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Biomedical subjects

R R Burton

Publications and source records attributed to R R Burton.

At least 73 records · Page 4Linked to original sources
PubMed1976

Cardiac pathology associated with high sustained +Gz: I. Subendocardial hemorrhage.

Adult miniature swine were exposed to various levels and durations of +Gz. After exposure, all swine were euthanized and necropsied. Gross, histologic, and electronmicroscopic observations were made on the heart tissue. Subendocaridal hemorrhage (SEH) was commonly found in the left ventricle, rarely in the right ventricle, and its severity was directly related to : a) level and duration of G exposure, b) heart rate, and c) catecholamine activity. SEH was made more severe with i.v. atropine 4 mg, and prevented with i.v. propranolol 20 mg. Heart hemorrhage was usually limited to the immediate subendocardial region and frequently surrounded Purkinje's fibers. In severe cases, however, hemorrhages penetrated several millimeters into the heart muscle and sometimes penetrated Purkinje's fibers. Restraint of unanesthetized swine in the centrifuge couch, low G-levels, and/or i.v. injections of atropine or epinephrine produced minimal SEH lesions.

Animals↗
PubMed1976

Cardiac pathology associated with high sustained +Gz: II. Stress cardiomyopathy.

The myocardial pathology of 14 pigs exposed to HSGz stress of 9 and 15, or 3, 7, and 9 Gz was studied; six control pigs were used as comparisons. Four pigs received propranolol prior to centrifugation and four pigs received atropine. Hearts were studied by light and electron microscopy. Myocardium from stressed pigs showed myofibrillar degeneration, pooling of mitochondria, and cell death. Lesions occurred in random cells of the subendocardium and papillary muscles. Purkinje fibers were also involved. Pretreatment with atropine increased the number of dead cells found and propranolol increased the number of cells showing myofibrillar degeneration. It is postulated that this is a pluricausal cardiomyopathy similar to several experimental conditions. Significance to aerospace medicine is briefly discussed.

Animals↗
PubMed1975

Ventricular activation process in minipigs.

Because the form of QRS from the body surface of pigs is different from that of carnivores or ungulates, and because that form is dependent upon pathways of ventricular activation, this study was designed to study pathways of ven tricular activation in pigs. Twelve pigs were anesthetized and right or left hemithoracotomies were performed to expose the heart. Contiguous bipolar electrograms were recorded from button electrodes on the epicardium and from both faces of the interventicular septum, and from multipolar plunge electrodes introduced into the intramural regions of both ventricles. Electrograms were recorded simultaneous with the Z-axis ECG at 625 mm/sec paper speed on a photographic oscillograph. Times of arrival of waves of activation at numerous points in the ventricle were referenced to the peak of the R-wave in the Z-axis ECG. During the initial 10 msec of QRS, the apical-third of the interventricular septum is activated from left to right. During the next 40 msec of QRS, waves of activation originating at the cranial portion of the right ventricle and the caudal portion of the left ventricle engulf the epicardium toward the interventricular septum and slightly in an apico-basilar direction. Activity begins slightly earlier at the caudal aspect of the left ventricular free-wall and terminates on the pulmonary conus region. During the terminal 30 msec of QRS, the basilar third of the interventricular septum is activated in a general apico-basilar direction. Through regions of either right or left ventricular free-walls was a general endocardial to epicardial activation observed. These pathways of ventricular activation may be explained by the rather complete penetration of Purkinje fibers through both ventricular free-walls in a manner similar to that of ungulates but different from carnivores and primates.

Animals↗
PubMed1975

Physiologic effects of seatback angles 45degrees (from the vertical) relative to G.

Eight experimental subjects from the USAF Sschool of Aerospace Medicine (SAM) and four YF-16/17 test pilots were exposed to a simulated aerial combat maneuver (SACM) which included a maximum G exposure of 6 s at 8 G. The following physiologic parameters were examined relative to seatback angles of 23degrees, 28degrees, and 40degrees; heart rate and rhythm; arterial oxygen saturation; performance; intrathoracic (esophageal) pressure; arterial pressure; and subject comfort, effort, and fatigue. Relaxed and straining high sustained G (HSG) tolerances (6 G for 60 s) were also determined using only SAM subjects. The advantages of the 40 degree setback angle during the SACM included increased subject comfort, less fatigue and effort, greater pilot acceptance and a statisically significant reduction in the increased mean heart rate associated with G exposure. On the other hand, a statistically significant reduction in arterial oxygen saturation was obtained during the SACM at 40 degrees compared with the 23 degree back angle. An increase in relaxed G tolerance was found with the 40degree seatback angle--statistically significant only compared with the 28 degree seatback angle.

Aerospace Medicine↗
PubMed1975

Heart pathology associated with exposure to high sustained +Gz.

The pathology of +Gz acceleration was examined using unanesthetized adult miniature and immature "farm-type" swine, with and without anti-G suit inflation. Following single exposures of +8 or 9 Gz for 45 to 90 s--acceleration exposures that have been shown "tolerable" to man--swine were sacrificed and a detailed necropsy performed. Considering only the adult miniature swine, the endocardial area of the left ventricles showed evidence grossly of recent hemorrhage of varying severity involving both the wall and papillary muscles. The degree and location of the subendocardial hemorrhage were quantitated by grading the area of ventricle involved--1 (slight) to 4 (extensive). Of the 23 adult miniature pigs autopsied, the scores for papillary muscle hemorrhage, after one exposure to +9 Gz (45 to 90 s) ranged from a mean of 2.3 to 3.3 and the extent of ventricular wall involvement was 2.5 to 3.3. Histologically, heart hemorrhage was limited to the subendocardial area, primarily involving the space between heart muscle and the endocardium and was particularly evident surrounding Pukinje's fibers. Similar studies using immature farm-type swine (not miniature pigs) found these younger swine (4 to 5 months of age) to be less susceptible to such endocardial hemorrhage. Heart tissue recovery in these pigs following one exposure to +9 Gz for 45 s, required approximately 14 d. It appears that this lesion is similar, although less severe, than heart muscle lesions associated with loss blood volume (hemorrhagic shock) studies and may have similar physiologic bases. It was concluded that particular attention should be made of the endocardium of victims of high-performance aircraft accidents.

Age Factors↗
PubMed1975

Gravitational effects on body composition in birds.

Gallinaceous birds, presenting a wide range of body size, were adapted physiologically to hyperdynamic environments, provided by chronic centrifugation. Chemical composition was measured directly on prepared carcasses, which were anatomically comparable, and more amenable to analysis than the intact body. Body mass and body fat decreased arithmetically with increasing field strength and also with increasing body mass. Water content of lean tissue increased in hyperdynamic environments, but irrespectively of body size.

Acceleration↗
PubMed1975

Transfer functions for arterial oxygen saturation during +Gz stress.

Discrete, finite, Fourier transforms of input +Gz stress and output arterial oxygen saturation (Sao2) were used to obtain transfer functions between G and Sao2 in 12 subjects. Ensemble averaging of transfer functions based on responses to variable G stress provided reasonable capability for predicting Sao2 responses to sustained 6-G stress. Prediction of responses to variable G stress from transfer functions based on responses to sustained G stress was unsuccessful, however. A synthetic transfer function with physiologic explicability and substantial predictive ability was obtained from an impulse response fabricated from simple mathematical functions.

Aerospace Medicine↗