Thomas Adams

Role of cranial bone mobility in cranial compliance.

Increases in intracranial pressure are normally buffered by the displacement of blood and cerebrospinal fluid from the cranium when there is an increase in intracranial volume (ICV). How much pressure increases with an increase in ICV is expressed in the calculation of cranial compliance (delta ICV/delta P, where delta P is change in pressure) and elastance (delta P/delta ICV). Data reported here indicate that the movement of the cranial bones at their sutures is an additional factor defining total cranial compliance. Using controlled bolus injections of artificial cerebrospinal fluid into a lateral cerebral ventricle in anesthetized cats and a newly developed instrument to quantify cranial bone movement at the midline sagittal suture where the bilateral parietal bones meet, we show that these cranial bones move in association with increases in ICV along with corresponding peak intracranial pressures and changes in intracranial pressure. External restraints to the head restrict these movements and reduce the compliance characteristics of the cranium. We propose that total cranial compliance depends on the mobility of intracranial fluid volumes of blood and cerebrospinal fluid when there is an increase in ICV, but it also varies as a function of cranial compliance attributable to the movement of the cranial bones at their sutures. Our data indicate that although the cranial bones move apart even with small (nominally 0.2 ml) increases in ICV, total cranial compliance depends more on fluid migration from the cranium when ICV increases are less than approximately 3% of total cranial volume. Cranial bone mobility plays a progressively larger role in total cranial compliance with larger ICV increases.

Dose-response of intravenous butorphanol to increase visceral nociceptive threshold in dogs.

Abstract This study was designed to determine the effective analgesic dose of butorphanol administered intravenously to obtund visceral nociception, as well as to determine duration of this effect. Additionally, cardiovascular changes and sedative effects were defined. Eight healthy dogs were each given five doses of butorphanol (0.025, 0.05, 0.1, 0.2, and 0.4 mg/kg) plus a sterile water placebo intravenously in a randomized blinded format. Antinociception was assessed using an inflatable Silastic balloon inserted into the colon. Blood pressures and pulse rates were measured with a noninvasive monitor. The greatest efficacy and longest duration of antinociception were produced by 0.4 mg/kg of butorphanol, with a duration of 38 ± 9 min. Arterial blood pressure and pulse rate did not vary at antinociceptive doses. Mild sedation was observed at all doses, which generally lasted longer than the antinociceptive effects. These data suggest that butorphanol can be given alone intravenously to provide visceral antinociception lasting 30–45 min without significant side effects.

Thermally induced respiratory responses of the unanesthetized goat.

Abstract Three, 2 year old, non-pregnant, unanesthetized, female goats with surgically exteriorized carotid loops were each exposed for 120 min to ambient temperatures (T a ) of 25, 30, 35 and 40 °C (with constant 40% relative humidity), representing thermoneutrality (T a 25 °C) and progressive levels of heat stress. Thermoregulatory adjustments were indexed in the last 30 min of each exposure by measurements of rectal (T re ) and 6 skin surface temperatures (T s ) as well as respiratory frequency (f), oxygen consumption ( o 2 ), and respiratory evaporative heat loss (E); blood samples were analyzed for H + and P CO 2 . Similar to other furred, domestic animals, the goat increased T s s, f and E at T a 40 °C, in comparison to responses at T a 25 °C. In contrast to other homeotherms, however, the goat progressively increased alveolar ventilation ( A ) at all T a s above 25 °C matched with increases in f and decreases in V T , even without an elevation in internal body temperature (T re s were 40.0, 40.0 and 40.2 °C at T a s 25, 30 and 35 °C respectively; T re at T a 40 °C was 41.2 °C). These data indicate that the goat is unique among other warm-blooded animals in that respiratory alkalosis accompanies increases in skin blood flow, minute ventilation and E at all stages of acute heat stress. In defending against hyperthermia, the goat does not appear to be able to increase E without increasing A .

Temperature regulation in adult quail (Colinus virginianus) during acute thermal stress

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.

Proposed methods for the measurement of regional renal blood flow using heat transfer analysis

The kidney, with its heterogeneous regional perfusion in the two anatomically and functionally distinct vascular beds of the renal cortex and medulla, and with its nonuniform blood vessel geometries, presents a unique challenge for measuring intrarenal blood flow distribution. Determining whole organ perfusion, on the other hand, is comparatively simple for the kidney, but it provides relatively little information about the suspected dependency of renal excretory function on local perfusion rate. Among the variety of methods proposed for gauging regional renal blood flow, some depend on measuring one or more of the tissues thermal properties. The most straightforward, but least reliable, involve measurements either of focal tissue temperature alone, or of regional tissue thermal gradients. Simply using heat as a diffusible indicator, however, is unreliable as a measure of blood flow, for many of the same reasons that using an inert gas in a dilution technique is unreliable. Recently developed thermal analytical methods, though, hold promise for measuring local tissue blood flow with accuracy and precision. Two of them are reviewed here. One depends on measurement of the effective thermal conductivity of a small mass of tissue by evaluating the steady state ratio between regional unidirectional heat flux across it and the associated temperature gradient in one vector along a segment of it through an imposed spheroidal heat field. The other depends on analyses of tissue temperature decay subsequent to a controlled pulse of heat delivered through a small inserted thermistor bead. Both techniques use bioheat transfer equations to deduce regional blood flow

