F. John Lewis

Digital computer calculation of human pulmonary mechanics using a least squares fit technique

Abstract We have calculated pulmonary mechanics on six human subjects using a digital computer to least squares fit the equation describing pulmonary mechanics: P= 1 C V+RV for the constants C and R, during both the inspiratory and expiratory cycles. Values for compliance and resistance were found to be statistically identical with those calculated by methods which use isolated points in the breathing cycle. No difference in mechanics was observed between inspiration and expiration. The methods advantages over isolated-points methods are that best-fit parameters are better representations; it calculates parameters independently for inspiration and expiration; and it functions in real time.

Continuous patient monitoring with a small digital computer

Abstract This monitoring system, which is centered on a small computer with a 12 bit word size and 8 K of core memory, is controlled by core resident programming which carries out continuous monitoring of several analog signals from 4 patients while a variety of programs are paged into core from disk or tape when needed. The continuous programs monitor the electrocardiograph for arrhythmias, the respiratory rate, temperature, indirect blood pressure and intra-arterial pressure with a cardiac output estimation. Paged programs provide respiratory mechanics, intermittent cardiac output and an analysis of blood gases in addition to service functions such as those which control the TV display and those which type graphs for the medical record. Peripheral instrumentation has been developed from commercially available equipment with some modifications and additions. The system is designed for growth. Expansion from continuous monitoring of 4–8 patients could be provided by adding 4 K of memory to core. The paging system will permit the additon of many new programs to handle intermittent functions.

Fungal endocarditis following cardiac surgery.

Excerpt The frequency of postcardiotomy endocarditis has been estimated to be less than 1%, and in the majority of the reported cases the offending organism has beenStaphylococcus aureus.1-4As of t...

Monitoring of Patients in Intensive Care Units

The impression grows that instrumentation for ICU’s has been oversold. Nonetheless, basic measurements of circulation, respiration, and metabolism that can be made by instruments are valuable, and a continuous recording, display, and analysis of these measurements is a proper objective.

THE EFFECT OF COOLING AND LOW MOLECULAR WEIGHT DEXTRAN ON BLOOD SLUDGING.

Summary o 1. If canine blood is cooled to 10° C. by the technique described, blood sludging will appear which usually disappears when the blood is rewarmed to a normal temperature. 2. Low molecular weight dextran (10% solution) administered in a dosage of 12 cc. per kilogram while the blood is cold decreases the blood sludging. Normal saline in similar or larger quantities apparently has no effect on the degree of blood sludging.

Mesenteric vascular response to hypothermia

Summary o 1. Total and segmental resistances were studied in the mesenteries of 37 dogs, and the effects of hypothermia, changes in blood viscosity and epinephrine on these resistances were compared. 2. Cooling to 15°C. caused an increased mesenteric resistance in 94 per cent of animals with approximately 90 per cent of the resistance rise contributed by the arterial segment. Small vessel resistance increased in 52 per cent. There was no evidence of venous constriction. 3. Blood viscosity appeared to play a minor role. 4. It is suggested that hemorrhagic necrosis of the bowel wall is due to intense vasoconstriction in the precapillary vessels with subsequent distal anoxia and cellular damage.

Hypothermia for open heart surgery.

Abstract 1. (1) For open intracardiac operations to repair atrial septal defects under hypothermia the patients body temperature has been lowered by surface cooling to approximately 29 °C (84.5 ° F). Sixty-five patients with atrial septal defects have been operated upon by the technic described and five minutes of cardiac inflow occlusion has been sufficient to repair most of the defects. 2. (2) Hypothermia also provides an effective method for operating on a few other intracardiac defects such as isolated pulmonary stenosis and aortic stenosis under direct vision. 3. (3) Some of the advantages and disadvantages of hypothermia are discussed.

Digital computer diagnosis of cardiac arrythmias in a single-lead electrocardiogram☆

Abstract The objective of this study was to develop a method to diagnose cardiac arrythmias from a singlelead ECG utilizing a digital computer programmed to identify R-R intervals and QRS widths, but no P-waves. This method is part of a larger system for on-line computer monitoring of several physiological variables in postoperative and intensive care patients. The ECG signal was transmitted to a PDP-9 computer where it was sampled 60 times/sec, converted to digital data, and then further converted to first order descending difference values upon which all identification procedures were done. A QRS complex, for example, was identified when the absolute first order descending difference value was greater than a certain level for each test ECG. Means, standard deviations and other statistical parameters were calculated from the R-R interval and QRS durations. Other, more complex, logical processes were used to evaluate the degree of irregularity. This was all done rapidly enough to provide real-time analysis. Eighteen types of arrythmias may be identified from these variables. Their validity was tested by comparison with the diagnoses made by a cardiologist. At present, the program can diagnose normal tracings, tachycardia and bradycardia, premature atrial contractions, premature ventricular contractions, atrial fibrillation with a high degree or reliability (90–95 per cent), intermittent and complete bundle branch blocks and sinus arrythmias with a moderate degree of reliability (80 per cent). For several other arrythmias, such as ventricular and paroxysmal tachycardias, sinus arrest, bigeminy and trigeminy, there is not sufficient evidence as yet to test validity. With only a single-lead and without P-wave identification, the system seems to identify quite reliably many of the arrythmias which threaten postoperative patients.