Biomedical subjects
Publications and source records attributed to K H Smith.
A 62 year old male presented with polymyalgia rheumatica and an abdominal aortic aneurysm. The aneurysm was resected and histological examination disclosed necrotizing giant-cell arteritis. This association seems to be unique.
The potency and anesthetic state produced by nitrous oxide alone were investigated in order to clarify its contribution to the effect of other anesthetic agents. Seven volunteers anesthetized with 1.55 atm absolute N2O in a pressure chamber displayed muscle rigidity with jerking movements, labored and rapid breathing, sweating, and dilated pupils. At 1.1 atm absolute N2O, relaxation and quiescence occurred, sweating ceased, and pupil size decreased. Determination of MAC (using tetanic electrical impulses as the noxious stimulus) produced a mean value of 1.04 +/- 0.10 (SE) atm absolute. All subjects complained of nausea and vomiting after anesthesia.
Twenty-nine patients having myocardial infarction (MI) of recent origin (6 weeks or less) were evaluated and treated using a program in which assessment and progression were based not on generalized data but on the individual responses of each patient. Fourteen patients had complications including left ventricular impairment, continuing ischemia or rhythm disturbances, and 15 did not. Cardiac tolerance for the common self-care activities, walking and light exercise, was objectively defined by 3 levels of functional monitoring. The physician, occupational therapist and physical therapist evaluated the patient's responses to mild exertion, utilizing a 12-lead electrocardiogram (ecg), physical examination, 24-hour monitoring with a portable ecg, self-care evaluation and a modified treadmill screening test. Patient performance was assessed at each stage of testing and individualized activity levels were determined in accordance with cardiac responses. Thus patients progressed at their optimum rate with safety and without loss of time, ie, artificially induced invalidism. Following the 1st self-care evaluation, 3 patients were ordered to bedrest for further medical treatment while 26 were cleared for ward activity. When their conditions improved the 3 patients were reevaluated and began the program. The 15 patients without complications had appropriate responses to activity and proceeded to a mild exercise program with minimal observation. Of the 14 with complications, 5 experienced a temporary program interruption and 2 were dropped from the program secondary to severity of complications. The remaining 7 were progressed in the same manner as those without complication.
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The production of systemic gas bubbles by isobaric counter-equilibration of helium against 5 atmospheres saturated nitrox (0.3 ATA O2 in both mixes) in awake goats was demonstrated. Sixteen animal exposures (8 dives, 2 animals per dive) to a sudden isobaric gas switch from saturation on N2 to He were conducted; 8 saturations occurred at 132 fsw and 8 at 198 fsw. Central venous bubbles were detected acoustically by means of a Doppler ultrasonic cuff surgically implanted around the inferior vena cava of each animal. Bubbles occurred from 20 to 60 min after the switch in both the 132 fsw and 198 fsw exposures, but were not always present in the 132 fsw exposure, and did not persist for as long. Bubbles or other Doppler events were often detected for the entire isobaric period-12 h-following the gas switch in the 198 fsw exposures. Decompressions were conducted according to the USN saturation tables and were uneventful, with only occasional bubbles. Supersaturation ratios calculated to have occurred for a considerable period after the gas switch were approximately 1.15 (tissue gas tension pi, divided by ambient hydrostatic pressure, P) with maxima at 1.26 for the faster tissues. These values are limiting ones in USN decompression only for the slower tissues. In general, therefore, these results argue for reducing the permissible ascent criteria for the faster tissues-assuming bubbles are to be avoided-and allowing more time at stops for non-saturation decompression. Gas switches from a more soluble to a less soluble and/or more rapidly diffusing gas should therefore be avoided until physiological limits are well worked out.
When awake goats were subjected to isobaric gas switching from saturation (17 hours) on 4.7 atmospheres of nitrogen (0.3 atmosphere of oxygen) to 4.7 atmospheres of helium (0.3 atmosphere of oxygen), bubbles detected by 5-megahertz Doppler ultrasound in the posterior vena cava 20 to 60 minutes after the switch continued for 4 hours. Similar experiments carried out at 6.7 atmospheres of inert gas and 0.3 atmosphere of oxygen produced more bubbles for as long as 12 hours after the gas switch. This is believed to be the first objective demonstration of the phenomenon of deep isobaric supersaturation under transient operational diving conditions at relatively shallow diving depths. Detection of bubbles by Doppler ultrasound confirms the potential importance of the phenomenon to shallow saturation diving and holds promise for better quantitification of its effects as well as those of its counterpart, isobaric undersaturation, which can confer a decompression advantage.
Formulation of safe decompression procedures still requires unproven assumptions regarding both gas equilibration rates and the associated ascent criteria. Although the assumption of symmetry of uptake and elimination rates has been suspect for several years, few data are available. Measurements of actual mixed venous blood nitrogen content [vN2] during compression and following decompression in chronically catheterized awake dogs have clearly demonstrated that desaturation is markedly slower than saturation, and that this effect can be imposed by decompression. The disappearance of arteriovenous nitrogen concentration differences during desaturation following a decompression that produced decompression sickness indicates that cardiopulmonary and cardiovascular changes induced by mechanisms associated with decompression per se can potentiate its deleterious effects. Current US practices do not provide for such asymmetry, while those used in the UK have incorporated this in their models for the last decade.
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Visual success in the treatment of monocular congenital cataracts requires early surgery, and aggressive, long-term amblyopia management and optical correction. These children will have their only normally seeing eye patched for a significant percentage of their early childhood years. We have been concerned about the possibility of an adverse psychological impact of this form of treatment. This study utilized two standardized testing instruments to evaluate the incidence of developmental delay and behavioral problems in children treated for monocular congenital cataracts. A total of 22 children were evaluated with one or both of these instruments and compared to a control group of 18 normal siblings. There was no statistically significant evidence of developmental delay or increased behavioral problems in the treatment group.
Experimental dysbaric osteonecrosis associated with inadequate decompression has been induced in mature female swine. The bone collagen from the radiologically defined lesion in the femur has been analyzed. The total collagen contents were the same for the epiphyseal (F-1), the metaphyseal (F-2), and the diaphyseal (F-3) regions. Soluble bone collagen content obtained by sequential extraction of the samples with acetic acid urea, guanidine, lithium chloride and potassium thiocyanate, decreased by approximately 20% in going from the F-1 to the F-2 to the F-3 regions for both experimental and control samples. The amino acid compositions and acrylamide gel electrophoresis patterns were the same for control and experimental samples. Spectral changes with the MBTH reaction were different for control and experimental collagen samples from all bone regions. The spectral shift and pattern changes which occurred from pH 4 to pH 1 suggested a higher average content of unsaturation in the collagen associated aldehyde groups in the experimental than in the control samples. These findings suggest an enhanced ability to remodel collagen which would be consistent with the histological observation of increased derangement of collagen fibers in the experimental bone samples.