Biomedical subjects

P D McCormack

Publications and source records attributed to P D McCormack.

14 recordsLinked to original sources

PubMed1990

Tumbling and spaceflight: the Gemini VIII experience.

A malfunctioning orbital flight attitude thruster during the flight of Gemini VIII led to acceleration forces on astronauts Neil Armstrong (commander) and David Scott (pilot) that created the potential for derogation of oculo-vestibular and eye-hand coordination effects. The spacecraft attained an axial tumbling rotation of 50 rpm and would have exceeded this had not the commander accurately diagnosed the problem and taken immediate corrective action. By the time counter-measure controls were applied, both astronauts were experiencing vertigo and the physiological effects of the tumbling acceleration. Data from the recorders reveal that one astronaut experienced -Gy of 0.92 G-units, and the other +Gy of 0.92 for approximately 46 s. Both received a -Gz of 0.89 G-units from the waist up with a +Gz of 0.05 from the waist down. A substantial increase of time and/or an increase in rpm would ultimately have produced incapacitation of both astronauts. NASA corrected the Gemini thruster problem by changing the ignition system wiring. Future space-craft undertaking long-term missions could be equipped with unambiguous thruster fault displays and could have computer-controlled automatic cutoffs to control excessive thruster burns.

Acceleration↗

PubMed1985

Increase in phi X174 DNA radiation sensitivity due to electric fields.

The application of an external electric field simultaneously with gamma irradiation to an aqueous suspension of phi X174 DNA (in the RFI form) is shown to increase significantly the number of strand breaks. Tritiated DNA allowed the number of single-strand breaks to be estimated from changes in the scintillation of electrophoretic gel band associated with the fastest mobility moiety. At 400 V (approximately 2400 V cm-1) the corrected increase (corrected for phoresis of DNA on the stainless-steel plates) in the G-value yield is 38%. The increase in damage with field strength appears to follow the increase in reduced dichroism. Dichroism results correspond at 400 V to approximately 10% of the maximum orientation. Our results support the conjecture that this significant increase in DNA-radiation interaction with an electric field is due to field-induced conformation changes in the molecule.

Bacteriophage phi X 174↗

PubMed1984

Aging and recognition memory: methodological and interpretive problems.

The recognition memory and aging literature has been reviewed with the purpose of evaluating the notion that the elderly encode semantic information in a more variable manner than the young. Because of methodological, as well as interpretive problems, only a handful of the investigations may be given serious consideration. It is recommended that future investigators report hits, false alarms, sensitivity and response-bias measures. It is also recommended that a concerted effort be made to equate age groups for response bias, that complete details of experimental procedures be reported and that appropriate statistical tests be made.

Adolescent↗

PubMed1984

Prediction of arterial wall failure under acceleration stress in high-performance aircraft.

Experimental results indicate that the passive mechanics (no smooth muscle action) of the larger arteries, such as the aorta and pulmonary, in humans are closely related to the elastin content at low strain and to the collagen content at high strain. In an aerial combat maneuver, the acceleration stress typically rises to a maximum, remains there for several seconds, and then falls off. The arterial wall viscoelastic property relevant here is hysteresis. The strain remaining when the stress is removed is called "permanent set." This so-called permanent set will decay away exponentially with a comparatively long time constant on the order of several hundred seconds. A first approximation to the permanent set, after a hysteresis loop has been executed, has been derived. Collagen can only stretch by 20% before failing. Choosing combat scenarios in which the maneuver is repeated at 1-min intervals so that the decay in permanent sets can be ignored, the number of maneuvers required to damage or rupture the collagen is computed for ranges of acceleration (g) values equivalent to increases in the arterial intraluminal pressures. The calculations are done for the external carotid, abdominal aorta and pulmonary arteries. For example, applying the continual recruitment of collagen fibers theory to the pulmonary artery produces the following result. The permanent set at net acceleration value of 5 g is 0.085 and the number of sequential maneuvers required to damage 2.5% of the collagen is 2.4. Based on discontinuous recruitment of 100% collagen at a strain of 1.7 in the pulmonary artery, the number of maneuvers required to rupture the collagen would be 58 at an acceleration of 5 g. At 10 g, this number falls to about 10 maneuvers. The results emphasize the importance of present protective measures, such as the use of G suits and valsalva maneuvers. But these measures can only reduce the effects predicted here, not eliminate them. The results also highlight the necessity for servo-controlled seat orientation, and for the introduction of integrating accelerometers for all aircrew to record acceleration exposure history.

Acceleration↗

PubMed1982

Coding of spatial information by young and elderly adults.

Two experiments are reported in which the presumed automatic nature of spatial coding is examined. In Experiment 1, 48 young and 48 elderly female adults, half of each group aware and half unaware of the task requirements, studied 16 cards with four nouns arranged vertically on each card. They were then given these 64 targets, as well as 64 distractors, and were required to sort the targets into one of four input spatial locations and to discard distractors. Awareness of the location requirement had no effect on performance and the two age groups were equivalent with respect to overall spatial memory accuracy. In a second experiment, 40 young and 40 elderly unaware female adults were shown 64 cards with one noun per card in one of four spatial locations. There were no reliable age differences in location performance; the young adults, however, exhibited superior free recall.

Adolescent↗

PubMed1979