Lee G. Deneault

Assessment of the immediate effects of cardiopulmonary bypass on left ventricular performance by on-line pressure-area relations.

BACKGROUND Pressure-volume relations have been established as useful measures of left ventricular (LV) performance. Application of these methods to the intraoperative setting have been limited because of difficulties acquiring LV volume data. Transesophageal echocardiographic automated border detection can measure LV cross-sectional area as an index of volume, which can be coupled with pressure data to construct pressure-area loops on-line. The purpose of this study was to evaluate intraoperative LV performance in patients undergoing coronary bypass surgery before and immediately after cardiopulmonary bypass using on-line pressure-area relations. METHODS AND RESULTS Studies were attempted in 13 consecutive patients. Simultaneous measures of LV cross-sectional area, LV pressure, and electromagnetic flow probe-derived aortic flow recorded on a computer work station interfaced with the ultrasound system. Pressure-area loops were compared with simultaneous pressure-volume loops constructed from pressure and flow data during inferior vena caval occlusions before and after bypass. Pressure-volume calculations (end-systolic elastance, maximal elastance, and preload-recruitable stroke work) were then applied to pressure-area loops with area substituted for volume data. Changes in stroke force from pressure-area loops were closely correlated with changes in estimates of stroke work from pressure-volume loops for individual patients before bypass (r = .99 +/- .03, SEE = 5 +/- 2%, n = 10) and after bypass (r = .96 +/- .05, SEE = 5 +/- 2%, n = 9). Pressure-area estimates of end-systolic elastance, maximal elastance, and preload-recruitable stroke force decreased significantly from before to after cardiopulmonary bypass in the 7 patients with paired data sets. Load-dependent measures of LV function (stroke volume, cardiac output, and fractional area change) were unchanged after surgery in these same patients. CONCLUSIONS Intraoperative pressure-area loops may be acquired and displayed on-line using transesophageal echocardiographic automated border detection and readily analyzed in a manner similar to pressure-volume loops. LV performance was depressed immediately after cardiopulmonary bypass compared with before. On-line pressure-area relations may be clinically useful to assess LV performance in patients undergoing cardiac surgery in whom load and contractility may be expected to vary rapidly.

Two-dimensional Echocardiographic Automated Border Detection Accurately Reflects Changes in Left Ventricular Volume

The objective of this study was to determine the relationship of on-line measurements of left ventricular cavity area generated by echocardiographic automated border detection to true volume measured by an intraventricular balloon in an isovolumically contracting isolated canine heart preparation. Seven excised dog hearts had placement of an intraventricular balloon and were perfused in an ex vivo apparatus. Left ventricular area data from the midventricular short-axis plane and pressure data were recorded on a computer through a customized hardware and software interface with the ultrasound system. Left ventricular volumes were varied from 5 ml to maximal values (30 to 40 ml) at 1-milliliter increments. Three increasing and decreasing volume ramps were analyzed on each of seven hearts for a total of 1260 simultaneous measurements. Linear regression analysis correlated mean automated border detection area with absolute volume from each preparation. A predominantly linear relationship was observed with an average correlation of r = 0.97 (y = 0.16x-0.69, SEE = 0.31 cm2, p < 0.01). Left ventricular area measures for six of seven dogs varied little during isovolumic contraction (< 0.4 cm2) but did show a systematic cardiac cycle-related variability in one dog (28% change in area, maximum to minimum, over all volumes). In conclusion, the relationship between cross-sectional area and left ventricular volume was predominantly linear and varied little during isovolumic contractions in the normal canine left ventricle. Echocardiographic automated border detection appears to be a promising method to reflect changes in left ventricular volume.

