Jose I. Ferreiro

Respiratory Suppression and Swallowing from Introduction of Fluids into the Laryngeal Region of the Lamb

Summary: Introduction of 0.9% NaCl or undiluted fetal tracheal fluid into the laryngeal region produced no suppression of breathing in lambs during the perinatal period. As NaCl or tracheal fluid solutions were increasingly diluted with water, progressively greater respiratory suppression associated with rapid swallowing was observed. Introduction of amniotic fluid was associated with variable suppression of respiration. The swallowing induced by the dilute solutions was as rapid as two swallows per sec. Lambs 3 months of age swallowed when water was introduced into the laryngeal region, but were able to alternate swallows between breaths without suppression of breathing.Speculation: The suppression of breathing by presence of certain fluids in the laryngeal region may have important clinical implications. At birth, aspiration of amniotic fluid into the laryngeal area could seriously suppress breathing under certain conditions. In the pre-term or newly born infant, introduction of fluids with low osmolality into the laryngeal region might initiate this detrimental reflex more strongly than in older children. Finally, the aggravated response where life-threatening apnea develops from presence of small amounts of fluid in the laryngeal region might occur especially in neonatal disease states predisposing to apneic episodes. Under such conditions, swallowing could clear the liquid from the laryngeal region so that this area would be free of fluid at subsequent postmortem examination. Death from apnea could occur as terminal hypoxia supervenes, leaving little evidence for the pathologist to define the cause of death.

Initiation of breathing by cold stimulation: Effects of change in ambient temperature on respiratory activity of the full-term fetal lamb

The effects on breathing were studied in the submerged, exteriorized, full-term lamb during alteration of its ambient temperature. Slow cooling from an environmental temperature of 40° C. to 27° C. resulted in rhythmic breathing in 32 consecutive experiments. Rewarming of the water temperature invariably caused respiratory activity to cease. Monitoring of brachial arterial blood gas values and of umbilical venous blood flow revealed no significant changes in these parameters during the cooling or rewarming challenges.

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.

Pulmonary blood velocity profile variability in open-chest dogs: Influence of acutely altered hemodynamic states on profiles, and influence of profiles on the accuracy of techniques for cardiac output determination

SummaryClinical investigations focused on finding characteristics of noninvasively obtained measurements of pulmonary blood velocity that can be used to quantitate pulmonary blood flow and/or pulmonary pressure have often yielded results whose imprecision has been attributed to flow pattern variability. To determine flow pattern variability in an in vivo animal model in varying hemodynamic states, main pulmonary artery blood velocity waveforms were recorded in 17 dogs at 2-mm intervals along an anterior to posterior wall-oriented axis using a 20-MHz pulsed Doppler needle probe. Control data were obtained before the animals were subjected to altered flow (atrial level shunts) and pressure (10% O2 inhalation) states. Instantaneous velocity profiles were computed throughout the cardiac cycle. Estimates of pulmonary blood flow were obtained assuming an elliptical model of the pulmonary artery which allowed computation of velocity at all points in the cross section, based on the measured values along the axis. Model-based estimates were compared to measured values and estimates obtained in the traditional fashion, i.e., the product of centerline velocity and cross-sectional area. Results clearly showed marked interanimal variability, even in control states. Reverse flow in the posterior half of the vessel, which tended to become more pronounced with increased pulmonary artery pressure, was observed during late systole and early diastole. Elevated pulmonary blood flow tended to increase the maximum velocities along the anterior wall relative to midline velocities. Neither estimate of cardiac output yielded consistently accurate results (r=0.77 for model-based method,r=0.80 for area times central velocity method). Findings of this study, which highlight the dependency of waveform characteristics on sampling site, the large degree of intersubject variability, and the need for large or multiple sample volumes for pulmonary blood flow determination, help clarify inconsistencies observed by clinicians and suggest that future work with animal models will facilitate a greater understanding of the determinants of human pulmonary velocity waveforms.

DIASTOLIC SHAPE OF THE RIGHT VENTRICLE OF THE HEART

Knowledge of right ventricular (RV) shape is important to the understanding of RV mechanical function and for the improvement of clinically important RV volume estimation techniques. Refinements to the simplest conceptions of RV shape are presented statistically here, based on a quantitative analysis of three‐dimensional magnetic resonance (MR) images of excised lamb hearts.

