M. Eriksen

Respiration-synchronous fluctuations in stroke volume, heart rate and arterial pressure in humans.

1. Simultaneous recordings of beat‐to‐beat left cardiac stroke volume (SV, pulsed ultrasound Doppler), mean arterial pressure (MAP) and heart rate (HR) were obtained in ten healthy young adults during spontaneous respiration at supine rest, before and after cholinergic blockade by atropine (0.035 mg kg‐1). 2. Respiration‐synchronous fluctuations in SV, HR, cardiac output (CO) and MAP were quantified by spectral analysis of the recordings of each of these variables. 3. Before atropine administration, respiration‐synchronous fluctuations in HR and SV were prominent. The changes in HR and SV were inversely related and variation in SV was the main source of respiratory variability in CO. Respiration‐synchronous fluctuations in MAP were mainly caused by variations in CO. 4. After cholinergic blockade, respiratory HR variations were eliminated, whereas the respiratory fluctuations in SV persisted. The fluctuations in CO and MAP increased. In this situation, mechanically induced variations in SV were not counteracted by inverse HR fluctuations and the influence on CO thus increased. 5. The main source of respiratory fluctuations in MAP in supine humans is thus variation in SV, while inverse, vagally mediated HR variations tend to reduce the fluctuations in CO and MAP.

Improved method for cardiac output determination in man using ultrasound Doppler technique

An existing ultrasound Doppler method for measuring cardiac output has been improved and refined, partly by locating the sampling volume higher up in the aorta while still using the aortic ring size as the effective transverse flow area. The basis for using this technique is the approximately rectangular systolic velocity profile in the aortic orifice in physiologically and anatomically normal subjects, and the fact that this profile velocity is conserved as the maximum velocity in the ascending aorta for some 3 to 4 cm above the valves. This higher location of the sampling volume improves Doppler signal quality, and does not reduce the accuracy of the method, as can be confirmed in each experimental subject. Together with automatic computer-based online signal analysis, the technique employed enables us to make continuous long-term beat-to-beat measurements of cardiac output in subjects without aortic valve disease or grossly deforming disease of the aortic root.

Effect of pulsatile arterial diameter variations on blood flow estimated by Doppler ultrasound

High-resolution measurements of common carotid and femoral arterial diameters have been performed by ultrasound echo devices. When combined with pulsed Doppler measurements of cross-sectional averaged velocity in the same vessels, exact calculations of flow were made possible. The median peak-to-peak pulsatile diameter variations were 0.19 mm (2.8 per cent) in the femoral artery and 0.49mm (6.7 per cent) in the common carotid artery. Flow values were calculated either by taking the time-averaged diameter as a constant value, or by taking into account the dynamic variations in diameter. In comparing the two values, a quantification of the magnitude of error introduced by the averaging of the diameter was made possible. An error in the range 1.5–3.8 per cent was found for the femoral artery, whereas the error in the common carotid artery was in the range 0.4–3.6 per cent despite the larger amplitude of the pulsations in this vessel.

A heterodyne ultrasound blood velocity meter.

A new heterodyne ultrasound doppler blood velocitymeter has been constructed. The instrument operates in two switchable frequencies (1·5 MHz and 6 MHz) and switchable in pulsed or continuous mode.

Noninvasive measurement of arterial diameters in humans using ultrasound echoes with prefiltered waveforms.

A system for the direct measurement of the inner diameters of selected human arteriesin situ has been developed. Ultrasound pulses are emitted perdendicular to the vessel axis, and reflected from the wall material interfaces. Improved depth resolution is achieved by using a high-frequency transducer, and by inverse filtering of the signal. This is performed by emitting a waveform calculated beforehand to give an optimum time resolution in the received echo. Echoes from both innerand outer surfaces of the vessel walls are discriminated, and the inter-echo time intervals can be measured with an accuracy of 33ns, corresponding to approximately 26μm. By repeating the measurements through the cardiac cycle, the diameter variations can be accurately described.

Connection between skin arteriovenous shunt flow fluctuations and heart rate variability in infants

Large, spontaneous fluctuations in blood flow to acral skin, caused by synchronous opening and closing of arteriovenous anastomoses (AVAs), have been demonstrated in adults in a thermoneutral environment. Individual AVA constrictions were accompanied by a diphasic heart rate (HR) response, indicating the presence of an autonomic rhythm which affected both skin AVA activity and heart rate variability. In the present study, 24 neonates were examined on day 2 (range 1-3 days) and re-examined at 14 weeks (11-17 weeks). The presence of rhythmic, synchronous fluctuations in laser Doppler flux in the palm of the hand and sole of the foot in 20 of 24 neonates strongly indicated the presence of functional skin AVA at birth. Both neonates and 3-month-old infants showed a diphasic HR response in association with cutaneous AVA constrictions. The infant response differed from the adult response mainly by the longer duration of the secondary bradycardia. This may reflect different properties of the baroreceptor reflex in infants and adults.