On-line estimation of changes in left ventricular stroke volume by transesophageal echpcardiographic automated border detection in patients undergoing coronary artery bypass grafting

Echocardiographic automated border detection can determine the interface between blood and myocardial tissue and calculate left ventricular (LV) cavity area in real-time. The objective was to determine if on-line measurements of LV cavity area by transesophageal automated border detection could be used to determine beat-to-beat changes in stroke volume in humans. Studies were attempted on 9 consecutive patients, aged 66 +/- 8 years, undergoing coronary bypass surgery. Stroke volume was measured by electromagnetic flow from the ascending aorta, and LV cavity area was measured at the midventricular short-axis level. Simultaneous area and flow data were recorded on a computer workstation through a customized interface with the ultrasound system. Recordings were performed during baseline apnea and rapid alterations induced by inferior vena caval occlusions before and after cardiopulmonary bypass. Measurements of stroke area (maximal area-minimal area) were correlated with stroke volume for matched beats. Data were available for analysis on 8 of 9 patients before and on 5 patients after cardiopulmonary bypass for 644 beats. Stroke area was closely correlated with stroke volume both before (mean R = 0.94 +/- 0.03, SEE = 0.33 +/- 0.12 cm2) and after (mean R = 0.92 +/- 0.05, SEE = 0.59 +/- 0.81 cm2) cardiopulmonary bypass. The slopes of these stroke area-stroke volume relations were quite reproducible from before to after cardiopulmonary bypass in the same patient but varied between individual patients. Transesophageal automated border detection has potential for on-line estimation of changes in stroke volume in selected patients.

Assessment of left ventricular performance by on-line pressure-area relations using echocardiographic automated border detection

OBJECTIVES The purpose of this study was to evaluate left ventricular performance by on-line pressure-area relations using echocardiographic automated border detection in the in situ canine heart in a manner similar to pressure-volume analyses. BACKGROUND Echocardiographic automated border detection can measure ventricular cavity area as an index of volume and may be interfaced with pressure to construct pressure-area loops on-line. METHODS Eight anesthetized open chest dogs had simultaneous measurement of ventricular pressure, aortic flow and midventricular short-axis area. Pressure-area loops were constructed by a computer workstation interfaced with the ultrasound system. Stroke area (Maximal area--Minimal area) and stroke force (integral of P dA [P = pressure; A = area]) values during inferior vena cava (n = 8) and aortic (n = 4) occlusions were compared with stroke volume and estimates of stroke work, respectively. Inotropic modulation was induced with dobutamine infusion (2 to 5 micrograms/kg body weight per min), followed by propranolol infusion (2 to 5 mg). End-systolic and maximal elastance and preload recruitable stroke force (stroke force versus end-diastolic area) were derived for each period. RESULTS Changes in stroke area and stroke force were significantly correlated with changes in stroke volume and estimates of stroke work during caval occlusion (n = 8) (r = 0.87 +/- 0.02, SEE = 8 +/- 1% and r = 0.90 +/- 0.03, SEE = 8 +/- 2%, respectively). In dogs with aortic occlusion (n = 4), changes in stroke area significantly correlated with changes in stroke volume for pooled data (r = 0.84, SEE = 8%, y = 1.0x + 3). Ventricular performance increased with dobutamine infusion (n = 7): end-systolic elastance 30 +/- 11 to 67 +/- 24 mm Hg/cm2 (p < 0.02 vs. control values); maximal elastance 37 +/- 11 to 82 +/- 26 mm Hg/cm2 (p < 0.02 vs. control values); preload recruitable stroke force 81 +/- 24 to 197 +/- 92 mm Hg (p < 0.02 vs. control values). Decreases occurred with propranolol infusion (n = 5) end-systolic elastance 20 +/- 4 to 13 +/- 4 mm Hg/cm2 (p < 0.002 vs. control values); maximal elastance 29 +/- 8 to 15 +/- 5 mm Hg/cm2 (p < 0.002 vs. control values); preload recruitable stroke force 66 +/- 14 to 40 +/- 9 mm Hg (p < 0.002 vs. control values). CONCLUSIONS On-line pressure-area relations are a potentially useful means to assess left ventricular performance in a manner that is quantitatively similar to the predicted responses of pressure-volume relations.

