G. W. Henry

Characteristics of blood flow velocity in the hypertensive canine pulmonary artery

Pulmonary artery blood flow velocity was measured in 15 dogs by a recently developed direct intraluminal pulsed Doppler technique. Changes in velocity characteristics under conditions of experimentally induced hypoxic pulmonary hypertension were observed. Experimental conditions (fractional inspired oxygen concentration = 0.10) produced significant increases in mean pulmonary artery pressure and pulmonary vascular resistance. Overall and maximal negative velocity increased with pulmonary hypertension. Negative velocity occurred predominantly in the posterior half of the pulmonary artery during both control and experimental conditions. With pulmonary hypertension, diastolic negative velocity increased only in the posterior half of the pulmonary artery and systolic negative velocity decreased only in the anterior half. More basic knowledge of pulmonary artery blood flow characteristics may facilitate an informed approach to noninvasive detection of pulmonary hypertension. Direct measurements by this recently developed intraluminal technique will be useful in studying various conditions with altered pulmonary blood flow.

Induction of right ventricular hypertrophy with obstructing balloon catheter. Nonsurgical ventricular preparation for the arterial switch operation in simple transposition.

BackgroundRecently, a successful result with a rapid two-stage arterial switch operation (ASO) was reported for patients with transposition of the great arteries (TGA) with low left ventricular pressure. In this procedure, the interval between pulmonary arterial banding and ASO was approximately 1 week. This successful result indicates the possibility of a nonsurgical ventricular preparation procedure using an obstructing balloon catheter prior to ASO. Methods and ResultsA SF atrioseptostomy catheter was inserted directly into the main pulmonary artery in six lambs aged 20 to 38 days. After the chest was closed, the balloon was inflated twice a day for a period of 2 to 2.5 hours. This procedure was performed for 4 consecutive days. After the final inflation, the ratio of right ventricular weight to total ventricular weight was compared with that in an age-matched control group. After the final inflation, the peak systolic right ventricular pressure and the percentage of peak systolic right ventricular to peak systolic aortic pressure rose to 85.6±4.7 mm Hg (mean±1 SD) and 79.6±8.6%, respectively. The percentages of the right ventricular weight to the total ventricular weight were significantly higher after the balloon inflation than those in the control group in terms of wet heart weight (29.5±1.2% versus 23.0±1.0%o; P<.0001) and dry heart weight (27.0±2.0% versus 21.0±1.1%; P<.0001) ConclusionsThe myocardial mass in the right ventricle increased after 4 days of intermittently applied pressure overload. Nonsurgical preparation of the ventricle for ASO in TGA is feasible.

The Effects of Curvature on Fluid Flow Fields in Pulmonary Artery Models: Flow Visualization Studies

In vitro pulsatile flow visualization studies were conducted to assess the effects of varying radii of curvature of the right ventricular outflow tract (RVOT) and main pulmonary artery (MPA) on the flow fields in the main, right, and left pulmonary arteries of a one month lamb pulmonary artery model. Three glass flow-through models were studied; one with no curvature, one with the correct anatomic curvature, and one with an overaccentuated curvature on the RVOT and MPA. All other geometric parameters were held constant. Pulsatile flow visualization studies were conducted at nine flow conditions; heart rates of 70, 100, and 140 bpm, and cardiac outputs of 1.5, 2.5 and 3.5 l/min with corresponding mean pulmonary pressures of 10, 20, and 30 mmHg. Changes were observed in the pulmonary flow fields as the curvature of the outflow tract, heart rate and mean pulmonary pressure were varied. An increase in vessel curvature led to an increase in the overall radial nature of the flow field as well as flow separation regions which formed faster, originated further downstream, and occupied more of the vessel area. At higher heart rates, the maximum size of the separation regions decreased, while flow separation regions appeared earlier in the cardiac cycle and grew more quickly. Heart rate also affected the initiation of flow reversal; flow reversal occurred later in the cardiac cycle at lower heart rates. Both heart rate and mean pulmonary pressure influenced the stability of the pulmonary flow field and the appearance of coherent structures. In addition, an increase in mean pulmonary pressure increased the magnitude of reverse flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous measurement of pulmonary blood flow using a retractable pulsed Doppler probe.

