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Biomedical subjects

B C Hodgkin

Publications and source records attributed to B C Hodgkin.

At least 19 recordsLinked to original sources
PubMed1990

Electrocardiographic effects of experimental myocardial infarction in pigs.

Myocardial infarctions were produced in young domestic farm pigs by ligating coronary arteries. Arteries ligated in four groups were (A) left anterior descending, (B) branches of left anterior descending, (C) left circumflex, and (D) right coronary artery. After 7 or 8 days, the hearts were removed and dissected and the infarcted areas measured. Vectorcardiograms were taken before ligation and just before termination. High recording speeds and sensitivities were used so that details of the QRS complexes could be seen. Difference vectors were computed as a function of time during QRS. In groups A and B, statistically significant differences in QRS components before and after ligation were found. Also, there were statistically significant correlations between vectorcardiographic deflections and the ratio of infarct weight to heart weight. The changes were related to known excitation patterns of the pig heart.

Animals↗
PubMed1989

Dipole moment of in vivo and isolated perfused rabbit hearts.

We have measured magnitude and location of heart dipole moment during QRS in 46 New Zealand white rabbits. The spatial magnitude curve had one to three peaks. Mean values were M1 = 80 +/- 10 microA-cm (N = 5) pointing to right anterior and caudal, M2 = 260 +/- 15 microA-cm (N = 42) directed slightly to left of due anterior and caudal, and M3 = 236 +/- 9 microA-cm (N = 43) pointing towards left posterior and cephalad. The mean thorax resistivity was 250 ohm-cm. For 23 rabbits, M2/M3 greater than 1 and for 16 rabbits, M2/M3 less than 1. Mean times of occurrence of the three peaks were 5.8, 11.2, and 19.6 ms, respectively. Spatial magnitude curves for hearts perfused at the center of a sphere showed usually one major peak at about 19 ms. Locuscardiograms of in vivo hearts were also measured. By comparing M values for in vivo and isolated hearts, we found that M1 values agreed closely but mean M2 measured from the hearts in vivo was 2.5 times that for the isolated hearts, and M3 for in vivo hearts was about two-thirds that for isolated hearts. We relate these differences to the effects of intracardiac blood and lungs on the measured dipole moment.

Animals↗
PubMed1982

Noninvasive measurement of systolic and diastolic blood pressure in swine.

Arterial blood pressure was measured noninvasively using Doppler ultrasound and an occluding cuff. The subjects were 28 domestic pigs (10-49 kg) anesthetized with pentobarbital sodium (25 mg/kg). Indirect pressure measurements were made with the Doppler unit placed over the radial or the ulnar artery proximal to the carpal joint. Comparison was made with directly measured pressure to determine the reliability and reproducibility of the indirect method. Direct systolic pressures between 73 and 230 mmHg and diastolic pressures between 52 and 165 mmHg were measured. There was no significant difference between directly and indirectly measured systolic pressure (P greater than 0.20). Indirectly measured diastolic pressure tended to be lower than direct diastolic pressure, the difference by the paired t test being significant to P = 0.06. For systolic pressure the sample correlation coefficient was 0.94, and for diastolic pressure, 0.88. Both systolic and diastolic blood pressure can be accurately measured in the anesthetized pig using Doppler ultrasound and an occluding cuff.

Animals↗
PubMed1981

Cardiac electrical resultant dipole moment of spontaneously hypertensive rats.

The cardiac electrical resultant dipole moment (RDM) of 17 spontaneously hypertensive rats (SHR) was compared with that of 17 Wistar-Kyoto rats (WKY), 65-100 days of age. Relative to body weight, left ventricular weight was 23% greater and right ventricular weight was 18% greater for SHR than for WKY. Left ventricular wall thickness was 11% larger and myocyte diameter was 13% larger for SHR than for WKY. RDM orientation for SHR was more dorsal, leftward, and cranial from middle to end of qRS. The second spatial magnitude peak of QRS, M2, was significantly smaller for SHR than for WKY (P less than 0.001) whereas M3 for SHR was significantly greater than for WKY (P less than 0.001). The alterations in RDM of SHR are greater than can be accounted for simply on the basis of increased cell size. The excitation sequence for SHR might be different from that of WKY. Results show the necessity of considering the details of the spatial magnitude curve during QRS.

Animals↗
PubMed1980

Effects of PEEP and of increased frequency of ventilation during CPR.

Previous reports have attributed increased carotid blood flow to lung ventilation during CPR. This study was undertaken to determine whether PEEP (20 torr airway pressure) or increased frequency of ventilation (3:1) improved arterial pressure, flow, and blood gases. Thirty-three domestic pigs were studied using three protocols (standard 5:1 CPR, 5:1 CPR plus PEEP, 3:1 CPR) distributed such that comparisons could be made between groups as well as within the same pig. For intrapig comparisons, PO2 was significantly improve (p less than 0.05) by PEEP (delta PO2 = 9.7 +/- 13.0 torr). PCO2 was significantly less (p less than 0.005) for 3:1 compared to 5:1 (delta PCO2 = -4.7 +/- 2.1 torr). For group comparisons, PO2 was 55.5 +/- 12.9 torr without and 70.1 +/- 16.3 torr with PEEP (p less than 0.025). For 3:1, PO2 was 66.3 +/- 11.6 torr that was greater (p less than 0.10) than for 5:1. When ventilation was temporarily halted, phasic changes in flow with ventilation were replaced by nearly constant flow approximately equal to maximal flow when ventilation was provided. PEEP and more frequent ventilation improved blood oxygenation but at the expense of carotid blood flow.

