Biomedical subjects

V Q Lance

Publications and source records attributed to V Q Lance.

9 recordsLinked to original sources

PubMed1977

Systolic time intervals utilizing ear densitography. Advantages and reliability for stress testing.

Systolic time intervals were determined in 10 volunteer subjects at rest and during a variety of cardiocirculatory stresses to further evaluate the ear densitogram derivative as a replacement for the carotid pulse curve. There was close tracking of the two methods not only for left ventricular ejection time (r = +0.98), but also for pre-ejection period (r = +0.98). The results confirmed that this technically simple and remarkably stable wave form permits reliable measurement of the systolic time intervals both at rest and during the actual performance of stress.

Adult↗

PubMed1977

Physiological responses to prompt and sustained squatting. Measurement by systolic time intervals.

Ten healthy men, ages 22 to 35, were studied non-invasively standing (control), at the onset of squatting ('prompt squat'), and at two minutes of squatting. Squatting produced decreases in heart rate, isovolumic contraction time, pre-ejection period, and pulse transmission time from onset of depolarisation to the first heart sound, left ventricular ejection time, and the ejection time index. These results of systolic time intervals are consistent with the bradycardia and increased ventricular filling induced by squatting. Major changes from control measurements were found at the onset of squatting, showing the impact of prompt squat of left ventricular performance.

Adult↗

PubMed1977

Postural effects on the noninvasive baselines of ventricular performance.

The effects of posture on time-based noninvasive measurements were determined utilizing the sequence supine-sitting-standing in a formal protocol in which observer biases were eliminated by blinding the measurement and calculation phases. Compared to the supine posture, the sitting and standing postures produced significant increases in heart rate, isovolumic contraction time, pre-ejection period and pre-ejection periog/left-ventricular ejection time and significant decreases in ejection time and ejection time index. The response patterns are consistent with their hemodynamic correlates cited in the literature which show increased adrenergic activity and decreased venous return in the sitting and standing postures, the effect on venous return being dominant.

Adult↗

PubMed1977

Comparative orthostatic responses: standing vs. head-up tilt.

In both physiologic and clinical studies, standing is often loosely equated with head-up tilt(HUT) although the cardiovascular effects of these variants of orthostasis have not been formally compared, except for heart rate. The effects of HUT and standing were measured noninvasively in male volunteers satisfying identical criteria for age and normal status. In both postures, there were significant increases in heart rate, pre-ejection period, isovolumic contraction time, and the ratio of pre-ejection to ejection period, and significant decreases in ejection period and ejection time index. All of these changes were greater for standing than for tilt. Pulse transmission time changed significantly (-14%) only with tilt. We conclude that head-up tilt and standing are rather comparable but not physiologically identical forms of orthostasis.

Adult↗

PubMed1976

Ejection time--heart rate relationship during exercise.

The slope of the regression equation for left ventricular ejection time (LVET) vs heart rate (HR) is the appropriate factor for correcting LVET for HR. Because the regression relationship varies under different conditions, we determined the LVET-HR equations for subjects (1) seated at rest on a bicycle ergometer, and (2) during uninterrupted bicycle exercise. In 18 normally active male volunteers, ages 22-37, HR and LVET were measured under the two conditions and the regression relationship for LVET on HR determined for each. Regression equations are as follows: (1) LVET = 379-1.8 HR +/- 11.0 for subjects seated at rest on a bicycle ergometer, and (2) LVET = 371-1.2 HR +/- 13.9 for subjects performing upright bicycle exercise. The slope factors (1.8 and 1.2) differed significantly (p less than 0.01). The data indicate that considerable error can result from arbitrarily applying to exercising or resting subjects a correction factor which does not fit the conditions of the data to be corrected.

Adult↗

PubMed1976

Heart rate--left ventricular ejection time relations. Variations during postural change and cardiovascular challenges.

Regression equations for heart rate (HR)--ejection time (LVET) relations provide the appropriate factors for predicting or correcting left ventricular ejection time at any HR. We investigated HR-LVET regressions under different conditions common to both physiological and clinical studies of LVET which had been selected because of predictably different physiological responses. Ten normal subjects were studied during both supine and sitting rest and during isometric handgrip (IHG) in both supine and sitting postures and 10 during head-up tilt. Unexpectedly, as compared with pre-exercise rest on a bicycle ergometer, the slope for the resting state on a chair was slightly flatter, and LVET values were uniformly higher throughout the range of HRs measured. Differences among HR-LVET slopes and intercepts appeared to reflect the established behaviour of stroke volume and ejection rate under the conditions studied. Differences observed among intercepts, especially in supine vs. upright postures, are substantial and require that the appropriate intercept be applied in predicting LVET at a given HR. differences among slopes, while not statistically significant, may, under practical conditions, lead to unacceptable error if the appropriate slope factor is not used in correcting LVET for HR.