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)

Flow visualization in anatomically accurate, flow-through models of the main pulmonary artery trunk

To study the effect of maturational geometric changes on flow characteristics in the pulmonary artery trunk, anatomically accurate, acrylic flow-through models were constructed from four flexible silicone rubber casts obtained in situ in lambs weighing 2.4, 7.8, 9.5, and 11.5 kg. A silicone rubber cast of the right heart was fabricated by injecting the superior caval vein in situ with liquid silicone rubber (Dow Cornings HS-II RTV, Midland, MI). Each cast was used as a template for a transparent acrylic mold of the pulmonary artery trunk and primary generation branches. The acrylic block was then fitted with a curved rigid Plexiglass inflow tube (to simulate the curvature of the right ventricle) just proximal to the pulmonary valve sinuses and mounted in a closed loop system driven by a variable speed pulsatile pump (to simulate physiological flow rates between 0.5 and 4.0 lmin−1) A blood analog solution of polystyrene beads (Rohm & Haas Amberlite, Philadelphia, PA) suspended in a 45% by weight glycerine solution was illuminated by a laser source (15 mwatts, Siemens, Germany) to trace the flow patterns. Two flow field planes of the main pulmonary artery trunk—one parallel, and one perpendicular, to the origins of the right and left arterial branches—were visualized and video recorded (Canon H660 8mm, Japan) for subsequent analysis. A prominent vortex, originating in the center of the main pulmonary artery and directed inferiorly toward the inner wall, was noted in the flow field plane perpendicular to the bifurcation in the 9.5 and 11.5 models. These characteristics were less developed in the 7.8 kg model and not present in the 2.4 kg model, possibly because the angle of curvature was less acute than in the larger models. In the flow field plane parallel to the bifurcation, the patterns were more complex, principally influenced by turbulence in the main pulmonary artery (which increased at higher flow rates) and the geometric changes in the branch pulmonary arteries.

Characterization of Pulmonary Artery Blood Velocity Patterns in Lambs

Optimal management of patients with congenital heart disease often depends on the ability to assess pulmonary vascular impairment and monitor pulmonary hemodynamics. Need for improved techniques has prompted investigations of relationships between abnormal pulmonary circulations and pulmonary artery blood velocity patterns that can be observed noninvasively with pulsed Doppler ultrasound. Features commonly associated with pulmonary hypertension in humans (observed in the main pulmonary artery) are increased flow reversal [1,2], decreased rise time (time from onset of systole to peak velocity)[3–6] and a velocity waveform with a triangular or skewed shape, [7] as illustrated in Figure 1. Unfortunately, none of the techniques derived for estimating pulmonary pressure and flow solely from features of pulmonary velocity waveforms has been proven sufficiently reliable to be widely adopted in clinical practice. Failure has been attributed to individual variability and changing flow patterns in various parts of the pulmonary trunk [8,9]. Though studies examining the effects of acutely altered pulmonary hemodynamics on velocity patterns in animals have been reported, [10–12] surprisingly little work has been reported using animal models with chronically altered hemodynamics. Thus the goal of this report is to describe progress made in our laboratory in examining the velocity patterns in animal models of chronically elevated pulmonary blood pressure and flow, which are more analogous to the patient population of interest.

Intuitive modeling of right ventricular shape

A quantitative characterization of the shape of the right ventricle (RV) of the heart is needed for accurate modeling of the mechanics of the ventricle as well as for better measuring the volume of the ventricle from technologies such as 2D ultrasound, bi-planar ventriculography, and sonomicrometry. A technique was thus developed for modeling RV shape. First, a high-resolution MR image set was obtained of the freshly excised lamb heart under various passive pressurizations of both ventricles ranging from 5 to 30 cmH2O simulating end-diastole in the beating heart. Typically, 2-3 full images were obtained for each heart. Images were obtained with a multislice spin-echo T1-weighted sequence with the slice plane orientation early equal to the short-axis view of the heart. A 3D characterization of shape was obtained by first characterizing inter-slice changes in shape and orientation and then characterizing the shape of a single representative slice. The slice chosen to represent the RV was in the region directly below the tricuspid valve since it is both near to the apex-base center of the RV and has the greatest size. Intuitive deformations were applied to an initial circular arc anchored at the endpoints of the freewall and initially passing through a point near the center of the freewall contour, so as to best match the true freewall contour. These include a leaning of the circular arc parallel to the septal axis, a flattening perpendicular to the septal axis, a tucking-in or sharpening of the curvature near the junction with the septum, and a pinching- in at a point or points near its center towards the septum, all, in an attempt to account for the asymmetry and non- circularity deformed circular arc which effectively produces tow independent arcs. For all but one of the anterior and posterior arcs in 13 heart shapes, pinch-deformed arcs could be obtained whose average radial distance from the true RV chamber contour was less than 0.9 mm and averaged 0.5 mm for the anterior arc and 0.66 mm for the posterior arc. Worst- case deviation in parameters of the pinched-arc model of cross-sectional shape, and radii of curvature and the RV freewall-septum junction angle due to worst-case deviation in landmark location are 19 percent +/- 11 percent, 10 percent +/- 6 percent, 10 degrees +/- 4 degrees, and 12 degrees +/- 6 degrees. If landmark localization variability is minimized with a rigid translate offset scale model of the landmark region, average measurement error as determined in an adjacent slice comparison was 11 percent +/- 5 percent, -3 percent +/- 2 percent, 7 degrees +/- 2 degrees, and -7 degrees +/- 2 degrees.