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Biomedical subjects

B Christie

Publications and source records attributed to B Christie.

67 records · Page 4Linked to original sources
PubMed1979

Essential hypertension in black and white subjects. Hemodynamic findings and fluid volume state.

Systemic hemodynamics (cardiac output, intraarterial pressure, total peripheral resistance) and intravascular volume (plasma volume and red cell mass) were measured in a population of 126 black and white patients, 51 with borderline hypertension and 75 with established essential hypertension. The findings were compared with those in 29 age-matched normotensive control subjects of both races. The white patients with established hypertension demonstrated a faster heart rate than the black patients (less than 0.05); this difference was more pronounced during upright tilt (p less than 0.02). No significant difference in cardiac index, total peripheral resistance, plasma volume or total blood volume was found between the two racial populations. Cardiac index correlated directly with plasma and total blood volume in black patients (r = 0.32, p less than 0.05) and white patients (r = 0.35, p less than 0.001) as well as in the whole study population (r = 0.36, p less than 0.001). The regression lines were similar in the two races. Further, a negative correlation was observed between the total peripheral resistance and plasma volume (r = -0.31, p less than 0.001) or total blood volume (r = -0.34, p less than 0.001), and it was similar in both races (blacks r = -0.48, p less than 0.01; whites r = -0.25, p less than 0.05). Age correlated significantly with total peripheral resistance in the white patients (r = 0.35, p less than 0.001) and in the total study population (r = 0.28, p less than 0.001). We conclude that, for every given age or level of arterial pressure, systemic hemodynamics are similar for the black and white patients with essential hypertension. These data, therefore, do not support the clinical impression that basic pathophysiology and hypertensive vascular disease are different in the black patient with essential hypertension.

Adult↗
PubMed1979

Systemic haemodynamic effects of biofeedback in borderline hypertension.

1. Six patients with borderline hypertension underwent training in exteroceptive biofeedback (BFB) in order to increase or decrease arterial pressure. 2. Systemic haemodynamics, intravascular volume and peripheral renin activity were determined before, during and after training sessions. 3. BFB training resulted in a significant reduction in mean arterial pressure (from 116 +/- 4.6 to 101 +/- 2.5 mmHg) mediated through a fall in total peripheral resistance; cardiac output, heart rate, intravascular volume and plasma renin activity remained unchanged. 4. In contrast, the increase or decrease of arterial pressure that occurred during BFB training was produced predominantly through changes in cardiac output and heart rate respectively, whereas total peripheral resistance under these circumstances remained unaffected. 5. The haemodynamic effects of BFB seem remarkably similar to the immediate or chronic effects of beta-adrenoreceptor blockade, initially producing a fall in cardiac output followed by a reduced arterial pressure associated with a decreased total peripheral resistance.

Biofeedback, Psychology↗
PubMed1975

Stimulus complexity, EEG abundance gradients, and detection efficiency in a visual recognition task.

Occipital EEG was monitored while subjects inspected 27 projected patterns. The number (N) and variety (V) of elements in the patterns were varied systematically. There were three levels of N (6, 12 or 24 elements) and three levels of V (circles, squares or hexagons occupying all, one half or one third of the element locations for all levels of N). Subjects were instructed that they would be required in a post-test to recognize the patterns, among patterns which had not appeared; they were also informed that the patterns had been constructed according to a set of simple rules, but the nature of these rules was not made fully explicit. The EEG was quantified by means of low-frequency analysis, yielding measures of abundance (theta, alpha and beta) and mean dominant frequency. For the recognition task, nine stimulus items were embedded among 45 items. Recognition efficiency was measured by means of the signal detection theory discrimination index (d'). The results were as follows: (i) Both N and V were inversely related to alpha abundance (P less than 0-01); (ii) the strongest relationship between stimulus parameters and the EEG held for N and EEG beta activity (13-5-19-5 Hz;P less than 0-001), where again the EEG and N were inversely related; (iii) there was a significant (P less than 0-05) direct relationship between N and theta activity; (iv) contrary to prediction, mean dominant alpha frequency decreased as N increased; (v) d' correlated significantly with a number of effects for N, i.e. subjects who exhibited greatest EEG discriminability of items during exposure of the patterns, subsequently obtained the higher detection scores in the recognition task. The work described therefore demonstrates that only only do stimulus parameters have systematic effects upon brain activity as measured by the EEG, but that such effects have functional value and reflect aspects of efficiency. The results are fully compatible with arousal theory constructs relating physiological reactivity and performance.

Adolescent↗