Adult↗

PubMed1976

Noninvasive stress testing. Methodology for elimination of the phonocardiogram.

Measurement by systolic time intervals (STI) of cardiac responses requires extremely careful recording during actual stress test performance. Previous work indicated no significant changes in the pulse transmission time (PTT) during exercise and other challenges. Since external STI depend on the carotid pulse offset by the PTT as an aortic curve equivalent, stable PTT implies that timing of the carotid upstroke (CARu) and the carotid incisura (CARIN) would respectively track the pre-ejection period (i.e., the externally calculated onset of the aortic upstroke) and the aortic incisura which is externally timed by the aortic component of SII (IIA). In ten subjects, STIs were recorded at supine rest, sitting, standing, during prompt and sustained squatting and during isometric and dynamic exercise. The results demonstrated the tracking of both points: regression slopes and correlation coefficients were close to 1.00 for each series and for each subset. Coefficients of correlation (r) and of determination (r2) were uniformly high for all challenges except isometric handgrip (IHG). Since left ventricular ejection time is obtained directly from the pulse curve, with the exception of IHG, STI responses during stress testing can be measured without a phonocardiogram.

Adult↗

PubMed1975

Effects of age on responses to isometric exercise. Isometric handgrip in noninvasive screening for cardiovascular disease.

Isometric handgrip (IHG) imposes an acutely increased afterload on the left ventricle. Utilizing systolic time intervals, we studied various responses to IHG, measured as changes from resting values with near-maximum IHG, in old normal (ON) subjects, young normal (YN) subjects, and old patients with hypertensive heart disease (HHD) and patients with coronary artery disease (CAD). There were no differences in responses to IHG between ON and patients with HHD or patients with CAD. However, there were clear differences between the responses of ON and YN subjects. Increase in heart rate (HR) was much more prominent in YN (ON vs. YN = +11.6 +/- 2.6 vs. +15.6 +/- 5.7 beats per minute p less than 0.001). Pre-ejection period (PEP) end isovolumic contraction time (IVCT) increased in ON but decreased in YN (PEP + 6.2 +/- 1.7 vs. -11.0 +/- 3.7 msec., p less than 0.001; IVCT +8.1 +/- 2.2 vs. -13.8 +/- 3.4 msec., p less than 0.001. Shortening of LVET was much more marked in YN (-6.5 +/- 4.1 VS. -63.3 +/- 9.9 msec. p less than 0.001), but this was entirely due to the HR differences since there was no difference in ejection time index (+ 5.1 +/- 3.4 vs. -0.4 +/- 7.3 msec. p greater than 0.5). IHG produced no significant differences between ON and YN in the timing of the "mitral" component of the first heart sound (q-Im), in the ratio PEP/LVET, or in pulse transmission time (PTT). By contrast, resting control PTT was markedly short in ON, especially those with CAD. Resting PTT in ON was 27.1 +/- 2.6 msec.; in YN 43.7 +/- 1.4 msec.; in CAD patients 20.7 +/- 1.3 msec. We conclude that even near-maximal IHG does not seem to be an adequate noninvasive screening test for cardiovascular disease in that age alone seems to have the most significant influence on the responses.

Adult↗

PubMed1975

Constant-load versus heart rate-targeted exercise: responses of systolic intervals.

Eight normal male volunteers were studied during bicycle ergometry at constant work loads of 50, 100, and 150 W for 4 min each and heart rate-targeted exercise to rates which matched those during the end of the 4th min at each constant work load. Systolic intervals measured prior to and during exercise included: Q-IM, isovolumic contraction time (IVCT), preejection period (PEP), left ventricular ejection time (LVET), ejection time index (ETI), PEP/LVET, and pulse transmission time (PTT). Directional changes during both exercise methods were consistent with previously reported results. Comparable control values indicated equivalent starting points for each bout and confirmed recovery from preceding exercise. There was striking similarities within each matched exercise set for Q-IM, IVCT, PEP, and PEP/LVET. LVET was significantly shorter for rate targeted exercise. We conclude that either constant-load or rate-targeted bicycle ergometry may be employed with choice of method determined by the purpose of the protocol and that systoloc intervals (except LVET) should not be importantly altered owing to the method chosen.

Adult↗