Charles M. Philips

Measurement of cardiac output by thermal dilution

Abstract The cardiac output was determined by the thermal dilution technique in dogs and calves, and the results were compared with the simultaneously determined electromagnetic flowmeter measurements of aortic flow. For these measurements the indicator, saline solution at room temperature, was injected into the superior vena cava, and the sensing thermistor catheter was placed in the main pulmonary artery. A simple analog computer solved a modified Stewart-Hamilton equation and displayed the calculated cardiac output on a digital readout meter. One hundred twenty simultaneous measurements were made in dogs and 76 determinations in calves. The standard error of estimate, when compared to electromagnetic flowmeter determinations, was approximately 10 percent of mean cardiac output (450 ml/min in dogs and 750 ml/min in calves). Since the measurement of aortic flow by the electromagnetic flowmeter does not include coronary flow, this discrepancy is to be expected. The reproducibility of the method was assessed by evaluating successive pairs of thermal curves recorded within 1 minute. The standard deviation of the difference between successive determinations was approximately 3.5 percent. Initial trials in 8 patients undergoing cardiac catheterization and in 14 patients in the operating room and intensive care unit have shown the method to be highly useful and practical.

Intraoperative venous dilation and subsequent development of deep vein thrombosis in patients undergoing total hip or knee replacement.

This patient study was based on the observation of characteristic intimal lesions in jugular and femoral veins removed from dogs a few hours following total hip replacement. The lesions, small localized intimal tears, suggested that smooth muscle and connective tissue, might have dilated beyond the ability of intima to accommodate. Intraoperative venous dilation correlated with the incidence of intimal lesions. It was postulated that surgical trauma resulted in circulating vasoactive substances which caused venous dilation and that dilation of smooth muscle and connective tissue beyond the yield point of intima resulted in intimal rupture. Similar intraoperative dilation and lesions, in patients might predispose to development of deep vein thrombosis (DVT). Total hip (THR) and total knee (TKR) replacement patients were selected for study because: (a) of the high incidence of DVT and (b) blood circulation is present in THR but not in TKR patients during operation. Ultrasound was used to monitor cephalic vein diameter during the perioperative period. Development of DVT postoperatively was compared with intraoperative venous dilation. In THR patients, intraoperative venous dilation ranged from 6%-56%. One of nine patients with dilation less than or equal to 17% developed DVT while 12 patients with dilation of greater than or equal to 22% developed DVT, giving a correct prediction of 95%. Of four patients in the intermediate range (19%, 20%), two developed DVT and two did not. The sharp demarcation was to be expected because of abrupt rupture of viscoelastic material when the critical point of elongation is exceeded.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous measurement of left ventricular volume in the dog: II. Comparison of washout and radiographic technics with the external dimension method

Abstract Single plane angiocardiographic studies were performed using casts of the left ventricular cavity of the canine heart. Good agreement was found between true and calculated volume. End-diastolic volume estimated (EDV) from angiocardiographic measurements and that estimated with a method based on external cross-sectional areas and length (EAL), calibrated in each subject, correlate within 10 per cent. These data support the validity of either model. However, at end-systole, x-ray calculations always yielded an underestimation of the volume when compared with measurements by the EAL method. Immediate changes in ventricular dynamics were studied during and after the injection of 1.0 ml./kg. of Renografin. End-diastolic and stroke volumes were found to increase. Measurements by the EAL method were also compared with those from thermal washout recordings. A systematic overestimation of EDV and underestimation of SV/EDV was found. The difference was greater at faster heart rates. A linear relation between EDV, SV and ESV was found under conditions of volume overload.

Method of predicting the occurrence of deep vein thrombosis by non-invasive measurement of vessel diameter

A method of predicting the occurrence of deep vein thrombosis after a surgical procedure comprises monitoring changes in the internal diameter of a blood vessel using a non-invasive ultrasound technique. The frequency and magnitude of changes in vessel diameter are used to predict whether deep vein thrombosis will occur.

Continuous measurement of left ventricular volume in the dog

Abstract Evidence is presented to show that a volume index derived from the ellipsoid model, and applied in open chest dogs by use of direct and continuously measured external dimensions, is compatible with left ventricular volume changes and can be calibrated in absolute terms in the dead heart of the same subject. The over-all accuracy of the method is better than ±2 ml. It is useful to study volume-dependent variables which characterize myocardial performance in the living animal. It can also be used as a standard in animals against which to compare left ventricular volume measurements made by angiocardiography or indicator washout.

Perfluorochemical elimination from the lungs: Effect of initial dose

Liquid‐assisted ventilation with perfluorochemical (PFC) has been beneficial in a variety of respiratory diseases in animals and humans. Although PFC evaporation from the lungs is in part dependent on ventilation strategy and positioning, guidelines for initial and replacement dosing are unclear. We hypothesized that PFC evaporative loss over time is dependent on the size of the initial dose. Juvenile rabbits (n = 18) were ventilated using constant animal position and ventilator strategy. PFC (perflubron: LiquiVent ) was instilled endotracheally, using four groups with initial doses of 2, 6, 12, and 17 mL/kg. A previously described thermal detector that measures PFC in expired gas was used to calculate loss rate, residual perflubron in the lung, and volume loss as a % of initial fill volume.

A Simple Technique to Measure the Rate and Magnitude of Shortening of Single Isolated Cardiac Myocytes

A simple and inexpensive method for measuring the extent and rate of shortening of single myocytes was developed. The image of a single cardiac myocyte was focused through a 10x objective of an inverted microscope and projected onto a linear photodiode array having 256 self-scanning elements. This array was used as an edge detector to define cell length. The output from the array was fed into a digital-to-analog converter to produce an output voltage proportional to the myocyte length. In the present experiments the total scanning time for all the 256 elements was set at either 1.5 or 5 ms, thus allowing for detection of myocyte length changes during contraction. Results obtained using this system showed that the extent of shortening was 8.04 ±0.48 percent of the resting cell length (n = 15). The rate of shortening in these cells was 99.49 ±8.02 percent of the resting cell length/s. Similar results were obtained using a high speed film.

COMBINED ECMO AND PARTIAL LIQUID VENTILATION (PLV) IN HUMAN NEONATES: LIQUIVENT® PERFLUOROCHEMICAL (PFC) ELIMINATION. † 1368

COMBINED ECMO AND PARTIAL LIQUID VENTILATION (PLV) IN HUMAN NEONATES: LIQUIVENT® PERFLUOROCHEMICAL (PFC) ELIMINATION. † 1368

Transient heat transfer in human endometrium during cryoablation

This paper presents an experimental study and numerical prediction of the transient heat transfer behavior inside the uterus during application of a PFC fluid into the endometrium cavity in order to achieve cryoablation. The numerical prediction is based on a 1-D finite difference method of the bio-heat equation using the Crank Nicolson scheme. The numerical method is first validated by a 1-D physical model by measuring temperature history at several locations within a silicone rubber sheet. Good comparisons are obtained by comparing numerical predictions with the experimental data obtained from eight intact, hysterectomized uteri during cryoablation.

PIV measurement of fluid flow inside a human uterus model for cryoablation

A new technique has been proposed that allows cryoablation to be achieved on the entire inner surface of the endometrium by circulating very cold perfluorochemical (PFC) fluid inside the human uterus. To understand the PFC flow field inside the uterus during cryoablation, a uterus model was constructed; a fluid delivery system including the fluid delivery probe was designed and built to simulate the PFC flow during cryosurgery. With particle image velocimetry (PIV), the fluid flow inside the uterus was investigated at room temperature to display a 2-D whole field velocity contour and vector plot.