Animals↗
PubMed1978

The difference vector: assessment of effects of changes or interventions.

Vector dipole moments were measured on young pigs before and one week after ligation of the left anterior descending coronary artery. Vectors were obtained for the three peaks of vector spatial magnitude, M. Preoperative, postoperative, and difference vectors were measured for each peak. If excitation is normal except through the infarcted tissue, the difference vector should be more closely related to the infarct because the normal excitation cancels out. It was found that the postoperative vector was changed by the infarct but that the difference vector was a better indication of infarction. This paper was designed to introduce the method using experimental data for a small number of pigs.

Animals↗
PubMed1978

Effect of ventricular end-diastolic volume on vectorcardiographic potentials of the pig.

The Brody hypothesis proposes that alterations in end-diastolic blood volume will produce changes in the magnitude of cardiac electrical potentials recorded at the body surface. To test this hypothesis, several procedures that affect end-diastolic volume were applied in 28 anesthetized domestic piglets. The pig dipole moment magnitude curve is typified by two peaks, designated M2 and M3, which responded to these procedures. Doubling heart rate by electrical pacing or hemorrhage of 20 ml/kg produced reduction in M2 by 30% and 29%, respectively. M3 rose by 27% and 29%, respectively, under these two conditions. Reduction of end-diastolic volume by partial occlusion of the vena cava produced similar effects. Maneuvers increasing end-diastolic volume produced directionally opposite effects. Temporary aortic coarctation of phenylephrine injection caused an increase in M2 with no change in M3, accompanied an acute elevation of arterial pressure. Thus, the pig electrocardiogram shows changes, attributable to adjustments in end-diastolic volume, consistent with the Brody hypothesis, suggesting potentials for this technique in monitoring changes in end-diastolic volume.

Action Potentials↗
PubMed1977

Effect of hematocrit on electrocardiographic potentials and dipole moment of the pig.

The Brody hypothesis posits that blood in the heart chambers enhances body surface potentials due to radially oriented excitation and diminishes those due to tangentially oriented excitation. Evidence supporting the hypothesis has been found in models and in dogs. The current study was performed in pigs (Sus scrofa), anesthetized with sodium pentobarbital, to determine whether the phenomenon could also be demonstrated in a species having a ventricular activation pattern distinctly different from that of dogs. Hematocrit was varied from normal 35.3 +/- 1.1% to as low as 19.8% by hemodilution and to as high as 68.0% by hemoconcentration. Surface potentials early in QRS increased and those late in QRS decreased in hemodilution experiments, while the reverse was true in hemoconcentration experiments. Total QRS duration was 38.0 +/- 0.8 ms. The first peak in resultant dipole moment magnitude, at 5.4 +/- 0.2 ms, was inversely related to blood resistivity with a linear regression correlation coefficient r = -0.76; the second peak, at 10.9 +/- 0.1 ms, was directly related, r = 0.52; and the third peak, at 17.5 +/- 0.2 ms, was directly related, r = 0.89. When interpreted in accordance with the Brody hypothesis, changes in body surface potentials and in resultant dipole moment were consistent with radial excitation of the apical septum, ill-defined orientation of free ventricular wall excitation, and tangential excitation of basal left ventricle and septum.

Animals↗
PubMed1976

Magnitude, direction and location of the resultant dipole moment of the pig heart.

Vectorcardiograms were obtained from 50 young domestic pigs using the Nelson lead system. Compensation for body size and shape is achieved and the resultant dipole moment magnitude reflects heart size. A strong relationship was found between heart size and maximum magnitude. Dipole moment magnitude increased as four pigs increased from five to ten weeks of age. The dipole moment during QRS is considered in light of known pig heart excitation pattern. Dipole locations during QRS, calculated by computer solution of the Gabor-Nelson equations, were in agreement with heart location and excitation data.

Age Factors↗
PubMed1975

Determination of the locus of the heart vector from body surface measurements: model experiments.

Based on the Gabor-Nelson equations a technique is described for measuring the location of the resultant heart dipole (locus-cardiogram). The technique uses three rows of eight electrodes, a head and a foot lead. Experiments with a male and a female human torso model showed good agreement between actual andmeasured dipole locations. The presence of intrathoracic electricla inhomogeneities shifts theapparetn locus of the dipole toward the highly conductive mass. The conductivity of the volume conductor and the dipole monent value do not introduce any error into the computed locus of the dipole. It is concluded that the technique is accurate and simple enough to be used for experimental and clinical observation.

Body Surface Area↗
PubMed1975

Sum of two vectors having an included angle greater than ninety degrees.

If the angle between two vectors is acute an increase in either vector will increase the resultant. If the angle is obtuse, however, an increase in one vector may either decrease or increase the resultant. A mathematical derivation and a simple geometric construction are presented. The theory is applied to vectors in the horizontal plane in right ventricular hypertrophy. It is shown that as the right ventricular vector is increased from a small value, the resultant vector may first decrease and then increase again with a continuous clockwise rotation.

Cardiomegaly↗