An improved method for water vapor detection

We describe improvements in and details for the construction, calibration and use of a device using a thermal conductivity cell for the measurement of low-level rates of water evaporation (E) from a small surface area. E is measured from 0.0 to 1.0 mg·min−1 with a correlation coefficient of 0.999 between measured and independently verified rates and amounts of water evaporation. Data are available as a recordable analog d.c. voltage as well as in digital display for E and for the amount of water evaporated during an operator defined time period. The device we describe is noninvasive and it is designed to be constructed of conventional components. It is useful not only for measuring transcutaneous water diffusion in normal and diseased skin, but also it is adequately sensitive and rapidly responding to follow thermoregulatory and psychogenic sweating in small (nom. 1.0 cm2) skin areas. It can also be used to measure accurately and precisely the rates at which water is adsorbed by and removed from inanimate materials, as well as to determine how much water they store.

Mechanoptical transducer for quantifying activity in small insect muscles

Abstract Contraction strength, frequency, rate, relaxation rate, as well as transient and static muscle lengths were quantified for onion fly ( Delia antiqua ) oviducal muscle to demonstrate the application of a newly developed, sensitive, rapidly responding, stable and linear mechanoptical transducer system. Contractile patterns were also differentiated for the complex array of muscle segments in the oviduct. Computer-assisted analysis of analogue records showed that within-train contraction strength varied inversely as a function of contraction frequency in a train. Also, a tonic component, assumed to be a function of contraction frequency and the viscoelastic properties of the tissue, was superimposed on trains of phasic, longitudinal contractions. The transducer system described in this report provides opportunities to quantify contraction phenomena occurring at intervals approaching 1 ms in small (nom. 1 mm) tissue samples with resolution in the order of 1 μg of force and 10 μm of displacement.

Homeothermic development in the bobwhite (Colinus virginianus)

Abstract 1. 1. Evaporative heat loss (E), O2 consumption, CO2 production and internal body temperature (Tb) were measured in bobwhite (1–65 days of age) at specific ambient temperatures (Ta). 2. 2. tb at ta 25°C increased from 27.6° in 1-day-old quail to 41.1°C in the adult. 3. 3. Improvements in thermal stability are attributed to augmented rates of metabolic heat production (H) and a diminution in total thermal conductance. 4. 4. Inability of immature quail to maintain constant tb is not attributed to excessive rates of E. The ratio of E ti H did not change after day 6, when the major increase in thermoregulatory ability occurred in the quail.

Eflfects of a Tranquilizer on Body Temperature

Summary Four young adult mongrel dogs were exposed twice untranquilized to each of 3 environmental temperatures: 4.4° C, 23.9° C and 37.8° C and exposed twice tranquilized with 2.2 mg/kg propiopromazine hydrochloride. Rectal temperatures were monitored and recorded continuously during 2-hour exposures. Little difference was noted in rectal temperature response for tranquilized and untranquilized animals at the 23.9° C exposure. Tranquilized animals showed a greater decline in internal temperature at an environmental temperature of 4.4° C than control and when tranquilized showed a rise in rectal temperature during heat exposure (37.8° C)

Entrapment in Small, Enclosed Spaces: A Case Report and Points to Consider Regarding the Mechanism of Death

The mechanism of death due to confinement in an enclosed space is usually ascribed to asphyxia from oxygen deprivation. We report the case of the decomposed remains of a 23-year-old man discovered in an unused industrial size refrigerator in which the mechanism of death is heatstroke. The investigation of the death indicates the subject most likely voluntarily entered the refrigerator and for unknown reasons, closed the door. Injuries identified at autopsy and damage to the inside of the structure indicate he struggled to exit the cabinet. The autopsy shows no significant natural disease processes and toxicology studies were negative. The diagnosis of heat stroke typically rests on the evaluation of multiple features, including the age and size of the decedent, the ambient temperature, the medical history of the decedent, whole body hydration, body fat content, alcohol and drug use, medication history, general physical condition, and many other factors. The diagnosis of heatstroke due to confinement in an enclosed container requires evaluation of the heat stress of the container, the heat strain experienced by the individual, autopsy findings suggesting signs of a struggle to exit the container, and other factors. In all such cases, a careful death investigation with correlation of autopsy findings is required to accurately determine the mechanism and cause of death. We suggest that for all such deaths, physiological and environmental factors promoting hyperthermia and heatstroke be considered as a possible mechanism of death, along with those associated with the more obvious danger of asphyxiation.