The feasibility of measuring pulmonary blood flow (PAQ) continuously using a removable, extraluminal 20 MHz pulsed Doppler probe, which has been used successfully to measure aortic blood flow, was assessed in seven anesthetized mongrel dogs. Simultaneous recordings were made from the Doppler probe (range‐gated 5‐6 mm from the anterior wall of the main pulmonary artery) and an electromagnetic flow probe (encircling the aorta) over cardiac outputs (CO) ranging from 0.2 to 5.5 L/min. Assuming a flat velocity profile and a fixed cross‐sectional area, PAQ was initially calculated as the product of area and mean velocity. Regression analyses (PAQ = a + b X CO) indicated good intraanimal linear correlations in six animals (r greater than or equal to 0.84) and no correlation in one animal (r = 0.003); however, PAQ was consistently higher than CO and interanimal variability was marked, as suggested by large deviations in mean intercept and slope values (a = 1.67 +/‐ 1.09 L/min and b = 0.70 +/‐ 0.33). Results improved (r greater than or equal to 0.79 in all animals, a = 0.47 +/‐ 0.52 L/min, and b = 0.77 +/‐ 0.21) when the method to estimate PAQ was altered to assume that the starting cross‐sectional area was the area that would make baseline PAQ and CO agree, and that the area during each subsequent CO level changed as a function of pulmonary artery pressure and an estimate of pulmonary artery compliance. Results of this study imply that it will be more difficult to use this Doppler probe to monitor CO from the pulmonary artery than it was from the aorta due to the elliptical, more compliant pulmonary vessel walls and the irregular pulmonary artery velocity profile.

Pulmonary blood velocity patterns in an animal model of pulmonary hypertension

Relationships between pulmonary artery blood velocity patterns and elevated pulmonary artery pressure and resistance were studied in an animal model of chronic pulmonary hypertension. Monocrotaline pyrrole was injected into the right atria of 1-3-day-old lambs. The animals were subjected to an acute terminal study 4-6 weeks postinjection. Using an intraluminal 20-MHz pulsed Doppler probe, pulmonary blood velocity was measured at 2-mm intervals across the posterior-anterior axis, from which 2-D instantaneous velocity profiles were reconstructed and the characteristics of the waveforms examined. Preliminary computations indicate that the significant increase in pulmonary blood-flow reversal observed near the posterior wall in normal lambs with acute pulmonary hypertension created by hypoxia is not always present in animals with chronic pulmonary hypertension. However, the triangular shape of the waveform associated with pulmonary hypertension is apparent in all studies, and the maximum value of the ratio of reverse flow to forward flow calculated by sampling site correlated significantly with both pulmonary artery pressure and pulmonary vascular resistance.<<ETX>>

Blood Flow Velocity Profiles in Pulmonary Branch Arteries in Lambs

We studied the detailed profiles of blood flow in the right and left pulmonary arteries using 20 MHz pulsed Doppler ultrasound equipment in a lamb model. Fourteen lambs aged four to six weeks were selected. In six lambs, monocrotaline pyrrole was injected parenterally to create pulmonary hypertension (PH group). Eight other lambs served as unaltered controls (control group). The blood flow velocities were sampled in 1mm increments along the anterior-posterior axis of the branch arteries. The maximum velocity of the forward flow in the left pulmonary artery was higher than that in the right pulmonary artery in the control group (71.7 +/- 15.9 cm/s vs 60.2 +/- 13.5; p < 0.05). The fastest backward flow was located at the posterior position of the vessel in the right pulmonary artery in the control group (71.7 +/- 15.9 cm/s vs 60.2 +/- 13.5; p < 0.05). The fastest backward flow was located at the posterior position of the vessel in the right pulmonary artery in the control group. No significant bias in location was shown in the left pulmonary artery. Using indices of P90, acceleration time, P90*AcT, the velocity waveforms in the PH group were compared with those in the control group. In the left pulmonary artery, every index in the control group showed a significantly greater value that in the PH group. On the other hand, no significant differences were found between either group in the right pulmonary artery.