Rapid Estimation of Left Ventricular Contractility from End-Systolic Relations by Echocardiographic Automated Border Detection and Femoral Arterial Pressure

Automated echocardiographic measures of left ventricular (LV) cavity area are closely correlated with changes in volume and can be coupled with LV pressure to construct pressure-area loops in real time. The objective was to rapidly estimate LV contractility from the end-systolic relations of cavity area (as a surrogate for LV volume) and femoral arterial pressure (as a surrogate for LV pressure) in patients undergoing cardiac surgery. Methods:Studies were attempted on 18 consecutive patients with recordings of LV pressure, LV area, and femoral arterial pressure on a computer workstation interfaced with the ultrasound system. End-systolic pressure-area relations (in terms of pressure-area elastance [E′es) from pressure-area loops during inferior vena caval occlusions were determined before and immediately after cardiopulmonary bypass using both LV and arterial pressure by semiautomated and automated iterative linear regression methods. Results:Data sets were available for 13 patients before and 8 patients after bypass (21 studies in 14 patients). E′es by arterial pressure was closely correlated with E′es by LV pressure: r=0.96, standard error of the estimate=2 mmHg/cm2, y=1.01 X -0.7 by the semiautomated method and r=0.94, standard error of the estimate=3 mmHg/cm2, y=1.02 X -0.5 by the automated method. Analysis of semiautomated and automated estimates of E′es from arterial pressure and E′es using LV pressure by the Bland-Altman method showed no systematic measurement bias and calculated limits of agreement of 8 and 9 mmHg/ cm2, respectively. Similar decreases in E′es by arterial and LV pressure occurred from before to after bypass in 7 patients with paired data sets: 32 ± 12 to 15 ± 6 mmHg/cm2 and 32 ±15 to 15 ± 7 mmHg/cm2, respectively (P<0.05 for both). Conclusions:On-line femoral arterial pressure and LV area data by echocardiographic automated border detection may be used to rapidly calculate E′es as a means to estimate LV contractility in selected patients.

Regurgitant reflux, vs non‐regurgitant reflux, is preceded by rectus abdominis contraction in infants

Abstract Infants commonly regurgitate during some, but not all, gastro‐oesophageal reflux episodes. As several different mechanisms for reflux episodes have been identified, it was hypothesized that the mechanisms for regurgitant and non‐regurgitant reflux differ. To test whether regurgitant episodes are associated with, and perhaps propelled by, rectus abdominis contraction, ten infants, aged 9–30 weeks (median 16.5 weeks), with regurgitant reflux and no other cause for their regurgitation, were studied with concurrent distal oesophageal pH probe monitoring and surface electromyography of the rectus abdominis muscles. Reflux episodes with material emanating from the mouth (regurgitant reflux) were distinguished from those without visible regurgitation, and were characterized as being, or not being, temporally associated with rectus abdominis activity.

Sensory evoked potentials: a system for clinical testing and patient monitoring.

There is increasing interest in the use of averaged sensory evoked potentials for diagnostic testing and patient monitoring. This testing technique offers an opportunity to obtain information on function in the central nervous system and can be used in uncooperative and comatose patients. However, in the clinical situation background noise is often high, due for example to posturing by the patient, and even with extensive signal averaging it can be difficult to determine whether a response is present. This paper describes a data acquisition technique we have implemented for patient testing in the intensive care unit and the operating room to facilitate analysis of the responses. The averaging system delivers the stimulus in the middle of the data window, providing a pre-stimulus control interval from which to estimate residual background noise in the average. In addition, two averages are formed simultaneously to determine reproducibility of the response. This technique has been modified to provide a method of continuous monitoring that allows rapid detection of large changes in the response plus automatic tracking of selected response peak parameters.

