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Biomedical subjects

A C Witham

Publications and source records attributed to A C Witham.

At least 19 recordsLinked to original sources
PubMed1975

The effect of upright tilt on the volume of the failing human left ventricle.

The effect of a passive change from supine to 25-degree head-up tilted position on left ventricular volume was studied by echocardiography and other noninvasive techniques in 18 normal subjects, 6 patients with compensated LV volume overloading, and 12 patients with LV failure. In normal subjects and patients with compensated LV volume overloading, 10 minutes of head-up tilt resulted in a significant decrease in the echocardiographic LV internal dimension equivalent to a decrease in the calculated LV end-diastolic volume of 27 and 16 per cent, respectively. In contrast, no change in LV end-diastolic dimension and volume was noted during tilt in the patients with LV failure. The response of heart rate, blood pressure, and LV ejection fraction to this intervention was insignificant in all groups. These data indicate that volume preload is unresponsive to postural changes in patients with LV failure but not in normal subjects or in those with compensated LV volume overloading. It is suggested that the effect of posture on LV volume and output is primarily determined by the absence or presence of LV failure and the consequences of it on the peripheral circulation.

Adolescent↗
PubMed1975

Systolic time intervals by echocardiography.

Technical difficulties in recording phonocardiogram or indirect carotid pulse occasionally preclude determination of the systolic time intervals. Accordingly, an alternative method was tested in 52 patients, using high-speed strip chart recording of the aortic valve echocardiogram. Satisfactory records were obtained in 36. The interval from opening to closing of the aortic valve (ejection time) was subtracted from the interval between the Q wave of the electrocardiogram and the closing of the aortic valve (total electromechanical systole) to provide the pre-ejection period. When these intervals and the pre-ejection period/ejection time ratio were compared to corresponding values obtained by conventional methods from the simultaneously recorded phonocardiograms and indirect carotid pulses, a high degree of correlation (r greater than 0.97) was found. Differences between the two methods for each interval were insignificant, being greatest in the case of the ejection time but never exceeding 16 msec. These findings indicate that the echocardiogram of the aortic valve provides an alternative, noninvasive method for determination of the systolic time intervals whenever the usual methods fail.

Adolescent↗