Pulmonary input impedance spectra in models of chronically altered pulmonary hemodynamics

Pulmonary input impedance spectra were estimated in one-month-old lambs whose circulation had been altered during the first few days of life to mimic the pulmonary. hemodynamic states observed in infants and children with left-to-right shunts (high flow) and /or pulmonary vascular obstructive disease (high pressure). Spectral results obtained from the animal models were compared with those obtained from a computer simulation based on morphometric and hemorheologic data compiled for the 4 kg cat. Spectral features examined included the frequency of the first modulus minimum (indicative of the pulse wave reflection and/or pulse wave velocity) and characteristic impedance (average resistance to pulsatile flow). High flow (shunt-open/shunt-closed ratio>2.1) resulted in a slight spectral shift to the right with little change in characteristic impedance in both the lamb and the passive computer simulation models. High pressure (mean pulmonary artery pressure >28 mmHg) in the lamb model resulted in a marked shift to the right with a doubling of characteristic impedance.<<ETX>>

Pulse Wave Reflections In A Lamb Model Of Pulmonary Hypertension

The relationship between wave reflections and ventricular/vascular coupling of lambs with nmal pulmonary pressures (CONT) and pulmonary hypertension (PH) was examined. We compared reflection indexes quantitating changes in magnitude and timing of the positive reflected pressure wave. Results indicate that the reflected wave returns earlier in the PH group compared to the CONT goup (0.39 sec vs 0.62 sec; pd.005). In contrast to the CONT group, in the PH group the duration of the reflected wave is longer in systole (0.61 sec vs 0.38 sec) but shorter in diastole (0.26 sec vs 0.64 sec) (~~0.005). using a frequency domain averaging technique described previously [l]. Forward and reverse pressure and flow waveforms were calculated using the method described by Westerhof et al[21, based on characteristic impedance (2). Zc estimates were obtained by dividing the slope of the upstroke of the pressure wave at max (dPAP/dt) by the slope of the flow waveform at max (dPAQ/dt) [ 11. A global reflection coefficient (REF) was calculated as the ratio of the amplitude of reflected pressure wave to the amplitude of forward pressure wave. Wave reflection indexes quantitating changes in the timing of the positive reflected wave included the following ratios: the onset of the reflected wave/systolic interval (RBT); the duration of the reflected wave during systole/systolic interval (RST); and the duration of the reflected wave during diastole/diastolic interval (RDT).

Two-dimensional Pulmonary Artery Velocity Profiles Tn Growing Lambs

METHODS The nature of the velocity profiles in the main pulmonary artery was examined in two dimensions using growing lambs. Lambs in two age groups--2 weeks and 4 weeks were selected for study. Using an intraluminal 20 MHz pulsed Doppler probe, pulmonary blood velocity waveforms were recorded at 2 mm intervals along two axes: the anteriorposterior axis (AP) and the right-left axis (RL). Instantaneous velocity profiles were computed throughout the cardiac cycle and the characteristics of the profiles examined. Results obtained along the anterior-posterior axis were consistent with findings previously obtained; marked negative velocity along the posterior wall was observed. However, unlike the findings in previous studies, negative velocities of lesser magnitude were evident near the left wall of the right-left axis.

Comparison of techniques for assessing pulmonary input impedance spectra

A six-element lumped parameter model of the pulmonary circulation was used to evaluate two signal-averaging techniques for calculating the pulmonary input impedance spectra of normal lambs. Pulmonary artery pressure and pulmonary artery flow data obtained simultaneously in the main pulmonary artery were subjected to time-domain averaging and frequency-domain averaging techniques. Input impedance was determined by a cross-power spectral method designed to retain the periodicity of the signals. Preliminary studies indicate that the impedance spectra determined from noise-free input flow data to the model closely approximated the model-derived impedance spectra for a wide range of heart rates. The addition of noise signals to the noise-free input data produced impedance spectra that were consistently in agreement with model spectra for the lower-order (1-3) harmonics but not for the higher-order terms.<<ETX>>