Changes in electrocardiographic morphology reflect instantaneous changes in left ventricular volume and output in cardiac surgery patients

We examined the relation between changes in R-to-T wave amplitude ratios (R:T) and left ventricular (LV) performance as cardiac output was rapidly varied by inferior vena caval occlusion in 6 subjects prior to cardiopulmonary bypass. To assess the influence of contractility, paired studies before and after bypass were performed in 4 subjects. Stroke volume and cardiac output were assessed by aortic flow probe, and transesophageal echocardiographic LV area measures using the automated border-detection method were used to give LV stroke area, stroke force, maximal LV area, fractional area change, end-systolic elastance, and preload recruitable stroke force. Data were collected on computer and analyzed by linear regression. Significant changes in R:T and measured LV variables during the inferior vena caval occlusion were stroke volume (r = 0.81), LV stroke area (r = 0.77), LV stroke force (r = 0.81), maximal LV area (r = 0.78), and cardiac output (r = 0.80). However, R:T varied inconsistently in relation to fractional area change. After cardiopulmonary bypass, the linear relation between R:T with LV stroke force, LV stroke volume, and maximal LV area persisted, but at a lesser slope. Although absolute pre-inferior vena caval occlusion R:T did not correlate with end-systolic elastance or preload recruitable stroke force, the change in the slope of these linear relations correlated well with the change in end-systolic elastance after surgery (r = 0.92). Instantaneous changes in electrocardiographic morphology reflect changes in LV preload-dependent variables, whereas long-term changes in electrocardiographic morphology may also reflect changes in contractile state.

Detection of hemodynamic changes in clinical monitoring by time-delay neural networks.

Small changes that occur in a patients physiology over long periods of time are difficult to detect, yet they can lead to catastrophic outcomes. Detecting such changes is even more difficult in intensive care unit (ICU) environments where clinicians are bombarded by a barrage of complex monitoring signals from various devices. Early detection accompanied by appropriate intervention can lead to improvement in patient care. Neural networks can be used as the basis for an intelligent early warning system. We developed time-delay neural networks (TDNN) for classifying and detecting hemodynamic changes. A matrix of physiological parameters were extracted from raw signals collected during cardiovascular experiments in mongrel dogs. These matrices represented several episodes of stable, decreasing, and increasing cardiac filling in normal, exerted, and heart failure conditions. The TDNN were trained with these matrices and subsequently tested to predict unseen cases. The TDNN perform remarkably not only in identifying all hemodynamic conditions, but also in quickly detecting their changes. On average, the networks were able to detect the hemodynamic changes in less than 1 s after the onset. Based on the results of this pilot investigation, the use of this form of TDNN to successfully predict hemodynamic conditions appears to be promising.

Estimation of left ventricular compliance using on-line echocardiographic automated border detection and pressure data

The end-diastolic pressure-volume relationship can be used to describe left ventricular (LV) compliance. The objective of this study was to utilize measurements of LV cavity area by echocardiographic automated border detection and pressure data to estimate the end-diastolic pressure-volume curve in an isolated heart preparation where true volume could be measured by an intraventricular balloon. Six dog hearts were excised for placement of an intraventricular balloon and a micromanometer catheter and perfused in anex vivo circuit. Mid-ventricular short-axis images were used to measure cross-sectional area by automated border detection while LV volumes were increased from 5 ml to maximal volume (30–40 ml) in each preparation. Simultaneous area and pressure data were recorded on a computer workstation through a customized interface with the ultrasound system. Three runs of varying LV volumes at 1 ml increments were performed on each of 6 hearts for a total of 1,080 simultaneous measurements. Pressure-volume and pressure-area curves were analyzed by linear regression analyses, the slope of which was used to estimate compliance. End-diastolic pressure-area and pressure-volume relationships were significantly correlated with mean r=0.97 ± 0.02 (p<0.001) from individual hearts. The slopes which served to estimate compliance of the individual pressure-area and pressure-volume curves were similar and differed by only 7±4%. A similar correlation was observed by second order regression analyses with r=0.97±0.01 (p<0.001) for pressure-area and r=0.98±0.01 (p<0.001) for pressure-volume relationships. The end-diastolic pressure-area curves may potentially be used to estimate LV compliance, although the clinical application of this method remains to be validated.