriptive, cross-sectional study. SETTING: Rehabilitation hospital. PARTICIPANTS: Consecutive sample of 35 participants (mean age, 65.7+/-2.6 y; mean days poststroke, 17.6+/-2.2 d). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Graded maximal exercise test using semirecumbent cycle ergometry. A subset (n=20) performed repeated tests to determine test-retest reliability and presence of practice effects. RESULTS: Thirty-one (89%) participants completed the exercise test without symptomatic responses (mean peak level of oxygen consumed [Vo(2)peak], 10.7 mL.kg(-1).min(-1); peak work rate, 39 W). Twelve (34%), 15 (44%), and 3 (9%) participants achieved oxygen consumption per unit time (Vo(2)) plateau, respiratory exchange ratio, and heart rate criteria, respectively. Although test-retest correlations were high (intraclass correlation coefficient range, .67-.87), higher Vo(2)peak (1.0 mL.kg(-1).min(-1), P=.04) and work rate (7.3 W, P=.01) were observed with repeated testing, with no associated increase in reaching standard criteria for Vo(2)max. CONCLUSIONS: This work has important implications for developing guidelines for measuring aerobic capacity early after stroke. Although maximal exercise testing using semirecumbent cycle ergometry is feasible, standard Vo(2)max criteria are not consistently appropriate. At least 1 practice trial is recommended before the actual evaluation is performed.

Adult↗

PubMed2004

Effects of bilateral vestibular loss on podokinetic after-rotation.

We asked what the role of the vestibular system is in adaptive control of locomotor trajectory in response to walking on a rotating disc. Subjects with bilateral vestibular loss (BVL) were compared to age- and gender-matched controls (CTRL). Subjects walked in place on the surface of a rotating disc for 15 min and then attempted to step in place without vision on a stationary surface for 30 min. CTRL subjects demonstrated podokinetic after-rotation (PKAR), involuntarily and unknowingly turning themselves in circles while attempting to step in place. PKAR in CTRLs was characterized by a rapid rise in turning velocity over the first 1-2 min, followed by a gradual decay over the remaining 28 min. Subjects with BVL also demonstrated PKAR and had no knowledge of their turning. However, PKAR in BVLs was characterized by an extremely rapid, essentially instantaneous rise. Subjects with BVL immediately turned at maximum velocity and exhibited a gradual decay throughout the entire 30 min period. Despite this difference in the initial portion of PKAR in BVLs, their responses were not significantly different from CTRLs during minutes 2 to 30 of the response. These results suggest that vestibular inputs normally suppress PKAR velocity over the first 1-2 min of the response, but do not greatly influence PKAR decay. PKAR is therefore a process mediated primarily by somatosensory information and vestibular inputs are not required for its expression. Additionally, the absence of vestibular inputs does not result in increased somatosensory sensitivity that alters podokinetic intensity or decay time constants.

Adaptation, Physiological↗