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Biomedical subjects

D R Richmond

Publications and source records attributed to D R Richmond.

11 recordsLinked to original sources
PubMed1991

Blast criteria for open spaces and enclosures.

A review of the history of blast research is presented from before World War II to the present time. The mechanisms of blast injury and the nature of the injuries are described. Casualty criteria applicable to man's exposure to single blasts in open terrain as a function of overpressure duration and orientation are given. Damage-risk criteria for man exposed to repeated blasts of low and high intensity are described. The hazards from blast waves entering open structures are described with criteria for personnel located in a standard two-man open foxhole. Methods of establishing the air blast dose in a variety of exposure conditions are illustrated. The present state-of-the-art on personnel protection afforded by rigid and soft protective garments is given. Information on animal response to blast waves generated inside enclosures from the firing of recoilless weapons and the detonation of high-explosive charges is discussed along with the problem of defining the extent of performance decrement in relation to the air blast dose.

Acoustic Stimulation↗
PubMed1990

Nonauditory injury threshold for repeated intense freefield impulse noise.

Exposure to impulse noise is an important occupational health concern. The risk of injury to auditory structures is well recognized and provides the cornerstone for present safety standards. For freefield impulse noise, nonauditory injury is dependent on peak pressure, positive phase duration (or impulse), and number of exposures. Trivial laryngeal petechiae are shown to precede nonauditory injury to more critical organs (ie, pulmonary and gastrointestinal systems). This study identifies the critical impulse noise thresholds causing trivial laryngeal petechial changes resulting from exposure to 5, 25, and 100 repetitions of specific levels of impulse noise. Because of anatomical differences, sheep should be slightly more susceptible to impulse noise laryngeal petechial changes than man; therefore, it seems reasonable to set the absolute limits for human occupational exposure levels below those causing laryngeal petechiae in sheep for persons wearing adequate hearing protection. This study does not address human auditory injury that may occur above or below these exposure limits even with proper hearing protection.

Accidents, Occupational↗
PubMed1989

Physical correlates of eardrum rupture.

Eardrum (tympanic membrane) rupture in humans and animals in relation to various blast pressure-time patterns was reviewed. There were few systematic studies on eardrum rupture as a consequence of blast overpressure. Most reports did not describe the area of the eardrum destroyed. The peak overpressures required to produce a 50% incidence of eardrum rupture (P50) were summarized. Most of the animal data pertained to dogs. The highest P50 for dogs, 296 kPa, was associated with smooth-rising overpressure. For complex wave patterns occurring inside open shelters subjected to nuclear blasts, the P50 was 205 kPa. For fast-rising blasts in a shock tube it was 78 kPa, and 105 kPa for statically applied pressures. The duration of the overpressure was not a factor unless it was very short. The influence of the orientation of the head to the oncoming blast was demonstrated. An ear facing the blast may receive reflected overpressures several times that for one side-on to the blast. An ear on the downstream side of the head was exposed to about the same overpressure as the side-on ear. A P50 for humans of 100 kPa and a threshold of 35 kPa has been used widely in blast criteria. A recent study suggests a threshold (P1) of about 20 kPa, and gives the overpressures required to produce minor, moderate, and major eardrum ruptures. These data were presented in the form of curves showing the overpressures as a function of duration required to inflict a P1 and a P50 of eardrum rupture of the three levels of severity.

Animals↗
PubMed1988

Cloth ballistic vest alters response to blast.

Ballistic wounds have been and will remain the principal cause of casualties in combat. Cloth ballistic vests (CBV) play an important role in limiting critical wounds from fragments and small-arms fire. There is an increased risk of primary blast injury on the modern battlefield. In a previous study, volunteers were exposed to short-duration blast waves of low peak pressure (18.6 +/- 0.8 kPa). Pressure measurements made in the distal esophagus as an estimate of intrathoracic pressure (ITP) were significantly higher (p less than 0.05) when the standard U.S. Army ballistic jacket was worn (8.7 +/- 1.2 kPa) than when fatigues alone were worn (7.4 +/- 0.7 kPa). In this study 58 sheep were exposed to nominal blast levels of 115, 230, 295, and 420 kPa peak pressure in groups of 12, 18, 16, and 12, respectively. Half of each group was fitted with a CBV. Lung weight index (LWI), lung weight expressed as a percentage of body weight, was used as a measure of blast injury. Use of the CBV was associated with a significant increase in LWI (p less than 0.05) which averaged 21% for the two middle exposure groups. At the 420 kPa level, two of six non-CBV animals died as opposed to five of six animals wearing the CBV. Intrathoracic pressure was generally higher in the CBV group. Likely mechanisms of injury enhancement include an increase in target surface area and an alteration of the effective loading function on the thorax. This information may be useful in the triage and treatment of casualties exposed to intense blast environments.

Animals↗
PubMed1979

Coronary bypass grafting in early stages of acute myocardial infarction.

Acute coronary bypass surgery was performed in four patients with early anterior myocardial infarction due to severe proximal stenosis of the left anterior descending artery. Improvemnet of left ventricular anteroapical wall contraction was detected at the completion of the operation, in the early postoperative phase, and six to 18 months after surgery. It is concluded that critically ischaemic myocardium was salvaged by revascularization.

Adult↗
PubMed1979

mm vs mV.

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Cardiomyopathy, Hypertrophic↗
PubMed1976

Cardiovascular action of verapamil in the dog with particular reference to myocardial contractility and atrioventricular conduction.

Verapamil (Isoptin) caused a dose-dependent peripheral vasodilation, increase in myocardial contractility, and tachycardia in the anaesthetized dog. Propranolol pretreatment blocked the cardiac stimulation following verapamil but the vasodilation was unaltered. Inflation of a thoracic aortic balloon prevented the fall in intravascular pressure and reduced the tachycardia and positive inotropic responses. These experiments suggest that clinical doses of verapamil cause peripheral vasodilation which leads to a sympathetic reflex induced increase in heart rate and myocardial contractility. Verapamil also had a direct myocardial depressant action which became evident at doses above the range used clinically. The drug increased the PR interval in conscious dogs for up to 60 minutes. This effect was partly mediated through cholinergic stimulation and partly through a direct depression on atrioventricular conduction.

Animals↗
PubMedDate not supplied

The effect of heart rate on indices of myocardial contractility in the dog.

1. Changes in heart rate were evoked by atrial pacing in anaesthetized dogs with no pretreatment and in dogs given reserpine or guanethidine for 72 h. The effect of alterations in heart rate were related to two indices of myocardial contractility: the maximal rate of change of left ventricular pressure (dp/dt), and an index which was independent of initial fibre length (dp/dt)/IIT, where IIT is integrated isometric tension. 2. An increase in heart rate in control dogs was accompanied by a rise in both dp/dt and (dp/dt)/IIT confirming that the Bowditch staircase does exist in the intact ventricle. The regression line relating heart rate to (dp/dt)/IIT was significantly steeper than that relating heart rate to dp/dt because the reduction in left ventricular preload at high heart rate tends to attenuate the rise in dp/dt. 3. Reserpine, but not guanethidine pretreatment was accompanied by either a slight decrease or no change in (dp/dt)/IIT during pacing. 4. Acute elevation of (dp/dt)/IIT by either calcium or isoprenaline infusion in reserpine pretreated dogs did not restore the Bowditch effect. 5. Acute depression of (dp/dt)/IIT by propranolol and pentobarbitone was accompanied by a greater rise in (dp/dt)/IIT with pacing in control dogs and a rise rather than a fall in reserpine-pretreated dogs.

Animals↗